Abstract: A new method to determinate the degree of hydrolysis(DH) of protein hydrolysate was established in this paper. Defatted soybean flour was used as substrate and fermented by a microorganism strain which could yield proteinase. The soybean protein in defatted soybean was hydrolyzed into soybean peptides under the effect of proteinase secreted from the microorganism strain. DH of soybean protein in fermented broth of different fermentation time was determined by the new method and the data was compared with what derived from routine method reported in document. Results showed that the new method established in this paper was rapid, simple, sensitive and repeatable. It could be used to measure the DH of soybean peptides hydrolyzate fermented by microorganism and also the DH of protein hydrolyzate resulted by other technology.

Key words: DH (degree of hydrolysis), protein hydrolysis, microorganism fermentation