Gastric juice in the human stomach showed significant bacteria killing properties, partly due to pepsin. The typical pepsin concentration in gastric juice is 0.5e1.0 g in L [34]. It was found that the addition of pepsin (1.0 g/L) to a gastric medium having pH~4.0 resulted in a decrease in the D-values of B.cereus cells in the stationary phase. However, the D-values for psychrotrophic strains appeared to decrease more markedly than in the case of mesophilic strains. The effect of pepsin on the cells in the exponential phase of growth at pH~4.5was opposite.Namely,the addition of pepsin increased the D-values by 60%. The influence of pepsin increased as the pH values of the medium decreased, which may be correlated with the optimal
proteolytic activity for this enzyme (pH 1.2e2.5