Effect of high pressure on the survival rate and antibacterial activity of Bifidobacterium strains.

The effect of pressures of 1000, 700 and 400 MPa/15 min on the survival rate of Bifidobacterium infantis 1/1 was studied. 24 h milk cultures, Garsch cultures, and yogurt--to which centrifuged cell biomass of these bacteria was introduced--were subjected to pressurization. It was found that a pressure of 1000 MPa inactivated populations from 10(7) to 10(9) cfu/ml in all the environments examined. Only tens of cells in milk cultures survived a pressure of 700 MPa. Populations reduced by 4 or 5 log, depending on the environment, survived a pressure of 400 MPa. The greatest number of cells died in yogurt, where population reduction was 5 log. Bifidobacterium infantis 1/1 in milk cultures produced antibacterial metabolites active towards 89% of pathogenic bacteria strains: Enterobacteriaceae rods and species S. aureus, L. monocytogenes, B. cereus. Garsch cultures inhibited the growth of 67% of the same test strains. The antibacterial effect of experimental yogurt was much weaker than that of cultures, but it inhibited the growth of a higher number of test strains than control yogurt. Culture and yogurt pressurization with 700 MPa caused inactivation of antibacterial metabolites in all the environments.