Abstract: In this study, soybean protein isolate (SPI) was pretreated by ultrasonic prior to alcalase hydrolysis. Single factor and orthogonal array design methods were employed to deal with the effects of length of ultrasonic treatment and some hydrolysis conditions (substrate concentration, enzyme/substrate ratio, hydrolysis temperature, initial pH and hydrolysis duration) on the degree of hydrolysis (DH) of SPI. The results showed that a maximum DH of 12.21% was obtained when 5.0% SPI was first subjected to ultrasonic pretreatment for 30 min, followed by hydrolysis at pH 8.0 and 55 ℃ for 4.0 h with alcalase added at 5.0% (on the basis of substrate amount).

Key words: soybean protein isolate (SPI), ultrasonic, alcalase, degree of hydrolysis (DH), technique conditions