Propriedades antioxidantes e reológicas de geleia de goiaba com

UNIVERSIDADE ESTADUAL DE MARINGÁ
CENTRO DE CIÊNCIAS AGRÁRIAS
Programa de Pós-Graduação em Ciência de Alimentos
PROPRIEDADES ANTIOXIDANTES E REOLÓGICAS DE GELEIA DE
GOIABA COM ADIÇÃO DE SUCO DE UVA CONCENTRADO
RÚBIA CARVALHO GOMES CORRÊA
Maringá
2012
RÚBIA CARVALHO GOMES CORRÊA
PROPRIEDADES ANTIOXIDANTES E REOLÓGICAS DE GELEIA DE
GOIABA COM ADIÇÃO DE SUCO DE UVA CONCENTRADO
Dissertação
apresentada
ao
Programa de Pós Graduação em
Ciência
de
Universidade
Alimentos
da
Estadual
de
Maringá para obtenção do grau
de
Mestre
em
Ciência
de
Alimentos.
Orientadora:
Profa.
Dra.
Angélica Marquetotti Salcedo
Vieira
Maringá
2012
Orientadora
Profa. Dra. Angélica Marquetotti Salcedo Vieira
Co-orientadora
Profa. Dra. Rosangela Bergamasco
BIOGRAFIA
Rúbia Carvalho Gomes Corrêa nasceu em 26 de junho de 1986 na cidade de
Maringá - PR. Concluiu o Ensino Fundamental na escola Notre Dame de Maringá e o
Ensino Médio no Colégio Marista de Maringá.
Em 2004 ingressou no curso de Engenharia de Alimentos da Universidade
Estadual de Maringá, graduando-se em 2009. Durante o mesmo ano, realizou estágio
curricular obrigatório na COCAMAR Cooperativa Agroindustrial.
No ano de 2010, iniciou o mestrado no Programa de Pós-Graduação em
Ciência de Alimentos - UEM. Neste mesmo período passou a integrar, como bolsista
recém-formada, o projeto de extensão universitária Suporte Técnico à Agroindústria
Familiar de Conservas, financiado pela Fundação Araucária do Paraná. Em 2011
concluiu o "Curso de Especialização em Biotecnologia Aplicada à Agroindústria", do
Departamento de Biologia Celular e Genética - UEM.
Participou de trabalhos nas áreas de Tecnologia de Produtos Vegetais,
Aproveitamento de Subprodutos e Tecnologia de Alimentos Dietéticos e Nutricionais,
com experiência em análises físico-químicas, microbiológicas e sensoriais em
alimentos.
DEDICO
Aos meus amados pais Susy e Pedro
Aos meus irmãos e amigos Susana, Pedro e Raísa
AGRADECIMENTOS
Primeiramente agradeço a Deus, que sempre esteve a meu lado e colocou em meu
caminho pessoas capacitadas para me auxiliarem, mas também queridas que
permanecerão para sempre em meu coração.
Aos meus pais, por investirem constantemente em minha vida, e por sonharem junto
comigo a realização deste mestrado.
À professora Angélica, que me acompanha desde a graduação, pelo incentivo,
orientação, paciência, generosidade, carinho e presença constante.
À professora Rosangela, pelo grande otimismo, carinho e generosidade.
Ao professor Charles, que nos recebeu na Universidade Tecnológica Federal do Paraná
campus Campo Mourão, pela orientação valiosa, generosidade e essencial ajuda neste
trabalho.
À querida Gisele, por ter me acolhido em sua casa por diversas vezes, além de ter
colaborado em todas as etapas desta pesquisa, sendo acima de tudo uma grande amiga e
exemplo.
Aos amigos e colegas do mestrado, em especial à Katieli, pela amizade, incentivo,
companheirismo e grande ajuda nos momentos mais difíceis.
À Universidade Estadual de Maringá, por mais esta oportunidade de formação e
crescimento profissional.
Aos professores do Programa de Pós-Graduação em Ciência de Alimentos - UEM, por
terem contribuído para a minha formação, amadurecimento, e por servirem de
inspiração.
À Lúcia e à professora Rosane, pela competência e dedicação ao trabalho realizado no
PPC.
À CAPES e à Fundação Araucária pelo suporte financeiro e incentivo à pesquisa.
A todos que contribuíram de alguma forma para a realização deste trabalho.
APRESENTAÇÃO
Esta dissertação de mestrado está apresentada na forma de artigo científico, que será
submetido para a revista Lebensmittel-Wissenschaft & Technologie / LWT - Food
Science & Technology, com extrato qualis A2 referente à avaliação trienal 2010 e com
fator de impacto 2,292 para o mesmo ano.
Rúbia Carvalho Gomes Corrêa, Gisele Teixeira de Souza Sora, Charles Windson
Isidoro Haminiuk, Rosangela Bergamasco, Angélica Marquetotti Salcedo Vieira.
Antioxidant and rheological properties of guava jam with addition of concentrated
grape juice.
Autores:
Rúbia Carvalho Gomes Corrêa1 ([email protected])
Gisele Teixeira de Souza Sora1 ([email protected])
Charles Windson Isidoro Haminiuk2 ([email protected])
Rosangela Bergamasco3 ([email protected])
Angélica Marquetotti Salcedo Vieira4 ([email protected])
Filiações:
1
Universidade Estadual de Maringá, Programa de Pós-Graduação em Ciência de
Alimentos.
2
Universidade Tecnológica Federal do Paraná, campus Campo Mourão.
3
Universidade Estadual de Maringá, Departamento de Engenharia Química.
4
Universidade Estadual de Maringá, Departamento de Engenharia de Alimentos.
GENERAL ABSTRACT
INTRODUCTION. The oxidative stress originated by reactive oxygen species (ROS)
is fundamentally linked to the manifestation of numerous chronic and degenerative
diseases. Fortunately, studies have strongly demonstrated that a diet rich in antioxidants
can protect from health harms caused by the oxidation process. Guava (Psidium guajava
L.) is a popular tropical fruit characterized by excellent nutritional and sensory
properties, besides an extraordinary content of carotenoids, especially lycopene.
Because fruits constitute the major dietary source of phenolic compounds, it has been
suggested that fruit juices have potential to be used as functional ingredients in food
industry. As grapes are rich sources of potent antioxidants with proven cardio protective
properties, concentrated grape juice could be applied as a potential functional ingredient
in food formulations. In this context, guava and concentrated grape juice could figure as
great raw materials in jam formulations, thus originating potential functional products
with a high sensory appeal.
AIMS. The present study aimed to develop production technology of guava jam with
addition of concentrated grape juice, prioritizing the antioxidants profile and rheological
characterization of this new product.
MATERIALS AND METHODS. The following elements were used in the jams
processing: pink guava fruits, Paluma cultivar; commercial sucrose; mineral water; high
methoxyl pectin; citric acid and potassium sorbate. The concentrated grape juice was
obtained by reverse osmosis process from the natural juice of Isabel cultivar grapes.
One standard formulation (GP) and one enriched formulation (GS), in which
concentrated grape juice was added in the proportion of 29.70%, were elaborated.
