A symbiotic relationship exists between ST and LB in mixed cultures (31); carbon dioxide, formate, peptides, and numerous amino acids liberated from casein are involved. Associative growth of rod and coccus results in greater acid production and flavor development than the single-culture growth (32,33). It has been established that numerous amino acids liberated from casein by proteases of LB stimulate growth of ST (34,35). In turn, ST produces CO2 and formate, which stimulates LB (35-38). During the early part of the incubation, ST grows faster and removes excess oxygen and produces the stimulants noted above. After the growth of ST has slowed because of increasing concentrations of lactic acid, the more acid tolerant LB increases in numbers (22,29,39). For a one-to-one ratio of rod and coccus, inoculum level, time, and temperature of incubation must be controlled and bulk starter should be cooled promptly.
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