Emulsões estabilizadas por microgéis de isolado proteico de soja: reologia e produção de microcápsulas por spray drying
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Data
2018-09-03
Autores
Benetti, João Vitor Munari
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Emulsões óleo em água (O/W) são sistemas formados por dois líquidos imiscíveis, envolvendo a presença de uma fase contínua (água), uma fase dispersa (óleo), um emulsificante e energia introduzida por meio de agitação ou cavitação. A energia transmitida é capaz de aumentar a área interfacial entre as fases dispersa e contínua, enquanto o emulsificante adsorve na interface, estabilizando o sistema. A emulsificação é uma etapa anterior e fundamental à microencapsulação de compostos lipofílicos por spray drying, em que gotas de emulsão são rapidamente desidratadas em uma câmara de secagem, possibilitando a microencapsulação da fase dispersa. Neste trabalho, objetivou-se produzir emulsões O/W utilizando microgéis de isolado proteico de soja (SPI) como estabilizantes, avaliar a estabilidade e o comportamento reológico das emulsões em diferentes concentrações de cloreto de sódio (NaCl) e, posteriormente, produzir microcápsulas por spray drying, avaliando o potencial dos microgéis de SPI como material de parede. Suspensões com 10% m/m de SPI foram preparadas em água deionizada e submetidas à desnaturação por aquecimento a 80 ºC por 30 minutos, seguido de resfriamento a 4 ºC por 12 h. Após a formação do gel, as suspensões foram diluídas para 6% m/m de SPI com água ou soluções de NaCl e homogeneizadas sob alta pressão ou sonicadas para produção dos microgéis, usados para estabilizar emulsões O/W com diferentes teores de óleo produzidas por homogeneização a alta pressão ou sonicação. As emulsões sonicadas foram submetidas à secagem em spray dryer para produção de micropartículas contendo óleo encapsulado. Os microgéis de SPI foram caracterizados quanto à distribuição de tamanhos de partícula e ao potencial zeta. As emulsões O/W foram avaliadas quanto ao comportamento reológico, estabilidade e morfologia. A adição de NaCl influenciou diretamente no tamanho das partículas de SPI e em seu potencial zeta, visto que a presença do sal diminuiu a repulsão eletrostática entre os microgéis e resultou na formação de aglomerados. A reologia das emulsões foi avaliada por cisalhamento em regime permanente, observando-se o aumento do índice de consistência dos fluidos pseudoplásticos com o aumento da concentração de NaCl ou da fase dispersa (óleo) nas emulsões. Todas as emulsões se apresentaram estáveis por, pelo menos, 21 dias a temperatura de 25 ºC. O processo foi caracterizado quanto ao rendimento, e as microcápsulas de óleo foram caracterizadas quanto a retenção de óleo, umidade e morfologia. A secagem se mostrou mais eficiente para emulsões com teor de óleo mais baixo (5 a 7,5 %) e submetidas a secagem em temperaturas mais altas (160 a 170 °C). As microcápsulas apresentaram retenção de óleo acima de 80% e umidade adequada para produtos em pó (< 4%). As imagens das microcápsulas produzidas mostraram a formação de microesferas contendo óleo aprisionado na matriz proteica. Os microgéis de SPI se mostraram capazes de estabilizar emulsões com diferentes teores de óleo, além da possibilidade de serem utilizados como material de parede para microencapsular compostos lipofílicos por spray drying.