Guava jams were therefore prepared using different concentrations of sugar (39.52 %
and 19.80%) and pectin (0.69 %, and 0.99 %). For the physicochemical characterization
of the jams, the following analyses were performed: total soluble solids (°Brix), acidity
(% citric acid), moisture and total sugar. In order to investigate the antioxidant potential
of the guava jams, fresh samples were subjected to sequential extractions with methanol
and acetone, and in the end of the process the two extracts were combined. The amount
of phenolic compounds in the extracts was determined by the Folin-Ciocalteu
colorimetric method and gallic acid were used as standard. The results were expressed
as gallic acid equivalents (GAE). Extracts of the guava jams and the concentrated grape
juice used as a enriching ingredient were analysed by High-performance liquid
chromatography (HPLC) to quantify different phenolic compounds. Standards of gallic
acid, catechin, caffeic acid, p-coumaric acid, ferulic acid, resveratrol, quercetin and
kaempferol were used to obtain the standard curve. Two antioxidant systems, which act
by distinct mechanisms, were used to evaluate the antioxidant activity of the guava
jams. That were the β-carotene-linoleic acid coupled oxidation system and the 1,1Diphenyl-2-picrylhydrazyl radical (DPPH•) method. The stability of the phenolic
compounds and the antioxidant activity of the jams were evaluated through 90-day
storage at room temperature (on average 25°C). The rheological behaviour of the
samples were assessed at temperatures of 25°C, 35°C, 45°C and 55°C using a
Brookfield rheometer model DVIII with a SC4-34 spindle. The data of deformation rate
and shear stress were adjusted by the Power Law model, while the effect of temperature
on apparent viscosity was described by an equation analogous to Arrhenius.
RESULTS AND DISCUSSION. The results showed all jam formulations had total
soluble solids content compatible with the requirements of the Brazilian legislation,
which establishes a minimum of 65 °Brix for total soluble solids in jam. The values
obtained for the moisture content in GP and GS, which were 36.34% and 37.16% (wet
basis), respectively, were also in accordance with the legislation. The total sugar content
found for both guava jam formulations are close to the values related in other
references. The acidity (% citric acid) found for GS formulation was higher than the
value found for GP formulation, which indicates that the addition of grape juice
promoted a increasing in the jam acidity, though GS acidity value still is in accordance
to legislation parameters. As expected, was found a greater concentration of phenolic
compounds (PC) in the GS formulation than in the GP formulation, and most important,
the enriched jam showed a PC content of more than two times the standard formulation
content. Moreover, the data obtained over the monitoring period showed a decreasing
on the PC content with the days, for both GP and GS formulations. The pair of guava
jams presented similar stability over the storage time, since the PC content of GP
formulation dropped 32.18% while the PC content of GS formulation dropped 36.21%.
The major compound identified in the samples was the flavonoid catechin, followed by
gallic acid and quercetin in very minor concentrations. The GS formulation presented
greater contents of galic acid, caffeic acid, p-coumaric acid and ferrulic acid than the GP
formulation, and even presented superior contents of these compounds than the
concentrated grape juice that was added to its formulation. In this last, was found an
extraordinary content of catechin in addition to less representative contents of the other
compounds, reason why the addition of concentrated grape juice in guava jam
formulation provided a significant contribution in terms of phenolic compounds,
especially in terms of catechin. Among the phenolic compounds quantified in the guava
jams, catechin represented 99.93% and 52.58%, respectively, of the total value of
compounds found for GS and GP. In the guava jams extracts were also found low
contents of quercetin and kaempferol. The GS formulation showed a content of
quercetin 2-fold higher than the GP formulation, while both formulations showed
equivalent contents of kaempferol. At the 45th day of storage, the results obtained for the
measure of antioxidant activity of the jams by the β-carotene-linoleic acid system were:
among the positive controls used in this test, Trolox showed the highest value of
antioxidant activity , which were 58.28 ± 2.78% at 100 ppm; GS presented an
antioxidant activity of 53.862 ± 0.388%, that were 18.5% higher than the value found
for GP; and the antioxidant activity of the positive controls BHT, Trolox and Propyl
gallate were not significantly different (p < 0.05).The data of the antioxidant activity
monitoring of the guava jams based on the β-carotene method, during 90-day storage,
surprisingly revealed a increasing in antioxidant activity with time, for both jams and
for the positive controls. So the antioxidant activity of GP at the end of the 90-day
storage was 1.7-fold higher than the value found for the 1st day, and GS showed a
corresponding increase of 1.5-fold the original value. This results could be explained by
a possible transformation in the phenolic compounds with time, where the originated
polyphenols presented lower antioxidant activity in the hydrophilic DPPH• system and
greater activity in the lipophilic β-carotene system. On the results of the DPPH• assay at
the 45th day of storage, the antioxidant activity ranged from 95.86 ± 0.15 % (Propyl
gallate) to 63.94 ± 1.03 % (GP). GS extract showed better antioxidant efficiency value
than GP extract, with an antioxidant capacity of 67.93 ± 0.81 %. The EC50 values,
inversely proportional to the antioxidant activity values, were of 25.45 ± 1.03 µg/mL for
GP and 20.40 ± 0.22 µg/mL for GS, which indicates that the enriched jam provided
higher protection against oxidation than the standard guava jam. In the rheological
behaviour study of both guava jams, the values of consistency coefficient, K, and the
flow behaviour index, n, were obtained by curve fitting using least square method. The
satisfactory regression coefficients, R2, all superior to 0.984, showed the effectiveness
in fitting. The n values, found for the pair of samples, showed that GP and GS exhibited
exhibited a non-Newtonian shear-thinning behaviour (n < 1) at all evaluated
temperatures. The increasing of temperature showed no significant influence on the
pseudoplasticity of both guava jams. Also the phenomena of decreasing on consistence
coefficient, K, with temperature, was observed. There were a decreasing in the GP and
GS values of apparent viscosity with increasing shear rate and temperature. A close
observation on the apparent viscosity results showed that the GS formulation suffered
higher drop in its viscosity than the GP formulation, with the temperature increasing.
GP and GS values of apparent viscosity dropped 26.78% and 34.67%, respectively,
when the temperature increased from 25°C to 55°C. The GS formulation presented
higher apparent viscosity values than GP formulation, for all evaluated temperatures.
The values of activation energy found for GP and GS were of 8.16 kJ.mol-1 and 12.47
kJ.mol-1, respectively, which indicate that the GP was more sensitive to temperature
changes than GS, thus, the enriched formulation presented higher stability than the
standard formulation when exposed to temperature variation.
CONCLUSIONS. The incorporation of concentrated grape juice in the jam formulation
promoted an increase of more than 2-fold in its phenolic compounds content, with
catechin representing 99.93% of the total value of compounds found for GS,
furthermore, provided an increase in the antioxidant activity of the product in almost
20%. This way, the consumption of the enriched guava jam could potentially deliver
health benefits by the supply of natural antioxidants, especially the flavonoid catechin.
The enriched guava jam exhibited a non-Newtonian behaviour and behaved as a shear
thinning fluid for all evaluated temperatures. The Power Law model described
appropriately the rheological behaviour of the elaborated jam. This study revealed that
the guava jam enriched through the addition of concentrated grape juice constitute a
new product with a notable antioxidant potential, even greater than the potential
presented by the standard guava jam, worldwide appreciated delicacy.
