Effect of freeze drying on the metabolic viability of lactic acid bacteria

The survival rates of Lactobacillus plantarum ST-Ⅲ and Lactobacillus bulgaricus in the presence of cryoprotectants such as 15%sucrose,10%trehalose,15%sucrose +2% sodium glutamate and 10%reconstituted skim milk(RSM)were estimated.In addition,we determined the activities of hexokinase(HK),pyruvate kinase(PK),lactate dehydrogenase(LDH),extracellular proteins was higher and intercellular Ca2+ 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 activities of LDH were significantly different prior to and after freeze-drying.Meanwhile,the results showed extracellular proteins was higher and intercellular Ca2+ was lower in absence of cryoprotectants than in the presence of cryoprotectants.These results suggested that freeze-dying inactivated key enzymes(LDH)and damaged membrane structure and function.These led to decrease in viability of lactic acid bacteria during freeze-drying.