γ-聚谷氨酸钠对面包酵母的抗冻作用及其机理

Antifreeze effect and mechanism of sodium poly-γ-glutamate on backers’ yeast cells

γ-聚谷氨酸钠(γ-PGA钠)是由γ-聚谷氨酸与钠离子结合而成的水溶性物质,可以食用,无色无味。γ-PGA钠作为面包酵母抗冻剂,具有较强的实用性。在0.03～0.40℃/min的冷冻速率、-7～-60℃的冻藏温度条件下,探讨了γ-PGA钠对面包酵母的抗冻作用及其机理。实验结果表明,酵母细胞存活率在冻藏初期逐渐下降,6d后趋于稳定。γ-PGA钠对酵母的抗冻作用明显高于葡萄糖和谷氨酸。γ-PGA钠抑制了冷冻和冷藏过程中大冰晶的产生、以及冰晶的重结晶。在冷冻速率大于0.27℃/min、冻藏温度低于-30℃、冻藏时间6d的条件下,添加1%的γ-PGA钠使酵母细胞存活率从无γ-PGA钠时的36.5%上升到67.5%。γ-PGA钠、葡萄糖和谷氨酸的抗冻活性分别为2.48、2.03和1.42。细胞存活率(η,%)随抗冻活性(Aa,-)的增加呈线性上升。γ-PGA钠具有较大抗冻活性的机理是,γ-PGA钠的解离度较大,并且Na+能够固定较多的水分子。

Sodium poly-γ-glutamate （Na-γ-PGA）, a water-soluble polyamide composed of poly-γ- glutamic acid and sodium ion, is edible, tasteless, colorless and odorless. It is considered as a potential cryoprotectant for backers＇ yeast. In the present study, the antifreeze effect of Na-γ-PGA on bakers＇ yeast cells was investigated in the freezing rate range of 0.03-0.40 ℃/min and the storage temperature range of -7--60 ℃. The mechanism of the antifreeze effect was also discussed. The experimental results showed that the survival ratio of yeast cells decreased at the beginning, and was constant after 6 dduring frozen storage. Na-γ-PGA had greater antifreeze effect on the yeast cells than glutamic acid and glucose. It inhibited both the generation of big-size ice crystals during freezing and the recrystallization of ice crystals during freezing storage. Under the condition of a freezing rate at 0.27 ℃/rain, a storage temperature at -30 ℃and storage time at 6 d, the survival ratio of yeast cells was increased from 36.5% to 67.5% by adding 1% of Na-y-PGA. Na-y-PGA, glucose and glutamic acid had an antifreeze activity of 2.48, 2.03 and 1.42 respectively. The survival ratio of yeast cells （η, %） increased linearly with increasing antifreeze activity （Aa, -）. The high antifreeze activity of Na-y-PGA was resulted from its high dissociation degree and the high capability of Na＋ to combine water molecules.