RESUMO GERAL
INTRODUÇÃO. O estresse oxidativo originado por espécies reativas de oxigênio
(ROS) é fundamentalmente ligado à manifestação de inúmeras doenças crônicas e
degenerativas. Felizmente, estudos têm demonstrado que uma dieta rica em
antioxidantes pode proteger dos danos à saúde causados pelo processo oxidativo. A
goiaba (Psidium guajava L.) é uma fruta tropical popular caracterizada por excelentes
propriedades nutricionais e sensoriais, além de um conteúdo extraordinário de
carotenóides, especialmente licopeno. Devido ao fato das frutas constituírem a principal
fonte dietética de compostos fenólicos, têm-se sugerido que os sucos de frutas
apresentam potencial para serem utilizados como ingredientes funcionais na indústria de
alimentos. Como uvas são ricas fontes de potentes antioxidantes com comprovadas
propriedades cardioprotetoras, o suco de uva concentrado pode ser aplicado como um
potencial ingrediente funcional em formulações de alimentos. Neste contexto, goiaba e
suco de uva concentrado poderiam figurar como ótimas matérias-primas na formulação
de geleias, originando assim produtos com potencial funcionalidade e grande apelo
sensorial.
OBJETIVOS. O presente estudo teve como objetivo desenvolver tecnologia de
produção de geleia de goiaba com adição de suco de uva concentrado, priorizando o
perfil de antioxidantes e caracterização reológica deste novo produto.
MATERIAL E MÉTODOS. Os seguintes elementos foram utilizados no
processamento das geleias: goiabas vermelhas do cultivar Paluma; sacarose comercial;
água mineral; pectina de alto grau de metoxilação; ácido cítrico e sorbato de potássio. O
suco de uva concentrado foi obtido por processo de osmose inversa a partir do suco
natural de uvas do cultivar Isabel. Uma formulação padrão (GP) e uma formulação
enriquecida (GS), na qual o suco de uva concentrado foi adicionado na proporção de
29,70%, foram elaboradas. As geleias de goiaba foram, portanto, preparadas com
diferentes concentrações de açúcar (39,52% e 19,80%) e pectina (0,69% e 0,99%). Para
a caracterização físico-química das geleias, as seguintes análises foram realizadas:
determinação de sólidos solúveis totais (°Brix), acidez (ácido cítrico %), umidade e
açúcares totais. A fim de investigar o potencial antioxidante das geleias de goiaba, as
amostras frescas foram submetidas a extrações sequenciais com metanol e acetona, e ao
final do processo os dois extratos foram combinados. A determinação de compostos
fenólicos nos extratos foi feita pelo método colorimétrico de Folin-Ciocalteau e ácido
gálico foi utilizado como padrão. Os resultados foram expressos como equivalentes de
ácido gálico (GAE). Extratos das geleias de goiaba e do suco de uva concentrado
utilizado como ingrediente enriquecedor foram analisados por Cromatografia Líquida
de Alta Eficiência (CLAE), para a quantificação de diferentes compostos fenólicos.
Padrões de ácido gálico, catequina, ácido caféico, ácido p-cumárico, ácido ferúlico,
resveratrol, quercetina e kaempferol foram usados para obter a curva padrão. Dois
sistemas antioxidantes, que agem por mecanismos distintos, foram utilizados para
avaliar a atividade antioxidante das geleias de goiaba. Estes foram o sistema de cooxidação do β-caroteno/ácido linoléico e o método de sequestro do radical livre 1,1difenil-2-picrilhidrazil radical (DPPH •). A estabilidade dos compostos fenólicos e da
atividade antioxidante nas geleias foi avaliada durante 90 dias de estocagem à
temperatura ambiente (média de 25°C). O comportamento reológico das amostras foi
avaliado em temperaturas de 25°C, 35°C, 45°C e 55°C utilizando um reômetro
Brookfield modelo DVIII com spindle SC4-34. Os dados de taxa de deformação e
tensão de cisalhamento foram ajustados pelo modelo de Lei da Potência, enquanto que o
efeito da temperatura sobre a viscosidade aparente foi descrito por uma equação análoga
à de Arrhenius.
RESULTADOS E DISCUSSÃO. Os resultados mostraram que todas as formulações
de geleia atingiram o teor de sólidos solúveis compatíveis com as exigências da
Legislação Brasileira, que estabelece um mínimo de sólidos solúveis totais de 65 °Brix
para geleias. Os valores obtidos para o teor de umidade em GP e GS, que foram 36,34%
e 37,16% (base úmida), respectivamente, também encontravam-se de acordo com a
legislação. O teor de açúcar total encontrado para ambas as formulações de geleia de
goiaba estão próximos aos valores relatados em outras referências. A acidez (% de ácido
cítrico) encontrada para a formulação GS foi maior do que a acidez encontrada para a
formulação GP, o que indica que a adição de suco de uva promoveu um aumento na
acidez da geleia, embora o valor de acidez de GS ainda se encontrasse em conformidade
com os parâmetros da legislação. Como esperado, foi descoberto uma maior
concentração de compostos fenólicos (CF) na formulação GS do que na formulação GP,
e mais importante, a geleia enriquecida apresentou um conteúdo de CF equivalente a
mais de duas vezes o conteúdo da formulação padrão. Além disso, os dados obtidos ao
longo do período de monitoramento mostraram um decréscimo sobre o teor de CF com
os dias, tanto para a formulação GP quanto para a formulação GS. Ambas as geleias de
goiaba apresentaram estabilidade semelhante ao longo do tempo de armazenamento,
uma vez que o conteúdo de CF da formulação GP caiu 32,18%, enquanto que o
conteúdo de CF da formulação GS caiu 36,21%. O principal composto identificado nas
amostras analisadas foi o flavonoide catequina, seguido pelo ácido gálico e quercetina
em concentrações muito menores. A formulação GS apresentou teores maiores de ácido
gálico, ácido caféico, ácido p-cumárico e ácido ferrúlico do que a formulação GP, e até
mesmo apresentou teores superiores destes compostos quando comparada ao suco de
uva concentrado que foi adicionado à sua formulação. Neste último, foi encontrado um
conteúdo extraordinário de catequina, além de conteúdos menos representativos dos
outros compostos, razão pela qual a adição de suco de uva concentrado na formulação
da geleia de goiaba proporcionou uma significativa contribuição em termos de
compostos fenólicos, especialmente em relação à catequina. Entre os compostos
fenólicos quantificados nas geleias de goiaba, a catequina representou 99,93% e
52,58%, respectivamente, do valor total de compostos encontrados para GS e GP. Nos
extratos de geleia de goiaba também foram encontrados baixos teores de quercetina e
kaempferol. A formulação GS apresentou um conteúdo de quercetina duas vezes maior
do que a formulação GP, enquanto ambas as formulações apresentaram teores
equivalentes de kaempferol. No 45o dia de armazenamento, os resultados obtidos para a
medida da atividade antioxidante das geleias de goiaba pelo sistema β-caroteno-ácido
linoléico foram: entre os controles positivos utilizados no ensaio, Trolox apresentou o
valor mais elevado de atividade antioxidante, que foi de 58,28 ± 2,78%, a 100 ppm; GS
apresentou uma atividade antioxidante de 53,862 ± 0,388%, a qual foi 18,5% maior do
que o valor encontrado para GP; e as atividades antioxidantes dos controles positivos
BHT, Trolox e Galato de propila não foram significativamente diferentes (p < 0,05). Os
dados de monitoramento da atividade antioxidante das geleias de goiaba baseado no
método do β-caroteno, durante 90 dias de armazenamento, surpreendentemente
revelaram um crescimento da atividade antioxidante com o tempo, para ambas as
geleias e os controles positivos. Assim, a atividade antioxidante de GP ao final do
armazenamento de 90 dias foi 1,7 vezes mais elevada do que o valor encontrado para o
1o dia de armazenamento, e GS mostrou um aumento correspondente de 1,5 vezes o
valor original de atividade antioxidante. Este resultado pode ser explicado por uma
possível transformação nos compostos fenólicos com o tempo, em que os polifenóis
originados apresentaram menor atividade antioxidante no sistema hidrofílico do método
DPPH• e maior atividade antioxidante no sistema lipofílico do método do β-caroteno.
