Effects of different pre-cooking treatments on peeling and quality of

Arch. Geflügelk. 2002, 67 (2), 83 – 86, ISSN 0003-9098. Verlag Eugen Ulmer GmbH & Co., Stuttgart
Effects of different pre-cooking treatments on peeling
and quality of hard-cooked fresh eggs
of young and old layers
Einfluss der Behandlung vor dem Kochen auf die Schälbarkeit und die Qualität hartgekochter frischer Eier von jungen und alten Legehennen
El Beeli1, M. Y., M. A. Grashorn2 and W. Bessei2
Manuskript eingegangen am 18. Oktober 2000, angenommen am 24. Juni 2002
Introduction
Materials and Methods
The use of hard-cooked eggs is increasing in daily life in
developed countries. Industry for hard cooked egg is developing to meet the demands (Britton and Fletcher,
1987). Fresh laid eggs have an excellent interior quality
but, are very difficult to peel after cooking (Britton and
Fletcher, 1987; Irmiter et al., 1970). Difficult peeling
with partial destruction of the albumen surface is the main
problem. Large losses of edible parts of the egg occur
when coagulated egg albumen adhere to the shell during
peeling. This problem of peeling hard-cooked eggs has
been associated with the pH of the albumen (Swanson,
1959; Meehan et al., 1967; Reink and Spencer, 1964;
Fry et al., 1966; Fuller and Angus, 1969). Albumen
with pH of 8.7 or more results in easy shell removal of
hard cooked eggs. In a good quality peeled hard cooked
egg, the shell does not break during cooking, peels off
easily and the yolk should be well centered and free of
any dark rings (Irmiter et al., 1970). To meet these criteria,
several factors should be considered, including temperature of the egg, pH of the albumen, temperature of the
heating medium, length of the cooking period, strength of
the shell and quality of eggs (Irmiter et al., 1970).
Several pre-cooking treatments of hard-cooking eggs
have been reported with positive effects on peeling quality: making a small hole (2.4 mm) at the large end, storing
the eggs at 50 C, exposing eggs to ammonium hydroxide
fume in a closed system for 10 minutes, storing eggs in a
closed environment with 10% NaOH solution and rapid
cooling after cooking and reheating for a short time
(Swanson, 1959; Fuller and Angus, 1969; Irmiter et al.,
1970; Hale and Britton, 1974; Britton and Fletcher,
1987). The Poultry and Egg National Board reommended
piercing of the shell at the large end prior to hard cooking
for easy and good peeling (Anon, 1966).
The objectives of this investigation were to study the
effects of various pre-cooking treatments on peeling and
quality of fresh hard-cooked eggs of young and old layers
to ensure minimum shell cracking, ease of peeling and
smooth appearance of the peeled eggs.
Fresh laid eggs were collected from old Rhode Island Red
layers of 22 months of age and young Lohmann LSL
layers of 7 months of age within 15 and 12 hours after
being laid, respectively. The birds were housed at the Research Farm ‘Unterer Lindenhof’ of the University of Hohenheim. After collection eggs were immediately transported to the laboratory, candled individually, and only
eggs with intact shells were used for the experiment. In
each treatment prior to cooking, eggs were weighed individually and air chambers were measured in mm. Four (4)
eggs were randomly selected for determination of the
pH of the albumen. A total of 9 treatments were conducted within each breed, and 25 eggs were randomly allotted to each treatment.
The treatments were, 1) immediate cooking without any
treatment (control); 2) piercing of the eggs at the large
end prior to cooking with a small needle device (diameter
1 mm); 3) piercing at the large end and storing at room
temperature (18–20 C) for 24 hours prior to cooking; 4)
immediate cooking in 2.5% (v/v) citric acid solution; 5)
immediate cooking in 5% (v/v) citric acid solution; 6) immediate cooking followed by rapid cooling in running
water (19 C) for 10 minutes and reheating for 5 minutes;
7) storing the eggs above a 500ml layer of 10% NaOH
(w/v) solution at 20 C in an air tight dessicator for 48
hours; 8) storing the eggs at room temperature (18–20 C)
for 2 days with large end at top; 9) and storing the eggs at
room temperature (18–20 C) for 7 days with large end at
top (Table 1).
