Investigations on the influence of dextran during beet sugar

Transcrição

Investigations on the influence of dextran during beet sugar
production with special focus on crystal growth and morphology
Vorgelegt von
M.Sc.
El-Sayed Ali Abdel-Rahman Soliman
aus Sohag (Ägypten)
Von der Fakultät III - Prozesswissenschaften
der Technischen Universität Berlin
zur Erlangung des akademischen Grades
Doktor der Ingenieurwissenschaften
-Dr.-Ing.genehmigte Dissertation
Promotionsausschuss:
Vorsitzender: Prof. Dr. rer. nat. F. Behrendt
Berichter: Prof. Dr. -Ing. T. Kurz
Berichter: PD Dr.-Ing. R. Schick
Berichter: Assoc. Prof. Dr. S. Ahmed
Tag der wissenschaftlichen Aussprache: 13.08.2007
Berlin 2007
D 83
This work is dedicated to:
The memory of my parents
My wife Asmaa
I
Contents
ACKNOWLEDGMENT
“My great thanks to ALLAH for all gifts he gave me’’
In the first place, I would like to thank in the first place my supervisor Prof. Dr. T.
Kurz, for many decisive scientific contributions, continued support, his
recommendations, motivations, countless discussions and for his helpful guidance
and valuable advices. He gave me the opportunity to extend my scientific education
at numerous of international conferences. Special thanks also go to Dr .R. Schick, for
his valuable advice, encouragement and scientific contributions. I would like to thank
Prof. Dr. Fleischer, for supporting this work. I can not forget to extend my thanks to
Prof. Dr. Ezzat Abdalla, president of Assiut University. I gratefully acknowledge
Prof. Dr. S. El-Syiad for his advice and encouragement. I could never have
embarked and started all of this without his prior teaching in sugar technology. Thus
he opened up an unknown area to me. I am gratefully thanking Prof. Dr. I. Makkawy
for his help in statistical analyses of this work. I thank Dr. S. A. Ahmed for his helps
in this work. My deep thanks go to Dr. Q. Smejkal, for his scientific contributions in
the progress of the work. Also, thanks are given to all staff members of the
Department of Food Process Engineering, Technische Universität Berlin, who gave
me hands during the progress of the work, in particular, Dr. B. Seidel, Dr. K.
Ruprecht, S. Gramdorf, S. Jährig, S. Brodkorb, A. Bagherzadeh, H. Rudolph, A.
Hentschel, Y. Pierre, Dr. F. Idler, P. Seifert, R. Krämer, A. Gebauer, M. Fischer
and R. Groß. I gratefully acknowledge Jülich sugar factory, especially, Dr. M.
Lorenz, Aarberg sugar factory, especially, T. Frankenfeld and Delta sugar factories
especially H. Gad. My special thanks go to my wife Asmaa for her support and
comfortable atmosphere during this work. I am extremely grateful to the Egyptian
Government and Missions Office for the financial support during my studies in
Germany, especially, Prof. Dr. Galal Elgemeie.
Finally I am deeply thank all staff members, my colleagues and workers of the Food
Science and Technology Department, Faculty of Agriculture, Assiut University,
Egypt for their continuous encouragements.
II
Contents
CONTENTS
ACKNOWLEDGMENT ............................................................................................I
CONTENTS .............................................................................................................. II
LIST OF FIGURES ...................................................................................................V
LIST OF TABLES ................................................................................................... IX
1
Introduction and outline ................................................................................... 1
2
Review of literature ........................................................................................... 5
2.1
Structure of dextran ..................................................................................... 5
2.2
Microbial loading in sugar factories ............................................................ 7
2.3
The common methods of dextran fractions determination ........................ 11
2.4
Dextran content during the process of sugar production ........................... 13
2.5
Dextrans associated with processing problems ......................................... 16
2.6
Crystallization process............................................................................... 19
2.6.1
Growth rate of sucrose crystals.......................................................... 19
2.6.2
Crystallization kinetics ...................................................................... 22
2.6.3
Parameters influencing crystallization kinetics ................................. 27
2.6.4
Crystal morphology ........................................................................... 29
2.7
3
The Economic gain .................................................................................... 32
Material and methods...................................................................................... 36
3.1
Material...................................................................................................... 36
3.2
Analytical methods .................................................................................... 36
3.2.1
Determination of dextran ................................................................... 36
3.2.1.1
Robert method................................................................................ 36
3.2.1.2
Haze method .................................................................................. 37
3.2.2
Microbiological experiments ............................................................. 37
3.2.2.1
Isolation ......................................................................................... 37
3.2.2.2
Identification.................................................................................. 37
3.2.2.2.1
Gas and acid formation ............................................................ 37
3.2.2.2.2
Catalase test ............................................................................. 38
3.2.2.2.3
Gram characteristics (KOH-Test)............................................ 38
III
Contents
3.2.2.2.4
Identification by API 50 CHL test........................................... 38
3.2.2.2.5
L/D-Lactic acid test ................................................................. 39
3.2.3
Crystallization experiments ............................................................... 39
3.2.3.1
3.2.3.1.1
Required amount of dextran and seed...................................... 40
3.2.3.1.2
Calculation of the growth rate of sucrose crystals:.................. 41
3.2.3.2
Dynamic viscosity.......................................................................... 42
3.2.3.3
Crystal morphology and surface topography................................. 42
3.2.3.4
Image analysis................................................................................ 42
3.2.4
4
Measurement of growth rate of sucrose crystals ........................... 39
Statistical analysis.............................................................................. 43
Results and discussion ..................................................................................... 44
4.1
Sensitivity and accuracy of different methods for the determination of
dextrans of varying molecular mass ...................................................................... 44
4.2
4.1.1
Robert’s Copper method sensitivity .............................................. 44
4.1.2
Haze method sensitivity................................................................. 48
Microbial sources of dextran an identification of relevant microorganisms
in sugar factories.................................................................................................... 51
4.3
Levels of dextran contents in different sugar beet factories ...................... 55
4.4
Quality of factory final products and their relationship to the levels of
dextran during different industrial periods ............................................................ 58
4.5
Influence of dextran concentrations and molecular fractions on the rate of
sucrose crystallization in pure sucrose solutions ................................................... 63
4.5.1
Influence of different temperatures on growth rate of sucrose crystals
in the presence of dextran .................................................................................. 69
4.6
Elucidation of crystallization kinetics in presence of dextran molecules.. 72
4.7
Influence of dextran molecule fractions on sucrose solution viscosity ..... 74
4.8
Influence of dextran on the morphology and surface topography of sucrose
crystals in presence of dextran............................................................................... 76
4.8.1
Crystal morphology ........................................................................... 76
4.8.2
Surface topography ............................................................................ 77
4.9
Technical and technological consequences and future perspectives ......... 86
Contents
IV
5
Summary........................................................................................................... 90
6
References......................................................................................................... 94
7
Appendix......................................................................................................... 102
8
C. V. and List of Publications ....................................................................... 106
V
List of figures
LIST OF FIGURES
Figure 1: Dextran formed from sucrose by Leuconostoc m......................................... 5
Figure 2: Chemical structure of dextrans ..................................................................... 6
Figure 3: Micrographs of four strains of Leuconostoc spp by scanning electron
microscopy (SCIMAT, 2006) ............................................................................... 9
Figure 4: Growth curves of Leuconostoc mesenteroides subsp. mesenteroides MCRI
1 in MRS broth at 30-40°C (Hamasaki et al., 2003) (30°C (•), 35°C ( ), 37°C
( ), and 40°C (X). ABS, absorbance)................................................................. 10
Figure 5: The major steps for the manufacture of sugar from sugar beets (Südzucker
AG website, Germany) ...................................................................................... 15
Figure 6: Growth rate at 60 °C as a function of supersaturation at different purities,
(Schliephake and Ekelhof, 1983)........................................................................ 21
Figure 7: Crystal growth rate as a function of temperature at different purities and
constant supersaturation (Schliephake and Ekelhof, 1983)................................ 21
Figure 8: Surface reaction coefficient kR dependent upon the reciprocal value of the
absolute temperature T given for different purities (Ekelhof, 1997).................. 25
Figure 9: Hypothetical crystal (a) with schematic drawing of the three kinds of faces
PBCs (b) ............................................................................................................. 26
Figure 10: Diagrammatic representation of the processes involved in crystal growth
from solution, according to Elwell and Scheel ,(1975) as modified by Kruse and
Ulrich, (1993)..................................................................................................... 27
Figure 11: The viscosity of the pure and impure sucrose solution according to
Ekelhof, (1997)................................................................................................... 29
Figure 12: Schematic representation of a sucrose crystal with the surface designation
according to Vavrinecz ( 1965) .......................................................................... 30
Figure 13: (A) Sucrose crystal growth in the presence of dextran (40g/100g water),
(B) One of the crystals shown in (A) and (C) Sucrose crystal growth in the
presence of glucose, fructose and dextran (50g/100g water each) (According to
Bubnik et al., (1992)........................................................................................... 31
Figure 14: Partitions of sugar loss during different process stages of sugar production
(Ekelhof, 1997)................................................................................................... 33
Figure 15: Colony of bacteria mixed in a 5% solution of H2O2 demonstrating a
positive and negative test for producing of catalase. ......................................... 38
List of figures
VI
Figure 16: Pilot scheme of laboratory crystallization device..................................... 40
Figure 17: Standard Curves of dextran T40, T500 and T2000 by copper complex
method................................................................................................................ 45
Figure 18: Sensitivity of copper complex method to determine dextran T40 in
sucrose solutions ................................................................................................ 47
Figure 21: Sensitivity of Haze method to determine dextran T40 in sucrose solutions
............................................................................................................................ 49
Figure 22: Sensitivity of Haze method to determine dextran T500 in sucrose
solutions ............................................................................................................. 49
Figure 23: Sensitivity of haze method to determine dextran T2000 in sucrose
solutions ............................................................................................................. 50
Figure 24: Deteriorated sugar beet after harvesting................................................... 52
Figure 25: Microorganisms growth in sugar beet raw juice at room temperature ..... 53
Figure 26: Scanning electron micrograph of the isolated Leuconostoc mesenteroides.
............................................................................................................................ 55
Figure 27: Dextran levels at 3 Egyptian factories (F1, F2 and F3) during the
production processes .......................................................................................... 56
Figure 28: Dextran levels in final products (white sugar and molasses) of 3 Egyptian
factories (F1, F2 and F3).................................................................................... 57
Figure 29: The relationship between the three factories based on cluster analysis of
some characters (Single linkage squared Euclidean distance)........................... 58
Figure 30: The relationship between molasses purity and the industrial periods. ..... 59
Figure 31: Influence of the industrial period on the dextran amount during production
processes ............................................................................................................ 60
Figure 32: Dextran levels in sugar and molasses production of different industrial
periods ................................................................................................................ 61
Figure 33: The relationship between the dextran content in syrup and different
produced sugars.................................................................................................. 62
Figure 34: The partitions of dextran during different crystallization stages at different
industrial periods................................................................................................ 62
List of figures
VII
Figure 35: Dry substance content of mother liquor in isothermal crystallization
experiments at 60 °C in pure sucrose solution and after addition of 500, 1500
and 2000 mg/kg DS of dextran T40................................................................... 64
Figure 36: Growth rate of sucrose crystals in isothermal crystallization experiments
at 60 °C in pure sucrose solution and after addition of 500, 1500 and 2000
mg/kg DS of dextran T40................................................................................... 64
experiments at 60 °C in pure sucrose solution and after addition of 500, 1500
and 2000 mg/kg DS of dextran T500................................................................. 65
at 60 °C in pure sucrose solution and after addition of 500, 1500 and 2000
mg/kg DS of dextran T500................................................................................. 66
Figure 39: Dry substance contents of mother liquor in isothermal crystallization
experiments at 60°C in pure sucrose solutions and after addition of 500, 1500
and 5000 mg/kg DS of dextran T2000............................................................... 67
Figure 40: Growth rates of sucrose crystals in isothermal crystallization experiments
at 60°C in pure sucrose solutions and after addition of 500 - 5000 mg/kg DS of
dextran T2000 .................................................................................................... 67
experiments at 60 °C in pure sucrose solution and after addition of 1500 mg/kg
DS of dextran T40, T500 and T2000 ................................................................. 68
at 60 °C in pure sucrose solution and after addition of 1500 mg/kg DS of
dextran T40, T500 and T2000............................................................................ 69
Figure 43: Dry substance content at 70, 65 and 60°C in control and in presence of
dextranT2000 (1500 and 5000ppm) during crystallization process................... 70
Figure 44: Growth rate of sucrose crystals at 60, 65 and 70 °C after addition of 1500
mg/kg DS of dextran T2000............................................................................... 71
Figure 45: Growth rate of sucrose crystals at 60 and 70 °C after addition of 5000
mg/kg DS of dextran T2000............................................................................... 71
Figure 46: The scheme of the two processes of diffusion and surface reaction. 2λ=
gap between crystals, λ= half distance between crystals, δ = thickness of the
boundary layer, kD = diffusion coefficient, kR = surface reaction, NS = non-sugar,
List of figures
VIII
CL, CG, CSat are the sucrose concentrations of liquor, boundary layer and
saturation at the crystal-solution interface. ........................................................ 73
Figure 47: Dextran adsorption on impure particles.................................................... 73
Figure 48: Influence of addition of 1500 mg/kg DS of T40, T500 and T2000 dextran
on the dynamic viscosity of a 60% sucrose solution between 50 and 70 °C ..... 74
Figure 49: Influence of different dextran concentrations (500, 1500, 2500, 5000 ppm)
on the dynamic viscosity at different temperatures (50-70°C) .......................... 75
Figure 50: The crystal surface of a sucrose crystal during the drying process
(according to Bunert und Bruhns 1995)............................................................. 76
Figure 51: Effect of dextran on morphology of sucrose crystals, a) Normal crystal, b)
Crystal grown in presence of dextran (needle crystal) and c) Impure particles on
crystal surface (crystal grown in technical sucrose solution)............................. 77
Figure 52: An example of influences of dextran T40 on sucrose crystal shape during
the crystallization process .................................................................................. 77
Figure 53: Surface topography of a laboratory sucrose crystal grown in absence of
dextran at 60°C................................................................................................... 78
Figure 54: Surface topography of sucrose crystal grown in the presence of 1500 mg
dextran T40 per kg DS at 60 °C......................................................................... 79
Figure 55: Surface topography of a sucrose crystal grown in the presence of 5000 mg
dextran T2000 per kg DS at 60°C...................................................................... 80
Figure 56: Effect of crystallization temperature on the surface topography in the
presence of dextran ............................................................................................ 81
Figure 57: Turbidity phenomena in many European sugar beet factories (a, b) during
the thick juice campaign..................................................................................... 82
Figure 58: The magnification image of Figure 57 ..................................................... 83
Figure 59: After product sugar crystal in one of European sugar beet factory during
the thick juice campaign..................................................................................... 83
Figure 60: 3-product scheme of crystallisation.......................................................... 85
Figure 61: Influence of dextran on many crystallization parameters during
crystallization process. ....................................................................................... 86
Figure 62: The relationship between dextran additions and crystallization time during
the crystallization process .................................................................................. 87
List of Tables
IX
LIST OF TABLES
Table 1: The linkage structures of dextran................................................................... 7
Table 2: Sucrose consumption and dextran production at different time intervals,
Leuconostoc mesenteroides 3A; culture medium 10% sucrose basal medium;
incubation temperature 30 °C (Guglielmone et al., 2000) ................................. 10
Table 3: Dextran in process streams measured at different Louisiana sugar
factories(F1, F2, F3 and F4) (Cuddihy and Day, 1999)..................................... 16
Table 4: Summary of the detrimental effects of dextran in terms of the losses it leads
to according to Singleton et al., (2001). ............................................................. 18
Table 5: Effects of dextran in juice on molasses purity ............................................. 34
Table 6: Dextran levels and sucrose loss in raw sugars (Bose and Singh, 1981) ...... 34
Table 7: Conclusion of evaluation of Roberts and Haze methods to determine
different dextran molecules................................................................................ 51
Introduction and outline
1
1
More than 100 countries produce sugar, 74 % of which is made from sugar cane
grown primarily in the tropical and sub-tropical zones of the southern hemisphere,
and the balance from sugar beet which is grown mainly in the temperate zones of the
northern hemisphere (SIL, 2007).
The world sugar production in 2005/06 and 2006/07 was estimated as 152.710 and
160.203 (million tons, raw value), 79 % of which is produced by the world's top ten
sugar producers. On the other hand the world consumption was 149.782 and 153.008
(million tons, raw value) in 2005/06 and 2006/07, respectively (Gudoshnikov, 2007).
