Efeito da aplicação de coberturas comestíveis com reaproveitamento dos subprodutos da goiaba sobre a secagem e sobre a qualidade nutricional e sensorial de goiabas vermelhas
Carregando...
Data
2016-08-19
Autores
Todisco, Katieli Martins [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
Neste trabalho propôs-se investigar o uso de subprodutos oriundos da goiaba para o desenvolvimento de coberturas comestíveis à base de pectina a serem aplicadas sobre goiabas em pedaços, avaliando seu efeito sobre a cinética de secagem e sobre características físico-químicas, compostos bioativos, fração volátil e aceitação sensorial da fruta desidratada. Goiabas vermelhas foram selecionadas pelo teor de sólidos solúveis (10 °Brix). A polpa da goiaba foi cortada em rodelas de 2,2 cm de diâmetro enquanto as cascas e o miolo com sementes foram triturados e peneirados, formando um purê de subprodutos. Foi utilizado um delineamento fatorial completo para duas variáveis independentes, temperatura de secagem e concentração de subprodutos nas coberturas (22), com quatro pontos axiais e cinco repetições do ponto central, com o objetivo de identificar as condições ótimas para retenção dos compostos bioativos, bem como para difusão da água durante a secagem de rodelas de goiaba. Para isso, o subproduto foi incorporado a uma solução aquosa com 2% de pectina amidada de baixa metoxilação, em concentrações variando de 0 a 50% de subprodutos sobre a solução total, que foi aplicada em fatias de goiaba e gelificada por imersão em solução de lactato de cálcio, previamente à secagem com ar quente aquecido (45,9 a 74,1 ° C). Como resultado, pôde-se observar que temperaturas em torno de 60 °C e concentrações de subprodutos de até 25% proporcionaram, simultaneamente, retenções significativas de carotenoides e de compostos fenólicos totais nas goiabas desidratadas. Em relação à cinética de secagem, a difusividade foi principalmente afetada pela temperatura, sendo que a concentração exerceu influência muito pequena, quase não afetando os tempos de secagem. Após esse estudo, foi selecionada a condição de temperatura de secagem de 60 °C, e a solução composta por 25% de subprodutos, para as próximas etapas. Coberturas compostas somente por pectina e por pectina com incorporação de subprodutos, na condição previamente selecionada, também foram investigadas na forma de filmes, com o intuito de avaliar seu comportamento separadamente da fruta. Foram determinadas características estruturais e morfológicas, propriedades físicas, térmicas e de sorção dos filmes. Os filmes compostos por pectina e subprodutos não apresentaram temperaturas de transição vítrea (Tgs), somente a polpa de goiaba desidratada apresentou transição de fase em torno de 30 °C. A adição dos subprodutos proporcionou certa cristalinidade ao filme de pectina, enquanto que os açúcares elevaram ligeiramente a capacidade de retenção de água do filme. A temperatura de transição vítrea encontrada na polpa de goiaba indicou que se a fruta desidratada apresentar níveis mais elevados de umidade à temperatura ambiente, esta se encontrará em estado gomoso, o que pode trazer maciez à fruta, que é bastante granulosa, como observado através das imagens obtidas por microscopia eletrônica de varredura (MEV). Os difratogramas de raios X (DRX) dos filmes de pectina mostraram comportamento amorfo e cristalino, simultaneamente. No filme de pectina que continha subprodutos de goiaba foram encontrados valores coincidentes com picos característicos de celulose microcristalina, sugerindo que os subprodutos proporcionaram maior cristalinidade a este filme. As imagens obtidas na microscopia (MEV) exibiram boa integração das coberturas comestíveis com a superfície da fruta em pedaços, mostrando que as coberturas se aderem à fruta, não modificando sua estrutura. Por fim, amostras de goiaba desidratadas sem coberturas e com coberturas elaboradas à base de pectina e pectina com subprodutos, esta última na condição previamente selecionada, foram avaliadas quanto à sua composição volátil, conteúdo de substâncias antioxidantes e aceitação sensorial. Na análise de aceitação sensorial, não houve diferença significativa entre as goiabas desidratadas para os atributos aparência, cor e impressão global, e intenção de compra. O atributo aroma foi o melhor avaliado, sendo que a goiaba com cobertura de pectina recebeu a maior media. Em relação ao perfil volátil das amostras desidratadas, verificou-se que a secagem em si traz perdas significativas nos compostos presentes na goiaba. No entanto, os principais compostos permaneceram após a secagem, e outros, como o hexanal ou o 1-hexanol, ficaram mais evidentes nas amostras secas. Os compostos antioxidantes apresentaram maiores retenções nas amostras com coberturas compostas por pectina e subprodutos, mostrando que os subprodutos conferiram mais efetividade aos revestimentos na goiaba.
