Effect of freeze drying and protectants on viability of the biocontrol yeast Candida sake

The effects of freezing method, freeze drying process, and the use of protective agents on the viability of the biocontrol yeast Candida sake were studied. Freezing at −20°C was the best method to preserve the viability of C. sake cells after freeze drying using 10% skim milk as a protectant (28.9% survival). Liquid nitrogen freezing caused the highest level of damage to the cells with viability <10%. Different concentrations of exogenous substances including sugars, polyols, polymers and nitrogen compounds were tested either alone or in combination with skim milk. There was little or no effect when additives were used at 1% concentration. Galactose, raffinose and sodium glutamate at 10% were the best protective agents tested alone but the viability of freeze-dried C. sake cells was always <20%. Survival of yeast cells was increased from 0.2% to 30–40% by using appropriate protective media containing combinations of skim milk and other protectants such as 5% or 10% lactose or glucose, and 10% fructose or sucrose.