Preparation of cross-linked soybean protein isolates and their rheological properties

A binary enzyme system consisting of two oxidases (horseradish peroxides and glucose oxidase) and glucose were used to cross-link soybean protein isolate (SPI) via a one-or two-step treatment. The relative dityrosine content of the modified SPIs was used as index to select suitable glucose, glucose oxidase, horseradish peroxides addition and reaction time by single factor trials for the one-step treatment, which were found to be 1.8%, 4.0U/g, 200U/g proteins and 3h, respectively. Under the appropriate reaction conditions, the modified SPIs by one-and two-step treatment had relative dityrosine content about 414 and 381, respectively. Compared to the original SPI, the aqueous dispersions of the modified SPIs exhibited higher apparent viscosity, storage and loss modulus. At the same time, one-and two-step treatment resulted in a reduced gelation time and lowered gelation temperature.