How to promote the growth of Lactobacillus acidophilus in milk?

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Lactobacillus acidophilus group lactic acid bacteria is a dominant lactobacilli in the human intestinal tract, and expected as useful probiotic strains. However, they usually grow poorly in milk than other yogurt starter lactic cultures. Therefore, the factors relating with the growth rate of L.acidophilus in milk were investigated. The amount of the remaining non-protein nitrogen components in fermented reconstituted milk were parallel to the growth rate of the strains. The relationship between the protease activity and growth rate of L.acidophilus in milk were investigated. The strains in L.acidophilus group which can grow well in milk were known to secrete the exocellular proteases at early stage of the cell growth, and the activity was kept constant while further incubation period. The results indicated that the high exocellular protease producing strains can preferentially grow in milk, because the low molecular nitrogen components should be supplied through hydrolysis of milk proteins by bacterial own proteases.Addition of casein hydrolyzed by 3 proteases showed all positive promoting effects on the acid production. In particular, casein treated with Protease p (Amano enzyme, Japan) showed the highest effect. The results indicated that the addition of the enzymatically digested casein to milk is a very useful way to accelerate the growth of L.acidophilus.The co-culture of the S.thermophilus with some strain of L.acidophilus was known to promote the growth of the L.acidophilus in milk. It is suggested the presence of some symbiotic relationship between two strains and the co-culture is a possible method for the production of probiotic fermented milk using L.acidophilus.