Nakamura Toshihide, Takagi Hiroshi, Shima Jun
National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan.
Cryobiology. 2009 Apr;58(2):170-4. doi: 10.1016/j.cryobiol.2008.11.012. Epub 2008 Dec 24.
Freezing tolerance is an important characteristic for baker's yeast, Saccharomyces cerevisiae, as it is used to make frozen dough. The ability of yeast cells to survive freezing is thought to depend on various factors. The purpose of this work was to study the viability of yeast cells during the freezing process. We examined factors potentially affecting their survival, including the growth phase, ice-seeding temperature, intracellular trehalose content, freezing period, and duration of supercooling. The results showed that the ice-seeding temperature significantly affected cell viability. In the stationary phase, trehalose accumulation did not affect the viability of yeast cells after brief freezing, although it did significantly affect the viability after prolonged freezing. In the log phase, the ice-seeding temperature was more important for cell survival than the presence of trehalose during prolonged freezing. The importance of increasing the extracellular ice-seeding temperature was verified by comparing frozen yeast survival rates in a freezing test with ice-seeding temperatures of -5 degrees C and -15 degrees C. We also found that the cell survival rates began to increase at 3h of supercooling. The yeast cells may adapt to subzero temperatures and/or acquire tolerance to freezing stress during the supercooling.
耐冻性是用于制作冷冻面团的面包酵母（酿酒酵母）的一项重要特性。酵母细胞在冷冻后存活的能力被认为取决于多种因素。这项工作的目的是研究酵母细胞在冷冻过程中的活力。我们考察了可能影响其存活的因素，包括生长阶段、晶种温度、细胞内海藻糖含量、冷冻时间以及过冷持续时间。结果表明，晶种温度显著影响细胞活力。在稳定期，海藻糖的积累在短暂冷冻后并不影响酵母细胞的活力，不过在长时间冷冻后确实会显著影响活力。在对数期，在长时间冷冻过程中，晶种温度对细胞存活比海藻糖的存在更为重要。通过比较晶种温度为-5℃和-15℃的冷冻试验中冷冻酵母的存活率，证实了提高细胞外晶种温度的重要性。我们还发现，过冷3小时后细胞存活率开始上升。酵母细胞可能在过冷期间适应零下温度和/或获得对冷冻应激的耐受性。
