Growth profile of Lactobacillus acidophilus group lactic acid bacteria in milk relating to their proteolytic activity

Lactobacillus (L) acidophilus group lactic acid bacteria Are dominant lactobacilli in the human intestinal tract, and are expected to be useful probiotic strains. However, they usually grow poorly in milk compared with other yogurt starter cultures. The relationships between the protease activity and the growth rate of L. acidophilus in milk were investigated. The addition of glucose in milk resulted in a no growth promotion effect, but the addition of a small amount of casein hydrolyzate improved the growth of L. acidophilus. The amount of the remaining non-protein nitrogen components in fermented reconstituted non-fat dry milk was parallel to the growth rate of the strains. The strains in the L. acidophilus group, which can grow well in milk, secreted the exocellular proteases at an early stage of the cell growth, and the activity was kept constant during a further incubation period. These results indicated that the high exocellular protease producing strains can preferentially grow in milk, because they can supply themselves with the low-molecular nitrogen components through the hydrolysis of milk proteins by their own proteases.