IV. PROTEOLYTIC ACTIVITY1

Abstract

Three methods were examined for their suitability to measure proteolysis brought about by microbial activity in soymilk. The Anson (or Hull) method, a colorimetric measurement of tyrosine and tryptophan, was not able to measure changes detectable by other methods and hence did not appear applicable for this work. Determination of non-protein nitrogen (NPN) to follow proteolytic changes in soymilk was feasible but was time- and labor-consuming. Dye-binding methods were found most workable. Lactobacillus delbrueckii and Streptococcus thermophilus exhibited proteolytic activity in soymilk but Lactobacillus casei did not. Two other microorganisms, Bacillus cereus and Micrococcus conglomeratus, and rennet were comparatively more proteolytic in soymilk than the lactic cultures.