In Egypt, total sugar production increased to 1.675 million tons a year in 2006/07
from 1.575 million tons in 2005/06, but consumption soared to over 2.5 million tons
a year (Gudoshnikov, 2007).
Sugar cane is the second most important crop in Egypt. Since the first sugar factory
was established in 1818, there are eight factories for raw and plantation white sugar
production from sugar cane as well as one refinery concentrated in middle and upper
Egypt (Khaleifah, 2001). In addition, there are four sugar beet factories in the north
of Egypt. There is an intention in the policy of the Egyptian government to expand
the cultivation of sugar beet in the new land in the north, consequently, the number
of beet sugar factories is increasing.
Regarding beet sugar production, differences between theoretical and practical
quality during sugar extraction from sugar beet and an increase of molasses purity
have been observed in the Egyptian sugar beet factories and in many another
countries, especially at the end of the industrial season. Climatic conditions and a
long time from harvesting to manufacturing cause a drop of sugar beet quality. Also
freezing and thawing cause considerable changes in the chemical composition and
thus processability of sugar beet (Kenter and Hoffmann, 2006). This is of particular
interest also for the European sugar industry as the European sugar factories intend a
prolongation of the industrial campaign to the freezing period.
2
In this context bacterial polysaccharides have been recognized as a serious problem
in sugar processing for more than 100 years (Scheibler, 1874). Since the early years
of sugar manufacturing, there have been many reports especially on the formation of
dextran, the main portion of bacterial polysaccharides during sugar processing, in
sugar factories and refineries.
Dextran fractions occurring in sugar beet and cane are almost entirely produced by
Leuconostoc mesenteroides, a ubiquitous bacterium especially prevalent in any sugar
field. The exact structure of each type of dextran depends on its specific microbial
strain of origin. During storage, several changes in beet quality may occur which
depend on the storage conditions such as duration and temperature. The presence of
dextran in the sugar factories leads to a falsely high polarization, increased viscosity,
lower evaporation rates, elongated crystals (needle grain) and increase of sugar loss
to molasses. However, the most damaging effects of high dextran concentrations in a
technical sucrose solution are foreseen in the crystallization. Dextran slows down the
crystallization rate or even inhibits crystallization (i.e., they have a high melassigenic
effect) (Clarke et al., 1997). Dextrans occurring during sugar production mainly
affect the growth rate and the shape of sucrose crystals during the crystallization
process. Decreasing growth rates and needle-like crystal growth cause relevant
economic and qualitative losses.
Many investigations suggested a minimization of dextran levels in the sugar factory
by controlling of microorganisms from beet harvesting to juice extraction. More
recent approaches propose the application of dextranase enzyme for the removal of
preformed dextran. However, these approaches were not practicable or uneconomical
(Day, 1984; Eggleston and Monge, 2005; Gupta and Prabhu, 1993). Furthermore,
due to the high solubility of most dextrans in water (above 30 mg/ml), it is very
difficult to remove dextrans from juice by filtration processes (Godshall et al., 1994;
James et al., 2000) and (Yanli.Mi, 2002). On the other hand, the treatment of juice by
the enzyme leads to an increase of dextran low molecular weight fractions, which are
soluble in water, and consequently, reach the crystallization process and cause
several problems in this step.
3
Consequently, the aim of this work was to identify the sources of dextran during beet
sugar production and to characterize the effects of dextran on the crystallization
process and the quality of the final sugar crystal. Also industrially relevant methods
to compensate the effects of dextran in sugar juices during the crystallization process
by variation of the process parameters crystallization temperature and supersaturation
during the crystallization process without any chemical additions should be
identified. In addition, the rate-limiting step in the crystallization process affected by
dextran, elucidation of diffusion and surface reaction phenomena in sucrose solutions
with dextran were studied.
To reach this aim, a specific knowledge is necessary especially about dextran
composition and the influence of dextran on other process variables during the
crystallization process. However, no information was available concerning the effect
of average molecular weight of the dextran fractions on the sugar production process.
OUTLINE OF THE THESIS
The main goals of this study are summarized in the following topics:
¾
Sensitivity and accuracy of different methods for the determination of dextrans of
varying molecular mass.
¾
Identification of microbial sources of dextran and identification of dextran
progression during sugar production.
¾
Characterization of the effects of different molecular fractions and concentration
of dextran on growth rate of sucrose crystals at different crystallization
temperatures. In order to provide representative results in the usual range of
occurring dextrans, molecular mass fractions of M = 40,000 g/mol (T40), M =
500,000 g/mol (T500) and M = 2,000,000 g/mol (T2000) were utilized.
¾
Presentation of an overview about overall crystallization kinetics in order to
explain the relationship between different factors influencing crystallization
kinetics and how they are influenced by dextran themselves.
¾
Characterization of the influence of dextran molecular fractions on crystal shape
and surface topography.
¾
4
Technical and technological consequences.
5
Review of literature
2
Polysaccharides are long chain molecules, either branched or straight. These
molecules are derived from two sources: the metabolic activities of the growing plant
(e.g. starch) and the metabolic activities of microorganisms (e.g. dextran) growing
during its life or at some stage in the subsequent processing (James and Day, 2000;
Wilson, 1996).
2.1
Structure of dextran
A polysaccharide usually referred to as dextran compound widely occurs in
deteriorated sugar cane and beet. These molecules are derived from the metabolic
activities of microorganisms growing during plant cultivation or at some stage in the
subsequent processing (James and Day, 2000).
Figure 1 exemplifies the production of dextran by the action of dextransucrase from
microorganisms, especially by Leuconostoc mesenteroides on sucrose. It can be seen
that sucrose is degraded to a fructose and a glucose molecule. The latter is
polymerized to dextran. Fructose is remaining in solution and can be determined
analytically, a method which is sometimes applied if dextran should be determined
(Clarke and Godshall, 1988).
(Leuconostoc m.)
Dextransucrase
Dextran
Fructose
Figure 1: Dextran formed from sucrose by Leuconostoc m.
6
Dextran is the collective name given to a large class of α-(1→6) linked glucose
polymers (Galea and Inkerman, 1993). Figure 2 shows the chemical structure of
dextran. It illustrates that most linkages in dextran structure are α-(1→6). Dextrans
are from the chemical point of view almost identical to amylose, but they have some
branching of the polymer chain, which prevents this kind of stacking (Walstra,
2003). The linkage in dextran molecules varies from 50 % to 97 % α-(1→6) of total
linkages. The linkages of α-(1→2), α -(1→3) and α- (1→4) are usually at branch
points (Steinbuechel and Rhee, 2005).
Glucose ring
α (1→6)
Carbon
Carbon
Oxygen
Oxygen
Hydrogen
Hydrogen
α (1→3)
n
Figure 2: Chemical structure of dextrans
The molecular differences in dextrans obviously influence the solubility; for any
given size, the greater the content of α-(16) the greater is the solubility.
Conversely, the higher the percentage of α-(13) linkages in a polymer the greater is
the decrease in water solubility (Day, 1992).
The degree of branching of dextrans depends on the microbial source and varies
widely among species. For example, while the dextran produced by Betacoccus
arabinosaceous has a unit chain length of only six or seven α-(16) linked glucosyl
residues and is highly branched, the dextran produced by Leuconostoc mesenteroides
B-512F may have a unit chain length of greater than 10,000 residues with less than
5 % branching (Kennedy and White, 1988).
An overview to the parameters affecting the particular molecular structure of dextran
is given by (Singleton, 2002). Table 1 shows the different linkage structures found in
dextran. On the other hand, the water soluble, high molecular weight dextran from
Leuconostoc m. NRRC B-512F consists of 95 % α-(16) linked α-D-glucopyranosyl
residues with 5 % α-(13) linked D-glucosyl or isomaltosyl side chains. However,
7
Leuconostoc m. NRRC 523 predominately produces a lower molecular weight, water
insoluble dextran which consists of only 66 % (16) linkages with 24 % (13) and
10 % (14) branched linkages (Edye et al., 1995; Jeanes et al., 1954; Robyt, 1986).
Table 1: The linkage structures of dextran
Dextran
Solubility
Linkages %
α1-6
α 1-3
5
L.m.B512F
Soluble
95
L.m. B1299
Less soluble
66
L.m. B1355
Soluble
54
S.m. B6715
Soluble
64
S.m. B6715
Insoluble
4
35
α 1-3Br
α 1-2
1
27
11
36
94
2
L.m. , Leuconostoc mesenteroides; S.m., Streptococcus mutans; Br, Branch linkage.Source: adapted
from (Robyt, 1986).
2.2
Microbial loading in sugar factories
Sugar beet is a major agricultural crop in temperate zones of the world, just as sugar
cane is a major crop in tropical zones. Beet harvesting commences when the weather
turns cold enough for storage of the harvested beets. Again, climatic conditions have
a great deal to do with operations. The tops of the beet are removed prior to
harvesting. Generally, harvesting is a mechanical method. A variety of lactic acid
bacteria (LAB), including Leuconostoc species are commonly found on crop plants
(Day, 1992).
Dextran was first reported to be formed from sucrose by strains of Leuconostoc
species in 1930 (Hucker and Pederson, 1930). Later, dextran was obtained in cellfree extracts from Leuconostoc mesenteroides (Hehre and Sugg, 1942). Different
strains of Leuconostoc mesenteroides produce dextran with different physical,
chemical and serological characteristics (Kobayashi and Matsuda, 1974). The
production of dextran depends on different factors (i.e. type of strain, environmental
conditions and reaction conditions between enzyme and substrate) (UI-Qader et al.,
2001). The yield of dextran increases during growth and maximum yield is obtained
at the end of exponential phase. Dextran yield was higher in media containing
nitrogen source supplemented with different salts (UL-Qader et al., 2005).
8
Morphologically, it is often difficult to separate leuconostocs from streptococci,
lactococci, and lactobacilli, because leuconostocs, lactococci, and streptococci may
form ovoid or even rod-shaped cells (in older cultures or under stress); and
lactobacilli (e. g., Lb. coryniformis or Lb. sake) may produce very short rods or
ellipsoid cells. This explains why, in the past, when identification of leuconostocs
was still based mainly on morphology and slime production, dextran-forming strains
of Lb. confusus were frequently misidentified as L. mesenteroides subsp.
mesenteroides (Holzapfel and Kandler, 1969).
Most strains in liquid culture appear as cocci, occurring single or in pairs and short
chains, however, morphology can vary with growth conditions. Cells grown in
glucose or on solid media may have an elongated or rod shaped morphology. Cells
are Gram positive, asporogenous and non-motile (Figure 3) (SCIMAT, 2006).
Leuconostoc species are differentiated from other lactic acid bacteria on the basis of
phenotypical criteria such as coccoid appearance, formation of gas, inability of
arginine hydrolysis, and production of the D (–)-lactate isomer from glucose, but the
formation of dextran from sucrose and cell wall composition may also be helpful for
identification (Holzapfel and Kandler, 1969).
The sugar fermentation pattern is of limited value for identification of the nonacidophilic leuconostocs because of the considerable variation among different
strains of the same species on the one hand and because of the similarity of the range
of fermented sugars of different species on the other (Holzapfel and Schillinger,
1992).
9
Leuconostoc citreum
Bar: 1 µm
Leuconostoc lactis
Bar: 1 µm
Leuconostoc cremoris
Bar: 2 µm
Leuconostoc mesenteroides
Bar: 1 µm
Figure 3: Micrographs of four strains of Leuconostoc spp by scanning electron microscopy
(SCIMAT, 2006)
Out of 15 different sugars, 13 may be fermented by strains of Leuconostoc
mesenteroides subsp. dextranicum and there are also many differences in the
fermentation pattern among different strains of Leuconostoc mesenteroides subsp.
mesenteroides. Only Lc. mesenteroides subsp. cremoris is easily distinguished from
the other leuconostocs by its very limited range of fermented sugars, consisting of
glucose, galactose, and lactose. Sugars most helpful for differentiation of the other
species seem to be arabinose, melibiose, trehalose, and xylose (Holzapfel and
Schillinger, 1992).
Hamasaki et al., (2003) reported that the optimum growth temperature of L.
mesenteroides subsp. mesenteroides was 30°C and the maximum was 37°C (Figure
4).
A recent study of Guglielmone et al., (2000) showed that Leuconostoc mesenteroides
(strain 3A) consumes sucrose very quickly (8.05 g/l/hr at 25 °C and 8.46 g/l/hr at
30 °C) during the first 6 hours of culture. This fermentative process implies a sucrose
consumption of 59 % at 25 °C and 62 % at 30 °C. At higher temperatures (37 °C and
40 °C) the percentage of consumed sucrose decreases to 47 % and 27 % respectively.
10
1.0
0.5
0.0
ABS (660 nm)
1.5
0
6
12
18
24
Incubation Time (hours)
Figure 4: Growth curves of Leuconostoc mesenteroides subsp. mesenteroides MCRI 1 in MRS
broth at 30-40°C (Hamasaki et al., 2003) (30°C (•), 35°C ( ), 37°C ( ), and 40°C (X). ABS,
absorbance)
The strain of organism studied was isolated from sugar cane juice in Argentina. Its
high fermentation rate consumed sucrose rapidly, stopping its growth and sugar
utilization 6 hours after incubation. From the sugar industry point of view, it is
important to know the consumption of sucrose in short periods as shown in (Table 2).
This is due to the importance of dextran in the sucrose loss by the direct sucrose
consumption as a source of energy (see Figure 1) and production of dextran, which
causes a reducing in the efficiency of manufacturing processes.
Table 2: Sucrose consumption and dextran production at different time intervals, Leuconostoc
mesenteroides 3A; culture medium 10% sucrose basal medium; incubation temperature 30 °C
(Guglielmone et al., 2000)
Time
(hours)
Consumed sucrose
(g/l)
Dextran production
(g/l)
1
2
3
4
5
6
9
15
18
24
48
08.50
17.00
25.40
33.80
42.30
50.80
51.90
53.40
54.10
55.50
57.50
0.35
0.60
0.80
0.90
1.08
1.30
2.25
5.10
7.00
13.00
13.20
2.3
11
The common methods of dextran fractions determination
In the sugar industry, several different methods are in use for the determination of
dextran. These methods are Haze method, ASI II method, Robert’s copper method,
Midland SucroTestTM, Optical Activity Ltd. DASA method and HPLC method
Nicholson and Horsley, (1959) developed the forerunner to the current haze assay.
This procedure involves the separation of material precipitated with alcohol to make
a 70 % v/v solution. The precipitated material is resolved in water and treated with αamylase to break down starch and trichloracetic acid (TCA) to precipitate proteins.
The dextran haze is quantified in a spectrophotometer at 720 nm. The absorbance is
compared with that obtained on a standard curve using dextran isolated from
Leuconostoc mesenteriodes (Day et al., 2002; Paton et al., 1994).
After degradation of starch by amylase, the ASI II method treats alcohol-precipitated
samples with dextranase and α-glucosidase. This results in the conversion of dextran
to glucose. The glucose produced is then quantified by the Nelson-Somogyi
arsenomolybdate method (Sarkar and Day, 1986).
Sarkar et al., (1991) compared the Haze test with the above method (ASI II method),
a GPC method (Saska and Oubrahim, 1987) and a polyclonal and monoclonal
antibody test. The ASI II method, being an enzyme based method, was suspected to
have problems at low dextran concentrations due to high degrees of branching. The
GPC method was difficult to quantify and not sensitive to all molecular weights. The
antibody tests did not detect dextran with a molecular weight below 150 kDa.
Another quantitative method for dextran detection has been proposed by Roberts
(Roberts, 1983) to compete with the haze assay. Like the original Nicholson and
Horsley method, all polysaccharide and protein constituents are precipitated and
redissolved in water. Then dextran is precipitated ”selectively” with copper sulphate.
The dextran from this latter precipitation is determined colorimetrically by phenolsulphoric acid. It was claimed that the Roberts method was independent of the
molecular weight of the dextran and was specific for dextran (Paton et al., 1994).
Sancho et al., (1998) devised a test based on stripping voltametry, which showed a
linear relationship to dextran concentration in standard sucrose solutions. The
performance of the procedure is compared with the Robert test (Roberts, 1983) and
12
performed better, especially at low dextran concentrations, but still in standard
solutions. The method is claimed to be faster and simpler than the Roberts test, but it
needs further investigation using real sugar samples.
Brown and Inkerman, (1992) developed an HPLC method that uses dextranase to
break the dextran down into isomaltose, which is subsequently quantified by HPLC.
The method was proposed as a reference method (Urquhart et al., 1993). However,
the procedure is technically difficult and time consuming. The dextran is isolated
using 80 % ethanol and then hydrolyzed with dextranase. The reaction is completed
and the amount of isomaltose produced is converted into dextran concentration by a
calibration function which bases on the usage of dextranase on standard dextrans.
The method has been critisised for assuming a homogeneous dextran structure.
Two new methods, the Midland SucroTestTM and the Optical Activity Ltd. DASA
methods are reported to determine only dextran. Midland SucroTestTM is an
immunological method that uses a monoclonal antibody to produce a linear increase
in turbidity with response to dextran. The dextran concentration is determined from
the change in turbidity after addition of the sample into a buffer solution containing a
monoclonal antibody and comparing the difference to a standard. Midland
SucroTestTM showed consistent results and a high correlation with the Haze test
(Day et al., 2002). This assay method is a rapid test that utilizes a minimum of
equipment, and is highly specific to dextran, but the cost per analysis is considered
too high for extensive use.
The DASA method uses a near infrared spectrometer to detect the change in optical
rotation in a sample prior to and after dextranase treatment. The dextran
concentration is calculated and displayed as a change in optical rotation in an OA
Ltd. SacchAAr 880 polarimeter. The DASA method was reported to give
erroneously high levels of dextran, due to either partial dextran hydrolysis or poor
filtration (Singleton et al., 2001).
The new monoclonal antibody test method is more sensitive and allows testing of
various process streams. Of great importance is, that the test can be conducted in
only three to five minutes, which is a significant improvement compared to all other
methods. The antibody attaches to dextran and produces a haze. The amount of haze
13
formed is directly proportional to the amount of dextran present. A specially
modified nephelometer (turbidimeter) is used to measure the turbidity of the haze
formed by the reaction of the antibody with dextran. However, this method is very
expensive and not available for use in sugar factories (Rauh et al., 1999).
2.4
Dextran content during the process of sugar production
Before dealing with the progression of dextran a short introduction to the sugar
production process should be given (comp. Figure 5). After harvesting, the beets are
hauled to the factory. Each load entering is weighed and sampled before tipping onto
the reception area, where it is moved into large heaps. The climatic and storage
conditions play an important role regarding the deterioration of beets (Kenter and
Hoffmann, 2006). The beets are conveyed into the factory in a water flume. Rocks
and weeds are removed prior to the beets being washed. The washing process
contributes to a reduction of dextran levels in the extracted juice. The washed beets
are then sliced into thin noodle-like strips called cossettes, which are then conveyed
to the extraction system. The aim of the diffusion is to extract the maximum amount
of sucrose with the minimum of impurities (non-sugar substances). The dry
substance and pH of extracted juice range from 10 to 18 % and 5.4 to 5.6,
respectively, which are quite favourable conditions for multiplication of
microorganisms such as Leuconostoc, Streptococcus and Lactobacillus spp., etc. , the
clarification process of juice practically eliminates the microorganisms present in it
(Gupta and Prabhu, 1993). To limit the thermophilic bacterial action, the feed water
may be dosed with formaldehyde. A control of feed water pH is also practiced (van
der Poel et al., 1998).
During juice purification, the juice from the extraction process is separated from
other non-sugar substances. Therefore, the juice is progressively heated and lime is
added at three different points in the juice purification system. The high temperature
and the lime break down the main part of the impurities in solution. Carbon dioxide
is then added and calcium carbonate precipitate is formed. The juice-calcium
carbonate mixture is then filtered to remove the calcium carbonate leaving the clear
juice. Dextran formation occurs during storage and the extraction process, whereas, it
is reduced during the clarification and filtration processes (Gupta and Prabhu, 1993).
14
The juice must then be concentrated by a multi-stage evaporator. The resulting thick
juice contains about 70 % solid. Some part of the thick juice is stored in large outside
tanks for processing after all harvested beets are processed. This allows the factory to
slice about 50 % more beets than the crystallization capacity can handle. Sugar is
crystallized from the thick juice by continued evaporation of water in vacuum pans.
The crystals are separated from the syrup in centrifugal machines. The crystals are
