11-6 |
Loss of functional properties of soy protein isolate during storage |
V. B. Martins, Departamento de Planejamento Alimentar e Nutrição- Faculdade de Engenharia de Alimentos, Universidade Estadual de Campinas -UNICAMP, Cidade Universitária Zeferino Vaz, CP 6121, Campinas-SP, 13083-970, Brazil and F. M. NETTO, Departamento de Planejamento Alimentar e Nutrição- Faculdade de Engenharia de Alimentos, Universidade Estadual de Campinas- UNICAMP, CP6121, Campinas-SP, 13083-970, Brazil. Currently, thousands of tons of soy protein are used as a functional ingredient in the food industry. However, information about the effect of the storage conditions of the protein isolates on their functional properties is still not available. The objective of this study was to evaluate the influence of the storage conditions on the gelation properties of soy protein isolate (SPI). SPI, with an initial aw of 0.19 (SPI-0.19), was conditioned in closed systems containing saturated solutions of MgCl2 and NaCl, with relative humidity values of 33% and 74%, respectively. The isolates SPI-0.33 (aw 0.33) and SPI-0.74 (aw 0.74) reached equilibrium after 20 days at 25oC and were conditioned in sealed packages and stored at 25 and 45°C for 210 days. During storage, the SPIs were evaluated for solubility, texture profile (TPA- TA-XT2 equipment), and gel microstructure by scanning electronic microscopy (SEM). The solubility of the SPIs decreased during the storage, 20% to 25% at 25°C and 38% at 45°C. An accentuated loss of cohesiveness of the SPI-0.74 gel was observed, 36% after 60 days at 25°C and 63% after 30 days at 45°C. The SPI-0.19 and SPI-0.33 were shown to be stable during storage at 25°C, however 36% reduction in gel cohesiveness of SPI-0.33, after 30 days stored at 45°C was observed. The analysis of the gel using SEM made it possible to observe the differences in gel characteristics, especially that made of SPI-0.74, which showed a coarse structure, which could be responsible for its low cohesiveness. The storage conditions, temperature and aw of the SPIs had influence on the stability of the SPIs. The results suggested that aw was the main factor affecting the functional properties such as solubility and geleification, important in the quality and use of SPIs.
Session 11, Food Chemistry: Proteins
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