Oil-in-water (O/W) emulsions are systems formed by two immiscible liquids, involving a continuous phase (water), a dispersed phase (oil), an emulsifier and energy input by homogenization or cavitation. The transmitted energy is able to increase the interfacial area between the dispersed and continuous phases, while the emulsifier adsorbs at the interface, stabilizing the system. The emulsification is an earlier and fundamental step to microencapsulation of lipophilic compounds by spray drying, wherein emulsion droplets are rapidly dehydrated in a drying chamber, enabling the microencapsulation of the dispersed phase. The objective of this work was to produce emulsions using soybean protein isolate (SPI) microgels as O/W emulsion stabilizers, to evaluate the stability and rheological behavior of the emulsions at different concentrations of sodium chloride (NaCl), and to produce microcapsules by spray drying of the emulsions, evaluating the potential of SPI microgels as wall material. Suspensions with 10 wt% SPI were prepared in deionized water and subjected to gelation by heating at 80 °C for 30 minutes, followed by cooling at 4 °C for 12 h. After gel formation, the suspensions were diluted to 6 wt% SPI with water or NaCl solutions and homogenized under high pressure or sonication to produce the microgels, which were used to stabilize O/W emulsions with different oil contents produced by high-pressure or ultrasound homogenization. The emulsions were then submitted to drying in spray dryer for production of oil microcapsules. SPI microgels were characterized regarding their particle size distribution and zeta potential. O/W emulsions were evaluated regarding their rheological behavior, stability and morphology. The addition of NaCl directly influenced the size of the SPI particles and their zeta potential, since the presence of the salt decreased the electrostatic repulsion between the microgels and, consequently, the gel particles were approached, forming agglomerates. The rheological behavior of the emulsions was evaluated by means of steady shear tests, and an increase in the consistency index of the pseudoplastic fluids was observed with increasing NaCl or dispersed phase concentration in the emulsions. All the emulsions were stable for at least 21 days at 25 °C. The process was characterized regarding yield. and the oil microcapsules were characterized regarding oil retention, water content and morphology. The drying process showed to be more efficient to emulsions with lower oil content (5 a 7.5 wt%) and subjected to higher drying temperatures (160 a 170 °C). The microcapsules presented oil retention higher than 80% and water content suitable for powdered products (< 4%). The images of microcapsules showed the formation of microspheres containing oil droplets trapped in the protein matrix. The SPI microgels were able to stabilize emulsions with different oil contents, in addition to the possibility of being used as wall materials to microencapsulate lipophilic compounds by spray drying.
Oil-in-water (O/W) emulsions are systems formed by two immiscible liquids, involving a continuous phase (water), a dispersed phase (oil), an emulsifier and energy input by homogenization or cavitation. The transmitted energy is able to increase the interfacial area between the dispersed and continuous phases, while the emulsifier adsorbs at the interface, stabilizing the system. The emulsification is an earlier and fundamental step to microencapsulation of lipophilic compounds by spray drying, wherein emulsion droplets are rapidly dehydrated in a drying chamber, enabling the microencapsulation of the dispersed phase. The objective of this work was to produce emulsions using soybean protein isolate (SPI) microgels as O/W emulsion stabilizers, to evaluate the stability and rheological behavior of the emulsions at different concentrations of sodium chloride (NaCl), and to produce microcapsules by spray drying of the emulsions, evaluating the potential of SPI microgels as wall material. Suspensions with 10 wt% SPI were prepared in deionized water and subjected to gelation by heating at 80 °C for 30 minutes, followed by cooling at 4 °C for 12 h. After gel formation, the suspensions were diluted to 6 wt% SPI with water or NaCl solutions and homogenized under high pressure or sonication to produce the microgels, which were used to stabilize O/W emulsions with different oil contents produced by high-pressure or ultrasound homogenization. The emulsions were then submitted to drying in spray dryer for production of oil microcapsules. SPI microgels were characterized regarding their particle size distribution and zeta potential. O/W emulsions were evaluated regarding their rheological behavior, stability and morphology. The addition of NaCl directly influenced the size of the SPI particles and their zeta potential, since the presence of the salt decreased the electrostatic repulsion between the microgels and, consequently, the gel particles were approached, forming agglomerates. The rheological behavior of the emulsions was evaluated by means of steady shear tests, and an increase in the consistency index of the pseudoplastic fluids was observed with increasing NaCl or dispersed phase concentration in the emulsions. All the emulsions were stable for at least 21 days at 25 °C. The process was characterized regarding yield. and the oil microcapsules were characterized regarding oil retention, water content and morphology. The drying process showed to be more efficient to emulsions with lower oil content (5 a 7.5 wt%) and subjected to higher drying temperatures (160 a 170 °C). The microcapsules presented oil retention higher than 80% and water content suitable for powdered products (< 4%). The images of microcapsules showed the formation of microspheres containing oil droplets trapped in the protein matrix. The SPI microgels were able to stabilize emulsions with different oil contents, in addition to the possibility of being used as wall materials to microencapsulate lipophilic compounds by spray drying.
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Palavras-chave
Sistemas dispersos, Reologia, Encapsulação, Spray drying, Desnaturação, Dispersed systems, Rheology, Encapsulation, Denaturation