Freshly laid eggs of Lohmann LSL layers were used to
study the effects of length of storage, temperature and precooking treatment on albumen and yolk pH. The eggs
were either pierced at the large end and stored for 3 and
6 days, or stored above a layer of 10% NaOH (w/v) solution for 3 and 6 days. All eggs were stored at 20 C and
36 C.
1
University of Gezira, Faculty of Agricultural Sciences, Department of Animal Sciences, Wad Medani, Sudan.
2
Dept. of Farm Animal Ethology and Poultry Science (470),
University of Hohenheim, Stuttgart, Germany.
Archiv für Geflügelkunde 2/2003
Method of Cooking
In all treatments the eggs were placed in cold tap water
(19 C) in one layer of 7 eggs. The volume of the water
in the pan was 4 : 1 (weight ratio of water to eggs). The
pan was covered with a lid and the water was brought
through slow boiling with an electric heater for 20 minutes
to a temperature of 98–100 C (Anon, 1981). After cook-
84
EL BEELI et al., Effects of pre-cooking treatments on peeling and quality of hard-cooked fresh eggs
Table 1. Experimental layout
Versuchsdesign
Treatment
Collection time
Old hens
1
9
10
9
10
9
10
9
10
9
10
9
10
9
10
9
10
9
10
7.95
Without treatment (control)
2
Pierced at the large end
3
Pierced at the large end þ stored at 18–20 C for 24 h
4
Cooked in 2.5% (v/v) citric acid solution
5
Cooked in 5% (v/v) citric acid solution
6
Immediate cooking þ rapid cooling þ reheating
7
Stored at 10% NaOH (w/v) solution at 18–20 C for 24 h
8
Stored at 18–20 C for 48 h
9
Stored at 18–20 C for 7 days
ing the eggs were placed in cold running tap water
(19 C) for 5 minutes. The water was drained and the eggs
were left at room temperature (18–20 C) for 10 minutes.
After cooling, the eggs were examined for cracks which
developed in the shell during cooking and cooling. Ease of
peeling and appearance of the peeled eggs were evaluated
in a 7 point rating scale developed by Irmiter et al. (1970)
with slight modification for the appearance of peeling. The
modification involved addition of zero score resulting in an
8 point rating scale. The percentage yields of the edible
portions were calculated by the equation, percentage
yield ¼ peeled egg (edible portion)/egg weight 100.
Statistical evaluation
Data were statistically evaluated and analysed by ANOVA
using the JMP package (SAS Institute). Arithmetic means
were compared by Student’s t-test and/or Duncan’s Multiple Range Test.
a.m–12
p.m–10
a.m–12
p.m–10
a.m–12
p.m–10
a.m–12
p.m–10
a.m–12
p.m–10
a.m–12
p.m–10
a.m–12
p.m–10
a.m–12
p.m–10
a.m–12
p.m–10
p.m
a.m
p.m
a.m
p.m
a.m
p.m
a.m
p.m
a.m
p.m
a.m
p.m
a.m
p.m
a.m
p.m
a.m
Young hens
Cooking time
(minute)
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
7.95
7.95
7.95
8.30
8.30
7.95
7.95
7.95
7.95
7.95
7.95
8.2
8.2
8.4
8.4
9.3
9.3
Results and Discussion
Cracking of eggs as influenced by various pre-cooking
treatments is shown in table 2. High cracking (23.8%) occurred in eggs of old hens (range 4.8–23.8%). Cracking
of young hen’s eggs was only 4.8% (range 0.0–4.8%).
High cracking occurred in old hens when fresh laid eggs
were immediately hard cooked without treatment, cooked
in 2.5% (v/v) citric acid solution, stored above 10%
NaOH or stored at 18–20 C for 48 h prior cooking.