Em relação aos resultados do ensaio com o método DPPH • realizados ao 45o de
armazenamento, os valores encontrados para a atividade variaram entre 95,86 ± 0,15%
(Galato de propila) e 63,94 ± 1,03% (GP). O extrato de GS apresentou um melhor valor
de eficiência antioxidante do que o extrato de GP, com uma capacidade antioxidante de
67,93 ± 0,81%. Os valores de EC50, inversamente proporcionais aos valores de atividade
antioxidante, foram de 25,45 ± 1,03 mg / mL para GP e 20,40 ± 0,22 mg / mL para GS,
o que indica que a geleia enriquecida proporcionou maior proteção contra a oxidação do
que a geleia padrão. No estudo do comportamento reológico de ambas as geleias de
goiaba, os valores do coeficiente de consistência, K, e do índice de comportamento de
fluxo, n, foram obtidos por ajuste de curva, usando para isto o método dos mínimos
quadrados. Os satisfatórios coeficientes de regressão, todos superiores a 0,984,
mostraram a eficiência do ajuste dos dados. Os valores de n, encontrados para as duas
amostras, indicam que GP e GS exibiram um comportamento não-Newtoniano e se
comportaram como fluidos pseudoplásticos (n <1) em todas as temperaturas avaliadas.
O aumento da temperatura não apresentou influência significativa sobre a
pseudoplasticidade de ambas as geleias de goiaba. Também o fenômeno do decréscimo
do coeficiente de consistência, K, com a temperatura, foi observado. Houve uma
diminuição nos valores de viscosidade aparente de GP e GS com o aumento da taxa de
cisalhamento e da temperatura. Uma observação mais acurada dos resultados de
viscosidade aparente mostrou que a formulação GS sofreu maior queda em sua
viscosidade do que a formulação GP, com o aumento da temperatura. Os valores de
viscosidade aparente de GP e GS caíram 26,78% e 34,67%, respectivamente, quando a
temperatura aumentou de 25°C para 55°C. A formulação GS apresentou maiores
valores de viscosidade aparente do que a formulação GP, para todas as temperaturas
avaliadas. Os valores de energia de ativação encontrados para GP e GS foram de 6,93
kJ.mol-1 e 9,02 kJ.mol-1, respectivamente, o que indica que GP foi mais sensível às
mudanças de temperatura do que a formulação GS, assim, a formulação enriquecida
apresentou maior estabilidade que a formulação padrão quando exposta à variações de
temperatura.
CONCLUSÕES. A incorporação do suco de uva concentrado na formulação da geleia
promoveu um aumento de mais de duas vezes no seu conteúdo de compostos fenólicos,
com catequina representando 99,93% do valor total de compostos encontrados em GS, e
ainda proporcionou um aumento na atividade antioxidante do produto em quase 20%.
Desta forma, o consumo da geleia enriquecida poderia oferecer benefícios à saúde,
através do fornecimento de antioxidantes naturais, especialmente a catequina. A geleia
enriquecida exibiu um comportamento não-Newtoniano e se comportou como fluido
pseudoplástico para todas as temperaturas avaliadas. O modelo Lei da Potência
descreveu adequadamente o comportamento reológico da geleia elaborada. Este estudo
revelou que a geleia enriquecida através da adição de suco de uva concentrado constitui
um novo produto, com um potencial antioxidante notável, ainda maior do que o
potencial apresentado pela geleia de goiaba padrão, iguaria apreciada em todo o mundo.
ANTIOXIDANT AND RHEOLOGICAL PROPERTIES OF GUAVA JAM WITH
ADDITION OF CONCENTRATED GRAPE JUICE
Authors: Rúbia Carvalho Gomes Corrêa1*, Gisele Teixeira de Souza Sora1, Charles Windson
Isidoro Haminiuk2, Rosangela Bergamasco3, Angélica Marquetotti Salcedo Vieira1.
Affiliations:
1
Universidade Estadual de Maringá, Programa de Pós-Graduação em Ciência de
Alimentos, Maringá, PR, Brazil.
2
Universidade Tecnológica Federal do Paraná, Programa de
Pós-Graduação em Tecnologia de Alimentos, Campus Campo Mourão, PR, Brazil.
3
Universidade Estadual de Maringá, Departamento de Engenharia Química, Maringá, PR, Brazil.
Abstract
In this research, guava jam with addition of concentrated grape juice (GS), a new product, was
studied for its antioxidant potential and rheological behaviour. Total phenolic content, 1,1diphenyl-2-picrylhydrazyl radical (DPPH•) scavenging activity and β-carotene-linoleic acid
couple oxidation assays were used to evaluate the antioxidant properties of the samples during
90-day storage. HPLC analysis was performed to quantify different phenolic compounds (PC).
The GS showed a PC content of 1109.23 ± 2.18 mg GAE/100g of jam at production, which
dropped 36.21 % through the monitoring period. The flavonoid catechin constituted the major
compound found in GS, corresponding to 99.93 % of the total value of compounds. The
antioxidant capacity measured by the antioxidant tests increased with time on the β-carotene
assay and decreased with time on the DPPH assay. The enriched guava jam exhibited a nonNewtonian shear-thinning behaviour at temperatures ranging from 25 to 55 °C. This study
revealed that the enriched jam constitutes a product with notable antioxidant potential, even
greater than the potential presented by the standard guava jam, worldwide appreciated delicacy.
Keywords: jam, guava, phenolic compounds, rheology
1. Introduction
The definition widely accepted by several organizations for “functional foods” is: “foods or
ingredients of foods that provide an additional physiological benefit beyond their basic
nutrition” (ADA, 2004; ILSI, 1999). Fruits and vegetables constitute the simplest form of this
food category, because they are originally rich in bioactive phytochemicals like polyphenols and
carotenoids. Due to the popularization of such information, a surge of research and product
development in the food industry emerged to meet demand from consumers for healthful food
(Day, Seymour, Pitts, Konczak & Lundin, 2009).
Guava (Psidium guajava L.) is a tropical fruit characterized by a low content of carbohydrates,
fats, proteins, high vitamin C and fibre levels (Gutiérrez, Mitchell & Solis, 2008), besides an
extraordinary content of carotenoids, especially lycopene (4–6 mg/100 g of edible portion)
(Wilberg & Rodriguez-Amaya, 1995). In addition to its nutritious profile, guava presents
notable sensory properties, serving as raw material in manufacturing of marmalades, jellies,
jams and juices, also due to its high perishability (Osorio, Forero & Carriazo, 2011).
Another fruit with remarkable content in antioxidants, including phenolic compounds, is the
grape. Grapes are rich sources of anthocyanins, catechins, proanthocyanidins, flavonols,
stilbenes, and other phenolics, all of them potent antioxidants that show cardio protective
properties (Zern & Fernandez, 2005), so that consumption of grape juice has been associated
with the decrease of platelet aggregation (Keevil, Osman, Reed & Folts, 2000).
