Natural Exopolysaccharides Enhance Survival of Lactic Acid Bacteria in Frozen Dairy Desserts

摘要

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 deg. C for 16 d (28 vs. 19/100). However, a small nonencapsulated strain of Lactobacillus delbrueckii sp. buharicus survived bet- ter 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 deg. C rather than at 40, 42.5, or 45 deg. C; 2) overrun at 50/100 rather than 100/100; and 3) storage at -17 deg. C rather than -23 or -29 deg. C. Sur- vival of strain ST1068 was unaffected by 1) neutraliza- tion of acid during growth or 2) substitution of nitrogen for air in building overrun.