These organisms are gram-positive, catalase negative, anaerobic/aerotolerant homofer-mentative, and produce D-(-) lactate (1.8%) and hydrogen peroxide (27). These cultures have h-galactosidase activity; only the glucose moiety of lactose is utilized and galactose is released in the medium (28). LB has high level of protease activity in milk that reaches its maximum during the log phase; ST produces highly active peptidase instead of protease (29,30). In a recent study (30), it was demonstrated that LB reached maximum protease activity between 4 and 8 hr after incubation and then declined rapidly. When grown singly in pasteurized reconstituted NFDM at 42 °C, ST and LB were less proteolytic compared to the mixed culture growth (24).
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