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Influence of heat treatment on the emulsifying properties of soy protein isolate and its enzyme hydrolysates |
C. Y. Takeiti, Departamento de Planejamento Alimentar e Nutrição- Faculdade de Engenharia de Alimentos, Universidade Estadual de Campinas- UNICAMP, CP6121, Campinas-SP, 13083-970, Brazil and F. M. NETTO, Departamento de Planejamento Alimentar e Nutrição- Faculdade de Engenharia de Alimentos, Universidade Estadual de Campinas-SP, Campinas-SP, 13083-970, Brazil. Heat treatment causes physicochemical alterations in proteins resulting in distinct functional properties. However, few studies have evaluated the influence of the structural modifications occurring during the process of obtaining the soy protein isolates (SPI) on the functional properties of their hydrolysates (HSPI). The objective of this study was to evaluate the influence of the heat treatment on the emulsifying properties of SPI and their HSPIs. Native SPI (SPIn) was obtained from defatted soy flour (Ceval-Brazil) submitted to different heat treatments (70, 80, 90°C/30') and hydrolyzed with a-chymotrypsin to 2 and 4% degrees of hydrolysis (DH) by the pH-stat method. The indexes of emulsifying activity (IEA) and of emulsifying stability (IES) were evaluated by a turbidometric technique. The molecular weight (MW) profile of the SPIs and their HSPI were determined by SDS-PAGE. The hydrolysates obtained showed distinct MW profiles, although presenting the same DH. This difference was probably due to the different degrees of denaturation of the 7S and 11S fractions, due to the heat treatments applied. The IEA decreased with the hydrolysis to 2% DH (107-186 m2/g) when compared to the SPIs (195-291 m2/g), although as the enzyme reaction progressed (4% DH), the values approached those of the intact isolates. Increases in temperature in the heat treatment of the SPIs, resulted in decreases in the IES of the HSPI with 2 and 4% of DH. The greatest IES value found was for IPSn and the smallest for the HSPI with 2% DH, obtained with IPS treated at 90°C The IES of the hydrolysates with 4% DH was slightly higher than that of the hydrolysates with 2% DH. The results showed that SPIs which suffered different pre-heat treatments, on being submitted to controlled hydrolysis, resulted in hydrolysates with differentiated profiles and functional properties.
Session 11, Food Chemistry: Proteins
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