Viability and beta-galactosidase activity of dairy propionibacteria subjected to digestion by artificial gastric and intestinal fluids

An important criterion to consider in the selection of strains for dietary adjuncts is the ability of the microorganisms to survive the severe conditi ons of acidity and bile concentrations usually found in the gastrointestina l tract. In the present work, we report the effects of digestions by artifi cial gastric and intestinal fluids on beta-galactosidase activity and survi val of four strains of dairy propionibacteria previously selected by their bile tolerance and beta-galactosidase activity. The strains were exposed to artificial gastric juice at pH values between 2 and 7 and then subjected t o artificial intestinal digestion. Both viability and beta-galactosidase ac tivity were seriously affected at pH 2. Skim milk and Emmental cheese juice exerted a protective effect on the parameters tested. The trypsin present in the intestinal fluid inactivated the enzyme beta-galactosidase in strain s of Propionibacterium freudenreichii but not in Propionibacterium acidipro pionici. Moreover, the presence of bile salts enhanced the beta-galactosida se activity of these strains by permeabilization of the cells during the fi rst hour of exposure. The intestinal. transit rate confirmed the permanence of the bacteria in the intestine for long enough to be permeabilized. Thes e results suggest that P. acidipropionici would be a good source of beta-ga lactosidase activity in the intestine. We also propose a practical and effe ctive in vitro method as a tool of screening and selection of potential pro biotic bacteria.