Studies have strongly demonstrated that a diet rich in antioxidants can protect from health
harms caused by the oxidation process. Especially the polyphenols, which present antiinflammatory, anti-carcinogenic, anti-atherogenic and cardio protective effects, besides a
protective role towards brain degenerative processes (Brenna, Ceppi & Giovanelli, 2009). The
oxidative stress originated by reactive oxygen species (ROS) is fundamentally linked to the
manifestation of numerous chronic and degenerative diseases (Azizova, 2002), being associated
to the occurrence of atherosclerosis, cancer, diabetes mellitus, cardiovascular and
neurodegenerative diseases, besides the ageing process itself (Valko, Leibfritz, Moncol, Cronin,
Mazur & Telser, 2007)
Since fruits constitute the major dietary source of phenolic compounds, it has been suggested
that fruit juices have potential to be used as functional ingredients in food industry (Karaaslan,
Ozden, Vardin & Turkoglu, 2011). In this context, concentrated grape juice could be applied as
a potential functional ingredient in food formulations, especially jams, also because the
combination of fruits tends to add a higher nutritional value and thus add value to the new
product.
Fruit jam is the delicacy obtained by cooking fruit, sugar and water until producing a gelatinous
consistency that, when extracted from its container, is able to remain in semi-solid state. It may
undergo the addition of acidulants and pectin, if necessary, to compensate for any deficiency on
natural acidity or pectin content of the fruit (Brazil, 2007).
It is acknowledged that the quantity of added sugar, proportion and kind of gelling agent, fruit
pulp content, besides the process temperature, are factors that directly influence the rheological
properties of fruit jams (Basu & Shivhare, 2010). The development of a new product, as a jam
with addition of concentrated fruit juice, demands the determination of its rheological
parameters, once the use of pre-existing parameters in industry could easily incur process errors.
This because of the importance of rheological behaviour to the design of processes such as
pumping, stirring and transport in pipelines (Branco & Gaspareto, 2005). Not least, the study of
rheological properties works as a great tool in quality control, also permitting the correlation of
food texture with sensory attributes (Basu & Shivhare, 2010).
Therefore, the present study aimed to develop production technology of guava jam with
addition of concentrated grape juice, prioritizing the antioxidants profile and rheological
characterization of this new product.
2. Materials and methods
2.1. Materials
The following elements were used for the preparation of the guava jams: pink guava fruits
(Psidium guajava, Paluma cultivar), provided by Sitio Centenario (Mandaguaçu, PR, Brazil);
commercial sucrose; mineral water; high methoxyl pectin (CPKelco, Limeira, SP, Brazil); citric
acid and potassium sorbate (Sigma–Aldrich Co., Steinheim, Germany). The concentrated grape
juice (Vitis labrusca) was obtained from the natural juice of Isabel cultivar grapes.
2.2. Jams Processing
One standard formulation (GP) and one enriched formulation (GS), in which concentrated grape
juice was added in the proportion of 29.70 %, were elaborated. Guava jams were therefore
prepared using different concentrations of sugar (39.52 % and 19.80 %), pectin (0.69 %, and
0.99 %).
The guava fruits were cleaned with a sodium hypochlorite solution, peeled and then its cores
(central part which contains all the seeds) were took out and discarded. The guava pulp was
processed in blender with enough mineral water to form paste, which was transferred to a
cooking pot with controlled heating, being constantly homogenized. After 15 minutes of
cooking process, the pectin and sucrose were added to the paste. Exclusively for GS
formulation, the addition of concentrated grape juice was made in the final stage of cooking, in
order to avoid and minimize the degradation of antioxidants by the heat. Next, the additives
were incorporated and the heating proceeded until the ending cooking point at 65°Brix. The
guava jams were bottled in sterilized jars.
2.3. Physicochemical characterization
All the physical-chemical analysis was performed in triplicate, with results expressed as mean ±
standard deviation (SD). The following analysis were performed according to regulations of the
(AOAC, 2005): total soluble solids (°Brix), acidity (% citric acid), moisture and total sugar.
2.4. Phenolic compounds extraction
Jam samples were weighed (g) in centrifuge tubes and extracted sequentially with 40 ml of
methanol/water (50:50, v/v) by agitation in a test tube rotary mixer at room temperature for 1 h.
The tubes were centrifuged at 6.000 rpm for 15 min and the supernatant was recovered. Then 40
ml of acetone/water (70:30, v/v) was added to the residue at room temperature, extracted for 60
min and centrifuged. Finally, methanol and acetone extracts were combined, made up to 100 ml
with distilled water and used to determine total phenolic compounds and antioxidant capacity
(Rufino, Alves, de Brito, Pérez-Jiménez, Saura-Calixto & Mancini-Filho, 2010).
Aliquots analyzed by HPLC suffered only methalonic extraction, as described above. The
supernatant was filtered in 0.25 µm of Millipore membrane (Millipore, Bedford, MA).
2.5. Phenolic compounds analysis
The amount of phenolic compounds in the guava jam extracts was determined by the FolinCiocalteau colorimetric method (Singleton & Rossi, 1965), using gallic acid as a standard.
Diluted samples or blanks (100 µL) were mixed with 5 mL of distilled water, Folin–Ciocalteau
reagent (500 µL), 1.5 mL of 15 % sodium carbonate (after 3 minutes) and finally, distilled water
enough to complete each 10 mL volumetric baloon. The mixture was incubated in the dark at
room temperature for 2 h. The absorbance was then measured at 765 nm using an UV⁄ Vis
double beam spectrophotometer T-80 (PG Instruments Limited, Beijing, China). The results
were expressed as gallic acid equivalents (GAE) using a calibration curve over the range of 5–
250 ppm (Vasco, Ruales & Kamal-Eldin, 2008).
High-performance liquid chromatography analysis was used to quantify the presence of
individual phenolic compounds. The Dionex Ultimate 3000 HPLC (Dionex, Idstein, Germany)
system was used, equipped with an Ultimate 3000 pump, Ultimate 3000 sampler column
compartment, Ultimate 3000 photodiode array detector, and Chromeleon software to qualify
and quantify the phenolic compounds. The Acclaim ® 120, C18 5 µm 120 A (4.6 mm x 250
mm) reversed-phase column was used to separate the phenolic compounds. The column was
kept at 40 °C throughout the analysis, and detection was performed at three wavelengths (280,
306, and 370 nm). The sample injection volume was 10 µL. The mobile phase (A) comprised
water acidified with 1% phosphoric acid and phase (B) with methanol. The elution of phenolic
compounds was performed by means of a gradient between both mobile phases. After 45
minutes, the column was held at 100% mobile phase B for 5 minutes. Phase (B) was then
gradually reduced until it reached the initial injection condition for column conditioning
purposes (95% A and 5% B). A flow of 1.0 mL/min was used. Standards of gallic acid,
catechin, caffeic acid, p-coumaric acid, ferulic acid, resveratrol, quercetin, kaempferol were
used to obtain the standard curve of the phenolic compounds. The tests were replicated twice.
