Abstract
The inhibitory effects of yogurt and yogurt whey on the production of putrefactive metabolites by intestinal bacteria were studied in vitro. Indole production by Esherichia coli 0-601 was found to decrease markedly upon addition of 3% yogurt whey, and the tryptophanase activity of the cells grown in the medium with yogurt whey was lower than that of cells grown in control medium. It was found that the decrease in tryptophanase activity was due mainly to repression by lactose from the yogurt whey. Ammonia production by Proteus mirabilis 7082 was inhibited slightly by addition of 3% yogurt whey in ureafree medium. Strain 7082 was found to possess urease and the enzymes which produce ammonia from amino acids such as arginine, leucine, aspartic acid, and asparagine. This strain produced ammonia when grown in medium containing each amino acid as the sole nitrogen source. The activities of these ammonia-producing enzymes were decreased in the low-pH reaction mixture. In addition, phenol production by Clostridium perfringens 7083 was inhibited slightly when grown in medium with 3% yogurt. It appeared that the lower phenol production was due to the decrease in culture pH with the growth of lactic acid bacteria.
