Effects of cryoprotectants on viability of Lactobacillus reuteri CICC6226

Freeze-drying is commonly used to preserve probiotics, but it could cause cell damage and loss of viability. The cryoprotectants play an important role in the conservation of viability during freeze-drying. In this study, we investigated the survival rates of Lactobacillus reuteri CICC6226 in the presence of cryoprotectants such as sucrose, trehalose, and reconstituted skim milk (RSM). In addition, we determined the activities of hexokinase (HK), pyruvate kinase (PK), lactate dehydrogenase (LDH), and ATPases immediately following the freeze-drying. The results showed that the differences in HK and PK activities with and without the cryoprotectants during freeze-drying were not significant, but cell viability and activities of LDH and ATPase were significantly different (P < 0.01) prior to and after freeze-drying. Meanwhile, the results showed that the maintenance of the membrane integrity and fluidity was improved in the presence of the 10% trehalose or 10% RSM than other treatments during freeze-drying. These results have provided direct biochemical and metabolic evidence of injured cell during freeze-drying. Freeze-drying damaged membrane structure and function of cell and inactivated enzymes (LDH and ATPases). The results imply that LDH and ATPases are key markers and could be used to evaluate the effect of cryoprotectants on viability and metabolic activities of L. reuteri CICC6226 during freeze-drying.