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 prote ctive agents on the viability of the biocontrol yeast Candida sake were stu died. Freezing at - 20 degreesC was the best method to preserve the viabili ty 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 dam age to the cells with viability < 10%. Different concentrations of exogenou s substances including sugars, polyols, polymers and nitrogen compounds wer e tested either alone or in combination with skim milk. There was little or no effect when additives were used at 1% concentration. Galactose, raffino se 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 prote ctive media containing combinations of skim milk and other protectants such as 5% or 10% lactose or glucose, and 10% fructose or sucrose. (C) 2001 Els evier Science B.V. All rights reserved.