Abstract: The procedure to obtain oligopeptide with soy protein isolate by sequential treatment with proteinase I and proteinase II was described. The optimum conditions of two proteinases including pH, temperature, substrate concentration and enzyme-substrate ratio (E/S) has been defined by a lot of experiments. The experiments were designed as follows: the reaction parameters of both techniques were the same except that technique one(T1) kept optimum pH of proteinase I for 3.5 h by adding NaOH, while technique two (T2) kept optimum pH of proteinase I only at first 30 min. The results showed that protein recovery rates are 87.0%, 89.0% respectively and protein conversion rates 89.1%, 90.5% respectively and acid soluble nitrogen rates 90.1%, 90.6% respectively. The molecular weight of peptide obtained by technique one lying between 500 and 610 is 80.5% of total hydrolyzed protein. The molecular weight of peptide obtained by technique two lying between 450 and 650 is 82.0% of total hydrolyzed protein. The results showed that the hydrolysis condition of technique two is better than that of technique one.

Key words: proteinase I, proteinase II, soybean protein isolated, oligopeptide