Abstract: In the present work, the effect of milk protein hydrolysates on probiotic cell counts and its stability during two weeks storage was studied. Probiotic bacteria, Lactobacillus acidophillus was used as pure culture. Proteolytic enzyme, alcalase novo was used to hydrolyze casein. The effect of five casein hydrolysates, which have a degree of hydrolysis of 4.7%, 7.1%, 8.8%, 10.1%, 12.6% respectively, to the growth of L. acidophilus were investigated by adding them to milk at a concentration ranging from 0.5 to 4g/L. Addition of casein hydrolysates with different degrees of hydrolysis enhance the growth of probiotic bacteria L.acidophilus generally. With the increase in adding level the stability of L.acidophilus increased. However, the highest viability and best stability of L.acidophilus was observed when casein was hydrolyzed to the degree of 8.8% and added at the level of 2g/L. This result shows that the addition of casein hydrolysates has a positive effect on the probiotic cell count and microbiological stability of fermented milks containing probiotic bacteria when controlled wisely. The research work has an important theoretical and practical value by helping dairy industry meet international standards of probiotic products.

Key words: probiotics, casein hydrolysate, cell count, viability