washed with water and then dried in a rotary drum drier (McGinnis, 1982; van der
Poel et al., 1998).
Looking specifically at the occurrence and progression of dextran in sugar
production, most of the available examinations are reported from trials in sugar cane
plants. Usually, dextran levels in sugar cane processing are higher than in sugar beet
processing as sugar cane grows in warm areas and is more vulnerable to infection by
microorganisms. Only few information is available about the progression of dextran
in sugar beet factories. In the following paragraph a short overview of reports should
be given.
Dextran producing bacteria are found in high sucrose areas, including the soil in
sugar cane fields, in sugar juices and on exposed equipment in cane and beet sugar
mills and sugar refineries (Clarke and Godshall, 1988; Robyt, 1986). Dextran levels
in cane are usually controlled by good planning of cane deliveries, and good hygiene
in the cane yard, the mills and the factory. However, there are times when weather
problems (storms, freeze) cause unavoidable damage to cane and delay deliveries. In
these cases, infection and dextran levels build up in cane before it reaches the factory
(Atkins and McCowage, 1984; Inkerman, 1980).
15
Extracting the juice
Evaporation of the juice
Purification of the juice
Crystallization
Figure 5: The major steps for the manufacture of sugar from sugar beets (Südzucker AG website, Germany)
16
Dextran levels as high as 10,000 mg/kg DS have been reported in syrup (Wells and
James, 1976). The level of dextran in raw sugar is of commercial importance because
it affects the purchase price for raw sugar (Clarke and Godshall, 1988). Levels in
raw sugar range up to 5000 mg/kg (total dextran) and in refined sugar up to 2500
mg/kg (total dextran). They added, that in recent years dextran concentration in raw
sugar has been risen because of the increased use of mechanical harvesting systems
which tend to damage the cane, allowing entry of the causative organisms into the
cane stalk (Khaleifah, 2001). As an example Table 3 documents the high dextran
levels in different Louisiana sugar factories (Cuddihy and Day, 1999).
Table 3: Dextran in process streams measured at different Louisiana sugar factories(F1, F2, F3
and F4) (Cuddihy and Day, 1999)
Samples
Dextran mg/kg DS*
F1
F2
F3
F4
Mixed Juice
2690
1094
1928
4650
Clarified Juice
2181
1094
1928
4560
Syrup
2602
1239
1986
3858
* Dextran measured by ASI2 method according to (Sarkar and Day, 1986)
2.5
Dextrans associated with processing problems
In sugar production, dextrans are undesirable compounds produced by contaminant
microorganisms from sucrose (Jimenez, 2005). On contrast, dextrans are used in the
manufacturing of blood plasma extenders, heparin substitutes for anticoagulant
therapy, cosmetics, and other products (Alsop, 1983; Kim and Day, 2004; Leathers et
al., 1995; Sutherland, 1996).
From an industrial point of view, studies have shown that Leuconostoc
mesenteroides strains are able to utilize high percentages of the sugar present in
juices in a short time period. This implies important losses if the infection level is not
controlled. High loss in product yield (sucrose) and contamination of the industrial
17
process cause various problems such as: an increase of juice viscosity which
produces blockage in the process line, pumps and filters; lower heat exchange;
evaporation diminution; decrease in the efficiency and output of crystallization;
crystal shape distortion; blockages in centrifuges and sucrose losses to molasses.
Dextran in juice, syrup and sugars can cause false polarization. Because dextran is
highly dextrorotatory, approximately three times that of sucrose and gives a falsely
high polarization, unless removed prior to test. Furthermore, high dextran levels
reduce the efficiency of clarification techniques used in polarization determinations
(Clarke et al., 1997; Cuddihy et al., 2000; Guglielmone et al., 2000).
In addition, the farmer is mainly paid based on the polarimeter reading, therefore,
there is an obvious need for a dextran test in the core laboratory. The benefits arising
from this would be the correction of the falsified reading and the identification of the
sources of dextran contamination entering the factory (Singleton et al., 2001).
Measurements of the sucrose content of juices by NIR polarimetry, at 880 nm, are
not affected by the yellow/brown color remaining after conventional filtration, using
a filter aid. Readings obtained using NIR polarimetry in comparison to those at the
sodium wavelength have been previously shown to be more reproducible, and more
sensitive to interference by high dextran concentrations (Wilson, 1996).
The NIR polarimeter is based on a linear relationship between the change in optical
activity produced by enzymatic cleavage of dextran and the original dextran
concentration. There is no significant difference in the initial change of optical
activity produced by enzymatic hydrolysis of different molecular weight dextrans
using dextranase (Singleton, 2002).
At the clarification stage in sugar production, abnormally high dextran levels cause
severe effects. Juice derived from deteriorated cane contains excess acids and
requires extra lime addition to neutralize the acidity. The presence of excess gums
increases juice viscosity, which retards the setting time in clarifiers and prevents
satisfactory removal of suspended matter. Consequently, the clarified juice is cloudy,
resulting in higher mud volumes at the filter station. Filtration of mud is also
impeded by the excess viscosity of the juice. Furthermore, Jimenez, (2005) reported
that the high viscosity of the juices and the presence of high molecular weight
18
dextrans in them along with other insoluble matter cause a blockage of the filters
provoking juice losses due to spills that are generally underestimated.
The changes in the physical properties of sugar solution have been attributed to
dextran mediated viscosity alterations. Effects are changes in heat transfer
characteristics and changes in the crystallization characteristic of the sucrose. The
most damaging effects of high levels of dextran are seen on crystal growth.
Laboratory studies in Australia have shown a sugar loss to molasses of between 1.2
to 1.4 purity points, which can be, expected for every 1,000 mg/kg DS of dextran in
molasses. This is equivalent to about 250 mg/kg DS in mixed juice (Miller and
Wright, 1977).
The problems associated with dextran contamination, in both the factory and the
refinery, are well documented in the literature and thus are briefly summarized in
Table 4.
Table 4: Summary of the detrimental effects of dextran in terms of the losses it leads to
according to Singleton et al., (2001).
Production losses
Sucrose losses
Direct financial losses
Increased viscosity leads to
Dextran
False polarimeter reading
reduced throughput due to:
formation
leads to overpayment to
farmer
¾ Poor filtration rate
¾ Reduced evaporation rate
¾ Reduced flocculation rate
¾ Slow mud settling
To molasses
(melassigenic
In trade of raw sugar as
effect)
part of dextran penalty
system using unreliable
tests
¾ Poor crystallization
(elongation)
2.6
19
Crystallization process
The most damaging effects of elevated dextran concentrations in a technical sucrose
solution are foreseen in the crystallization process. Dextrans slow down the
crystallization rate or even inhibit crystallization (i.e., they have a high melassigenic
effect).
There are different methods for sucrose crystallization and to follow the growth rate
of sucrose crystals during crystallization process. In this work, the isothermal
crystallization method was used to study the effect of dextran molecules on the
crystallization process without interference of other factors. Different authors in
literature focused the characterization of parameters influencing the crystallization
process as well as mathematical approaches for the description of crystallization
during sugar production.
2.6.1
Growth rate of sucrose crystals
The sucrose crystallization process is the transfer of sucrose from the solution phase
to the solid phase. Supersaturation is the measure of the driving force to cause this
transfer to take place.
There are three simple basic methods to grow crystals from a solution
¾ The evaporation method
¾ The slowly cooling method
¾ Isothermal crystallization method
The evaporation and the cooling method require the beginning with a saturated sugar
solution but the isothermal crystallization method requires beginning with a
supersaturated sugar solution. The evaporation method employs the use of heat to
separate the water from the sugar. The slow cooling method produces sugar crystals
by letting a hot saturated sugar solution cool down slowly. The slower the process,
the bigger sugar crystals are formed. The process may take several hours to several
days. The isothermal crystallization method as a laboratory method uses a constant
temperature for crystallization. The crystallization rate can be calculated by
following the progression of dry substance (WDS) in solution during the
crystallization process.
20
Six general systems for initiating crystals are recognized by McGinnis, (1982):
1- Homogeneous – new crystal particle formation as the result of
supersaturation only.
2- Heterogeneous - new crystal particle formation as the result of
supersaturation and the presence of foreign insoluble material.
3- Secondary - new crystal particle formation as the result of supersaturation and
in the presence of an ongoing, growing crystal crop.
4- Attrition – crystal population increase due to the fracture ore impact chipping
or breaking of existing, growing crystals into smaller particles, each capable
of growth.
5- Full Seeding – preparation of seed crystals by salting-out, grinding,
screening, or centrifugal separation, mixing as a slurry or magma; adding the
mixture as a controlled population into supersaturated liquor for growth only.
6- Ultrasonic – liquid conditions similar to homogeneous except a much lower
supersaturation. Ultrasonic irradiation creates mechanical perturbations
adequate to exceed the energy barrier of homogeneous nucleation.
According to Gillet, (1977) and Elahi, (2004), the success of the crystallization
process depends on several factors as follows:
¾ Supersaturation of solution
¾ Crystallization temperature
¾ Relative velocity between crystals and mother liquor
¾ Nature and concentration of impurities in solution
¾ The crystal surface area
Schliephake and Ekelhof, (1983) and Ekelhof, (1997) explained the relation between
the growth rate of sucrose crystals and many parameters such as supersaturation,
temperature and relative velocity between crystals and solution during the
crystallization process. The relationship between the growth rate of sucrose crystals
and the supersaturation of solutions with different purities is shown in Figure 6. The
increase of solution purity leads to an increase of growth rate.
21
Crystal growth in g/(m2.min)
1 .2
q = 10 0 %
0 .9
0 .6
q = 90 %
0 .3
q = 80 %
q = 70 %
q = 60 %
0
1 .0
1 .1
1 .2
1.3
1.4
S up e rs atu ra tio n c o e fficie nt
Figure 6: Growth rate at 60 °C as a function of supersaturation at different purities,
(Schliephake and Ekelhof, 1983)
Another important factor affecting the rate of sucrose crystallization is temperature.
Figure 7 shows the strong temperature effect on the crystal growth rate, a factor of
particular importance in cooling crystallization.
In addition Pot et al., (1984) investigated the effect of crystal size on the crystal
growth rate and found that the growth of crystals >100 µm is determined by the
diffusion velocity.
1.2
Crystal growth in g/(m2.min)
q = 100%
0.9
0.6
q = 90%
q = 80%
0.3
q = 70%
q = 60%
0
0
20
40
60
80
Temperature in °C
Figure 7: Crystal growth rate as a function of temperature at different purities and constant
supersaturation (Schliephake and Ekelhof, 1983)
22
The crystal growth rate is also affected by high molecular mass substances and
colorants in syrups, which are partially adsorbed on the crystal surface and thus
impede the insertion of sucrose molecules into the lattice (Grimsey and Herrington,
1996; Rogé et al., 2007).
2.6.2
Crystallization kinetics
Two fundamental crystallization theories are briefly described: the theory of the
adsorption layer, which deals with the crystal surface; and the diffusion theory,
which mainly considers the phenomena occurring at the crystal solution interface.
Another approach is proposed based on the chaos and complexity theory.
The chaos and complexity theory deals with the nonreversible thermodynamics of
the conditions apart from equilibrium. It is correlated also with the concept of
entropy, which, being a measure of disorder and uncertainty becomes the cause for
creation of new patterns of mass and energy dissipation. These are called “dissipative
structures from the 1977 Nobel laureate Ilya Prigogine”. Apart from the different
levels of concentration, viscosity, temperature, pressure, supersaturation, etc., of
mother liquor, there are different impurities, which influence sucrose crystal growth
morphology, modifying the habit of the crystals. The sugar crystal is an “equilibrium
structure but bears on its surface and on its inner structure as fingerprints the history
of a dissipative process” (Cbristodoulou, 2000).
The relation between the diffusion, surface reaction and crystallization rate of
sucrose was illustrated by (Cossairt, 1982; Ekelhof, 1997; Houghton et al., 1998;
Silin, 1958). If the diffusion theory is considered, the variation of the solution
concentration near the surface hast to be regarded.
The crystallization rate is given by a diffusion process of molecules through the
stagnant layer and the reaction process corresponding to the integration of molecules
into the crystal structure through the adsorption layer. These two steps can be
illustrated by equations 2-1 and 2-2:
dm
= k D ⋅ A ⋅ [c L − cG ]
dt
(Diffusion)
(2-1)
dm
= k R ⋅ A ⋅ [cG − cSat ] (Surface reaction)
dt
(2-2)
23
Where
Crystallization rate (were m mass and t time)
dm / dt
D
Diffusion coefficient (m2/s)
kD
Coefficient speed of the material transfer (m/s)
kR
Coefficient speed of surface reaction
A
Crystal surface (m2)
cL
Concentration of solution (kg/m3)
cG
Concentration of boundary layer (kg/m3)
csat
Mother liquor concentration at saturation point (kg/m3)
The Noyes and Whitney’s formula (Noyes and Whitney, 1897) below for
crystallization is used to review the basic control parameters of the crystallization
process:
dm
= k d ⋅ A ⋅ C sat ⋅ (SS − 1)
dt
(2-3)
where = Csat = concentration of saturated liquor and SS = supersaturation
Schliephake and Ekelhof, (1983) reported that, the change of the supersaturation at
the same time, the difference of concentration between concentration of solution (CL)
and concentration of saturated solution (Csat) causes a change of the crystal growth
rate. Thus, they derived the following equation to calculate kD from the above
equations:
⎛ dm 1 ⎞
⋅ ⎟ ⋅ kR
⎜
dt A ⎠
⎝
kD =
⎛ dm 1 ⎞
⋅ ⎟
k R (Δc − Δ * c ) − ⎜
⎝ dt A ⎠
(2-4)
where (Δc − Δ * c ) is the effective concentration difference (kg/m3)
The parameters k D and k R can vary depending upon the crystallization conditions,
and in particular upon temperature, stirring and the presence of non-sugars
(Mantovani and Vaccari, 1998).
24
There are many parameters which have an effect on the diffusion coefficient kD.
(Schliephake and Ekelhof, 1983) described the coefficient as
k D = f (TL , d K , ρ L ,η L , DL , ε )
(2-5)
where
TL
Temperature of solution
dK
Crystal diameter
ρL
Solution density
ηL
Solution viscosity
ε
Relative velocity volume
The relative velocity volume was calculated by the following equation:
ε=
m Su
−1
mCry
m Su
ρ
+ L −1
mCry ρ Cry
(2-6)
where
mSu
Crystal suspension mass
mCry
Crystal mass
ρ Cry
Crystal density
From the above equations, it can be stated that not only temperature can effect the
diffusion coefficient but also crystal diameter, density of solution, relative velocity
and solution viscosity which plays an important role in the diffusion processes in the
solution. Also, it can be indicated that the surface reaction coefficient is affected by
temperature and solution purity, where the other factors are constant
The surface reaction rate kR was calculated by means of the equation 2-7 for any
temperature.
k R = k R,0 ⋅ e
−
E a,R
RT
(2-7)
where Ea = activation energy of the surface reactions = 86.2 kJ/mol, R = general gas
constant = 8.3147 J/mol*K, T = absolute temperature (Kelvin) k
∞
= Frequency
factor. For pure sucrose solutions can be kR can be calculated with the help of
equation 2-7 for any temperature as follows:
25
k R = 3.892 E + 8 * 2.7182818
−(
86.2
)
RT
(2-8)
As far as temperature is concerned, it is well known that, at low temperature, the
crystallization process is controlled by the surface reaction whereas at high
temperature it is diffusion, which controls the crystallization process. These results
are similar to those reported by (Cossairt, 1982; Houghton et al., 1998).
The correlation between temperature and the surface reaction rate kR was illustrated
by (Ekelhof, 1997). The temperature dependence of the determined kR-values is a
linear connection like expected from Arrhenius relation (Figure 8) (Golovin and
Grerasimenko, 1959; Maurandi et al., 1988; Schliephake and Austmeyer, 1976) .
Figure 8: Surface reaction coefficient kR dependent upon the reciprocal value of the absolute
temperature T given for different purities (Ekelhof, 1997).
As expected by the recently introduced “spiral nucleation model”, this alternative
definition is found to be size-independent over the considered supersaturation range.
At the same time, the conventional overall growth rate expressed per time and
surface area units is found to be linearly dependent on crystal size. Besides being
theoretically consistent, the volumetric growth rate concept is of great practical
26
interest since crystal growth kinetics can be calculated in situations of unknown
crystal number and size. The two-way effect of crystal size on mass transfer rates and
on the integration kinetics is investigated by measuring the sucrose dissolution rates
under reciprocal conditions of the growth experiments. Both effects are adequately
described by combining a well-established diffusion-integration model and the spiral
nucleation mechanism (Martins and Rocha, 2000).
For a deeper insight into the theoretical growth morphology it is necessary to apply
the HP theory of Hartman and Perdok, (1955) on the crystal structure. This theory is
based on the study of the periodic bond chains (PBCs) that form during
crystallization. The faces are classified into three types, in the first case the faces are
so called F-faces (Flat), in the second case S-faces (Stepped) and in the third case Kfaces (Kinked). They occur as shown in Figure 9. The three types of faces have
different growth behaviors depending upon the different density of the growth sites
(kinks).
Figure 9: Hypothetical crystal (a) with schematic drawing of the three kinds of faces PBCs (b)
The several steps in the insertion of a molecule from solution into the crystal lattice
are shown in Figure 10. The driving force in this process is the supersaturation
maintained by either water evaporation or temperature reduction. With increasing
amount of evaporated water during evaporation crystallization, the crystal surface
becomes inadequate, the supersaturation increases and so a new crystal surface is
formed by false grain formation (Schiweck and Mannheim, 1998).
27
Crystal half layer
7+8
7
7
4
5
9
3
6
Step
1
2
7
Figure 10: Diagrammatic representation of the processes involved in crystal growth from
solution, according to Elwell and Scheel ,(1975) as modified by Kruse and Ulrich, (1993).
The description of Figure 10 can be summed up as follows: 1 Diffusion of hydrated
crystal building blocks from the solution to the crystal surface. 2 Adsorption of
hydrated crystal building blocks (cluster) and partial dehydration on the crystal
surface. 3 Surface diffusion of hydrated crystal building blocks to a step. 4
Adsorption of hydrated crystal building blocks and partial dehydration on the step. 5
Diffusion of hydrated crystal building blocks along a step to a semi-crystal position.
6 Insertion of crystal building blocks into a semi-crystal position and complete
dehydration; 7 Diffusion of the liberated hydrate envelope into solution. 8 Liberation
of latent heat on insertion of crystal building blocks into a semi-crystal position. 9
Desorption of hydrated crystal building blocks from the crystal surface into the
solution.
2.6.3
Parameters influencing crystallization kinetics
Whatever the origin, the polysaccharides from beet processing are found as minor
constituents in white sugar and their association with nitrogen and cations can cause
the coloration of the crystals. These polysaccharides generally have a high
hygroscopicity and their presence at the surface of sugar crystals my affect the
stability of crystalline sugar during storage and provoke caking. Moreover, occlusion
and crystal elongation (c-axis) are observed in presence of dextran (Gudshall, 1992;
Parrisch and Clarke, 1983).
During processing, macromolecules (e.g. dextran) increase viscosity, slow or inhibit
crystallization, and increase the loss of sucrose to molasses (i.e. they have a high
melassigenic effect). Because of their carbohydrate nature and high solubility, they
are difficult to remove in processing, and tend to be included in the raw sugar crystal,
28
going into the refining process and causing similar problems in refining (Cuddihy et
al., 2000; Godshall et al., 1994).
The viscosity is a dominating factor in the technology of the process. The growth rate
is sensitive to variation in crystal size and slightly influenced by surface integration,
with the diffusion step in crystal growth as a significant factor in determining the
overall rates (Gumaraes et al., 1995). Frenkel, (1958) has found that the absolute
viscosity of sugar solutions is related to the absolute temperature by an equation of
the form:
η = A *10B / T
(2-9)
where:
η
Dynamic viscosity
A and B
Constants
T
Temperature
Figure 11 shows the relationship between the viscosity in pure and impure solution
and solution concentration at different temperatures (40 to 80°C) according to
Schliephake and Ekelhof, (1983). They illustrated that the solution viscosity
increased with a decrease of temperatures. However, it increased with the increase of
solution concentration. These correlations between relative viscosity η u / η r and other
factors were described as follows:
⎡1 − q
⎤
wDS
(4.734 − 0.0379ϑ ) ⋅
= 1− ⎢
⎥
19 − 18wDS ⎦
ηr
⎣ 0.4
nu
(2-10)
29
η mPa.s
1000
100
10
1
0
20
40
W
DS
60
80
%
Figure 11: The viscosity of the pure and impure sucrose solution according to Ekelhof, (1997)