Storing eggs of old hens at 18–20 C for 7 days did not
alleviate the incidence of cracking (14.4%) (Table 2). This
result indicates that high cracking is most probably due to
the age of the old hens. This is in agreement with the
finding of Irmiter et al. (1970).
Eggs in treatments 1–8 showed poor or very poor
peeling (Table 3) and thus poor appearance (Table 4).
Fresh eggs of old and young layers stored at 18–20 C
for 7 days displayed easy peeling of 53 and 92% and
better appearance of 3.5 and 6.5, respectively (Table 4).
Table 2. Effects of pre-cooking treatment on the incidence of cracked shells after cooking and cooling
Einfluss der Vorbehandlung auf die Häufigkeit an defekten Schalen nach dem Kochen und Kühlen
Treatment
1
2
3
4
5
6
7
8
9
Without treatment (control)
Pierced at the large end
Pierced at the large end þ stored at 18–20 C for 24 h
Cooked in 2.5% (v/v) citric acid solution
Cooked in 5% (v/v) citric acid solution
Immediate cooking þ rapid cooling þ reheating
Stored above 10% NaOH (w/v) solution at 18–20 C for 48 h
Stored at 18–20 C for 48 h
Stored at 18–20 C for 7 days
Total
Mean
Number of cooked eggs
Number of cracked eggs
Old hens
n
Young hens
n
Old hens
Young hens
n
%
n
%
21
21
21
21
21
21
21
21
21
189
21
21
21
21
21
21
21
21
21
189
5
2
1
5
1
1
4
5
3
27
3
23.8
9.5
4.8
23.8
4.8
4.8
19.0
23.8
14.3
14.3
––
0
0
0
0
0
0
1
1
0
2
0.2
0.0
0.0
0.0
0.0
0.0
0.0
4.8
4.8
0.0
1.1
––
d.f ¼ 8; t (tab.) ¼ 2.31; t (calc.) ¼ 5.10; P < 0.05
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EL BEELI et al., Effects of pre-cooking treatments on peeling and quality of hard-cooked fresh eggs
85
Table 3. Ease of peeling scores of hard cooked fresh eggs of old and young layers
(as percentage)*
Schälbarkeit der hartgekochten Eier von alten und jungen Hennen (in Porzent)
Treatment
(7)
very
easy
(6)
excellent
(5)
good
(4)
fair
(3)
poor þ
(2)
poor (1)
very
poor
1
Without treatment (control)
––
––
––
––
––
––
2
Pierced at large end
––
––
––
––
––
––
3
Pierced at the large end þ stored for 24 h at 18 –20 C
––
––
––
4
2.5% citric acid solution
––
––
––
5
5% citric acid solution
––
––
––
6
Cooking þ rapid cooling þ reheating
––
––
––
7
Stored above 10% NaOH for 48h
––
––
––
8
Stored at 18–20 C for 48h
––
––
––
9
Stored at 18–20 C for 7 days
53.3
92.0
22.2
0.0
13.3
0.0
71.1
71.1
––
85.7
66.7
––
66.6
80.9
––
71.4
0.0
––
14.3
19.1
14.3 33.3
9.52
4.44 2.22
2.4
4.8
100
100
100
100
14.3
4.76
4.8
14.3
19.0
4.7
9.5
19.1
47.6
0.0
47.6
57.1
2.22
0.0
––
14.3
23.8
9.50
19.1
14.3
14.3
19.0
81.0
38.1
81.0
19.1
19.1
2.22
0.0
* The upper and lower figures correspond to old and young layers, respectively.