2.6. 1,1-Diphenyl-2-picrylhydrazyl radical (DPPH•) assay
The free radical scavenging activity was assessed with the DPPH• method as previously
described by (Mensor, Menezes, Leitão, Reis, Santos, Coube et al., 2001). Based on the total
phenolic compound values, six different concentrations of the jam extract were used to perform
the DPPH• assay. The 0.3 mmol L-1 DPPH• ethanol solution (1 mL) was added to 2.5 mL of
sample solutions of different concentrations, and the mixtures were allowed to react at room
temperature. After 30 min, the absorbance values were measured at 518 nm, and they were
converted into the antioxidant activity percentage (AA%) using the following equation:
⎡ (Abssample − Absblank )
⎤
AA% = 100 − ⎢
x100⎥
Abscontrol
⎣
⎦
(1)
Where
Abssample = sample absorbance
The antioxidant capacity was expressed as the concentration of antioxidant required to reduce
the original amount of free radicals by 50% (EC50) and values expressed as µg/mL.
2.7. β-Carotene bleaching method
The antioxidant capacity of each sample was estimated by the β-carotene bleaching method,
following the procedure described by (Emmons, Peterson & Paul, 1999) with modifications
proposed by (Prado, 2009). Aliquots of the β-carotene-linoleic acid emulsion (3 mL) were
mixed with 50 µL of the jam extract (100 ppm) (Haminiuk, Plata-Oviedo, Guedes, Stafussa,
Bona & Carpes, 2011), the mixtures were kept in a water bath at 50 °C. Spectrophotometric
readings were made at 470 nm 3 minutes after the mixing and then at 30–120 min intervals. The
antioxidant activity was expressed as percent inhibition relative to the control after incubation
for 120 min using the following equation:
⎛ DR − DRS
AOA = 100x⎜⎜ C
DRC
⎝
⎞
⎟⎟
⎠
(2)
where AOA is the antioxidant activity, DRC is the degradation rate of the control (ln(a ⁄ b) ⁄
120), DRS is the degradation rate of the sample (ln(a ⁄ b) ⁄ 120), a is the initial absorbance at
time zero, and b is the absorbance at 120 min. Trolox [(±)-6-hydroxyl-2,5,7,8tetramethlychromane-2-carboxylic acid], BHT (buthylated hydroxytoluene) and Propyl gallate
were used as standards with a concentration of 100 ppm.
The total phenolic content and the antioxidant activity of the guava jams, based on the both
DPPH• method and coupled oxidation of β-carotene-linoleic acid system, were evaluated during
90-day storage at room temperature (on average 25 °C).
2.8. Rheological behaviour study
This study assessed the rheological behaviour of guava jams at temperatures of 25 °C, 35 °C, 45
°C and 55 °C. Rheological measurements were performed using a Brookfield rheometer model
DVIII with a SC4-34 spindle endowed with a small sample amount adapter (Brookfield
Engineering Laboratories, Massachusetts, USA). A Tecnal Thermostatised T-184 thermostatic
bath (Tecnal, Piracicaba, São Paulo, Brazil) was used to adjust the temperature of jam samples
to a temperature range between 25 and 55 °C. The data on apparent viscosity (ηap), shear stress
(τ), and shear rate ( γ ) were collected by means of Rheocalc software (version V3.1-1,
Brookfield Engineering Laboratories, USA).
To perform the rheological analysis, 10 mL samples were used for each measurement (as
recommended by the manufacturer), which were kept for 15 minutes before testing for
temperature stabilization. In each experimental run, the ascending curve lasted for 2 minutes
with shear rates varying between 0,1 and 10 s-1. Two experimental runs were performed on each
sample; the resulting shear stress was the average of the two experimental values. The
experimental values of shear stress and shear rate were fitted to the rheological models of
Ostwald-de-Waele (Power Law).
τ = κγ n
where
τ = shear stress (Pa)
K = consistence index (Pa.sn)
n = fluid behaviour index (dimensionless)
γ = shear rate (s-1)
(3)
To non-Newtonian fluids, define the term apparent viscosity (ηap) is fundamental, since the
ratio between the shear stress (τ) and the rate of deformation (γ) is not a constant, being that for
the Power Law model, the apparent viscosity can be defined as (Guedes, Ramos & Diniz,
2010):
ηap = Kγ n−1
(4)
The apparent viscosity was calculated using the equation 4 and based on a deformation rate of
10 s-1. The effect of temperature on apparent viscosity is described by an equation analogous to
Arrhenius (Guedes, Ramos & Diniz, 2010):
⎛ Ea ⎞
⎟
⎝ RT ⎠
η ap = η 0 exp⎜
(5)
where
η ap = apparent viscosity (Pa.s)
η 0 = constant (Pa.s)
Ea = activation energy for viscous flow (kJ.g.mol-1)
R = gas constant (8,314J.g.mol-1.K-1)
T = absolute temperature (K)
2.8. Statistical analysis
Assays were performed in triplicate for each sample. The results were expressed as the mean
values ± SD. Data were evaluated by variance analysis (ANOVA) and the values that showed
significant mean difference were then treated by the post-hoc Tukey’s test, at probability (p ≤
0.05) level of 5%, using Statistica 7.1 software (StatSoft, Tulsa, OK, USA). The data of flow
curves for the two guava jam formulations were adjusted by the Power Law model (OstwaldDe-Walle) using the software Origin 7.1 (OriginLab Corporation, MA, USA) in order to obtain
the rheological and statistical parameters (n, K and R2).
3. Results and Discussion
3.1. Physicochemical characterization
The proximate composition of the principal raw material and formulated guava jams is
presented in Table 1. The results showed the pair of jams formulations had total soluble solids
content compatible with the requirements of the Brazilian legislation, which establishes a
minimum of 65 °Brix for total soluble solids in jam (Brazil, 2007), with no significant
difference between the values. The values obtained for the moisture content in GP and GS,
which were 36.34 % and 37.16 % (wet basis), respectively, were also in accordance with the
legislation. The total sugar content found for both guava jam formulations are close to the
values related by (Besbes, Drira, Blecker, Deroanne & Attia, 2009) for date jams. Statistically
significant differences were found between the GS and GP values of acidity (% citric acid). The
acidity value found for GS was more than 1.4-fold the value found for GP, which indicates that
the addition of grape juice promoted a increasing in the jam acidity, though GS acidity value
still is in accordance to legislation parameters.
Table 1
Composition of the concentrated grape juice, guava (Psidium guajava, var. Paluma) and guava
jams (GP and GS)
Property
Concentrated
Guava
GP
GS
grape juice
Moisture (%)
nd
84.96 ± 0.07a
36.34 ± 0,07 c
37.16 ± 0.09b
° Brix
18.40 ± 0.05b
7.40 ± 0.02c
65.04 ± 0.01a
65.08 ± 0.00a
Acidity (% acid citric)
1.20 ± 0.01a
0.63 ± 0.06c
0.87 ± 0.02b
1.24 ± 0.02a
Total Sugar A
nd
87.14 ± 0.51c
92.90 ± 0.13a
91.73 ± 0.13b
GP: standard formulation; GS: enriched formulation.
Means in line with different letters are significantly different (p < 0.05).
A
g /100 g dry matter.
nd = not determined
3.1. Phenolic compound content
Nowadays, is notable the increasing interest in the possible health-promoting effects of phenolic
compounds. In this sense, the characterisation, quantification and identification of these
compounds are fundamental to authenticate their potential health benefits in human nutrition
(Fischer, Carle & Kammerer, 2011). To that end, the stability of the phenolic compounds and
the antioxidant activity of the jam were evaluated through 90-day storage at room temperature
(on average 25 °C).
Table 2 shows the monitoring of the phenolic compounds (PC) content of the both guava jam
formulations during 90-day storage. As expected, it was found a greater concentration of
phenolic compounds in the GS formulation than in the GP formulation, and most important, the
enriched jam showed a PC content of more than 2-fold the standard formulation content.