2.6.4
Crystal morphology
The normal morphology shown by sucrose crystals grown from pure solution is
depicted in Figure 12 (Vavrinecz, 1965). The three primary hydroxyl groups at the C1' and C-6' (Fructose) and the C-6 (glucose) belong to the three hydroxymethyl side's
groups of the sucrose. The others are secondary hydroxyl groups at the heterocyclic
ring. The average values of the surface angles for proportional axis were measured
by different investigators as, a : b : c = 1.2543 : 1 : 0.8878 with an angle of the a to
the c axis of β = 103°30 (Vavrinecz, 1965). So far 15 different surfaces were
observed, which arise most frequently with the technical sucrose crystallization.
Under the influences of non-sugar materials and other factors, which affect on the
growth conditions such as e.g. temperature and supersaturation of solution, the
surface growth and thus the habit of the sucrose crystal can vary strongly (Bubnik et
al., 1992; Vaccari et al., 1999; Vaccari et al., 2002). The presence of
oligosaccharides such as raffinose, which is present in sugar beets, causes an
elongation of the crystal toward the b-axis to a needle form (Mantovani et al., 1967;
Vaccari et al., 1986). Dextran also causes an elongation of the crystal toward the c
axis due to slowing down the growth of the p and p’ surfaces (Sutherland and Paton,
1969).
30
Figure 12: Schematic representation of a sucrose crystal with the surface designation according
to Vavrinecz ( 1965)
Bubnik et al., (1992) studied the relationship between the c/b ratio if dextran
concentration was increased (Figure 13). They observed that the effect of dextran on
crystal elongation was much more striking compared to that obtained with invert
sugar and 300 % higher than for pure solution, at the highest impurity concentration.
This correlation between c/b and dextran concentration was described as follows:
Rd = Rs + ao ⋅ cd0.1 + bo ⋅ cd0.7
where:
Rd
c/b ratio in the presence of dextran
Rs
c/b ratio for pure sucrose solution (= 0.70)
cd
Dextran concentration (g/100 g water)
ao
Constant (0.1363)
bo
Constant (0.1234)
(2-11)
31
+
C
+
C
+b
(A)
+b
(A)
(A)
Figure 13: (A) Sucrose crystal growth in the presence of dextran (40g/100g water), (B) One of
the crystals shown in (A) and (C) Sucrose crystal growth in the presence of glucose, fructose and
dextran (50g/100g water each) (According to Bubnik et al., (1992)
Also, it was possible to calculate a two-parameter function which would permit
calculation of the c/b ratio as a function of both invert sugar and dextran
concentrations:
R = Ri + A ⋅ cd0.1 + B ⋅ cd0.7
R
c/b ratio in the presence of impurities
Ri
c/b ratio in the presence of invert sugar
cd
Dextran concentration (g/100g water)
with
A = a o + a1 + ci + a 2 ⋅ ci0.7
ao
Constant (0.1363)
a1
Constant (0.102)
a2
Constant (-0.00193)
c
Invert sugar concentration
with
B = bo + bi * ciC
bo
Constant (0.1234)
b1
Constant (-0.0147)
C
Constant (0.270)
ci
Invert sugar concentration
(2-12)
32
Dextran products of various molecular weight result from infections of Leuconostoc
sp. Also, a needle like elongation of the c axis of the crystal may be caused by highly
1-6 linked dextran. However, 1-4 and 1-3 linkages also yield refractory and slowboiling syrups, but show little c axis elongation (Cossairt, 1982). It is also reported
that smaller molecular weight dextrans are especially involved in the effect of c axis
elongation (Singleton, 2002)
From the processing point of view the development of re-entrant angles with their
effects is becoming worse as aggregates become more complex. These re-entrant
angles are traps for mother liquor and zones, which are extraordinarily difficult to
wash for the removal of impurities (non-sugars). The trapped mother liquor may
even be present as inclusions between the individual conglomerated crystals
(Houghton, 1998).
The effect that dextran has on sugar crystal shape, to elongate the crystal or cause
needle grain, also increases the loss to molasses by blinding centrifugal screens with
elongated crystals (Imrie and Tilbury, 1972)
2.7
The Economic gain
In a sugar factory, the crystallization is an important step, which determines the yield
of the sugar from sugar beet and cane. About 85% of the present sugar (sucrose) in
sugar beet can be crystallized as sugar product (Figure 14). The sugar losses are
almost 3% during the extraction and clarification processes and around 12% to
molasses (Ekelhof, 1997).
The existence of quality points for dextran in raw sugar contracts has provided a
standard for a penalty by refiners. The penalty is calculated from a sliding scale
based upon the sugar dextran concentration.
33
Beet
Extraction
Purification
NS
3%
100%
S
Evaporation
Multi-Stages for
Crystallization
85%
White
Sugar
12%
Molasses
Figure 14: Partitions of sugar loss during different process stages of sugar production (Ekelhof,
1997)
Studies in Australia have shown a sugar loss to molasses of 1.2 to 1.4 purity points,
which can be expected for every 1,000 mg/kg DS of dextran in molasses. This is
equivalent to about 250 mg/kg DS in mixed juice (Miller and Wright, 1977).
It is estimated that for every 300 mg/kg DS dextran in syrup there is a 1% increase in
molasses purity (the percentage ratio of sucrose in total solids in a sugar solution)
(Atkins and McCowage, 1984; Clarke et al., 1997; Godshall et al., 1994;
Guglielmone et al., 2000).
The presence of dextran above 250 mg/kg DS on solids in raw sugar brings forth
penalties from the sugar refiner (Chung, 2000; Day, 1992). Effects of dextran in juice
are shown in Table 5.
34
Table 5: Effects of dextran in juice on molasses purity
Dextran in juice
(ppm/WDS)
Effect
0
None
250
1 point loss in molasses purity
500
2 point loss in molasses purity
1000
Detectable crystal elongation, 5 point loss in molasses purity
1500
Significant operational problems
3000
Severe problems
Source: Adapted from Chung, 2000; Day, (1986).
The economic losses caused by dextran are continuous throughout the process, since
its early content in the juices falsely increases the amount of sugar calculated for
them and alters the production indicators of the factory. This is due to the
dextrorotatory characteristic of dextrans that polarize approximately three times more
than sucrose producing a high false polarization value (Jimenez, 2005).
The evaluation of dextran levels in raw sugars with the respective sucrose losses
incurred to produce these dextran levels and the amounts of fructose and acids (about
30% yield) formed is shown in Table 6
Table 6: Dextran levels and sucrose loss in raw sugars (Bose and Singh, 1981)
Dextran
Sucrose loss
Fructose formed
% Acid produced
(%)
(Kg /ton sugar)
(Kg /ton sugar)
0.05
0.20
0.99
0.07
0.10
0.40
1.98
0.17
1.50
2.00
9.90
0.70
35
These amounts of sucrose loss represent only those lost directly due to dextran
formation. Three to five times of these levels may be lost later in processing because
of the other organic material formed conjointly with dextran (Bose and Singh, 1981).
Dextran content in sugar is a major concern for end users such as candy
manufacturers. Contamination of the sugar with dextran, above a certain ppm level,
will affect hard candy processing. The impact is measured in changes in candy
thickness/weight and is related to dextran content in sugar (Haynes, 2004; Jimenez,
2005).
36
Material and methods
3 Material and methods
3.1
Material
Samples: sugar beet slices (cosettes), raw juice, clarified juice, thick juice and the
final products, sugar and molasses were collected from three different Egyptian
factories. Factories 1 and 2 belong to Delta Company in north Egypt and factory 3
belongs to Egyptian Sugar Company in middle Egypt.
Dextrans: Three different molecular mass fractions of dextran (T40: M~40,000
g/mol, product Nr. 31389, T500: M~500,000 g/mol, product Nr. 31392 and T2000:
M~2,000,000 g/mol, product Nr. 95771) from Sigma-Aldrich were utilized. All
fractions were produced by Leuconostoc ssp.
Chemical for analysis: all chemicals were obtained from Sigma-Aldrich, Germany.
3.2
3.2.1
Analytical methods
Determination of dextran
3.2.1.1 Robert method
Dextran was determined according to Roberts, (1983) and AOAC, (1990). Roberts
copper method determines dextran after polysaccharide precipitation from sugar
solutions by 80 % ethanol. Quantification is made calorimetrically using PhenolH2SO4, after a second precipitation with alkaline copper reagent. The amount of
dextran mDE in mg/kg DS in the samples was calculated as follows:
mDE =
1 1 C
⋅ ⋅ ⋅ E ⋅ F ⋅ 10 5
A B D
(3-1)
A
Dry substance ( wDS )
B
mL of aliquots taken for alcohol precipitation (10 ml)
C
mL of solution of alcohol precipitate (25 ml)
D
mL of aliquot taken for copper precipitation (10ml)
E
mL of final solution of copper-dextran complex (25ml)
F
mg/mL dextran (from standard curve)
37
3.2.1.2 Haze method
The determination of dextran in sugar solutions by a modified alcohol Haze method
is conducted according to the ICUMSA method (1994). The test sample is dissolved
in water. Soluble starch is destroyed by incubation with a suitable enzyme (Novo
Termamyl 120L, Novo Industri A/S, Bagsvaerd, Denmark). Protein is removed by
precipitation with trichloroacetic acid (TCA) followed by filtration with acid-washed
kieselguhr. The dextran haze is produced by diluting an aliquot of the treated, filtered
solution to twice the aliquot volume by the addition of ethanol. The turbidity of the
dextran haze is measured by reading the absorbance in a spectrophotometer at a
wavelength of 720 nm. The method is standardized against a commercially available
dextran.
3.2.2
Microbiological experiments
3.2.2.1 Isolation
Sugar beet, cossettes and raw juice were collected during the practical course (2005)
in the Department of Food Engineering, Technical University Berlin. Samples (10 g)
were token and diluted by sterilized distilled water to 100 g. The serial dilutions of
collected samples (10-1 to 10-6) were made and 1 ml portions of the appropriate
dilutions were pour-plated on MRS-Agar media (De Man et al., 1960). The
cultivated microorganisms were incubated anaerobically for 48 hours at 30±1 °C for
enumeration of microorganisms (Leuconostocs sp) (Beukes et al., 2001).
The MRS-broth (Bouillon) consists of (g/liter): Peptone from casein 10, meat extract
8.0, yeast extract 4.0, D (+)-glucose 20.0, di-potassiumhydrogenphosphate 2.0,
Tween 80 1.0, di-ammoniumhydrogencitrate 2.0, sodium acetate 5.0, magnesium
sulfate 0.2 and Manganese sulfate 0.04. To provide MRS-Agar media, agar was
added to the mixture.
3.2.2.2 Identification
3.2.2.2.1 Gas and acid formation
MRS-Bouillon with Durham tubes was used to perform this test with Lactic acid
bacteria according to Back, (1994).
38
3.2.2.2.2 Catalase test
The catalase test involves adding of 5 % hydrogen peroxide (H2O2) to a culture
sample or agar slant. If the bacteria in question produce catalase, they will convert
the hydrogen peroxide and oxygen gas will be evolved. The evolution of gas causes
bubbles (Figure 15) as an indicator of a positive test (Back, 1994).
Figure 15: Colony of bacteria mixed in a 5% solution of H2O2 demonstrating a positive and
negative test for producing of catalase.
3.2.2.2.3 Gram characteristics (KOH-Test)
After the mixing of the bacterial colony with ca. 3 % potassium hydroxide on a glass
slide, the KOH solution characteristically became very viscous and mucoid with
gram-negative bacteria. The KOH test was only considered positive if stringing
occurred within the first 30 s of mixing of the bacteria in KOH solution. Grampositive bacteria suspended in the KOH solution generally displayed no reaction
(absence of stringing) (Halebian et al., 1981).
3.2.2.2.4 Identification by API 50 CHL test
API 50 CHL Medium, intended for the identification of the genus Lactobacillus and
related organisms, is a ready-to-use medium, which enables the fermentation of 49
carbohydrates on the API 50 CHL strip to be studied.
A suspension is made in the medium with the microorganism to be tested and each
tube of the strip is inoculated. During incubation, carbohydrates are fermented to
acids, which produce a decrease in pH, detected by color change of the indicator. The
results make up the biochemical profile of the strain and are used in its identification
or typing.
39
3.2.2.2.5 L/D-Lactic acid test
For the determination of D- and L- lactic acid, the UV- method, cat. no.
11112821035 from R-Biopharm AG was used. In the presence of D-lactate
dehydrogenase (D-LDH), D-lactic acid (D-lactate) is oxidized to pyruvate by
nicotinamide-adenine dinucleotide (NAD). The oxidation of L-lactic acid requires
the presence of the enzyme L-lactate dehydrogenase (L-LDH). The equilibrium of
these reactions lies on the side of lactate. By trapping pyruvate in a subsequent
reaction catalyzed by the enzyme glutamate-pyruvate transaminase (GPT) in the
presence of L-glutamate, the equilibrium can be displaced in favour of pyruvate and
NADH. The amount of NADH formed in the above reactions is stoichiometric to the
amount of D-lactic acid and of L-lactic acid, respectively. The increase in NADH is
determined by means of its light absorbance at 334, 340 or 365 nm.
3.2.3
Crystallization experiments
3.2.3.1 Measurement of growth rate of sucrose crystals
A laboratory crystallization unit was built according to Wittenberg, (2001). The unit
scheme is given in Figure 16. A double glass wall crystallizer was equipped with
stirrer, automatic measurement devices for dry substance content (Refractometer
IPR2, Schmidt and Haensch) and temperature as well as temperature control. Data
processing was realized on a central computer unit. Dry substance and temperature
were determined every 120 s. Batch isothermal crystallization experiments were
carried at constant temperatures (60, 65 and 70 °C) by seeding syrup with a
supersaturation of 1.15. The experiment was stopped, when the supersaturation had
reached 1.05. Varying admixtures of different dextran fractions (T40, T500 and
T2000) at different concentrations (500 – 5000 mg/kg DS) were used.
40
2
M
1
T
Crystallizer
Central Computer
3
T +/-
Thermostat
4
Control unit
5
Figure 16: Pilot scheme of laboratory crystallization device
1- Thermometer
2 - Automatic Stirrer
3- Double glass wall
4- Cooling water
5- Refractometer (IPR2, Schmidt and Haensch)
3.2.3.1.1 Required amount of dextran and seed
The amount of dextran m DE in mg added to the crystallizing charge was calculated
according to Equation (3-2).
mDE = a ⋅ b
(3-2)
with
a = m So ⋅ w DS / 100
b = m # DE ⋅100 / (100 − wW, DE )
mSo
Total mass of solution in (kg)
wDS
Dry substance content in (%)
mW.DE Water content of dextran in %
m # DE Target dextran concentration in mg/kg DS
After reaching the required temperature, the solution in the crystallizer was seeded
with sucrose crystals (size 200 µm) using a syringe. The amount of seed mSeed in g
was calculated as follows:
41
mSeed
⎛d
= mMa ⋅ wCry ⋅ ⎜⎜ i
⎝ df
⎞
⎟⎟
⎠
3
(3-3)
mMa Mass of the massecuite in g
wCry Final crystal content in massecuite
di
Initial size of the crystal (200 µm)
df
Final size of the crystal
A sample was taken before the seeding point to carry out the first image analysis for
the evaluation of the solubilization process. Further on, samples for image analysis
were taken every 30 minutes in order to follow the growth of crystals through the
crystallization.
3.2.3.1.2 Calculation of the growth rate of sucrose crystals:
In the present work, crystallization was pursued basing on the change of the
refractometric dry substance content and the temperature as:
⎛ wDS, ML, t
⎞ ⎛ wDS, ML, t +1
⎞
ΔmS, Cry = ⎜⎜
⋅ mW ⎟⎟ − ⎜⎜
⋅ mW ⎟⎟
⎝ 100 − wDS, ML, t
⎠ ⎝ 100 − wDS, ML, t +1
⎠
Δ
(3-4)
Difference
mS, Cry Crystallized sucrose mass
t
Time (min)
wW
Mass of water which can be calculated as follow:
mW = mSo −
ML
(mSo ⋅ wDS,ML )
100
(3-5)
Mother liquor
The following equation helps to calculate the sucrose crystal surfaces area:
ACry = f A ⋅ mCry
2/3
⋅ nCry
ACry
Total crystal surfaces in m2
fA
Form factor (0.0423) according to Austmeyer, (1981)
(3-6)
42
mCry
Crystal mass
nCry
Number of crystals
The growth rate of sucrose crystals (G) in g /(m 2 ⋅ min) was calculated as follows
⎛ ΔmS,Cry
G = ⎜⎜
⎝ t
⎞ ⎛ 1
⎟⎟ ⋅ ⎜
⎜
⎠ ⎝ ACry
⎞
⎟
⎟
⎠
(3-7)
3.2.3.2 Dynamic viscosity
A capillary viscometer (Schott-Geräte, capillary no. 532 20/II, Apparatus no.
102221) was used. This viscometer is suitable to determine the kinematic viscosity of
Newtonian liquids according to DIN 51 562, part 1. The instrument constant K is
valid for the survey of the meniscus passage with stands type AVS/S, AVS/S-HT and
AVS/SK from Schott. It was evaluated as K = 0.1028 mm2/s2.
The kinematic viscosity v (mm2/s) can be calculated using the instrument constant in
the equation:
v = K ⋅t
t
(3-8)
Flow time in seconds corrected according to DIN 51 562, part 1.
The dynamic viscosity η (mPa.s) was calculated by:
η =ν ⋅ ρ
(3−9)
where
ρ
Solution density
3.2.3.3 Crystal morphology and surface topography
To examine of sucrose surface topography, a scanning electron microscope (SEM,
Hitachi S-2700) was used. After crystallization experiments, the mixture of crystals
and mother liquor (massecuite) was centrifuged and washed by water during
centrifugation, then dried in an oven at 70°C for 3 h.
3.2.3.4 Image analysis
For accurate estimation of the crystallization speed not only the sucrose crystals
quantity but also the beginning area of the sugar crystals is needed. Here, an image
analysis system (IMAGE), which enables a calculation of the middle diameter and
fractionation of sugar crystals was applied (Wagner, 2003).
3.2.4
43
Statistical analysis
Three-way ANOVA were considered in the present work to elucidate the main
effects of the methods of dextran determination with respect to concentrations and
molecular weights in addition to the interaction of these factors. At the same time the
concentration, the molecular weight factors and their interaction were considered in
each method of dextran determination. The homogeneity of variances was assumed
and Tukey-HSD was used at a significant of 0.05. The least sum of squares criterion
was applied to detect the best method for determination of dextran on the light of
molecular weights considered. These analyses were executed using SPSS-Package
release 9 (SPSS-Inc. 1998).
Results and discussion
4
44
4.1
Sensitivity and accuracy of different methods for the determination of
dextrans of varying molecular mass
In this work the sensitivity and accuracy of some common dextran determination
methods is examined in order to select the most appropriate for application in sugar
factories. In this context it must be mentioned that some important considerations are
required to be used in any method used in routine analysis of the sugar factories
according to (Singleton, 2002):
¾ Accurate: The test needs to be as accurate and reproducible as possible within
the constraints of time and simplicity.
¾ Specific: It must quantitatively detect total dextran and must not be biased
towards different molecular weights
¾ Rapid: The test must be able to cope with the high throughput of samples
arriving at factories and allow process decisions to be made quickly.
¾ Simple: To circumvent special training and employment of skilled staff for
repetitive testing the test must be easy to perform. To reduce sample time
sample preparation should also be straightforward and quick.
4.1.1
Robert’s Copper method sensitivity
It is very important to determine the amount of dextran in solution, performing a
standard curve with pure dextran solutions. Figure 17 shows the standard curves of
different dextran molecular fractions: T40, T500 and T2000. The results indicate that
the difference between low and high dextran molecular mass fractions increased
beginning at a dextran concentration ≥ 0.09 mg/ml. However, no significant
differences between all dextran standards were observed except at high dextran
concentrations.
45
Abs.(485nm)
1
0.9
R2 = 0.9863
0.8
R2 = 0.9933
0.7
R2 = 0.9687
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.02
0.04
0.06
0.08
0.1
0.12
Dex. conc. (mg/ml)
T40
T500
T2000
Figure 17: Standard Curves of dextran T40, T500 and T2000 by copper complex method.
From the mean of dextran standard curves, the dextran concentrations can be
calculated as follows:
m DE =
a − 0.033
7.6663
(4-1)
where
m DE
Concentration of dextran (mg/ml)
a = Sample extinction at 485nm.
From the present results, it can be indicated that the standard curve of dextran T2000
matched the measurement data for all molecular mass fractions better than other
curves, whereas R2 for T40 and T500 standard curves were 0.9863 and 0.9687,
respectively, while for T2000 was 0.9933. Consequently, in practical applications the
standard curve for T2000 was applied for all measurements to simplify the
calibration of measurement process, since it is an average of the other molecular
weight curves.
46
Figure 18 to Figure 20 show the patterns of dextran measured by the Robert’s
method and its recovery percentages in relation to the actual dextran added to sucrose
solutions for three different molecular mass fractions of dextran (T40, T500 and
T2000). The results indicated that the measured dextran was highly correlated with
actual ones (R2 > 0.993) whereas the recovery percentage exhibited variable
correlations (-0.891, 0.483 and 0.95 for T40, T500 and T2000, respectively). The
values of recovery percentage were testified against 100 % using least sum of square
referring to T2000 treatment to be the most accurate since its least sum of squares
was the lowest (109.64).
The patterns of variations in the recovery percentages under the effects of dextran
concentrations and dextran molecular weights were considered. The latter factor and
interaction with the concentration were significant (P < 0.01). The concentrations as a
factor have an insignificant effect on the recovery percentages (P = 0.062). Regarding
the measured dextran another pattern of variation was recorded since the
concentration and molecular weight main effects were significant (P<0.0001) with
insignificant interaction (P = 0.053) referring to their independence.
The results indicated that, at especially at low concentrations of the low molecular
dextran fraction T40 Robert’s method overestimated the dextran concentration. At
medium and high concentration recovery was satisfying for all dextran fractions.
47
120
100
2000
80
R2 = 0.9974
1500
60
1000
40
500
0
500
Dext.recovery (%)
Dex.measured (mg/kg DS)
2500
20
1000
1500
2000
Dextran present (mg/kg DS)
0
2500
Dex.recovery (%)
Figure 18: Sensitivity of copper complex method to determine dextran T40 in sucrose solutions
2500
2000
100
80
1500
R2 = 0.9952
1000
60
40
500
0
500
Dex. recovery (%)
Dext. measured (mg/kg DS)
120
20
1000
1500
2000
0
2500
Dex. recovery (%)
Figure 19: Sensitivity of copper complex method to determine dextran T500 in sucrose solutions
48
3000
2500
80
2000
R2 = 0.9952
1500
60
40
1000
Dex.recovery (%)
100
20
