Probiotic Cell Counts And Viability In Fermented Milks Supplemented With Milk Protein Hydrolysates

To the fermented milks containing probiotics, keeping the cell counts and stability of probiotic bacteria is most important for exerting functional efficacy. In the present work, the effect of milk protein hydrolysates on probiotic cell counts and its stability during five weeks storage was studied. Probiotic bacteria, Lactobacillus acidophillus 1.1854 was used as pure culture or in mixed culture with Streptococcus thermophilus 6038. Proteolytic enzyme, alcalase novo and trypsin was used to hydrolyze casein. First, hydrolyze milk proteins with two enzymes for different time, so the milk proteins'hydrolysates have different degrees of hydrolysis, to the growth of L. acidophilus 1.1854 were investigated by adding hydrolysates to milk at a concentration ranging from 0.1 to 4g/L,then keep the culture at 37℃until pH 4.5. The growth of probiotic bacteria was estimated using colony plate counts. The optimal of condition to perform enzymatic milk proteins hydrolysis are①c asein hydrolyze with alcalase, a maximum degree of hydrolysis could be obtained when the amount of enzyme alcalase added was 0.5mL, the concentration of substrates was 8%, the time of overall proteolytic reaction was 5400s, and the reaction temperature was 60℃. The final degree of hydrolysis at the end of 5400s reaction was 12.6%.②w hey hydrolyze with alcalase, a maximum degree of hydrolysis could be obtained when the amount of enzyme alcalase added was 0.5mL, the concentration of substrates was 8%, the time of overall proteolytic reaction was 5400s, and the reaction temperature was 60℃. The final degree of hydrolysis at the end of 5400s reaction was 6.87%.③c asein hydrolyze with trypsin, a maximum degree of hydrolysis could be obtained when the amount of enzyme alcalase added was 0.5mL, the concentration of substrates was 8%, the time of overall proteolytic reaction was 7200s, and the reaction temperature was 50℃. The final degree of hydrolysis at the end of 7200s reaction was 14.9%. Among the three milk protein hydrolysates, the best to the growth of probiotic is casein hydrolyze with trypsin, with a degree of hydrolysis is 6.2% and added at level of 1g/L. When it added in milk with probiotic Lactobacillus acidophillus 1.1854, the cell count is about 7.6×108cfu/mL, is 1.3 times of control. After a five weeks storage at 4℃, the cell count is about 4.7×108cfu/mL, is 3.2 times of control. The optimal condition of milk fermented with Streptococcus thermophilus 6038 and Lactobacillus acidophillus 1.1854 mixed together is 1:2 inoculum ratio, the fermention temperature is 41℃, with 6% ferment starter. When added the casein hydrolysate with a a degree of hydrolysis is 6.2% and added at level of 1g/L into the mixed culture, fermented to pH 4.5, after a five weeks storage at 4℃, the cell count in MRS and M17 culture are 1.29×108cfu/mL and 5.95×108cfu/mL, is 2 and 2.3 times of control respectively. 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.