Effects of Trehalose on Freeze Tolerance of Baker’s Yeast

A conventional baker’s yeast strain D incorporated trehalose into its cells from a YPG medium supplemented with trehalose. Cells cultured in a medium containing 3 to 5% trehalose increased to nearly 5 times the trehalose content of cells cultured in the absence of trehalose. After 1 day of frozen storage at -2O”C, cells cultured in 3% trehalose medium experienced a lesser decrease in both viability and CO, productivity than cells cultured in the absence of trehalose. Even after 10 days frozen storage, the strain D cultured in the 3% trehalose medium retained to nearly 50% of the viability and CO, productivity of the unfrozen cells. Although the freeze-tolerant yeast strains DFT and S. cerevisiae MAFF lo-03056 showed, during freezing, smaller decreases in viability than strain D, the large decreases in CO_2 productivity were comparable among all three strains. The CO_2 productivity in both freeze-tolerant strains cultured in the presence of 3% trehalose was about 60% of that in the unfrozen cells, even after 10 days of frozen storage. The CO_2 productivity and actin content of the cell-free extracts prepared from the strain D cultured in YPG medium decreased significantly to about 15% and 30% of those of the unfrozen cells, respectively, after 7 days of frozen storage. When the cells cultured in the presence of 3% trehalose were frozen-stored, the CO_2 productivity of the cellfree extracts prepared from 7-days frozen-stored cells decreased to 50% of that from the unfrozen cells. The actin content, however, did not decrease after the same frozen storage. In eukaryotic cells, the activities of some glycolytic enzymes are increased by association with actin. It seems that the native structure of actin is necessary for yeast CO, productivity after frozen storage