500
0
500
1000
1500
2000
0
2500
Dex.recovery (%)
Figure 20: Sensitivity of copper complex method to determine dextran T2000 in sucrose
solutions
4.1.2
Haze method sensitivity
Haze method reflects a pattern of variation in dextran measured similar to that of
Roberts’s method whereas the recovery pattern was different (Figure 21 to Figure
23). The recovery percentage increased with the increasing of dextran concentrations
for the three molecular weights considered (R = 0.96, 0.89, 0.74 for T40, T500 and
T2000 respectively). Testifying recovery percentages against 100 % with the least
sum of square (LSS) criterion, the Haze method was with the best for the molecular
weight of T2000 (Figure 23).
In the Haze method, dextran concentration and molecular weight factors and their
interactions were found to be significant in their effects on the recovery percentages
(P < 0.0001), which points at a dependent relationship between the two factors.
Similar pattern of significance for the estimated dextran T500 and T2000 were
recorded (P<0.0001). The accurate of Haze method with low dextran molecular mass
was shown in Figure 21. The results show the dextran recovery at concentrations
lower than 1000 mg/kg DS and at concentrations above 1500 mg/kg DS of T40 were
49
not accurate compared with the dextran recovery of experiments with T500 and
4000
180
3500
160
140
3000
Dex. recovery (%)
Dex. measured (mg/kg DS)
T2000.
120
2500
100
2000
80
1500
R2 = 0.9875
1000
40
500
0
500
60
20
1000
1500
2000
0
2500
Dextran present (mg/kg Ds)
Dex. recovery (%)
3500
120
3000
100
2500
80
2000
60
1500
1000
R2 = 0.9984
20
500
0
500
40
Dex. recovery (%)
1000
1500
2000
0
2500
Dex. recovery (%)
50
3000
120
2500
100
2000
80
R2 = 0.9875
1500
60
1000
40
500
20
0
500
1000
1500
2000
Dex. recovery (%)
0
2500
Dex. recovery (%)
Figure 23: Sensitivity of haze method to determine dextran T2000 in sucrose solutions
According to the recovery patterns (Figure 18 to Figure 23) and the least sum of
square (LSS) criterion, (Roberts method, 179, 553, 109, Haze method, 8428, 2535,
682 for T40, T500 and T2000 respectively), the Robert’s method can be considered
to be more precise. However, the overall factors including the method, like
concentration, molecular weight and their interaction were considered to discover
another pattern of variation in recovery percentages and determined dextran. For the
recovery percentages, all the factors, including the method and their interactions are
significant (P < 0.0001) whereas for the estimated dextran the method has no main
effect (P = 0.348).
From the above mentioned discussion, the sensitivities of Robert’s and Haze method
for determination of different dextran molecular mass fractions are summarized in
Table 7. The data demonstrate that the Robert’s method was more accurate for
different dextran molecular mass fractions than the Haze method. Furthermore, the
Haze method was too inaccurate to be genuinely useful as a dextran analysis method
especially, with low dextran molecular mass fractions. These results are consistent
with results from (Clarke et al., 1986; Curtin and McCowage, 1986; DeStefano and
Irey, 1986; Sarkar and Day, 1986).
51
Table 7: Conclusion of evaluation of Roberts and Haze methods to determine different dextran
molecules
Dextran levels
Dextran molecules
T40
T500
T2000
Haze
Copper
complex
Haze
Copper
complex
Haze
Copper
complex
≤ 500 mg/kg DS
-
+
+
+++
+
+++
1000-2000 mg/kg DS
+
++
++
+
++
+++
≥ 2000 mg/kg DS
-
+++
++
+
++
+++
4.2
not sensitive, + low sensitive, ++ sensitive, +++ high sensitive
Microbial sources of dextran an identification of relevant microorganisms
in sugar factories
In this chapter, the isolation and identification of Leuconostoc mesenteroides from
sugar beet factories is described. In contrast to other lactic acid bacteria, Leuconostoc
sp. can tolerate fairly high concentrations of salt and sugar (up to 50% sugar) and
initiates growth in vegetables more rapidly over a range of temperatures than any
other lactic acid bacteria. It produces carbon dioxide and acids which rapidly lower
the pH (Battcock and Ali, 1998). Furthermore, it produces high molecular mass
polysaccharides such as dextran, which causes many problems during the industrial
process in sugar factories.
Climatic conditions and harvesting method as well as storage place in sugar factories
are important factors influencing the deterioration of sugar beet by microorganisms.
The raw materials are vulnerable to enzymatic deterioration or microbial action
(Figure 24). Usually, in this regard hand-harvested sugar beet has a lower
deterioration rate after harvest than machine-harvested, whereas, the machine causes
a cutting of sugar beets through the harvesting. This means, they are vulnerable to
attack rapidly from the microorganisms.
52
Figure 24: Deteriorated sugar beet after harvesting
The enumeration of microorganisms in the collected samples (sugar beet, cossettes
and raw juice from beet sugar factory) after incubation on MRS-Agar at 30°C for 48
hours was performed. The mean counts of colonies were 2.5*103 cfu/g of the good
sugar beet sample. On the other hand, they were 34*103 cfu/g in the deteriorated
sugar beet.
Also, the results indicate that the count of microorganisms was reduced in cossettes
samples. Due to the more efficient washing procedure and lower initial soil loading in
beet processing there is less extraneous material brought into the factory. The mean of
total microorganism colonies in these beet sugar cossettes were almost 6*102 cfu/g
and they were found only in the dilutions 10-1 and 10-2.
It was observed that the number of microorganisms increased in raw juice after
extraction process. In the first day of the sugar beet manufacture, the number of
colonies in raw juice was 23*104 cfu/g. On the other hand, in the second and third
days, the microbial count increased to 4*106 and 3.5*105 cfu/g, respectively. This
increase was may be due to starting microbial contamination and an underdosed
usage of antimicrobial agents.
Figure 25 shows the relationship between growth of microorganisms and storage time
of sugar beet raw juice at room temperature. The counting of microorganisms in the
first time was 3.35*103 cfu/g, but after 1, 2, 3 and 4 hours it was 3.35*103, 6.9*103,
2.2*104 and 6.5*104 cfu/g, respectively. The suitable sugar concentration, pH and
temperature of raw juice apparent in an industrial surrounding contribute greatly to
the increase in the rate of growth of microorganisms. Day, (1992) reported similar
53
results. Also he described that during raw juice extraction in the diffuser a decrease of
the cossettes temperatures can occur, if a large percentage of damaged beets are
processed or the usual capacity of the extraction device is exceeded. Consequently,
the bacterial loading increases.
70000
Number of microorganisms
colonies in (cfu/g)
60000
50000
40000
30000
20000
10000
0
0
1
2
3
4
Time (hours)
Figure 25: Microorganisms growth in sugar beet raw juice at room temperature
The colonies morphology of isolated strains and cultural conditions are shown in
Appendix 1. The results show that 14 microorganism strains were isolated from the
collected samples Classical identification revealed the presence of seven bacteria
strains. The other colonies were yeasts and fungi. In this study, the identification of
Leuconostoc mesenteroides subsp. mesenteroides, which produces the dextrans, was
in the focus of interest.
On the basis of classical phenotypic analysis, all of isolated bacteria strains were
Gram-positive and gas forming (except S3 no gas formation). However, S1, S5, S12,
S13 and S14 were catalase negative while S2, S4 were catalase positive. In addition,
all strains produced acid from glucose (See Appendix 2).
The fermentation pattern of carbohydrates gives other keys for strain identification.
Fermentation patterns or profiles and biochemical characteristics were determined
54
using API 50 CHL (BioMérieux) for Leuconostoc ssp. The fermentation pattern
allows the isolate to be identified comparing the pattern to the characteristics of the
type strains. Even in optimized conditions, the change of color may sometimes take
so long for a given strain that it is difficult to conclude whether there is a positive or
negative reaction. Therefore, in this work, follow-up the color changing has taken
several days (five days). Identification results were obtained with the aid of the API
identification table (Bio Merieux) (see Appendix 3). From the five isolated bacteria
strain, the strain S1 belonged to the species Leuconostoc mesenteroides subspecies
mesenteroides/dextranicum. Another isolated strain could not be identified.
Another key to confirm the isolated Leuconostoc m. is the determination of produced
D-/L-lactate. The optical isomer of lactic acid was determined by using a D-/Llactate dehydrogenase kit. Our results indicated that the amount of D-Lactic acid
which produced by strain 1 (S1) was 7.367 g/L. whereas the amount of L-Lactic acid
was 0.387 g/L. In this case, the L & D – Lactic acid test confirms that the tested
strain was Leuconostoc m.
The morphology of strain 1 (S1) was examined by using scanning electron
microscopy (S-4200; Hitachi). Figure 26 shows that the strain 1 cells are spherical
and resemble very short bacilli with rounded ends. The size of cells is approximately
0.6 to 1.0 µm. Cells are arranged in single or pairs.
These results are in agreement with Lonvaud-Funel, (1999). He reported that the
Leuconostoc cells are often in short chains in nutrient media during the active growth
phase, whereas in their natural environment and more stressful conditions the chains
zone. From the abovementioned our results can be confirm the strain 1 (S1) is
Leuconostoc mesenteroides subsp mesenteroides which produced dextran molecules
in sugar industries.
55
Figure 26: Scanning electron micrograph of the isolated Leuconostoc mesenteroides.
Lonvaud-Funel, (1999) reported that the Leuconoistc cells are often in short chains in
nutrient media during the active growth phase, whereas in their natural environment
and more stressful conditions the chains zone.
From the abovementioned our results can be confirm that the strain 1 (S1) is
Leuconostoc mesenteroides subsp mesenteroides which produces dextran molecules
in sugar industries.
4.3
Levels of dextran contents in different sugar beet factories
The dextran level in beet juices and syrups depends on many factors such as
agricultural and climatic conditions, harvesting methods, length of time between
field and factory, length and condition of beet storage as well as the efficiency of all
manufacturing operations. The juices and syrups under study came from Egyptian
factories located in northern (Factory1 and 2) and middle Egypt (Factory 3).
Figure 27 exemplifies the progression of dextran concentrations along the production
process. The dextran levels in factories 1 (F1) and 2 (F2) were significantly higher
than in factory 3 (F3), which was mainly due to the fact that F3 had a shorter beet
campaign of only one month. In addition, the cultivation of sugarbeet in middle
Egypt is new compared to the cultivation in northern Egypt. The levels of dextran in
cossettes were 878, 1343 and 747 mg/kg DS for factories 1, 2 and 3, respectively.
During the extraction the dextran content increased by 4 %, 19 % and 17 % for F1,
F2 and F3, respectively. This means that the microbiological control in F1 was better
56
than in F2 and F3. In contrast, the lime-carbon dioxide juice purification reduced the
dextran content in juice to 40%, 50% and 60% for F1, F2 and F3 respectively by
removing insoluble dextrans during filtration steps. As mentioned above, soluble
dextran may lead to problems in the evaporation and crystallization, and
consequently to sugar loss.
The dextran levels in the final production steps (white sugar and molasses) of the 3
Egyptian factories are shown in Figure 28. The levels of dextran in white sugar
(sugar a) were 38.50, 62.38 and 21.00 mg/kg DS for factories 1, 2 and 3,
respectively. On the other hand were 314, 472 and 405 mg/kg DS in molasses for
factories 1, 2 and 3, respectively.
Dextran content (mg/kg DS)
1500
1200
900
600
300
0
Cossettes
Raw juice
Clarified juice
Thick juice
Samples
F1
F2
F3
Figure 27: Dextran levels at 3 Egyptian factories (F1, F2 and F3) during the production
processes
57
500
400
300
200
100
0
Sugar a
Molasses
Final products
F1
F2
F3
Figure 28: Dextran levels in final products (white sugar and molasses) of 3 Egyptian factories
(F1, F2 and F3)
The level of dextran in molasses was higher than in the resulting product (sugar).
This shows that the major amount of dextran was lost to the molasses during the
washing process to the molasses.
Based on the cluster analysis of some characters, the relationship between the 3
Egyptian factories was elucidated in Figure 29. The result indicated a correlation
between factory 1 and factory 3. This correlation may be due to the use of a good
sugar beet during the campaign, which leads to reduce the dextran levels during the
production processes. On the other hand, the use of the deteriorated sugar beets in
factory 2 caused an increase of dextran levels during the processes.
58
FACTORY1
FACTORY3
FACTORY2
2,2e5
2,4e5
2,6e5
2,8e5
3e5
3,2e5
3,4e5
3,6e5
3,8e5
4e5
Linkage Distance
Figure 29: The relationship between the three factories based on cluster analysis of some
characters (Single linkage squared Euclidean distance)
4.4
Quality of factory final products and their relationship to the levels of
dextran during different industrial periods
An increase of the molasses purity and sugar loss during the development of
industrial periods was observed in sugar beet factories in Egypt and many another
countries, especially at the end of the industrial season. In this chapter, we will
highlight on the correlation between the increase of sugar loss and the presence of
dextran during different industrial periods as well as during the production process
itself.
Figure 30 shows the relationship between molasses purity and the industrial periods.
The results indicate that molasses purity increased steadily during the campaign and
at the end of the industrial season, the dextran concentration was enhanced by 4.6 %.
Whereas, the dextran level in syrup increases from about 500 mg/kg DS during
March to 1200 mg/kg DS at the end of May. This value is in good accordance with
literature data given in Table 5 as starting levels of dextran were around 1000 mg/kg
DS. In the European factories, the presence of raffinose may lead to similar results,
whereas it increases at the end of the season.
59
60
59
Molasses purity %
+4.63%
58
57
+1.35%
0%
56
55
4
3
2
1
4
ay
3
2
1
M
3
2
4
Ap
ril
M
ar
ch
1
54
Industrial period
Molasses purity (Mean)
Molasses purity
Figure 30: The relationship between molasses purity and the industrial periods.
(Mean = mean of molasses purity in month)
The results obtained from the sugar factory 2 showed that despite an increase in the
percentage of sucrose in beet cossettes from 17.70 % in March to 18.34 % in May,
the sugar extraction quality decreased from 85.74 % to 81.21 % and the sugar loss in
molasses increased from 2.5 to 2.8 (kg/100kg beet) in March and May, respectively.
This is mainly based on the deterioration of the sugar beet crop by microorganisms.
Especially the presence of Leuconostoc mesenteroides leads to an increase of the
dextran levels during the production processes.
Figure 31 shows the dextran levels in raw juice, clarified juice and thick juice during
different industrial periods of factory 2. The results illustrated that the dextran levels
were higher in May than in March in all samples. The dextran amount increased from
March to May by 700 mg/kg DS to a range of 1000-1400 mg/kg DS, by 400 mg/kg
DS to a range 650-870 mg/kg DS and by 500 mg/kg DS to range of 740-1150 mg/kg
DS of raw juice, clarified juice and thick juice, respectively.
60
1600
Dextran contents (mg/kg DS)
1400
1200
1000
800
600
400
200
0
Raw juice
Clarified juice
Thick juice
Samples
March
12.May
21.May
28.May
Figure 31: Influence of the industrial period on the dextran amount during production
processes
Also, the amount of dextran in different sugar production steps (sugar a, b, d, g) and
in molasses was increased at the end of the industrial season (Figure 32). The results
indicated that the dextran levels increased with the developing crystallization steps.
They were lower in the initial crystallization stage and then increased gradually to
reach 103 mg/kg DS in the last crystallization stage (g-sugar, after the last production
step). These results confirm the importance of dextran effects during the later stages
of crystallization processes. In addition, the increase of sugar beet deterioration in the
end season causes an increase in the dextran levels in all crystallization stages.
61
500
450
400
350
300
250
200
150
100
50
0
March
12.May
21.May
28.May
Industrial period
Sugar a
Sugar b
Sugar g
Sugar d
Molasses
Figure 32: Dextran levels in sugar and molasses production of different industrial periods
The result in Figure 33 illustrates the relationship between dextran levels in syrup
and dextran levels in sugar during different crystallization steps. The dextran level in
white sugar and after product were 32 and 103 mg/kg DS, respectively, when the
dextran in syrup was 500 mg/kg DS, respectively. Furthermore, an increase in the
dextran level in syrup to 1100 mg/kg DS, increase the dextran amount of white sugar
and after product to 85 and 170 mg/kg DS, respectively, was observed. Lower
crystallization temperatures and the adsorptive properties of dextran contribute
greatly to the increase of dextran levels in the after product crystallization step.
Figure 34 shows the partitions of dextran in sugar a, b and molasses during March
and May. The dextran levels in all tested ‘a-sugar’ samples were lower than dextran
contents in ‘b-sugar’. The results indicated that about 45-50 % of dextrans in magma
tend to the molasses. However, about 17-20 % remain in sugar g (after product),
which normally is recycled to the first stage of crystallization. In addition, the
dextran levels increase with the increase of crystallization stages.
62
From the present results, it can be confirmed that the dextran concentrates on the
crystal surfaces due to the high ability of dextran to adsorb on surfaces. Furthermore,
the amount of dextran in sugar product depends on the amount of dextran in syrup
and the quality of the affination process.
180
Sugar g
160
Sugar d
140
Sugar b
120
Sugar a
100
80
60
40
20
0
500
600
700
800
900
1000
1100
1200
Dextran in syrup (mg/kg DS)
Figure 33: The relationship between the dextran content in syrup and different produced sugars
May
March
49%
6%
10%
11%
13%
45%
15%
15%
19%
Sugar a
Sugar d
Molasses
Sugar b
Sugar g (After product)
17%
Sugar a
Sugar d
Molasses
Sugar b
Sugar g (After product)
Figure 34: The partitions of dextran during different crystallization stages at different
industrial periods
4.5
63
Influence of dextran concentrations and molecular fractions on the rate of
sucrose crystallization in pure sucrose solutions
There are different methods to perform the crystallization experiment and follow the
growth rate of sucrose crystals during the crystallization process. In laboratory
isothermal crystallization experiments (as described under 3.2.3.1) the influence of
dextran on sucrose growth was studied without interference of other factors.
The effect of different dextran concentrations and molecular weight fractions on
crystallization rate in sucrose solutions will be discussed ahead to demonstrate the
complexity of the problem and to elucidate the methodology of performed
crystallization experiments. Based on first experiments the influence of temperature
on crystallization rate in presence and absence of dextran will be balanced, too. All
presented results finally demonstrate the sensitivity of the crystallization process on
dextran concentration in the system. From this, the consequences of dextran presence
for industrial crystallization units can be derived.
Figure 35 shows the dry substance contents of the mother liquor ( wDS , ML ) during the
crystallization (ϑ = 60°C) for a pure sucrose solution and after addition of 500, 1500
and 2000 mg/kg DS dextran T40. The results indicate that the dry substance of
mother liquor decreases during the crystallization process. The figure shows that
concentrations of up to 500 mg/kg DS of dextran T40 in the sucrose syrup have only
little effect on the dry substance decrease. However, concentrations between 1500
and 2000 mg/kg DS of dextran with the same molecular weight however give effect
on the exhaustion of mother liquor.
The growth rates of sucrose crystals calculated from the data shown in Figure 35
during the crystallization process for pure sucrose solution after addition of dextran
T40 of different concentrations (500, 1500 and 2000 mg/kg DS) at 60°C are shown
in Figure 36. Only small differences in the crystallization rates of control (without
dextran) and with addition of 500 mg/kg DS of dextran T40 were observed. On
contrary, the admixture of higher concentrations of T40 (1500-2000 mg/kg DS)
causes a serious retardation of crystallization rate and thus represents a danger for
crystallization process economy, in particular if industry-relevant supersaturations
above 1.1 are regarded. For example, at SS 1.12 the crystallization rate with 2000
mg/kg DS T40 is almost 15 % lower compared to the control experiment. On the
64
other hand, at supersaturation 1.13 (as indicated in the diagram), the growth rate is
reduced by 7.4 %, 9 % and 18 % after dextran T40 at concentrations of 500, 1500
and 2000 mg/kg DS, respectively, was added.
76.8
76.6
76.4
DS in (%)
76.2
76
75.8
75.6
75.4
75.2
75
0
20
40
60
80
100
120
140
160
Time (min)
Control
500 mg/kg DS
1500 mg/kg DS
2000 mg/kg DS
Figure 35: Dry substance content of mother liquor in isothermal crystallization experiments at
60 °C in pure sucrose solution and after addition of 500, 1500 and 2000 mg/kg DS of dextran
T40
4
3.5
G (g / m2 .min)
3
2.5
2
1.5
1
0.5
0
1.05
1.06
1.07
1.08
1.09
1.1
1.11
1.12
1.13
1.14
Supersaturation (SS)
Control
500 mg/kg DS
1500 mg/kg DS
2000 mg/kg DS
Figure 36: Growth rate of sucrose crystals in isothermal crystallization experiments at 60 °C in
pure sucrose solution and after addition of 500, 1500 and 2000 mg/kg DS of dextran T40
65
Figure 37 illustrates the relationship between the dry substance content and the time
of the crystallization process for pure sucrose solutions (control) and after addition of
dextran T500 (500, 1500 and 2000 mg/ kg DS) at 60 °C. An increase of molecular
weight of dextran from 40.000 (T40) (s. experiments above) to 500,000 (T500) at
60°C caused an increase of crystallization time. A relevant effect of dextran T500
was observed with concentrations higher than 500 mg/kg DS.
