Survival of yeasts stored after freeze-drying or liquid-drying

We investigated the survival mechanisms of freeze-dried or liquid-dried (L-dried) yeast cells in ampoules. Type strains of various yeasts were freeze-dried or L-dried and sealed in ampoules under high vacuum (< 1 Pa) or low vacuum (4.8 × 104 Pa), then stored at 37ºC (accelerated storage test) for up to 17 weeks. Among strains in each of the genera Saccharomyces, Saccharomycopsis, Debaryomyces, and Pichia, survival rates immediately after freeze-drying varied more widely than those after L-drying. Freeze-dried cells stored at 4.8 × 104 Pa had lower survival rates than those stored at < 1 Pa. L-dried cells stored at 4.8 × 104 Pa also had lower survival rates than those stored at < 1 Pa, but the decrease in survival was not as marked as in freeze-dried cells. Strains that had high survival rates immediately after freeze-drying tended to have small cells, to be osmotolerant, and to be able to utilize many kinds of carbohydrates. L-dried cells of most Candida strains had stable survival rates regardless of the vacuum pressure. In basidiomycetous yeasts, strains forming extracellular polysaccharides had markedly lower survival.