Influence of bile on beta-galactosidase activity of component species of yogurt starter cultures

The influence of bile on beta-galactosidase activity and the cellular integrity of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus salivarius ssp. thermophilus were tested. Two strains (OS 1 and OS 2) of L. delbrueckii ssp. bulgaricus and three strains (HC 15, 17, and 18) of S. salivarius ssp. thermophilus were studied. In the presence of .15% oxgall, beta-galactosidase activity of whole cells of both species was significantly increased. However, at a higher concentration (.3% oxgall), the beta-galactosidase activity was significantly less than in the presence of .15% oxgall. The presence of oxgall did not promote the cell lysis of any of the strains of either species. Additionally, the presence of oxgall did not cause the leakage of the enzyme from the cells. Thus, the presence of oxgall increased the cellular permeability to allow more substrate to enter the cells, thereby increasing beta-galactosidase activity, and, at higher concentrations, was inhibitory to beta-galactosidase activity of both species.