Abstract: Soy protein isolate (SPI) was modified by transgultaminase (TG) to improve its emulsifying properties so as to obtain modified SPI suitable for cold drinks and foods. Response surface design was used to explore the effects of enzyme addition amount and hydrolysis time and temperature on emulsifying activity index (EAI) and establish a mathematic model of optimal enzymatic hydrolysis conditions. Results showed that the optimal modification conditions were TG dosage of 0.93×10-4 g, hydrolysis temperature of 46 ℃and hydrolysis time of 1.2 h. Under the optimal conditions, the experimental EAI was 1.9658 m2/g, which was close to the predicted EAI of 1.9623 m2/g. Moreover, modified SPI revealed higher emulsion capacity than that of native SPI.

Key words: soy protein isolate, transglutaminase, modification, emulsion activity index