Effects of removal of non-network protein on the rheological properties of heat-induced soy protein gels

Effects of removal of non-network proteins by diffusion process on the storage modulus and loss modulus of soy protein isolate (SPI) gels and glycinin (11S) gels as a function of heating temperature and ionic strength were investigated. The composition of non-network proteins was determined by native-PAGE, non-reducing SDS-PAGE and reducing diagonal SDS-PAGE. Results showed that non-network proteins were composed of a majority of acid polypeptides (A), small amounts of AB subunits, soybean agglutinin, Bowman−Birk trypsin inhibitor, and lower amounts of α′, α and A3 polypeptides. The results further revealed that 11S gels had higher ratios of non-network proteins than SPI gels, due to the increased ratio of A polypeptides in 11S gel. In addition, the removal of non-network proteins from the gel was found to have no effect on the storage modulus, but on the other hand resulted in a decrease in the loss modulus, suggesting that the loss modulus of the gel network is closely related to non-network proteins. This study presents an approach to investigate the changes of storage modulus and loss modulus of globular gels in relation to the removal of non-network proteins, and provides valuable information on the composition and content of these proteins in gel network formed at various conditions.