Pre-cooking treatments investigated in this study failed
to raise the pH of the egg albumen to a level above 8.9
when held at 18–20 C. These results are inconsistent with
results from literature (Anon, 1966; Hale and Britton,
1974; Britton and Fletcher, 1987). This discrepancy
may be attributed to the temperature during pre-cooking
treatments, old age of the layers and the freshness of the
eggs. In treatments 1–8 eggs of old and young layers displayed a yield range between 74.5–79.0 and 70.5–84.2%,
respectively (Table 4). Whereas, highest yields of 85.4 and
86.6% were displayed, respectively, by eggs of old and
young layers stored at 18–20 C for 7 days. Generally,
eggs of young layers have a higher yield than that of old
layers. No improvement in yield of the edible portion was
achieved by any of the pre-cooking treatments used. This
was primarily due to poor peeling which may be attributed
to unfavourable temperature which did not enhance the
pre-cooking treatments to raise albumen pH. Tables 5a and
5b show the effects of length of storage, storage temperature and piercing or storage above NaOH for 3 and 6 days
at 20 and 36 C on pH of the albumen and the yolk. Both,
albumen and yolk pH were increased as storage period increased, whereas the effects of storage temperature were
minor. But, for the main effect temperature a rise in pH of
0.9 was observed for the albumen when eggs were stored
at 36 C. The effects of storage period on pH were more
Table 4. Apperance score of peeling and yield (%) of hard cooked fresh eggs of old and young hens*
Bewertung des Aussehens und des Anteils der verzehrbaren Masse (%) von gekochten Eiern alter und junger Hennen
Treatment
Appearance score**
% yield SD***
1
Without treatment (control)
2
Pierced at the large end
3
Pierced at the large end+stored at 18–20 C for 24 h
4
2.5% (v/v) citric acid solution
5
5% (v/v) citric acid solution
6
Cooking þ rapid cooling þ re-heating
7
Stored above 10% NaOH for 24 h
8
Stored at 18–20 C for 24 h
9
Stored at 18–20 C for 7 days
0.0
0.0
0.0
0.0
0.0
2.13
0.0
0.5
0.0
0.6
0.0
0.0
0.0
0.0
0.0
0.63
3.5
6.5
78.85.64b
70.54.80e
78.46.02b
76.84.88d
75.75.49bc
84.22.88b
79.0+5.43b
79.03.19d
77.85.43bc
81.12.52cd
78.92.68b
74.85.84e
74.55.69c
79.14.30d
75.85.86bc
81.64.58c
85.46.16a
86.61.47a
*
The upper and lower figures correspond to old and young layers, respectively .
** Evaluated on a modified 8 point rating scale according to Irmiter et al. (1970).
*** a, b, c, d, e Values in a vertical column with different superscripts are significantly different (p < 0.05).
Archiv für Geflügelkunde 2/2003
86
EL BEELI et al., Effects of pre-cooking treatments on peeling and quality of hard-cooked fresh eggs
Table 5a. Effects of length of storage, temperature and precooking treatments on albumen pH.
Einfluss der Lagerdauer, der Lagertemperatur und der Behandlung vor dem Kochen auf den pH-Wert des Eiklars
Storage days
3 days
Treatments
Piercing NaOH Piercing NaOH
Temperature 20 C
36 C
9.4
9.6
Mean
6 days
9.2
9.2
9.34b
9.6
9.7
Mean
9.4
9.5
9.40
9.47
9.55a
S.E. for temperature: 0.12; S.E. for storage days: 0.12; S.E. for treatment: 0.21
Means with different superscripts are significantly different (p < 0.05).
Table 5b. Effects of length of storage, temperature and precooking treatments on yolk pH.
Einfluss der Lagerdauer, der Lagertemperatur und der Behandlung vor dem Kochen auf den pH-Wert des Dotters
Storage days
3 days
Treatments
Piercing NaOH Piercing NaOH
Temperature 20 C
36 C
6.4
6.4
Mean
6 days
6.3
6.4
6.38b
6.5
6.7
Mean
6.4
6.4
6.4B
6.5A
6.50a
S.E. for temperature: 0.05; S.E. for storage days: 0.05; S.E. for treatment: 0.08
Means with different superscripts are significantly different (p < 0.05).
pronounced for the pre-cooking treatment NaOH. These
observations indicate that both storage time and temperature are crucial factors in raising albumen pH above 8.9.
