冷冻干燥对乳酸菌代谢活力的影响

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

以保加利亚乳杆菌和植物乳杆菌ST-Ⅲ为研究对象,用15%蔗糖、10%海藻糖、15%蔗糖+2%谷氨酸钠及10%脱脂乳为冷冻保护剂,与不加冷冻保护剂的样品进行冻干后菌种活力的对比,测定冷冻干燥后菌体中己糖激酶、丙酮酸激酶、乳酸脱氢酶的活力,胞外蛋白及胞内Ca2+的浓度变化。结果表明:冷冻干燥对菌体的己糖激酶和丙酮酸激酶影响不显著,对乳酸脱氢酶具有显著性的影响。同时,不加保护剂菌体的胞外蛋白含量明显高于添加保护剂的,而胞内Ca2+却远低于其他组。这一结果说明,冷冻干燥使代谢关键酶如乳酸脱氢酶失活,同时对细胞膜造成了损伤,从而引起细胞代谢活力的下降。

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.