Figure 38 shows the effect of dextran T500 at concentrations of 1500 and 2000
mg/kg DS on the growth rate of sucrose crystals at 60°C. This figure indicates that
the crystallization rate regarding a supersaturation of 1.13 in the sugar solution
without dextran (control) is the same as the crystallization rate at supersaturations of
1.134, 1.135 and 1.138 in presence of 500, 1500 and 2000 mg/kg DS of dextran
T500, respectively. Also, a stronger effect of dextran T500 than dextran T40 can be
observed at 60°C. As it can be seen from Figure 38 that the crystallization rates at
60°C at a supersaturation of 1.13 are reduced by 7 %, 10 % and 20 % in presence of
500, 1500 and 2000 mg/kg DS dextran T500, respectively.
76.8
76.6
76.4
DS in (%)
76.2
76
75.8
75.6
75.4
75.2
75
0
20
40
60
80
100
120
140
160
180
Time (min)
Control
500 mg/kg DS
1500 mg/kg DS
2000 mg/kg DS
60 °C in pure sucrose solution and after addition of 500, 1500 and 2000 mg/kg DS of dextran
T500
66
4
3.5
G (g/m2.min)
3
2.5
2
1.5
1
0.5
0
1.05
1.06
1.07
1.08
1.09
1.1
1.11
1.12
1.13
1.14
Control
1500 mg/kg DS
2000 mg/kg DS
500 mg/kg DS
pure sucrose solution and after addition of 500, 1500 and 2000 mg/kg DS of dextran T500
The results from Figure 37 and Figure 38 clearly demonstrate that the reduction of
growth rate at technologically relevant supersaturations is even more than described
in Figure 35 and Figure 36 (dextran T40). That means, if in a sugar house a thick
juice contains 1500 mg/kg DS dextran T500, the crystallization period will be
extended by up to 20 %.
Further experiments on the influence of high dextran concentrations were carried out
with dextran T2000. The mother liquor dry substance contents in the presence of
500, 1500 and 5000 mg/kg DS of dextran T2000 are shown in Figure 39. The time
till a supersaturation of 1.05 was reached increased by 21 %, 36 and 41 % after 500,
1500 and 5000 mg/kg DS dextran T2000 addition, respectively.
The growth rate of sucrose crystals at 60 °C and a supersaturation of 1.13 were 2.7,
2.4, 1.8 and 1.3 g/(m 2 ⋅ min) for control and after dextran T2000 addition of 1500
and 5000 mg/kg DS, respectively (see Figure 40). Here the crystallization rates were
reduced by 12, 33 % and 51 % after addition of 500, 1500 and 5000 mg/kg DS
dextran T2000
67
76.8
76.6
76.4
DS in (%)
76.2
76
75.8
75.6
75.4
75.2
75
0
20
40
60
80
100
120
140
160
180
200
Time (min.)
Control (60°C)
500 mg/kg DS
1500 mg/kg DS (60°C)
5000 mg/kg Ds (60°C)
Figure 39: Dry substance contents of mother liquor in isothermal crystallization experiments at
60°C in pure sucrose solutions and after addition of 500, 1500 and 5000 mg/kg DS of dextran
T2000
4
3.5
3
G (g / m2.min)
2.5
2
1.5
1
0.5
0
1.05
1.06
1.07
1.08
Control (60°C)
1.09
1.1
1.11
1.12
1.13
1.14
Supersaturation
(SS)
1500
mg/kg DS (60°C)
5000 mg/kg DS (60°C)
500 mg/kg DS
Figure 40: Growth rates of sucrose crystals in isothermal crystallization experiments at 60°C in
pure sucrose solutions and after addition of 500 - 5000 mg/kg DS of dextran T2000
68
The comparison of the effect of the different molecular mass fractions of dextran on
the degradation of dry substance contents of the mother liquor ( wDS , ML ) during the
crystallization at ϑ = 60°C for a pure sucrose solution and after addition of 1500
mg/kg DS dextran T40, T500 and T2000 is shown in Figure 41. The time till a
supersaturation of 1.05 was reached increased by 36 % compared with a pure sucrose
solution after addition of dextran T2000. In contrast, only a small effect was found
after addition of lower molecular mass fractions of dextran (T40 and T500) under the
same conditions.
Figure 42 shows the crystal growth rates of sucrose were calculated from the data
shown in Figure 41. The growth rate of sucrose crystals was reduced after dextran
T40, T500 and T2000 addition by 9 %, 10% and 33 %, respectively for an
industrially relevant supersaturation of 1.13.
76.8
76.6
76.4
DS in (%)
76.2
76
75.8
75.6
75.4
75.2
75
0
20
40
60
80
100
120
140
160
180
Time (min)
Control
T40
T500
T2000
60 °C in pure sucrose solution and after addition of 1500 mg/kg DS of dextran T40, T500 and
T2000
69
4
3.5
G (g / m2. min)
3
2.5
2
1.5
1
0.5
0
1.05
1.06
1.07
1.08
1.09
1.1
1.11
1.12
1.13
1.14
Control
T40
T500
T2000
pure sucrose solution and after addition of 1500 mg/kg DS of dextran T40, T500 and T2000
4.5.1
Influence of different temperatures on growth rate of sucrose crystals in
the presence of dextran
In this chapter, the role of the temperature during the crystallization is studied. As the
dextran molecular fraction T2000 showed the most relevant effect on crystallization
rate of sucrose crystals only results of experiments with this molecular fraction are
presented. Figure 43 shows mother liquor dry substance content at 60, 65 and 70 °C
in pure sucrose solution and after addition of 1500 and 5000 mg/kg DS of dextran
T2000. The results indicate that great differences in the rate of dry substance
reduction were apparent at the regarded temperatures. At a crystallization
temperature of 60 °C the crystallization time was extended by 33 % after the
admixture of dextran (5000 mg/kg DS) compared to the control experiment. At 70 °C
the extension of crystallization time for the same admixture was reduced to only 8 %.
It was observed that the degree of reduction at 70°C was higher than at 65 °C or
60°C considering all treatments. In contrast, the effect of dextran appeared to be
reduced at 70°C and increased at lower temperatures (65 °C and 60°C).
Also, a higher dextran concentration (5000 mg/kg DS) had a stronger effect on the
exhaustion of mother liquor than a concentration of 1500 ppm under the
70
experimental conditions. Hence, longer time of crystallization was required at low
temperatures and high dextran contents.
79
78.5
78
DS in (%)
77.5
70°C
77
76.5
65°C
76
75.5
60°C
75
74.5
0
50
100
150
200
Time (min)
Control (60°C)
Control (70°C)
5000 mg/kg Ds (60°C)
1500 mg/kg DS (70°C)
Control (65°C)
1500 mg/kg DS (60°C)
T2000-1500ppm (65°C)
5000 mg/kg DS (70°C)
Figure 43: Dry substance content at 70, 65 and 60°C in control and in presence of dextranT2000
(1500 and 5000ppm) during crystallization process
The influence of addition of 1500 and 5000 mg/kg DS of dextran on crystal growth
rates at 60 and 70 °C is shown in Figure 44 and Figure 45. The addition of 1500
mg/kg DS of dextran T2000 reduced the growth rate of sucrose crystals by 33 % at
60 °C, 24 % at 65°C and by 16 % at 70 °C. These results show the same tendency as
results from Ekelhof, 1997; Meade and Chen, (1977). However, growth rates
obtained in own experiments were higher than the former results of Ekelhof. This is
due the use of a fast mixing system during own experiments in contrast to the float
bed (without stirrer) crystallizator applied by Ekelhof. At a supersaturation of 1.13
addition of 5000 mg/kg DS of dextran T2000 reduced the growth rate of sucrose
crystals by 51 % and 24 % at 60 °C and 70 °C, respectively (see Figure 44 and
Figure 45).
The results indicate that higher temperatures (e.g. 70 °C) reduce the effect of dextran
on the crystallization rate especially in case of high levels of dextran in the
71
massecuite. Furthermore, crystallization temperature at 70°C improves the mother
liquor diffusion and consequently, the growth rate of sucrose crystals.
7
6
70°C
G (g / m2.min)
G (g/m2.min)
5
4
65°C
3
60°C
2
1
0
1.05
1.06
1.07
1.08
1.09
1.1
1.11
1.12
1.13
1.14
Control (60°C)
1500 mg/kg DS (70°C)
Control (70°C)
1500 mg/kg DS (60°C)
1500 mg/kg Ds (65°C)
Control (65°C)
Figure 44: Growth rate of sucrose crystals at 60, 65 and 70 °C after addition of 1500 mg/kg DS
of dextran T2000
7
2
G (g / m . min)
6
5
4
3
2
1
0
1.05
1.06
1.07
1.08
1.09
1.1
1.11
1.12
1.13
1.14
Control (70°C)
Control (60°C)
5000 mg/kg DS (70°C)
5000 mg/kg DS (60°C)
Figure 45: Growth rate of sucrose crystals at 60 and 70 °C after addition of 5000 mg/kg DS of
dextran T2000
4.6
72
Elucidation of crystallization kinetics in presence of dextran molecules
From the last chapter it could be seen that dextran has a strong influence on the
growth rate of sucrose crystals, especially considering high molecular fractions of
dextran. In this chapter, reasons for the influence of dextran on sugar crystallization
are discussed and illustrated with additional measurement results.
Figure 46 shows a model of sucrose crystallization adapted from Ekelhof, (1997) and
Thelwall, (2002). Around the crystal surface a boundary layer exists which consists
of three parts. The first boundary layer at the crystal surface is the reaction layer,
which has the least supersaturation (CG) as sugar had been removed from the solution
and deposited on the crystal. The second boundary layer is the main diffusion layer.
Here, there are two different flows in opposite directions. The first one is non-sugar
material and water from the exhausted reaction layer moving away from the surface
and back to the main mother liquor. The other flow is fresh syrup, which is moving
towards the crystal surface. The third and final layer, bulk of solution, is the main
body of the mother liquor and is the source of the sucrose molecules for further
deposition.
The movement of sucrose molecules through the diffusion layer (d2) depends on the
viscosity, which does have an important influence on the crystallization rate,
especially in the second boundary layer, as the higher viscosity will reduce the speed
of the molecular movement to and from the crystal surfaces (compare results in
chapter 4.7).
73
Diffusion layer
λ
Reaction layer
δ
Surface area
kR
kD
Crystal
cG
cSat
NS &
Water
d2
d3
Sucrose solution
cL
d1
Figure 46: The scheme of the two processes of diffusion and surface reaction. 2λ= gap between
crystals, λ= half distance between crystals, δ = thickness of the boundary layer, kD = diffusion
coefficient, kR = surface reaction, NS = non-sugar, CL, CG, CSat are the sucrose concentrations of
liquor, boundary layer and saturation at the crystal-solution interface.
Also, in impure sucrose solutions (sugar cane or beet syrup), dextran molecules are
adsorbed on the impure particles, consequently, the solution viscosity increases and,
additionally, the movement of sucrose molecules destined to crystal surfaces is
impeded (s. Figure 47). Hence the high molecular weight and the adsorption of
dextran affect the growth rate and the quality of sucrose crystals negatively.
Figure 47: Dextran adsorption on impure particles
74
These model suggestions are in accordance to Cossairt, (1982). He demonstrated that
some impurities are physically adsorbed on the different faces of the crystals in
varying and selective amounts. A portion of lattice sites becomes blocked; thereby it
comes to reduction or retardation of crystal growth.
4.7
Influence of dextran molecule fractions on sucrose solution viscosity
In this work, the solution viscosity is a determining parameter for diffusion
phenomena during crystallization of sucrose. Figure 48 demonstrates the influence of
dextran molecular weight fractions T40, T500 and T2000 on the dynamic viscosity
(η) of sucrose solutions (WDS = 60 %) at different temperatures (50-70°C). At 50°C
the dynamic viscosity of sucrose syrup was 14.35 mPa.s for control. On the other
hand, it was 14.63, 15.26 and 15.39 mPa.s with 1500 mg/kg DS dextran T40, T500
and T2000 additions, respectively. In addition, an increase of solution temperature to
70°C reduced the solution viscosity by 50 %.
16
15
14
η mPa.s
13
12
11
10
9
8
7
6
50
55
60
65
70
Temperature (°C)
Control
T40
T500
T2000
Figure 48: Influence of addition of 1500 mg/kg DS of T40, T500 and T2000 dextran on the
dynamic viscosity of a 60% sucrose solution between 50 and 70 °C
The results elucidate that at low temperatures dextran fractions T2000 and T500 have
more effect on solution viscosity than T40. However, the differences are reduced at
75
high temperatures. That illustrates the decrease of the diffusion rate in the mother
liquor during crystallization process in presence of high molecular weight fractions
of dextran (Figure 46).
Figure 49 shows the relationship between dextran addition and solution viscosity at
different temperatures. At 50 °C the solution viscosities increased after addition of
500, 1500, 2500 and 5000 mg/kg DS of dextran T2000 by 2.9 %, 6.45 %, 11.70 %
and 24.73 %, respectively. An increase of temperature from 50 to 70°C reduced the
solution viscosity to almost 50 % for all additions.
20
18
16
η (mPa.s)
14
12
10
8
6
4
2
0
Control
500
1500
2500
5000
Dextran contents (mg/kg DS)
50°C
60°C
70°C
Figure 49: Influence of different dextran concentrations (500, 1500, 2500, 5000 ppm) on the
dynamic viscosity at different temperatures (50-70°C)
The effects of dextran are not only of importance during the crystallization process,
but also after the centrifugation process and during the drying operation of the
sucrose crystals. These steps as well determine the quality of the resulting sucrose
crystals. Figure 50 shows the crystal surface during the drying process.
76
A fte r
c e n t r if u g a t io n
S a tu ra te d
s o lu t io n
A f t e r d r y in g
( u n s t a b le s t a t e )
G la s s y
s ta te
S a tu ra te d
s o lu t io n
C r y s t a llin e
phase
Figure 50: The crystal surface of a sucrose crystal during the drying process (according to
Bunert und Bruhns 1995)
It can be shown that the presence of dextran in the saturated solution on the crystal
surface leads to an increase of solution viscosity. So, heat transfer and consequently
water transport to the air is slow. Hence, an increase of the drying time contributes to
an increase of micro-crystals (fine crystal) due to nucleation on the crystal surfaces.
4.8
4.8.1
Influence of dextran on the morphology and surface topography of
sucrose crystals in presence of dextran
Crystal morphology
After the characterization of the influence of dextran on the crystal growth rate, in
this chapter the influence on crystal shape and topography shall be illustrated in this
chapter. In presence of dextran sucrose crystals are often elongated along the c axis
(Figure 51-b). Dextran influences the growth rates of individual crystal faces
(McGinnis, 1982) as described in chapter 2.6.4. In addition, the adsorption properties
of dextran causes the deposition of impure materials on crystal surfaces (Figure 51c), which reduces the sugar quality and increases the sugar loss to molasses.
77
+C
+A
+B
+C
+B
b
a
c
Figure 51: Effect of dextran on morphology of sucrose crystals, a) Normal crystal, b) Crystal
grown in presence of dextran (needle crystal) and c) Impure particles on crystal surface (crystal
grown in technical sucrose solution)
The relationship between the presence of dextran and elongation of crystals (c/b
ratio) was elucidated by Bubnik and Kadlec, (1996). They noticed that the variation
of the c/b ratio is a function of increasing concentration of dextran (s. chapter 2.6.4.).
Results of own experiments showed that the low molecular weight dextran caused an
elongation of crystals, despite the use of stirring during the crystallization process
(see Figure 52). This result is in good agreement with Singleton, (2002). He reported
that dextrans are responsible for crystal elongation along the c axis and that the
smaller molecular weight dextrans are especially involved in this effect. However in
own experiments a stirred crystallizer device and seeding crystals were applied.
Therefore, crystals are only slightly elongated and no pure needle crystal formation
took place.
Without dextran
T40-1000ppm
T40-2000ppm
Figure 52: An example of influences of dextran T40 on sucrose crystal shape during the
crystallization process
4.8.2
Surface topography
Microscopic examinations of the different faces of sucrose crystals were performed
by scanning electron microscopy (SEM). Figure 53 shows the surface topography of
78
a sucrose crystal which was grown in pure sucrose solution at 60°C. It was observed
that the crystal shapes has taken a normal form of a sucrose crystal. On the other
hand, the microscopic examination of a crystal surface shows the fine sugar crystal
on the crystal surface, which developed after the centrifugation process and during
the drying operation (comp. chapter 4.7).
20x
6000x
150x
1000x
Figure 53: Surface topography of a laboratory sucrose crystal grown in absence of dextran at
60°C
Figure 54 shows the effect of the low molecular dextran fraction (T40) on sucrose
crystal shape and the surface adsorption. The crystals shown are formed from 200
µm seed crystals and therefore no needle crystals are formed. In contrast, crystals
nucleated in the crystallizer in the presence of dextran (top left Figure 54) were small
needle crystals, which get lost to molasses easily during centrifugation and washing,
consequently, increasing the molasses purity. Also, an increase of micro-crystals on
the crystal surfaces took place compared with control was observed. So, rough
surfaces and gaps developed on the crystals. In this case, the main affect of low
molecular dextran is changing of crystal form to needle crystal. Consequently, there
is an increase in sugar loss to molasses.
79
20x
6000x
150x
1000x
Figure 54: Surface topography of sucrose crystal grown in the presence of 1500 mg dextran T40
per kg DS at 60 °C
Figure 55 shows the influence of the high molecular fraction dextran molecules
T2000 on sucrose crystal morphology and adsorption surface. It was observed that in
presence of this high molecular fraction of dextran the number of conglomerated
crystals (multiple crystals where two or more crystals have grown together)
increased. A scanning electron micrograph of a sugar crystal shows micro-particles
(sucrose crystals) strongly adsorbed on the crystal surface, which cause a rough
crystal surface with a number of gaps (comp. chapter 4.7). Consequently, non-sugar
and colorant particles can be adsorbed with dextran on the surface during the
technical crystallization process in the sugar factories. Also in this case, the removal
of impurities (non-sugars) is difficult during the washing of the crystals.
80
20x
150x
6000x
1000x
Figure 55: Surface topography of a sucrose crystal grown in the presence of 5000 mg dextran
T2000 per kg DS at 60°C
These results confirmed those reported by Cuddihy et al., (2000); Jimenez, (2005);
Karagodin, (1998); Rauh et al., (1999). They found that the increase of sugar
crystallization time causes the massecuites to become cooler than normal which
increases the already abnormally high viscosity of the fluid. An increase in washing
time of the centrifugals is needed to get the required quality of sugar, increasing total
centrifuging and purging time. Also, the needle-shaped crystal reduces the purging
efficiency of the massecuites in the centrifugals resulting in a poor separation of
crystal and molasses, hence reducing the refined quality of the sugar. Additionally,
dust production was mainly due to the breaking and crushing of conglomerates and
needle crystals near to the screens of centrifugals. Consequently, sugar fine corn in
the final product is increased. Such micro-particles may be seen on the surface of a
sugar crystal in Figure 55. The conglomerates contain higher ash than
unconglomerated sugar. The higher ash is contained in trapped mother liquor, either
partially dried in the re-entrant angles, or in the inclusions in those angles (Madsen,
1980; van der Poel, 1980). In addition, our results (not view) elucidated increase of
the turbidity in sugar solution, which was produced from deteriorated beet syrup.
81
Figure 56 shows the effect of crystallization temperature on the surface topography
in presence of dextran at different temperatures. It is obvious that at a crystallization
temperature of 70°C more perfect crystal surfaces are built than at 55°C. As a
possible reason, the increase of viscosity caused by dextran and the effects of
temperature on the viscosity of (dextran-) sucrose solutions decribed in chapter 4.7
can be suggested. Also in crystal topography, the influence of dextran seems to be
diminished by the application of higher temperatures as it could be observed for
crystal growth rates.
This effect can also be correlated to the increase of colorant and turbidity
components of sugar produced at low temperatures (after product). Additionally, the
presence of dextran can assist the adsorption of these particles on the crystal surface.
55°C
70°C
6000
x
Figure 56: Effect of crystallization temperature on the surface topography in the presence of
dextran
Rogé et al., (2007) reported that there is a good correlation between white sugar
turbidity and calcium ion concentration in stored syrups. As well they reported that
macromolecular organic substances (as for example dextran) may act a carrier for
components causing turbidity.
82
In many factories, despite the use of ion exchange to reduce calcium ion, turbidity
phenomena in the produced sugar were observed. Figure 57 shows the comparison
between a single sugar crystal without turbidity and a sample of a crystal with the
highest amount of turbidity. Figure 58 is the magnification image of Figure 57,
which shows the non-sugar particles on the crystal surface. Hence, the biggest
particles (> 5µm) were calcium carbonate while the small particles (<5µm) were
calcium oxalate. These particles were formed during the storage of syrup under
adverse conditions.
a
b
Figure 57: Turbidity phenomena in many European sugar beet factories (a, b) during the thick
juice campaign
83
Figure 58: The magnification image of Figure 57
In addition, an increase of elongated crystals in the after product crystallization step
as shown in Figure 59 was observed. These results are in good agreement with Rogé
et al., (2007), they reported that the elongation of face c is significant and such a
phenomenon increases with syrup turbidity.
Figure 59: After product sugar crystal in one of European sugar beet factory during the thick
juice campaign
From the technical sucrose crystallization point of view, the three stage
crystallization scheme is regarded as the standard scheme. The process of producing
sugar is through several stages, because the high concentration of non-sugar and the
84
increase of solution viscosity hinder the sugar separation from the mother liquor.
Generally, in the most systems of beet sugar crystallization, the after product sugars
(C- sugar) are dissolved and recycled to the first crystallization stage, where they are
added to the thick juice (Figure 60). In addition, in other systems, the C-sugar is sent
to the second stage. This means, if sugar syrup contains a considerable amount of
dextran, the dextran levels in after product sugar will be increased, consequently, the
dextran levels in the previous crystallization stage increase continuously.
From the abovementioned results (comp. chapter 4.4, Figure 33 and Figure 34), 1720 % of the dextran remains in the after product. So, in this case, the amount of the
dextran, which is recycled to the first crystallization stage, can be calculated. This is
