Natural exopolysaccharides enhance survival of lactic acid bacteria in frozen dairy desserts

Viable lactic acid-producing bacteria in frozen dairy desserts can be a source of beta -galactosidase for persons who absorb lactose insufficiently. However, freezing kills many of the cells, causing loss of enzymatic activity. Cultures selected for high beta -galactosidase activities and high survival rates in the presence of bile were examined for survivability during freezing in reduced-fat ice cream. Encapsulated S. thermophilus strains survived better than their nonencapsulated mutants in reduced-fat ice cream after freezing and frozen storage at -29 degreesC for 16 d (28 vs. 19%). However, a small nonencapsulated strain of lactobacillus delbrueckii sp. bulgaricus survived better than the large encapsulated strain in reduced-fat ice cream. Factors that improved survival of encapsulated S. thermophilus 1068 in ice cream were 1) harvest of cells in the late-log phase of growth at 37 degreesC rather than at 40, 42.5, or 45 degreesC; 2) overrun at 50% rather than 100%; and 3) storage at -17 degreesC rather than -23 or -29 degreesC. Survival of strain ST1068 was unaffected by 1) neutralization of acid during growth or 2) substitution of nitrogen for air in building overrun.