Study on freeze-tolerant baker's yeast

经7d冻藏后，普通面包酵母的活力和CO_2生产能力分别下降到未冻藏细胞的35%和25%。一株耐冻酵母在相同的贮藏条件下仍能保持75%的活力，但CO_2产率下降到30%。冻藏7天的酵母菌解冻后立即制备的无细胞提取物的CO_2生产力和DNase I抑制活性大大降低。然而，只有在耐冷冻酵母中，通过在解冻后在30 ℃下孵育冷冻储存的细胞，生产率和活性增加。增加工具放置在CO_2生产力之前。这些结果表明，酵母细胞的糖酵解系统和肌动蛋白在冻藏过程中受到损伤。两种酵母菌<262>在冻藏过程中都释放出吸A物质和Ca^&lt;2+&gt;.在两种酵母的无细胞提取物中，通过凝胶过滤检测到两个肌动蛋白峰。在冷冻保存后制备的常规酵母提取物中，这两个峰减少。与此相反，耐冻酵母在相同的贮存时间内，肌动蛋白的峰值并没有降低。两种酵母在冷冻储存后均降低了己糖激酶和丙酮酸激酶的活性。在常规酵母中的下降幅度大于耐受性酵母。磷酸果糖激酶在酶的较高分子量侧的级分处洗脱。在常规酵母中冷冻保存后，峰移向低分子量侧。冻藏后CO_2产率的降低是由于冻藏过程中己糖激酶和丙酮酸激酶活性的降低以及磷酸果糖激酶从酶复合物中解离所致。

After a 7-d-frozen storage, the viability and CO_2 productivity of conventional baker's yeast decreased to 35% and 25% of those of unfrozen cells, respectively. A freeze-tolerant yeast for frozen dough method kept 75% viability even after the same storage, but the CO_2 productivity decreased to 30%. The CO_2 productivity and DNase I inhibitory activity of action of the cell-free extracts prepared immediately after thawing from 7-d-frozen-stored yeasts largely decreased. Only in the freeze-tolerant yeast, however, the productivity and the activity were increased by incubating the frozen-stored cells at 30 ﾟC after thawing. The increase tool place in actin before in CO_2 productivity. These results suggest that glycolytic system and actin in yeast cells are subject to damages during frozen storage. Both the yeasts released A_<262>-absorbing substances and Ca^<2+> during frozen storage. In cell-free extracts of both yeasts, two peaks of actin were detected by a gel filtration. These two peaks decreased in the extract of the conventional yeast prepared after frozen storage. In contrast, the freeze-tolerant yeast did not decrease the peak of actin deven after the same storage. Both yeasts decreased hexokinase and pyruvate kinase activity after the frozen storage. The decrease was greater in the conventional yeast than the tolerant one. Phosphofruktokinase was eluted at a fraction of higher molecular weight side of the enzyme. The peak moved to the lower molecular weight side after the frozen storage in the conventional yeast. The decrease in hexokinase and pyruvate kinase activity adn the dissociation of phosphofructokinase from enzyme complex cause the decrease in CO_2 productivity after frozen storage.