important as this dextran increases the original dextran level in thick juice (syrup).
For example, if dextran level in syrup is 1000 mg/kg DS, the dextran level in the
after product will be about 170 to 200 mg/kg DS. Consequently, the dextran level in
syrup becomes about 1170-1200 mg/kg DS. However, this increase can only be
characterized qualitatively in this work, as the remaining dextran depends for
example on the number of crystallization stages and on the industrial period. Also,
the relation between dextran in syrup and dextran in sugar (comp. Figure 33)
depends on parameters of centrifugation process.
85
Vapor
5 5
Brüden
R
R
3630
R
52,05 t/h 3620-9
87,77 kPa
96,4 °C
4,42 t/h
10,49 t/h
35,24 t/h
9
R
R
4284 -1 0
C
ond en sation
Kondensation
R
42 64 -10
C ond
en sat ion
Kondensation
3910-0
Dissolved Raw
Rohzucker Kläre
sugar
Dissolved After
Nachprodukt
Kläre
product
Staub
Dust
4344-0
9
41 84-0
3010
1
41 74-0
43 14-0
W hite
Weißsu gar
zucker
1
3740-3
R aw
Rohs ugar
zu cker
1
4054-0
A3070
fter
Nach-ct
produ
p rodukt
63,94 t/h
75,0 °C
75,49 t/h
82,0 °C
8
4284
9
38,60 t/h
87,0 °C
R
0
10
3740-5
0
363 0-9
151,94 t/h
70,0 °C
9
R
190,01 t/h
80,0 °C
8
3870
3740-1
0
363 0-7
0
A ffin atio
run- off
Affination
Ablauf
3040
0
0
8
4264
10
33,75 t/h
80,1 °C
9
4194
Weißzucker
White
sugar
Zentrifuge
centrifuge
R
1
0
4294
Kondensat
4074- 0
9
3055
R
Rohzucker
Raw
sugar
Zentrifuge
centrifuge
1
0
3050
C ondens ate
Kondensat
R
Thin
juice
Dünnsaft
R
Aft er produ ct
Nachprodukt
crystalliz er
Kristalisator
3080
Condens ate
Condensate
Kondensat
R
After
Nachprodukt
produ ct
Zentrifuge
c entrifu ge
1
0
3090
R
1
2 28 -9
0
0
0
1
1
AIR
4064
4184
AIR /
VA POR
3100
Rohzucker
Dissolved
RawKläre
sugar
W hite sugar
Weißzucker
3740-7
C ondens ate
Kondensat
R
38 70 -6
4304
Dicksaft
Thick
juice
Cond
en sat ion
Kondensation
4334-0
30 00
3770-0
1
0
4054
9
R
0
1
4314
77,37 t/h
99,99% Purity
4264 -8
Dünnsaft
Thin juice
3870-5
R
228-7
4174
Nachprodukt
Dissolved
Kläre
After product
Figure 60: 3-product scheme of crystallisation
0
1
387 0-3
M olasses
Melasse
18,99 t/h
60,00% Pur
86
4.9
Technical and technological consequences and future perspectives
The
crystallization
process
depends
on
many
factors,
e.g.
temperature,
supersaturation, solution viscosity, quantity and nature of the impurities. Dextran has
a pronounced effect on the important parameters influencing the crystallization rate
of sucrose solutions. Moreover, according to the achieved results it can be stated that
the presence of dextran molecules in sugar syrup has a strong effect on the
production and the quality of produced sugar in sugar factories. Figure 61
summarizes the most important parameters influencing the crystallization in sucrose
solutions. The solution purity (q), the non-sugar content (NS), the viscosity (η) and
the rate of diffusion (kD) were affected directly by the presence of dextran. The
above described results confirmed that the crystallisation rate at a constant
temperature is decreasing with higher dextran concentrations. At technologically
relevant supersaturations and temperatures, the decrease of crystallization rate,
depending on molecular weight of added dextran fractions, amounts up to 50 %.
Nucleation rate
Rate of diffusion
DS
Temperature
NS
Growth rate of
sucrose crystals
q
Super -Saturation
Sucrose -Solubility
Dextran molecules
η
Relative velocity between
crystal and mother syrup
Stirring
Shape of crystals
Exhaustion of mother liquor
Figure 61: Influence of dextran on many crystallization parameters during crystallization
process.
Where: q = purity, NS = non-sugar, DS = dry substance and η = viscosity
Time reduction and low energy consumption in the crystallization process are of
particular interest in sugar factories. Figure 62 shows time periods for the reduction
of dry mass content by one percent for different dextran concentrations at 60°C and
70°C, respectively. At 60°C the crystallization periods were increased by 20 % and
87
68 % after the addition of dextran T2000 at concentrations of 1500 and 5000 mg/kg
DS, respectively. On the other hand, at 70°C the increase of crystallization time was
10 % and 21 %. Furthermore, an increase of crystallization temperature from 60°C to
70°C reduces the crystallization time by 8 %, 16 % and 33 % regarding admixtures
of dextran of 0 ppm, 1500 ppm or 5000 ppm, respectively. Moreover, the influence
of dextran increases strongly with both, the increase of molecular weight and the
decrease of crystallization temperature. Therefore, it is obvious, that a decrease in
crystallization temperature, e.g. from 70°C to 65°C, which is desirable regarding
energy aspects, is not applicable in occurrence of dextran. Technological measures to
manipulate only the high molecular fractions of dextran are not known so far.
2.5
68%
Crystallization time (hours)
2
20%
21%
10%
1.5
1
0.5
0
0 mg/kg DS
1500 mg/kg DS
5000 mg/kg DS
60°C
70°C
Figure 62: The relationship between dextran additions and crystallization time during the
crystallization process
In order to reach similar crystallization rates at the occurrence of dextran higher
supersaturations can be applied. However, the increase of supersaturation above a
certain level may cause spontaneous crystallization and thus the formation of fine
crystals. In practice, sugar factories have to work in the so called metastable zone
from 1 to 1.2 supersaturation (Brennan et al., 1976; van der Poel et al., 1998). Thus,
narrow boundaries are set considering an increase of supersaturation.
88
Basing on the abovementioned results future research topics are suggested on the
following topics:
¾ Study on the effect of other organic non-sugar substances (e.g. other
macromolecular polysaccharide fractions or proteins) on sugar process
productions and sugar quality. Rogé et al. (2007) reported that organic
macromolecules act as carrier for non-sugar substances causing problems
during crystallization and causing turbidity in the final sugar. This effect was
also proved for dextran in this work. However, no comprehensive work is
known regarding the composition of organic macromolecules occurring
during sugar production.
¾ In chapter 4.3 and 4.8 the relation between dextran concentration in syrup and
dextran concentration in sugar was illustrated. It was mentioned that this
relation is dependent on the crystallization and centrifugation regime. In order
to allow a precise process control to minimize the negative impact of dextran
a systematic investigation about the influence of relevant process parameters
(e.g. number of crystallization stages, amount of water for affination, type of
sugar production factory) on the transfer of dextran into the sugar has to be
realized. A qualitative and quantitative evaluation by determination of
dextran levels in the after product is suggested. This could be a valuable tool
to supplement available model based process control tools in the sugar
industry (Fiedler, et. al. 2007).
¾ Based on the described effects of dextran on the crystal surface (s. chapter
4.8.2), future studies will investigate the relationship between dextran levels
and especially the drying process in order to characterize parameters
influencing the formation of micro-crystals and the incorporation of microparticles (colorants and turbidity) on the crystal surface.
¾ Improvement of crystallization process at low temperatures (comp. chapter
4.6) by decreasing surface tension and viscosity using chemical agents during
the crystallization process.
¾ Usage of enzyme (dextranase) during the extraction process of sugar beet
juices to improve the filtration process (Clarke,1997). The latter leads to an
increase of the soluble dextran amount (low molecular mass) in juice. This
means an increase of dextran levels in syrup and, hence, an increase of low
molecular weight dextran. The low molecular weight fraction of dextran is
89
known to affect the crystallization process and the sugar loss to molasses
(needle crystals), which was proved in the present study (see chapter 4.8.1).
Furthermore, the enzyme treatment leads to increase of glucose, which causes
an increase of color formation during the evaporation process (Maillard
reaction) (Kroh, et. al. 2007). In addition, it causes a reduction of
crystallization rate. The future work will focus on dextran molecular weight
fractions and sugars deriving from enzyme treatment and on the effect of
these products on the sugar production process.
Summary
5
90
Summary
In the present study, the sensitivity and accuracy of the common methods of dextran
determination were investigated. Concentrations and progressions of dextran during
different sugar production processes and industrial periods were determined and for
the first time an evaluation of sugar and molasses quality was provided based on the
measurement results. Regarding the dextran determination, the results had shown a
significant effect of dextran concentration and molecular fractions on the Haze and
Robert’s methods. The data demonstrate that the Robert’s method was more accurate
for different dextran molecular mass fractions than Haze method. Furthermore, the
Haze method was too inaccurate to be genuinely useful as a dextran analysis method
especially considering low dextran molecular mass fractions.
The isolation and identification of Leuconostoc mesenteroides as an important source
of dextran in sugar beet factories was performed. It was observed, that the
microorganisms grow during the storage of sugar beet and also during the extraction
process. The mean counts of colonies were reduced after washing process from
2.5*103 cfu/g of the sugar beet sample to 6*102 cfu/g of cossettes samples. However,
the number of microorganisms increased in raw juice after extraction process to
reach almost 4*106. In addition, these numbers depend on the degree of deterioration
of the sugar beets. Dextran content increased during the extraction process by 4 % to
20 % for fresh and deteriorated sugar beet, respectively. In contrast, the lime-carbon
dioxide juice purification reduced the dextran content in raw juice by 40 % to 60 %.
The obtained results from Egyptian sugar beet factories showed a correlation
between the increase of sugar loss and the presence of dextran during different
industrial periods as well as during the production process itself..
As a main focus in this work the negative effects of the presence of dextran during
(isothermal) crystallization were investigated. The growth rate of sucrose crystals
and the quality of the sugar production in pure sucrose solution at different
temperatures were studied. To elucidate the influence of dextran on the growth rate
of sucrose crystals, different molecular mass fractions of dextran from 40,000 g/mol
(T40) to 2,000,000 g/mol (T2000) were admixed in different concentrations to pure
sucrose solution. The most pronounced effect of dextran was found with T2000 at
Summary
91
60°C. On the other hand, negligible influences of dextran T40 and T500 were
observed at the same temperature and supersaturation. The high adsorption ability
and the increase of solution viscosity particularly caused by high molecular fractions
of dextran were identified as the main reasons for the reduction of crystal growth
rate.
The application of lower temperatures during crystallization enhances the problems
deriving from dextran. Regarding the final crystallization steps (e.g. after product
crystallization), levels of dextrans and impurities are enhanced and the mentioned
problems will be amplified in these production steps.
From the morphological studies, it was found that the presence of dextran in sugar
mother liquor leads to elongation of the sucrose crystal shape (elongated along the caxis). In particular, the lower molecular mass fractions of dextran are involved in this
effect. A scanning electron microscope (SEM) was utilized for the evaluation of
crystal surfaces and crystal morphology. The surface topography of sucrose crystals
was affected by the presence of higher dextran molecular mass fractions (T2000),
which causes gaps, rough areas and strong adsorption of micro-particles (microcrystals) on the crystal surface. Again, the described influences are enhanced by the
application of lower temperatures.
In addition, in this work it could be confirmed that there is a correlation between the
dextran content in syrup and quality of sugar produced, in particular the turbidity of
the sugar. So, a relation which has already been described in recent literature for
organic macromolecules in general could be specified for dextran molecular
fractions. .
92
Summary
Zusammenfassung
In dieser Studie wurde die Empfindlichkeit und Genauigkeit der gebräuchlichen
Methoden
zur
Dextranbestimmung
unterschiedlichen
Produktionsprozessen
untersucht.
und
Basierend
industriellen
auf
den
in
Produktionsphasen
ermittelten Dextrangehalten wurde erstmals eine umfassende Bewertung des
Einflusses von Dextran auf die Zucker- und Melassequalität erstellt. Bezüglich der
Dextranbestimmung zeigten die Ergebnisse einen deutlichen Einfluss der
Dextrankonzentration und der molekularen Fraktionen auf die Haze- und RobertsMethode. Die Daten ergaben, dass die Robertsmethode für unterschiedliche DextranMolekulargewichtsfraktionen eine größere Genauigkeit zeigt als die Haze-Methode.
Vor allem bei kleineren Dextran-Molekulargewichtsfraktionen war die HazeMethode nicht für genaue Bestimmungen geeignet.
Im Rahmen dieser Arbeit wurde Leuconostoc mesenteroides , eine der wichtigsten
Quellen von Dextran in Rübenzuckerfabriken isoliert und identifiziert. Diese
Mikroorganismen wachsen sowohl während der Lagerung der Zuckerrüben als auch
während des Extraktionsprozesses. Während des Waschens und Schneidens der
Rüben nahm die durchschnittliche Koloniezahl von 2.5*103 cfu/g in der Rübenprobe
bis auf 6*102 cfu/g in den Schnitzeln ab. Die Koloniezahl erreichte jedoch im Laufe
der Extraktion bis zum Rohsaft wieder einen Wert von 4*106. Die Zahlen waren
jedoch stark vom Frischegrad der verarbeiteten Rüben abhängig.
Die Konzentration an Dextran nahm während der Extraktion von frischen bzw.
verdorbenen Rüben um 4 bzw. 20 % zu. Im Gegensatz hierzu verringerte sich der
Dextrangehalt um 40 bis 60 % während der Saftreinigung mit Kalk und CO2.
Ergebnisse
aus
Zusammenhang
ägyptischen
zwischen
der
Rübenzuckerfabriken
Zunahme
des
zeigen
einen
Zuckerverlustes
klaren
und
der
vorherrschenden Dextrankonzentration während verschiedenen Perioden der
Zuckerkampagne aber auch während den einzelnen Produktionsabschnitten auf.
Einen Schwerpunkt dieser Arbeit stellt die Untersuchung der negativen Einflüsse von
Dextran
während
des
(isothermen)
Kristallisationsprozesses
aus
reinen
Saccharoselösungen bei verschiedenen Temperaturen dar. Dextranfraktionen
verschiedener Molekularmassen zwischen 40000 g/mol (T40) und 2000000 g/mol
93
Summary
(T2000) wurden reinen Saccharoselösungen in verschiedenen Konzentrationen
zugesetzt, um den Einfluss von Dextran auf die Kristallwachstumsrate genau
charakterisieren zu können. Der stärkste Einfluss war bei dem Zusatz der Fraktion
T2000 bei 60°C zu detektieren. Im Gegensatz hierzu besaßen die Dextranfraktionen
T40 und T500 einen wesentlich geringeren Einfluss auf die Wachstumsrate bei
jeweils gleichen Temperaturen und Übersättigungen. Gründe hierfür liegen in der
hohen Adsorptionsfähigkeit und der Erhöhung der Viskosität der Zuckerlösung
insbesondere durch die hochmolekulare Fraktion von Dextran.
Die Absenkung der Temperaturen während der Kristallisation, wie es aus
ökonomischen Gründen häufig angestrebt wird, vergrößert die durch Dextran
ausgelösten
Probleme.
Insbesondere
in
letzten
Kristallisationsstufen
(z.B.
Nachproduktkristallisation) treten erhöhte Konzentrationen an Dextran und NichtZuckerstoffen auf, wodurch die beschriebenen Effekte noch verstärkt werden.
Um den Einfluss von Dextran auf die Kristallmorphologie und die Kristalloberfläche
evaluieren zu können, wurden elektronenmikroskopische Aufnahmen angefertigt.
Die Ergebnisse zeigen, dass die Kristallform (Verlängerung in Richtung der c-Achse)
durch die niedermolekulare Fraktion (T40) beeinflusst wird. Demgegenüber hat die
hochmolekulare Dextranfraktion T2000 einen starken Einfluss auf die Qualität der
Kristalloberfläche. Beobachtet wurden raue, lückenhafte Kristalloberflächen und die
Anhaftung von Mikro-Partikeln (Mikro-Kristalle) auf der Oberfläche. Die
beschriebenen Effekte werden wiederum durch den Einsatz tiefer Temperaturen
verstärkt.
In dieser Arbeit konnte ebenfalls ein Zusammenhang zwischen dem Dextrangehalt
und der Qualität des Zuckers, insbesondere der Zuckertrübung, gezeigt werden. Dies
spezifiziert für Dextran einen Zusammenhang, der in der aktuellen Literatur
allgemein für organische Makromoleküle schon beschrieben wird.
References
6
94
References
Alsop, R. M. (1983): Industrial Production of Dextrans. Progress in Industrial
Microbiology. 1-42. ed. M. E. Bushell. New York: Elsevier.
AOAC. (1990): Official Methods of Analysis, Arlington, VA.
Atkins, P. C. and McCowage, R. J. (1984): Dextran - A review. The Australian
experience proceeding of the International Dextran Workshop, New Orleans,
Louisiana, USA, 7-39.
Austmeyer, K. E. (1981): Untersuchungen zum Wärme-und Stoffübergang im
Anfangsstadium der Verdampfungskristallisation der Saccharose, Techn.
Univ. Carlo-Wilhelmina zu Braunschweig. Germany
Back, W. (1994): Kultivierung/Methoden, Brauerei, Winzerei, Bollmann Druck
GmbH, Zirndorf, Germany.
Battcock, M. and Ali, S. A. (1998): Bacterial fermentations. Fermented fruits and
vegetables a global perspective, V. d. T. d. C. FAO, ed., Food and
Agriculture Organization, Rome, Italy.
Beukes, E., M., Bester, B., H. and Mostert, J. F. (2001): The microbiology of South
African traditional fermented milks. International Journal of Food
Microbiology, 63, 189-197.
Bose, S. and Singh, L. (1981): Problems associated with dextran, the major
microbiological cause of sucrose loss and their remedies. Indian Sugar,
December, 603-608.
Brennan, J. G., Butters, J. R., Cowell, N. D. and Lilly, A. E. V. (1976): Food
Engineering Operations, Applied Science Publishers, London.
Brown, C. F. and Inkerman, P. A. (1992): Specific method for quantitative
measurement of the total dextran content of raw sugar. J. Agric. Food Chem.,
42, 227-233.
Bubnik, Z. and Kadlec, P. (1996): Formulas for calculation of properties of sugar
solutions and sucrose crystals. Zuckerindustrie, 121(1), 36-39.
Bubnik, Z. Vaccari, G., Mantovani, G., Sguadino, G., and Kadlec, P. (1992): Effect
of dextran, glucose and fructose on sucrose crystal elongation and
morphology. Zuckerindustrie, 117(7), 557-561.
Bunert, U., Bruhns, M. (1995): Thermische Bedingungen für die Silolagerung von
Weißzucker und Trockenschnitzelpellets. Zuckerindustrie 120 (4), 265-272.
Cbristodoulou, P. (2000): New approaches to crystallization theories. Abstracts for
SPRI 2000 conference on sugar processing research, Porto, Portugal.
Chung, C. C. (2000): A manual for the design and operation of sugar refining
facilities. Handbook of sugar refining, John Wiley & Sons, New York., 516517.
Clarke, M. A., Edye, L. A., Cole, F. and Kitchar, J. L. (1997): Sugarcane factory
trials with dextranase enzyme. Sugar Journal, 60, 20-22.
References
95
Clarke, M. A. and Godshall, M. A. (1988): Determination of dextran in raw cane
sugar by Robert's copper method: Collaborative study. Journal Association of
Analytical Chemists, 71(2), 276-279.
Clarke, M. A., Roberts, T. B. T. and Tsang, W. S. C. (1986): Update on dextran and
dextran analysis. Presented at S. I. T, Publication of Technical Papers and
Proceedings of the Sixty-Third Annual Meeting of Sugar Technologists,
Vancouver, Canada, paper No. 544.
Cossairt, G. W. (1982): Crystallization. Beet-Sugar Technology, R. A. McGinnis,
ed., Beet Sugar Development Foundation, USA, 371-465.
Cuddihy, J. A. and Day, D. F. (1999): The process and financial impact of dextran on
sugar factory. Midland Research Laboratories, Inc.
Cuddihy, J. A., Miguel, E. P. and James, S. R. (2000): The presence of total
polysaccharides in sugar production and methods for reducing their negative
effects. Midland Research Laboratories, Inc.
Curtin, J. H. and McCowage, R. J. (1986): Dextran measurement in cane products.
19th Congress ISSCT, 755-764.
Day, D., Cuddihy, J. A. and Rauh, J. S. (2002): Versatility of the Antibody dextran
test method. Midland Research Laboratories, Lenexa, Kansas, USA.
Day, D. F. (1984): Dextran control in the sugar house. Sugar Journal, 46, 16-18.
Day, D. F. (1986): Dextran-problems, solutions, current research. Paper presented at
the annual meeting of the American Society of Sugar Cane Technologists,
Baton Rouge, LA, USA, 6-7 Feb.
Day, D. F. (1992): Spoilage in the sugar industry. The lactic acid bacteria, B. J. B.
Wood, ed., Elsevier Applied Science, London and New York., 343-361.
De Man, J. C., Rogosa, M. and Sharpe, M. E. (1960): A medium for the cultivation
of lactobacilli. J. Appl. Bacteriol., 23, 130-135.
DeStefano, R. P. and Irey, M. S. (1986): Measuring dextran in raw sugars historical
perspective and state of the art. Journal American Society Sugar Cane
Technologists, 6, 112-120.
Edye, L. A., Clarke, M. A., Roberts, E. J. and Blanco., R. S. (1995): Dextran analysis
by N.M.R. Publication of Technical Papers and Proceedings of the SixtyThird Annual Meeting of Sugar Technologists, Vancouver, Canada, S. I. T,
55-64.
Eggleston, G. and Monge, A. (2005): Optimization of sugarcane factory application
of commercial dextranases. Process Biochemistry, 40(5), 1881-1894.
Ekelhof, B. (1997): Kristallisationskinetik der Saccharose in reinen und unreinen
Löِsungen. Dissertation, Techn. Univ. Braunschweig, Germany.
Elahi,
M. (2004): Untersuchung zur Optimierung der Kühlrate
Kühlungskristallisation von Nachprodukt-Kristallsuspensionen bei
Saccarosegewinnung. Dissertation, Techn. Univ. Berlin, Germany.
der
der
Elwell, D. and Scheel, H. J. (1975): High temperature solutions, Academic Press,
London.
References
96
Fiedler, Th., Smejkal, Q., Kroh, L.W. and Kurz T. (2007): Simplified Kinetics and
Colour Formation in Sucrose Solutions Based on a-Dicarbonyl Compounds.
Int J Food Engineering, submitted
Frenkel. (1958): Technological of beet sugar and raffination industry Moscou.
Galea, C. F. and Inkerman, P. A. (1993): Dextran analysis of raw sugar. Part I. A
specific method for total dextran. International Sugar Journal, 95 (1136),
309-313.
Gillet, E. C. (1977): Crystallization in Motion. Cane Sugar Handbook, Meade and
Chen, eds., John Wiley & Sons. Inc., Canada, 290-333.
Godshall, M. A., Legendre, B. L., Clarke, M. A., Miranda, X. M. and Blanco, R. S.
(1994): Starch, polysaccharide and proanthocyanidin in Louisiana sugarcane
varieties. International Sugar Journal, 98, 144-148.
Golovin, P. V. and Grerasimenko, A. A. (1959): Crystallization velocity of sucrose at
higher temperatures. ISSCT, 248-262.
Grimsey, I. M. and Herrington, T. M. (1996): The incorporation of colored