Moreover, the data obtained over the monitoring period showed a decreasing on the PC content
with the days, with significant differences between the values found at the 1st, 45th and 90th day
of storage, for both GP and GS formulations. The pair of guava jams presented similar stability
over the storage time, since the PC content of GP formulation dropped 32.18 % while the PC
content of GS formulation dropped 36.21 %.
Table 2
Phenolic compound content of the guava jam formulations in mg GAE/100g during 90-day
storage.
Jam samples
Storage time (days)
1st
45th
90th
GP
490.00 ± 0.54a
397.692 ± 1.63b
332. 308 ± 1.09c
GS
1109.23 ± 2.18a
870.769 ± 1.09b
759. 231 ± 1.63c
GP: standard formulation; GS: enriched formulation.
Means in line with different letters are significantly different (p < 0.05).
*
GAE: galic acid equivalents
Extracts of the guava jams and the concentrated grape juice used as an enriching ingredient
were analysed by HPLC to quantify different phenolic compounds. Figure 1 shows the
chromatograms corresponding to the samples, which were standard formulation (GP), enriched
formulation (GS) and concentrated grape juice. The major compound identified in the samples
was the flavonoid catechin, followed by gallic acid and quercetin in very minor concentrations.
Flavonoids have been reported to exhibit potent antioxidative and free radical scavenging
activities, and catechin is one of the most representative flavonoids in the human diet,
demonstrating, as other flavonoids, excellent antioxidant potential (Uzun, Demir, Kalender, Bas
& Kalender, 2010). Catechin is the basic monomeric unit of grape and wine proanthocyanidins
(Riberau-Gayon, Glories, Maujean & Dubourdieu, 2006), that present diverse pharmacological
effects, like cardioprotection and diuretic and hypotensive actions, being the main polyphenolic
component in tea and fruit (Uzun, Demir, Kalender, Bas & Kalender, 2010).
Figure 1
HPLC chromatograms of the standard formulation (GP), enriched formulation (GS) and
concentrated grape juice extracts.
How can be observed in Figure 1, the GS formulation presented greater contents of galic acid,
caffeic acid, p-coumaric acid and ferrulic acid than the GP formulation, and even presented
superior contents of these compounds than the concentrated grape juice that was added to its
formulation. In this last, was found an extraordinary content of catechin in addition to less
representative contents of the other compounds, reason why the addition of concentrated grape
juice in guava jam formulation provided a significant contribution in terms of phenolic
compounds, especially in terms of catechin. Among the phenolic compounds quantified in the
guava jams, catechin represented 99.93 % and 52.58 %, respectively, of the total value of
compounds found for GS and GP. In the guava jam extracts were also found low contents of
quercetin and kaempferol. The GS formulation showed a content of quercetin 2-fold higher than
the GP formulation, while both formulations showed equivalent contents of kaempferol.
3.2. Antioxidant activity assays
Considering that the antioxidant capacity of food is defined by a mixture of different
antioxidants, with diverse action mechanisms including synergistic interactions, it is
fundamental to associate more than one method to properly evaluate the antioxidant capacity of
foodstuff (Almeida, de Sousa, Arriaga, do Prado, Magalhães, Maia et al., 2011). For this reason,
two antioxidant systems, which act by distinct mechanisms, were used to evaluate the
antioxidant activity of the guava jams. That were the β-carotene-linoleic acid coupled oxidation
system and the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH•) methods. While the first method
determines the activity of a sample or composed to protect a lipid substrate from oxidation, the
method of inhibition of DPPH • radical is based on the transfer of electrons from an antioxidant
compound to an oxidant (Duarte-Almeida, Santos, Genovese & Latojo, 2006).
On the coupled oxidation of β-carotene and linoleic acid system, antioxidant capacity is defined
by the capacity of extracts to inhibit β-carotene bleaching promoted by free radicals generated
during linoleic acid peroxidation. Figure 2 (a) presents the antioxidant activity of the guava jam
extracts at the 45th day of storage, as measured by the bleaching of the β-carotene-linoleic acid
system. Among the positive controls used in this test, Trolox showed the highest value of
antioxidant activity (inhibition of the free radical peroxidation of lipids): 58.28 ± 2.78 % at 100
ppm, although antioxidant activity values found for Trolox, BHT and Propyl gallate were not
significantly different (p ≤ 0.05). The GS extract presented antioxidant activity only 7.6 %
lower than the Trolox, and still 18.5 % higher than the value found for GP formulation. This
result indicates the positive effect of the addition of concentrated grape juice in GS formulation,
improving its inhibition of lipid peroxidation.
Figure 2.
(A) Antioxidant activity of the guava jams by coupled oxidation of β-carotene and linoleic acid
at the 45th day of storage. (B) Antioxidant activity and EC50 values of guava jams on the DPPH•
assay at the 45th day of storage. ND = not determined. Bars with different letters are
significantly different (p < 0.05).
In the DPPH • method, the reduction of DPPH • radical by radical scavengers is evaluated
spectrophotometrically by monitoring the decrease in absorbance, as the DPPH radical is
decolorized from deep violet to pale yellow (Al-Dabbas, Al-Ismail, Kitahara, Chishaki,
Hashinaga, Suganuma et al., 2007). Namely, the DPPH• radical scavenging capacity assay
monitors the percentage of the DPPH• remaining after a given time (Brand-Williams, Cuvelier
& Berset, 1995). Antioxidant activity and EC50 values of guava jam extracts on the DPPH•
assay at the 45th day of storage are presented in Figure 2 (b). It can be seen that antioxidant
activity ranged from 95.86 ± 0.15 % (Propyl gallate) to 63.94 ± 1.03 % (GP). GS extract
showed better antioxidant efficiency value than GP extract, with an antioxidant capacity of
67.93 ± 0.81 %. The EC50 values, inversely proportional to the antioxidant activity values, were
of 25.45 ± 1.03 µg/mL for GP and 20.40 ± 0.22 µg/mL for GS, which indicates that the
enriched jam provided higher protection against oxidation than the standard guava jam.
The results of the antioxidant activity monitoring of the guava jams based on the coupled
oxidation of β-carotene and linoleic acid system during 90-day storage are presented in Table 3.
The data revealed an increasing in antioxidant activity with time, for both jams and for the
positive controls. The antioxidant activity of GP at the end of the 90-day storage was 1.7-fold
higher than the value found for the 1st day, and GS showed a corresponding increase of 1.5-fold
the original value.
Table 3
Antioxidant activity (%) of the guava jams based on the coupled oxidation of β-carotene and
linoleic acid system, during 90-day storage. Trolox, BHT and propyl gallate were used as
standards with a concentration of 100 ppm.
Sample
Storage time (days)
1st
45th
90th
GP
36.664 ± 1.168c
43.904 ± 0.447b
62.181 ± 1.481a
GS
44.485 ± 1.169c
53.862 ± 0.388b
66.966 ± 0.042a
BHT
38.307 ± 0.476c
46.014 ± 0.548b
69.114 ± 2.493a
Trolox
50.130 ± 1.297b
58.283 ± 2.781b
83.985 ± 1.723a
Propyl gallate
42.463 ± 1.852b
43.904 ± 0.447b
62.181 ± 1.481a
GP: standard formulation; GS: enriched formulation.
Means in line with different letters are significantly different (p ≤ 0.05).
