WHITE PARTICULATE FORMATION AS A RESULT OF ENZYMATIC PROTEOLYSIS OF PROTEIN SUBSTRATES IN BRINE-FERMENTED FOODS

Rice koji and rice-soy koji (1:1, w/w) were used as enzyme sources in combination with parahydroxyl benzoate (paraben), sulfanilamide, tetra cycline, chloramphenicol or glacial acetic acid as antimicrobial agent s for sufu fermentation. After 1 year of fermentation, no formation of white particulate was observed in rice koji products and in the rice- soy koji products with 10 mL/L of glacial acetic acid in the brines. C ompositional analyses revealed that pH, tyrosine content and total ami no nitrogen content of rice koji brines were lower than those of rice- soy koji brines. In a model system, a series of test tubes containing NaCl solution (150 g/L) and autoclaved soy koji or soybean used as pro tein substrates with supplements of various enzyme sources were fermen ted for 3 months at 35 degrees C. When an indigenous strain of Zygosac charomyces rouxii isolated from a fermented sufu brine or the sufu bri ne in which white particulates were present was respectively introduce d into the systems using autoclaved soy koji as substrate, no white pa rticulate was observed. However white particulates were observed in th e systems supplemented with soy koji extract, trypsin or pancreatin. W hen autoclaved soybean was used as the protein substrate, a white part iculate was observed only in the system containing soy koji extract. A mino acid analysis of the particulates showed tyrosine to be the major component and independent of protease origin and presence of microorg anisms. (C) 1997 Academic Press Limited.