Freeze Drying of Lactobacillus coryniformis Si3: Focus on Water

摘要

Freeze drying is commonly used to stabilize lactic acid bacteria. However, dehydra-tion tolerance differs among strains of lactobacilli and also other factors have been reported to influence freeze-drying survival. The effects of sucrose concentration, cell density, and freezing rate on freeze-drying survival of Lactobacillus coryniformis Si3 have been evaluated. The water activity (a_w) of the dry product, as well as selected thermophysical properties of importance for freeze drying, degree of water crystalliza-tion, and the glass transition temperature of the maximally freeze-concentrated amor-phous phase (T_g) were determined. Survival rates varied from 6% to 70% under different conditions, and all factors studied influenced the product's a_w and its survival of freeze drying. The most important factor for survival was the freezing rate. However, there were codependencies between freezing rate and formulation constituents, demonstrating the complexity of the system. The degree of water crystallization decreased and final a_w increased as a function of sucrose concentration. The degree of water crystallization and T_g were not affected by cell density up to 10~(11) colony forming units/mL where these thermophysical values decreased possibly due to increased amounts of unfrozen water.