Probiotic cell counts and acidification in fermented milks supplemented with milk protein hydrolysates

In the present work, the effect of milk protein hydrolysates on probiotic cell counts and acidification in fermented milks was studied. Two strains of probiotic bacteria, Lactobacillus acidophilus LA-5 and Lactobacillus rhamnosus LR-35, were used in mixed culture with Streptococcus thermophilus ST-7. The effect of three casein hydrolysates and three whey protein hydrolysates were investigated by adding them to milk at a concentration ranging from 0.25 to 4 g L-1. Addition of hydrolysate enhanced the growth of S. thermophilus and acidification, thus reducing the fermentation time, and growth of probiotic bacteria. On the other hand, survival of probiotic bacteria was improved when milk was added with hydrolysate. As a consequence, the addition of hydrolysate had a differential action on probiotic cell counts in fermented milks after storage, depending on the balance between its negative effect on growth of probiotic bacteria and its positive effect on the survival of probiotic bacteria. (C) 2003 Elsevier Ltd. All rights reserved.