These results could be explained by a possible transformation in the phenolic compounds with
time, where the originated polyphenols presented lower antioxidant activity in the hydrophilic
DPPH• system and greater activity in the lipophilic β-carotene system. The phenomenon of
changing in the phenolic profile during storage was related by (Baiano, Gambacorta, Terracone,
Previtalli, Lamacchia & La Notte, 2009) in their research over changes in phenolic and
antioxidant activity of olive oils during store. Corroborating the advantage of using both
methods for assessment of the antioxidant activity, (Alén-Ruiz, García-Falcón, Pérez-Lamela,
Martínez-Carballo & Simal-Gándara, 2009) highlighted that DPPH• and linoleic acid/β-carotene
assays provide complementary information, once the assays measure hydrophilic and lipophilic
antioxidants, respectively.
The evolution of DPPH • radical scavenging antioxidant activity in the guava jams with time,
through 90-day storage, is presented in Table 4. The values of antioxidant activity observed for
both guava jam formulations were significant, and as expected, smaller than the values of
antioxidant activity found for the positive controls. Over the whole storage period GS
formulation showed greater antioxidant activity than GP formulation, so that GS had an
antioxidant activity 10 % higher than GP at the first day of storage, advantage which was also
observed in the monitoring of antioxidant activity by the bleaching of the β-carotene-linoleic
acid system. The values of antioxidant activity of the jams remained rather stable throughout
storage, since there was a decreasing of 17.67 % for GP formulation and 18.68 % for GS
formulation. (Piljac-Žegarac, Valek, Martinez & Belščak, 2009) also observed a decreasing in
antioxidant capacity of dark fruit juices in 29-day refrigerated storage.
Table 4
Antioxidant activity (%) of the guava jams based on the DPPH• assay, during 90-day storage. Trolox, BHT and propyl gallate were used as standards with a concentration of 100 ppm.
Sample
Storage time (days)
1st
45th
90th
GP
65.884 ± 0.867a
63.938 ± 1.026a
54.241 ± 0.592b
GS
71.195 ± 0.433a
67.927 ± 0.806b
57.906 ± 0.296c
BHT
96.425 ± 0.144a
95.492 ± 0.220b
95.550 ± 0.052b
Trolox
96.170 ± 0.072a
95.130 ± 0.147b
95.864 ± 0.222a
Propyl gallate
96.476 ± 0.072a
95.855 ± 0.147b
95.026 ± 0.074c
GP: standard formulation; GS: enriched formulation.
Means in line with different letters are significantly different (p ≤ 0.05).
3.4. Rheological behaviour study
The rheograms in Fig. 3 and Fig. 4 show plots of shear stress versus shear rate of GP and GS
formulations, respectively, measured in a temperature range from 25 to 55 °C. As can be
observed in both rheograms, there were a decreasing in the shear stress with the increasing of
temperature.
Figure 3
GP rheogram for temperatures ranging from 25 to 55 °C.
Figure 4
GS rheogram for temperatures ranging from 25 to 55 °C.
The values of consistency coefficient, K, and the flow behaviour index, n, for both guava jams,
were obtained fitting the experimental data into the Power Law model. The correspondent
values are presented in Table 5, showing effectiveness in fitting with satisfactory regres0sion
coefficients, R2, all superior to 0.9885.
Table 5
Parameters from power law equation fitting τ = Kγn; consistency coefficient, K, and flow
behaviour index, n and apparent viscosity, ηap calculated at 10 s-1 of guava jams and
temperatures in °C.
Sample T(°C)
Consistency
Flow behaviour
Coefficient of
Apparent
coefficient, K
index, n
determination,
viscosity, ηap
n
GP
GS
2
(Pa.s )
(dimensionless)
R
25
344.61 ± 3.25
0.3230 ± 0.0052
0.9934
15.25 ± 0.12
35
347.65 ± 3.81
0.2900 ± 0.0061
0.9885
13.24 ± 0.02
45
308.48 ± 3.34
0.3017 ± 0.0060
0.9898
12.39 ± 0.89
55
285.49 ± 1.87
0.2956 ± 0.0036
0.9960
11.17 ± 0.33
25
401.19 ± 1.79
0.3883 ± 0.0024
0.9990
23.96 ± 0.61
35
390.58 ± 3.16
0.3545 ± 0.0044
0.9961
20.05 ± 1.33
45
334.77 ± 2.82
0.3289 ± 0.0046
0.9950
16.58 ± 1.03
55
329.84 ± 2.36
0.3341 ± 0.0039
0.9964
15.40 ± 2.03
(Pa.s)
GP: standard formulation; GS: enriched formulation.
The n values obtained for both samples, showed that GP and GS exhibited a non-Newtonian
shear-thinning behaviour (n < 1) at all evaluated temperatures. The increasing of temperature
showed no significant influence on the pseudoplasticity of both guava jams. Similar results
were observed by (Chin, Chan, Yusof, Chuah & Talib, 2009) when analysing pummelo juice at
50 °Brix, fluid with a total soluble solids value close to the approximated 65 °Brix found for our
guava jam formulations. The phenomenon of decreasing on consistence coefficient, K, with
temperature, was also observed by (Vitali & Rao, 1982) in guava puree and by (Basu &
Shivhare, 2010) in mango jam.
As presented in Table 5, there were a decreasing in the GP and GS values of apparent viscosity
with increasing shear rate and temperature. A close observation on the apparent viscosity results
shows that the GS formulation suffered higher drop in its viscosity than the GP formulation,
with the temperature increasing. The GP and GS values of apparent viscosity dropped 26.78 %
and 34.67 %, respectively, when the temperature increased from 25 °C to 55 °C. It also can be
seen in Table 5 that GS formulation presented higher apparent viscosity values than GP
formulation, for all evaluated temperatures.
The linear relationship of apparent viscosity (η ap ) by temperature (1 / T), for both samples, is
presented in Figure 5. The values of activation energy found for GP and GS were of 8.16
kJ.mol-1 and 12.47 kJ.mol-1, respectively, which indicate that the GP was more sensitive to
temperature changes than GS, thus, the enriched formulation presented higher stability than the
standard formulation when exposed to temperature variation.
Figure 5
The linear relationship of apparent viscosity (ηap) by temperature (1 / T) for the both GP and GS
formulations.
4. Conclusion
The incorporation of concentrated grape juice in the jam formulation promoted an increase of
more than 2-fold in its phenolic compounds content, with catechin representing 99.93 % of the
total value of compounds found for GS, furthermore, provided an increase in the antioxidant
activity of the product in almost 20 %. This way, the consumption of the enriched guava jam
could potentially deliver health benefits by the supply of natural antioxidants, especially the
flavonoid catechin. The enriched guava jam exhibited a non-Newtonian behaviour and behaved
as a shear thinning fluid for all evaluated temperatures. The Power Law model described
appropriately the rheological behaviour of the elaborated jam. This study revealed that the
guava jam enriched through the addition of concentrated grape juice constitute a new product
with a notable antioxidant potential, even greater than the potential presented by the standard
guava jam, worldwide appreciated delicacy.
Acknowledgements
The authors would like to thank the Brazilian Coordination for the Improvement of Higher
Education Personnel (CAPES), Federal University of Technology – Paraná (Campus Campo
Mourão), National Council for Scientific and Technological Development (CNPq; Process
Number 501535/2009-8) and Araucaria Foundation for financial support. We would also like to
thank CPKelco which donated the pectin used in jams preparation.
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