Growth of Clostridium perfringens in food proteins previously exposed to proteolytic bacilli.

Proteolytic sporeforming bacteria capable of surviving processing heat treatments in synthetic or fabricated protein foods exhibited no antagonistic effects on growth of Clostridium perfringens, but instead shortened the lag of subsequent growth of C. perfringens in sodium caseinate and isolated soy protein. Bacillus subtilis A cells were cultured in 3% sodium caseinate or isolated soy protein solutions. The subsequent effect on the lag time and growth of C. perfringens type A (strain S40) at 45 C was measured by colony count or absorbance at 650 nm, or both. B. subtilis incubation for 12 h or more in sodium caseinate reduced the C. perfringens lag by 3 h. Incubation of 8 h or more in isolated soy protein reduced the lag time by 1.5 h. Molecular sieving of the B. subtilis-treated sodium caseinate revealed that all molecular sizes yielded a similar reduced lag time. Diethylaminoethyl-Sephadex ion exchange fractionation and subsequent amino acid analysis indicated that the lag time reduction caused by B. subtilis incubation was not related to charge of the peptides nor to their amino acid composition. Apparently the shortened C. perfringens lag in these B. subtilis-hydrolyzed food proteins was a result of the protein being more readily available for utilization by C. perfringens.