EFFECT OF ACID CASEIN HYDROLYSATE AND CYSTEINE ON THE VIABILITY OF YOGURT AND PROBIOTIC BACTERIA IN FERMENTED FROZEN DAIRY DESSERTS

The effect of acid casein hydrolysate and cysteine on the Viability of yogurt bacteria (Streptococcus salivarius ssp. thermophilus and Lacto bacillus delbrueckii ssp. bulgaricus) and probiotic bacteria (Lactobac illus acidophilus and bifidobacteria) during a storage period of 12 we eks was assessed in fermented frozen dairy desserts. Three batches of fermented frozen dairy desserts were made with milk supplemented with acid casein hydrolysate or cysteine. The control batch was made with m ilk supplemented with 2% skim milk powder. Viable counts of yogurt bac teria and probiotic bacteria were enumerated and pH, titratable acidit y and beta-D-galactosidase activity measured at fortnightly intervals for 12 weeks. S. salivarius ssp. thermophilus was most stable in all t he samples of fermented frozen dairy desserts with counts greater than or equal to 10(7) cfu/g throughout the storage period. The counts of L. delbrueckii ssp. bulgaricus was reduced by 2 log cycles in the cont rol sample, whereas in those supplemented with acid casein hydrolysate and cysteine, the counts decreased by 1 and 2 log cycles respectively . The counts of L. acidophilus and bifidobacteria decreased to <10(2) cfu/g in the control samples, whereas the counts were > 10(5) cfu/g in the samples supplemented with acid casein hydrolysate or cysteine. Th e beta-D-galactosidase activity decreased rapidly in the control sampl e during 12-weeks storage at -18 degrees C, as compared with those pre pared with acid casein hydrolysate and cysteine.