This work aimed to assess the use of guava byproducts to develop edible pectin-based coatings to be applied on pieces of guava, evaluating its effect on the drying kinetics and on physicochemical characteristics, bioactive compounds, volatile fraction and the sensory acceptance of the dehydrated fruit. Red guavas were sourced in São José do Rio Preto – São Paulo, and selected for their soluble solid content (10 ºBrix). The guava pulp was cut into slices of 2.2 cm in diameter, while the peel and the core containing seeds were triturated and sieved, resulting in a byproducts puree. A complete factorial design was used for two independent variables (temperature and concentration of byproducts in the coatings (22)) with four axial points and five repetitions from the central point, in order to identify the optimum conditions for bioactive compounds retention, as well as water diffusion during the drying process of guava slices. For this, byproducts were mixed with a low-methoxyl amidated pectin solution (2%, w/w), at concentrations ranging from 0 to 50%. The solution was applied on guava slices and immersed into a gelling solution of calcium lactate prior to hot-air drying (45.9 to 74.1 ºC). It was observed that temperatures around 60 ºC and byproducts concentrations up to 25% simultaneously provided significant retention of carotenoids and total phenolic compounds in the dehydrated guava. Regarding the drying process, diffusivity was affected mainly by the temperature while byproduct concentration had a very small influence and almost did not change the drying times. After this study, temperature of 60 °C and the pectin coating solution with 25% of byproducts was selected for the next steps. Coatings made only with pectin and with pectin and those with 25% of byproducts were also assessed as films, in order to verify its behavior separated from the fruit. The structural and morphological film characteristics, physical and thermal properties and water sorption capacity were determined. The films made with pectin or pectin and byproducts showed no glass transition temperature (Tg), where as the dehydrated guava pulp showed a Tg around 30 ºC. The byproducts incorporation provided certain crystallinity to the pectin film, while the sugars slightly increased the film ability to retain water. The temperature of glass transition found in guava pulp showed that if the dehydrated fruit had higher levels of moisture at room temperature, it would become rubbery, which may bring softness to the fruit, that is a very granular material, as observed by images obtained by the scan electronic microscopy (SEM). The X-Ray diffractogram (XRD) of pectin films showed a crystalline and amorphous behavior, simultaneously. Values similar to characteristic peaks of microcrystalline cellulose were found for the films with pectin and guava byproducts, suggesting that the byproducts provided more crystallinity to the film. The images obtained by the microscopy (SEM) showed good interaction between the edible coatings and the fruit surface, because they adhered to the fruit without changing its structure. Finally, dehydrated guavas with pectin coating, with pectin and byproducts coating and without coating were evaluated according to their volatile composition, antioxidant compound content and sensory acceptance. The sensory acceptance analysis of the dried samples did not show significant differences for appearance, color, over all acceptance and purchase intent. The higher scores were attributed to the aroma, with the higher mean given to the pectin coated samples. As for the volatile profile of the dehydrated samples, it was observed that the drying process caused significant losses of these compounds in guavas; however, the main compounds remained after the drying and others, such as hexanal or 1-hexanol, became more evident in the dried samples. The antioxidant compounds showed more retention in the samples covered with pectin and byproducts, evidencing that the coatings with byproducts were more effective.
This work aimed to assess the use of guava byproducts to develop edible pectin-based coatings to be applied on pieces of guava, evaluating its effect on the drying kinetics and on physicochemical characteristics, bioactive compounds, volatile fraction and the sensory acceptance of the dehydrated fruit. Red guavas were sourced in São José do Rio Preto – São Paulo, and selected for their soluble solid content (10 ºBrix). The guava pulp was cut into slices of 2.2 cm in diameter, while the peel and the core containing seeds were triturated and sieved, resulting in a byproducts puree. A complete factorial design was used for two independent variables (temperature and concentration of byproducts in the coatings (22)) with four axial points and five repetitions from the central point, in order to identify the optimum conditions for bioactive compounds retention, as well as water diffusion during the drying process of guava slices. For this, byproducts were mixed with a low-methoxyl amidated pectin solution (2%, w/w), at concentrations ranging from 0 to 50%. The solution was applied on guava slices and immersed into a gelling solution of calcium lactate prior to hot-air drying (45.9 to 74.1 ºC). It was observed that temperatures around 60 ºC and byproducts concentrations up to 25% simultaneously provided significant retention of carotenoids and total phenolic compounds in the dehydrated guava. Regarding the drying process, diffusivity was affected mainly by the temperature while byproduct concentration had a very small influence and almost did not change the drying times. After this study, temperature of 60 °C and the pectin coating solution with 25% of byproducts was selected for the next steps. Coatings made only with pectin and with pectin and those with 25% of byproducts were also assessed as films, in order to verify its behavior separated from the fruit. The structural and morphological film characteristics, physical and thermal properties and water sorption capacity were determined. The films made with pectin or pectin and byproducts showed no glass transition temperature (Tg), where as the dehydrated guava pulp showed a Tg around 30 ºC. The byproducts incorporation provided certain crystallinity to the pectin film, while the sugars slightly increased the film ability to retain water. The temperature of glass transition found in guava pulp showed that if the dehydrated fruit had higher levels of moisture at room temperature, it would become rubbery, which may bring softness to the fruit, that is a very granular material, as observed by images obtained by the scan electronic microscopy (SEM). The X-Ray diffractogram (XRD) of pectin films showed a crystalline and amorphous behavior, simultaneously. Values similar to characteristic peaks of microcrystalline cellulose were found for the films with pectin and guava byproducts, suggesting that the byproducts provided more crystallinity to the film. The images obtained by the microscopy (SEM) showed good interaction between the edible coatings and the fruit surface, because they adhered to the fruit without changing its structure. Finally, dehydrated guavas with pectin coating, with pectin and byproducts coating and without coating were evaluated according to their volatile composition, antioxidant compound content and sensory acceptance. The sensory acceptance analysis of the dried samples did not show significant differences for appearance, color, over all acceptance and purchase intent. The higher scores were attributed to the aroma, with the higher mean given to the pectin coated samples. As for the volatile profile of the dehydrated samples, it was observed that the drying process caused significant losses of these compounds in guavas; however, the main compounds remained after the drying and others, such as hexanal or 1-hexanol, became more evident in the dried samples. The antioxidant compounds showed more retention in the samples covered with pectin and byproducts, evidencing that the coatings with byproducts were more effective.
Descrição
Palavras-chave
Cinética de secagem, Difusão, Pectina, Propriedades térmicas, Compostos antioxidantes, Perfil volátil, Drying kinetics, Diffusion, Pectin, Thermic properties, Antioxidants compounds, Volatile profile