compounds in sucrose crystals. Zuckerindustrie, 121, 40-45.
Gudoshnikov, S. (2007): World sugar market-Back to Surplus. World Perspectives
for Sugar Beet and Cane as a Food and Energy Crop, Sharm El Sheikh,
GL1.1/1-11.
Gudshall, M. A. (1992): The isolation of a high molecular weight colorant from
white beet sugar. Sugar Processing Research, S. P. R. I, Inc., 312-319.
Guglielmone, C. d., Diez, O., Cardenas, G. and Oliver, G. (2000): Sucrose utilization
and dextran production by Leuconostoc mesenteroides isolated from the
sugar industry. Sugar Journal, 62, 36-40.
Gumaraes, L., Susana, S., Bento, L. S. M. and Rocha, F. (1995): Investigation of
crystal growth in a laboratory fluidized bed. International Sugar Journal, 97,
199-204.
Gupta, A. P. and Prabhu, K. A. (1993): Control of Leuconostoc contamination in
sugar industry. International Sugar Journal, 95(11379), 93-97.
Halebian, S., Harris, B., Finegold, S. M. and R D Rolfe, R. D. (1981): Rapid method
that aids in distinguishing Gram-positive from Gram-negative anaerobic
bacteria. J. Clin. Microbiol., 13(3), 444-448.
Hamasaki, Y., Ayaki, M., Fuchu, H., Sugiyama, M. and Morita, H. (2003): Behavior
of Psychrotrophic Lactic Acid Bacteria Isolated from Spoiling Cooked Meat
Products. Appl Environ Microbiol, 69(6), 3668-3671.
Hartman, P. and Perdok, W. G. (1955): On the relations between structure and
morphology of crystals I. Acta Crystallographica, 8, 49-52.
Haynes, L. (2004): Dextran in Refined Sugar. 2004 SPRI Conference Abstracts of
Presentations, April, 4-7, 2004.
Hehre, E. J. and Sugg, J. Y. (1942): Serologically reactive polysaccharides produced
through the action of bacterial enzymes: I. Journal of Experimental Medicine,
75, 339-353.
References
97
Holzapfel, W. and Kandler, O. (1969): Zur Taxonomie der Gattung Lactobacillus
Beijerinck. VI. Lactobacillus coprophilus subsp. confusus nov. subsp., eine
neue Unterart der Untergattung Betabacterium, Zentralbl. Bakteriol.
Parasitenkd. Infektionskr. Hyg. Abt., 2(123), 657-666
Holzapfel, W. and Schillinger, U. (1992): The Genus Leuconostoc. A. Barlows; H.
G. Trüper;M. Dworkin;W. Harder and K. H. Schleifer, eds., the Prokaryotes,
Berlin.
Houghton, B. J., Dutton, J. V., Harvey, C. W. and Sissons, A. (1998): Sugar
Technology Beet and Cane sugar manufacture, P. W. v. d. Poel; H. Schweck
and T. Schwartz, eds., Beet Sugar Development Foundation, Denver, USA,
653-656.
Hucker, G. J. and Pederson, C. S. (1930): Studies on the Coccaceae. XVI. The genus
Leuconostoc, New York State Agricultural Experiment Station, 167, 3-8.
ICUMSA. (1994): International commission for uniform methods of sugar analysis.
Colney, England. GS 1-15.
Imrie, F. K. E. and Tilbury, R. (1972): Polysaccharides in sugar cane and its
products. Sugar technol. Rev., 1, 291-361.
Inkerman, P. A. (1980): An appraisal of the use of dextranase. 17th Congress Int.
Soc. Sugar Cane Technol, Manila, Philippines, 2411–2427.
James, A. C. and Day, D. F. (2000). The process and financial impact of dextran on a
sugar factory. Midland Research Laboratories, Inc.
James, A. C., Miguel E. P. and James. S. R. (2000). The presence of total
polysaccharides in sugar production and methods for reducing their negative
effects. Midland Research laboratories, Inc.
Jeanes, A., Haynes, W. C., Wilham, C. A., Rankin, J. C., Melvin, E. H., Austin, M.
J., Cluskey, J. E., Fisher, B. E., Tsuchiya, H. M. and Rist, C. E. (1954):
Characterization and classification of dextrans from ninety-six strains of
bacteria. Journal of the American Chemical Society, 76, 5041-5052.
Jimenez, E. R. (2005): The dextranase along sugar-making industry. Biotecnologia
Aplicada, 22(1), 20-27.
Karagodin, M. (1998): New batch centrifugal performance at a raw sugar factory.
Sugar y Azucar, Oct., 26-38.
Kennedy, J. F. and White, C. A. (1988): Carbohydrate Chemistry, Oxford
University, New York.
Kenter, C. and Hoffmann, C. (2006): Changes in the quality of frost-damaged
sugarbeet during storage as affected by temperature and variety.
Zuckerindustrie, 13(2), 85-91.
Khaleifah, M. A. (2001): Effect of Dextran on Sugarcane quality and raw sugar
manufacture. Dissertation, Assiut univ., Egypt.
Kim, D. and Day, D. F. (2004): Detrmination of dextran in raw sugar process
streams. Food Science and Biotechnology, 13(2), 248-252.
Kobayashi, M. and Matsuda, K. (1974): The dextransucrase isoen-zyme from L.
mesenteroides NRRL B-512F. Biochim. Biophys. Acta, 370, 441-449.
References
98
Kroh, L. W. Fiedler, T. and Wagner, J. (2007): The formation of colored compounds
in technical sucrose solutions – new knowledge about their molecular basics
and molecular size distribution. Zuckerindustrie 132 (1), 25–32.
Kruse, M. and Ulrich, J. (1993): Kristallwachstum in der Lösugskristallisation als
Drei-Stufen-Modell, Chem. Ing. Techn., 65, 60-63.
Leathers, T. D., Hayman, G. T. and Cote, G. L. (1995): Rapid Screening of
Leuconostoc mesenteroides Mutants for Elevated Proportions of Alternan to
Dextran. Current Microbiol, 31, 19-22.
Lonvaud-Funel, A. (1999). "Leuconostoc." Academic Press, University Victor
Segalen, Bordeaux, France.
Madsen, R. F. (1980): Rührwerke in Kochapparaten. Erfahrungen der DDS.
Zuckerindustrie, 105, 234-237.
Mantovani, G., Gill, I. G. and Fagioli, F. (1967): Einfluss der Kristallstruktur von
Nichtzuckerstoffen auf die Änderung des Habitus von Saccharose. Zucker,
20, 663-668.
Mantovani, G. and Vaccari, G. (1998): Crystal growth. Sugar Technology, P. W. van
der Poel; H. Schiweck and T. Schwartz, Bartens, Berlin, 653-656.
Martins, P. and Rocha, F. (2000): Using Volumetric Growth Rates to Characterize
Sucrose Crystallization. Abstracts for SPRI 2000 conference on sugar
processing research, Porto, Portugal.
Maurandi, V., Mantovani, G., Vaccari, G. and Rossi, A. (1988): Kinetik und
Technologie
der
Erschöpfung
von
Nachprodukt-Kochmassen.
Zuckerindustrie, 113, 791-794.
McGinnis, R. A. (1982): Beet-Sugar Technology, Beet Sugar Development
Foundation, USA.
Meade, G. P. and Chen, J. C. P. (1977): Cane Sugar Handbook, John Wiley and
Sons, New York.
Miller, K. F. and Wright, P. G. (1977): Experiments with molasses exhaustion. The
Queensland Society of Sugar Cane Technologists, Watson Ferguson and
Company, Brisbane, Queensland, Australia, 205-213.
Nicholson, R. I. and Horsley, M. (1959): Impurities in Sugar Processing,
Determination of Dextran and Starch in Cane Juices and Sugar Products. J
Agric Food Chem, 7(9), 640-643.
Noyes, A. A. and Whitney, N. R. (1897): The Rate of solution of solid substances in
their own solutions. Journal of American Chemical Society, 19, 930-934.
Parrisch, F. W. and Clarke, M. A. (1983): Effects of oligosaccharides and
polysaccharides one sucrose crystallization. Tienen, 467-481.
Paton, N. H., Player, M. R. and Urquhart, R. M. (1994): A modified dextran assay
for raw sugar, S.I.T., Publication of Technical Papers and Proceedings of the
Sixty-Third Annual Meeting of Sugar Technologists, Vancouver, Canada,
Paper 666.
References
99
Pot, A., Kuijvenhoven, L. J., Nie, d., L. H. and Jong, d., E. J. (1984): A Study on the
Formation Factors of Crystal Size Distribution in Industrial Sucrose
Crystallizers. Zuckerindustrie, 109, 305-313.
Rauh, J. S., Cuddihy, J. A. and Falgout, R. N. (1999): Analyzing dextran in the sugar
industry: A review of dextran in the factory and a new analytical technique.
Midland Research Laboratories.
Roberts, E. J. (1983): A quantitative method for dextran analysis. International
Sugar Journal, 85, 10-13.
Robyt, J. F. (1986): Dextran. Encyclopedia of Polymer Science and Engineering, H.
F. Mark; N. M. Bikales; C. G. Overberger and M. G., eds., John Wiley &
Sons, New York, NY, 752-767.
Rogé, B., Bensouissi, A. and Mathlouthi, M. (2007): Effect of calcium on white
sugar turbidity. Zuckerindustrie, 132(3), 170-174.
Sancho, D., Deban, L., Martinez, L., Pardo, R. and Vega, M. (1998): Direct
determination of dextran in sugar juices from sugar refining processes by
stripping voltammetry. Journal Environ. Sci. Health, A 33(6), 1171-1184.
Sarkar, D. and Day, D. F. (1986): Dextran analysis: A modified method. J. Amer.
Soc. Sugar Cane Tech., 6, 102-107.
Sarkar, D., Day, D. F., Clarke, S. J. and Saska, M. (1991): Dextran analysis a
comparison of methods. J. Amer. Soc. Sugar Cane Tech., 11, 69-99.
Saska, M. and Oubrahim, Y. (1987): Gel permeation chromatography of sugarcane
products. Sugar Journal(June), 22-25.
Scheibler, C. (1874): Untersuchungen über die Natur der gallertartigen Ausscheidung
(sog., Froschlaich), welche bei der Saftgewinnung aus Rüben beobachtet
wird. Zeitschrift des Vereins der Rübenzucker Industrie, 24, 309-319.
Schiweck, H. and Mannheim, A. S. (1998): Batch evaporating crystallization. Sugar
Technology, P. W. Van der Poel; H. Schiweck, and T. Schwartz, eds.,
Bartens, Berlin, 714-720.
Schliephake, D. and Austmeyer, K. E. (1976): Einige Aspekte zur Theorie und Praxis
der Zuckerkristallisation. Zucker, 29, 293-301.
Schliephake, D., and Ekelhof, B. (1983): Beitrag zur vollständigen Berechnung der
Kristallisationsgeschwindigkeit der Saccharose. Zuckerindustrie, 108(12),
1127-1137.
SCIMAT. (2006). "Leuconostocs " http://www.magma.ca/~pavel/science/
Leuconostoc.htm.
SIL.
(2007). "International Sugar Stats." SUGAR ILLOVO LIMITED,
http://www.illovosugar.com/worldofsugar/internationalSugarStats.htm.
Silin, P. M. (1958): La Technologie de Production de Sucre de Betterave et le
Raffinage. Wyd. Piszezepromizdat Moscou.
Singleton, V. (2002): Review article: advances in techniques of dextran analysis - A
modern day perspective. International Sugar Journal, 104(1239), 132-136.
References
100
Singleton, V., Horn, J., Bucke, C. and Adlard, M. (2001): A new polarimetric
method for the analysis of dextran and sucrose. International Sugar Journal,
103(1230), 251-254.
SPSS-Inc. (1998). "SPSS for windows, release 9, SPSS-Inc."
Steinbuechel, A. and Rhee, S. K. (2005): Polysaccharides and Polyamides in the
food Industry, Wiley-VCH Verlag GmbH & CO. KGaA.
Südzucker, AG (2007): http://www.suedzucker.de/produkt/schema/index.shtml.
Sutherland, D. N. and Paton, N. (1969): Dextran and crystal elongation. International
Sugar Journal, 71(131-135).
Sutherland, I. W. (1996): Extracellular Polysaccharides. Biotechnology, G. R. H.-J.
Rehm, A. Puhler and P. Stadler, ed., Products of Primary Metabolism, New
York: Wiley-VCH Verlag. GmbH & CO. KGaA.
Thelwall, C. (2002): Evaporative crystallisation. Publication of Technical Papers
and Proceedings of the Sixty-Third Annual Meeting of Sugar Technologists,
Vancouver, Canada.
UI-Qader, S. A., Iqbal, L., Rizvi, H. A. and Zuberi, R. (2001): Production of dextran
from sucrose by a newly isolated strain of Leuconostoc mesenteroides
(PCSIR-3) with reference to L. mesenteroides NRRL B-512F. Biotechnol.
Appl. Biochem., 34, 93-97.
UL-Qader, S. A., Iqbal, L., Aman, A., Shireen, E. and Azhar, A. (2005): Production
of Dextran by Newly Isolated Strains of Leuconostoc mesenteroides PCSIR-4
and PCSIR-9. Turkish Journal of Biochemistry, 31(1), 21-26.
Urquhart, R. M., McCowage, R. J. and Inkerman, P. A. (1993): Dextran analysis of
raw sugar. part II. Acomparison of methods. International Sugar Journal, 95,
344-346.
Vaccari, G., Mantovani, G., Sguadino, G., Aquilano, D. and Rubbo, M. (1986): The
raffinose effect on sucrose morphology and kinetics. Sugar technol.Rev, 13,
133-178.
Vaccari, G., Mantovani, G., Sguadino, G., Tamburini, E. and Aquilano, D. (1999):
Fructo-oligosaccarides and Sucrose Crystal Growth Morphology.
Zuckerindustrie, 124(34-39, 536-541).
Vaccari, G., Wawro, P., Tamburini, E., Sguadino, G. and Bernardi, T. (2002):
Cooling crystallization of microfiltered raw juice and of Traditional thick
juice: A Comparison. Zuckerindustrie, 127(22-28).
van der Poel, P. W. (1980): Qualitätsbeeinflussung der Zuckerkristalle durch die
Arbeit mit Rührwerken Erfahrungen bei der CSM. Zuckerindustrie, 105, 237240.
van der Poel, P. W., Schiweck, H. and Schwartz, T. (1998): Sugar Technology,
Bartens, Berlin.
Vavrinecz, G. (1965): Atlas der Zuckerkristalle, Verlag Dr. Albert Bartens KG,
Berlin.
References
101
Wagner, G. (2003): Entwicklung eines automatisierten Bildanalyseverfahrens zur
Beurteilung der Kristallqualität in Saccarosekristallsuspensionen, Techn.
Univ. Berlin, Germany.
Walstra, P. (2003): Physical Chemistry of foods, Marcel Dekker, Inc, New York,
USA.
Wells, W. D. and James, G. P. (1976): Rapid dextran formation in stale cane and its
processing consequences. Queensland Society of Sugar Cane technologists,
287-293.
Wilson, T. E. (1996): A comparison of raw sugar polarisation methods. International
Sugar Journal, 98(1168), 169-174.
Wittenberg, A. (2001): Beitrag zur Optimierung der
Saccharosekristallisation. Dissertation, Techn. Univ. Berlin.
technischen
Yanli. Mi. (2002): Protection Mechanisms of Excipients on Lactate Dehydrogenase
during Freeze-Thawing and Lyophilization. Dissertation, Tennessee.,
Memphis.
102
Appendix
7
Appendix
Appendix 1: The characterization morphology of isolated strains
Strains
Source
Isolation
Colony
morphology
S1
Raw juice
Media:
MRS-Agar
Temperature:
30°C
S2
Raw juice
S3
Raw juice
S4
Raw juice
Like S1
S5
Raw juice
S6
Raw juice
S7
Raw juice
S8
Raw juice
S9
Raw juice
S10
Cossettes
S11
Cossettes
S12
Raw juice
Round, lobate,
glistening, but
lobate / unclear
d= 1.5 mm
Like S4 but
translucent
Round, translucent,
filamentous,
lobate,bristly, d =
3.5 mm
Round, entire
margin, convex,
yellow-brown, dull,
d=1.5 mm
white, entire
margin, irregular,
glistening, d=2 mm
Round, entire
margin, red, convex,
not translucent, d=2
mm
lobate, no entire
margin
Like S1
S13
Raw juice
S14
Raw juice
Round, entire
margin, white,
convex, glistening,
d=1mm
Round, entire
margin, convex,
glistening, centre
structured/clear,
margin translucent,
d = 1 mm
Round, entire
margin, centre
structured/unclear,
margin translucent
Microscopy
Notices
Coccus,
single
Bacteria
7*102 cfu/g
Coccus,
single
Bacteria
6*102 cfu/g
Coccus,
Single and
diplococcus
Bacteria
3*102 cfu/g
single
Yeast ,
1*102 cfu/g
Bacteria
2*102 cfu/g
Coccus,
Diplococcus
single
single
Yeast cells
8*102 cfu/g
Yeast
2*102 cfu/g
Yeast cells
1*103 cfu/g
Yeast cells
1*103 cfu/g
Yeast cells
Yeast cells
Coccus
Bacteria
Like S2
Coccus
Bacteria
Like S1
Coccus
Bacteria
103
Appendix
Appendix 2: Characterizations of the isolated bacteria strains
Strains
Test
Gas formation
Gram (KOH-
Catalase test
Test)
Acid
formation
S1
+
+
-
+
S2
+
+
+
+
S3
-
+
+
+
S5
+
+
-
+
S12
+
+
-
+
S13
+
+
-
+
S14
+
+
-
+
104
Appendix
Appendix 3: Analyze the API 50 CHL Test for Leuconostoc
Sugar
Strains
Leu.m.ssp cremoris
Leu.m.ssp m../ dextranicum1
Leu.m.ssp m./ dextranicum2
S1
S5
S12
S13
S14
Time
(Day)
0 123
4
5
-
- - -
-
-
- - - +++
-
- - - +++ +++ +++
1
-
- - - +++
++
+++ - - -
2
-
- - - +++
++
+++ - - -
5
-
- - - +++
++
1
-
- - -
2
-
- - -
5
-
- - -
1
-
- - - +++
-
-
- - -
2
-
- - - +++
+
-
- - -
5
-
- - - +++
+
-
1
-
- - - +++
-
-
- - -
2
-
- - - +++
+
-
5
-
- - - +++
+
-
1
-
- - - +++
-
2
-
- - - +++
-
5
-
- - - +++
-
-
6
7 8 9 10
11
-
- - - +++ +++
12
-
21
22
23
24
25
-
-
-
-
-
-
-
-
-
-
-
+ ++
-
-
-
-
-
-
-
+++
+++
+++ +++ +++
-
-
-
-
-
-
-
+++
+++
-
+++
-
-
-
-
-
-
-
+++
++
++
+
+++ +++ +++
-
-
-
-
-
-
-
+++
+++
+++
+++ - - - +++ +++ +++ +++
-
-
-
-
-
-
-
+++
+++
+++ +++ +++
-
+++ +++ - - - +++ +++ +++ +++
-
-
-
-
++
-
+++
-
+++
-
-
+++ +++ - - - +++ +++ +++ +++
-
-
-
-
+++
-
+++
-
+++
++
-
+++ +++ - - - +++ +++ +++ +++
-
-
-
-
+++
-
+++
-
+++
+++ +++ +++
++
-
13 14 15 16 17 18 19 20
+++ - - - +++ +++ +++ +++
++
++
++
+
+++ +++ +++
-
-
+++
++
-
-
-
-
-
-
-
-
++
+
+
+++ +++ +++
-
-
-
-
+++
-
+++
++
++
++
+++ +++ +++
-
-
-
-
+++
-
+++
++
++
-
+++
-
-
-
-
-
-
-
-
-
- - -
-
+++ +++
++
-
-
-
-
+++
-
-
- - -
-
+++ +++ +++
-
-
-
-
+++
-
-
-
- - -
++
+++ +++ +++
-
-
-
-
+++
-
-
-
-
- - - +++ +++ +++ +++
-
-
-
+++
-
-
-
-
- - - +++ +++ +++ +++
-
-
-
+++
-
-
-
++
-
+
++
++
+++
++
++
++
+++ +++
+
++
++
+
+++
++
++
+++
++
+
+
++
++
+++
+++
++
+++
+++
+++
+++
++
+++
+++
++
++
++
+++
+++ +++ +++
+++
+++ +++ +++
105
Appendix
Sugar
Strains
Leu.m.ssp cremoris
Leu.m.ssp m../ dextranicum1
Leu.m.ssp m./ dextranicum2
S1
S5
S12
S13
S14
Time
(Day)
26
27
28
29
30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
-
+
-
-
- - -
-
-
47
48
49
-
-
-
+
-
-
-
-
-
-
-
-
-
-
-
+++
+++
+++
++
+++ +++ +++
-
- ++ - - - +++ +++ -
-
-
-
-
-
+
-
-
+
+
+++
+
+++ +++ +++
-
- +++ - - -
+ +++ -
-
-
-
-
-
+
-
+
1
-
++
+++
-
+++ +++
-
- +++ - - - ++ +++ -
-
-
-
-
-
+
-
+
2
-
+++
+++
-
+++ +++ +++
-
- +++ - - - ++ +++
-
-
-
-
-
+
-
+
5
+++
+++
+++
++
+++ +++ +++
-
- +++ - - - ++ +++ -
-
-
-
-
-
+
-
+
1
++
+++
+++
++
++ +++ +++
-
-
-
- - -
-
++ -
-
-
-
-
-
-
-
-
2
+++
+++
+++
+++ +++ +++ +++
-
-
-
- - -
-
++ - +++ -
-
-
-
-
-
-
5
+++
+++
+++
+++ +++ +++ +++
-
-
-
- - -
-
++
-
-
-
-
-
-
1
++
+
+++
-
+++ ++ +++
-
-
-
- - - ++ ++ -
-
-
-
-
+
-
+
2
++
+++
+++
-
+++ +++ +++
-
- +++ - - - ++ +++ - +++ -
-
-
-
++
-
++
5
++
+++
+++
++
+++ +++ +++
-
- +++ -
-
-
-
-
-
-
1
+
-
+++
-
+++ +++ +++
-
-
-
-
-
-
+
-
-
2
++
++
+++
+++ +++ +++ +++
-
- +++ - - - ++ +++ - +++ -
-
-
-
++
-
-
5
++
+++
+++
+++ +++ +++ +++
-
- +++ - - - ++ +++ - +++ -
-
-
-
++
-
-
1
++
+++
+++
++
2
++
+++
+++
5
++
+++
+++
-
-
-
-- ++ +++ - +++ -
- - -
- +++ -
-
-
+++
-
-
-
- - - ++
++
-
-
+++
-
-
-
++
+++
+++
+++ -
-
-
- - - ++
-
-
++
+
-
-
-
-
-
-
++
-
-
+
-
-
-
-
++
-
-
+++
++
106
C.V. and list of publications
8
C. V. and List of Publications
Curriculum Vitae / Lebenslauf
El-Sayed Ali Abdel-Rahman Soliman
geboren am 20.04.1968
in Sohag (Ägypten)
Hochschulausbildung:
1987- 1991
Studium Lebensmitteltechnologie an
Universität, Ägypten, Abschluss Bachelor
1993 – 1999
Studium Lebensmitteltechnologie “Biochemical and
Technological studies on Mungbean seeds” an der Assiut
Universität, Ägypten, Abschluss Magister
1999-2003
Oberassistent an der Abteilung Lebensmitteltechnologie,
Fakultät Landwirtschaft, Assiut Universität
ab 2003
Stipendium der ägyptischen Regierung für promovierte
Wissenschaftler
ab Juli 2004
Wissenschaftlicher
Mitarbeiter
am
Fachgebiet
Lebensmittelverfahrenstechnik an der TU Berlin
Promotionsthema
“Untersuchungen
zum
Einfluss
höhermolekularer Polysaccharidfraktionen auf das
Kristallwachstum in Saccharoselösungen”
ab Juli 2006 bis Juli
2007
Stipendium
von
der
TU-Berlin
zum
Thema
“Untersuchungen zur Bildung und Beseitigung von
Trübungen
aus
konzentrierten
technischen
Saccharoselösungen”
Berufstätigkeit:
Praktikum
•
•
•
•
•
Lehrerfahrung:
der
Assiut
Training course on modern techniques in molecular
biology and their practical applications (Assiut Uni.)
Praktikum in der Zuckerfabrik Jülich AG, Thema “
Untersuchung zur Trübsaftbildung im gelagerten
Dicksaft” (Deutschland)
Praktikum in den Zuckerfabriken Aarberg und
Frauenfeld zum Thema
“ Dar Zusammenhangs
zwischen Saftqualität und Zuckerqualität in der
Dicksaftkampagne ” (Schweiz)
Praktikum am FG Lebensmittelverfahrenstechnik, TUBerlin, zum Thema Zuckertechnologie (Deutschland)
PIW Projekt Prozessingenieurwissenschaften im FG
Lebensmitteverfahrenstechnik, TU-Berlin, zum Thema
„Zuckerbäckerei“ (Deutschland)
Agricultural Biochemistry, Principles of Food Technology,
Food Chemistry and Analysis, Food Chemistry, Sugar
Technology and Special Products Technology
107
List of Publications
Veröffentlichungen in Zusammenhang mit dieser Arbeit / Publication in
conjunction with this thesis
[1] E. A. Abdel-Rahmana; Q. Smejkal, R. Schick, El-Syiad, S. and Kurz, T. (2006)
Influence of high dextran concentrations and molecular fractions on the rate of
sucrose crystallization in pure sucrose solutions. Journal of Food Engineering,
Available online 5 July 2007
[2] E. A. Abdel-Rahman, R. Schick, T. Kurz (2007) Influence of dextran on sucrose
crystallization. Zuckerindustrie, 132 (6), 453-460.
Weitere Veröffentlichungen / Other Publications
[1] El-Rify, M.N.; El-Geddawy, M.A.H; El-Fishawy, F.A; and Abdel-Rahman, E.
A. (2000) Effect of processing on the amino acid composition and protein quality of
mung bean seeds. Mansoura University Journal of Agricultural Sciences, pp. 93-102.
A. (2000) Effect of some technological processes on the gross chemical composition
and mineral contents of mung bean seeds. Mansoura University Journal of
Agricultural Sciences, pp. 103-113.
[4] E. A. Abdel-Rahmana, M. A. El-Geddawyb, F. A. El-Fishawyb, T. Kurz and M.
N. El-Rify (2006) Isolation and physico-chemical characterization of mung bean
starches, International of Food Process Engineering (submitted).
[5] E. A. Abdel-Rahmana, M. A. El-Geddawyb, F. A. El-Fishawyb, T. Kurz and M.
N. El-Rify (2006) The changes in the lipid composition of mung bean seeds as
affected by processing methods. International of Food Process Engineering
(accepted).
108
Conference Contributions
Vorträge/Poster
[1] Abdel-Rahman, E. A. (1997) Evaluation of Mungbean seeds for technological
utilization. Workshop on Mungbean crop in Egypt. Oral presentation, (National
Center for Research, Cairo, Egypt, May 1997)
A. (2000) Effect of processing on the amino acid composition and protein quality of
mung bean seeds. First Mansora Conference of Food Science and Dairy Technology,
Oral presentation (Mansoura, Egypt, October. 2000).
A. (2000) Effect of some technological processes on the gross chemical composition
and mineral contents of mung bean seeds. First Mansoura Conference of Food
Science and Dairy Technology, Oral presentation (Mansoura, Egypt, October. 2000).
[4] Abdel-Rahman, E. A.; El-Syiad, S. and Kurz, T. (2006) Influence of high
dextran concentrations and molecular fractions on the rate of sucrose crystallization
in pure sucrose solutions. 13th World Congress of Food Science and Technology
‘Food is Life’, Poster presentation, (Nantes, France, September 2006).
[5] E. A. Abdel-Rahman; Q. Smejkal, R. Schick, El-Syiad, S. and Kurz, T. (2007)
Influence of dextran concentrations and molecular fractions on crystallization
kinetics in pure sucrose solutions. World Perspectives for Sugar Beet and Cane as a
Food and Energy Crop. Poster presentation (Sharm El Sheikh, Egypt March 2007).
[6] T. Kurz, E. A. Abdel-Rahman, R. Schick. (2007) Influence of dextran on
sucrose
crystallization.
CITS
23rd
General
Assembly,
Oral
presentation
(Warnemünde, Germany May 2007)
[7] E. A. Abdel-Rahman, R. Schick, T. Kurz (2007) Einfluss von Dextran auf die
Zuckerkristallisation. Frühsommertagung Technik, Pfeifer & Langen, Oral
presentation (Bielefeld, Germany 31th May to 01 June 2007).
109
Eidesstattliche Erklärung
Hiermit erkläre ich, dass ich die vorliegende Arbeit selbstständig und ohne fremde
Hilfe verfasst und andere als die angegebenen Hilfsmittel nicht verwendet habe.
Berlin, den 17. Juli 2007
El-Sayed Soliman

Investigations on the influence of dextran during beet sugar

Transcrição

Documentos relacionados

Healthy milk teeth are a gift from nature …

Full Text in pdf

Scent Crystal®

Timetable and Advertising Rates 2016

The Konftel 100 – the hassle free conference phone - IT

PDF of article - Crystallography Journals Online

Some facts about Casino Tschechien Grenze Furth Wald

the pdf here

Abstract

366 THE EDINBURGH GAZETTE, MARCH 24, 1865.