The physiological and cellular responses of different types of wine yeast strains (industrial strains AWRI R2 and Freddo and newly selected strain Saccharomyces cerevisiae B) to hyperosmotic stress (sorbitol as the osmoticum) were studied. A modified model synthetic medium was used to better understand the protection that trehalose provides wine yeasts under single-stress conditions. Exposing cells in the midexponential growth phase to 1.7 M sorbital enhanced production of glycerol and increased glycerol-3-phosphate dehydrogenase activity in all three wine yeasts, especially in industrial strain AWRI R2. However, dramatic accumulation of trehalose and an increase in trehalose-6-phosphate synthase activity were found only in Freddo and S. cerevisiae B. Strains Freddo and S. cerevisiae B also showed higher tolerance to hyperosmotic stress than AWRI R2. The survival rate of strains Freddo and S. cerevisiae B was >90% during stress treatment but was ~50% for strain AWRI R2. Glycerol was the main osmolyte used by wine yeast under hyperosmotic stress. The accumulation of trehalose was strain-dependent and endogenous trehalose correlated with acquisition of tolerance to hyperosmotic stress. A preliminary application of heat shock (leading to trehalose accumulation) was given to strain AWRI R2 before hyperosmotic stress treatment. Pretreatment with heat shock improved its osmotolerance markedly and the accumulation of trehalose played an important role. Results suggest that when glycerol is induced, trehalose could enhance osmotolerance of wine yeasts significantly. Trehalose was an important osmoprotectant.
- Copyright © 2010 by the American Society for Enology and Viticulture