This is in agreement with the findings of Fuller and Angus (1969), who found that the ease of peeling of hard
cooked eggs was increased by increasing storage time,
especially when held at 50 C good peeling properties appeared at a pH above 8.9.
It can be concluded that the temperature during precooking treatments is the most limiting factor for subsequent improvement of peeling quality of hard cooked
eggs. Ageing of eggs turned to be the best effect. Temperature during pre-cooking treatment may act as an artificial ageing.
Summary
The effects of different pre-cooking treatments on peeling
and quality of fresh laid eggs of old and young hens were
investigated. Ease of peeling and appearance of peeled
eggs were evaluated in a 8 points rating scale.
High (23.8, 4%) and low (4.8, 0%) incidence of egg
cracking during cooking was observed for fresh eggs of
old and young hens, respectively. This indicated that high
cracking is due to the age of the old hens. Most pre-cooking treatments showed poor or very poor peeling with
poor appearance. Eggs of old and young hens stored at
18–20 C for 7 days displayed a peeling of 53 and 92%
(very easy) and appearance score of 3.5 and 6.5, respectively. Non of the investigated pre-cooking treatments
raised albumen pH above 8.9 when held at 18–20 C for
not more than two days. The temperature during pre-cooking treatments appeared to be a limiting factor in raising
albumen pH and peeling quality of hard-cooked eggs. It
may act as an artificial ageing of eggs.
Keywords
Layers, egg quality, hard-cooked eggs
Zusammenfassung
Einfluss der Behandlung vor dem Kochen auf die Schälbarkeit und die Qualität hartgekochter frischer Eier von jungen
und alten Legehennen
Der Einfluss verschiedener Behandlungen vor dem Kochen auf
die Schälbarkeit und die Qualität von frischen Eiern alter und junger Legehennen wurde untersucht. Die Schälbarkeit und das Aussehen der geschälten Eier wurde anhand einer Skala mit 8 Punkten bewertet.
Der Anteil an Knickeiern war bei den alten Hennen höher als
bei den jungen. Die Streuung betrug für die alten Hennen 4,8 bis
23,8% und bei den jungen Hennen 0 bis 4,8%. Dies bestätigte
die Erwartung, dass alte Hennen mehr Knickeier produzieren. Die
meisten der vor dem Kochen angewendeten Behandlungen führten zu einer schlechten Schälbarkeit und zu einem unbefriedigenden Aussehen der geschälten Eier. Für bei 18–20 C über 7 Tage
gelagerte Eier wurde bei den alten Hennen eine Schälbarkeit von
53% und eine Note von 3,5 für das Aussehen ermittelt, während
die entsprechenden Werte für die jungen Hennen 92% bzw. 6,5
betrugen. Unabhängig von den Vorbehandlungen stieg der pHWert im Eiklar nicht über 8,9, wenn die Eier bei 18–20 C weniger als 2 Tage gelagert wurden. Das Anstechen der Eischalen vor
dem Kochen am stumpfen Ende führte zu einem Gewichtsverlust.
In ähnlicher Weise verminderte sich das Eigewicht mit der Lagerzeit und der Lagertemperatur. Insgesamt spielte die Temperatur
bei der Vorbehandlung der Eier eine große Rolle. Bei zu geringen
Temperaturen wurde ein Anstieg des pH-Wertes verhindert und so
die Schälbarkeit verschlechtert. Die Temperatur kann daher als
Faktor zur künstlichen Eialterung herangezogen werden.
Stichworte
Legehenne, Eiqualität, hartgekochte Eier
References
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Poultry and Egg National Board.
Anon, 1981: Eggcyclopedia. American Egg Board, Park Ridge,
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Britton, W. M. and D. L. Fletcher, 1987: Influence of storage
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Correspondence: Dr. Mohamed Yousif El Beeli, Department of Animal Science, Faculty
of Agricultural Sciences, University of Gezira, Wad Medani. P. O. Box, 20. Sudan;
e-mail: [email protected]
Archiv für Geflügelkunde 2/2003