Survival of lactic acid bacteria and their lactases under acidic conditions
1990
Shah, N. | Jelen, P.
Effects of sonication, survival, and beta-galactosidase activity of four lactic cultures were investigated in pH 1.5-3.5 range. Lactobacillus delbruekii subsp. bulgaricus and Streptococcus thermophilus exhibited the highest beta-galactosidase activity in skim milk and broth systems, respectively. The beta-galactosidases from L. delbruekii subsp. bulgaricus, S. thermophilus, and L. acidophilus showed optimum activity in the neutral pH range and 55 degrees C. Viable count of all four cultures decreased most rapidly at pH 1.5, but L. acidophilus and L. delbruekii subsp. bulgaricus survived better than the other organisms. The decrease of enzyme activity of unsonicated cultures with pH was slight, especially at pH 3.5. However, acidification of sonicated cultures to pH 3.5 or lower resulted in rapid and permanent loss of enzyme activity.
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