Freeze-Drying Preservation of Yeast Adjunct Cultures for Cheese Production

Abstract

Freeze-Drying Preservation of Yeast Adjunct Cultures for Cheese Production Four yeast strains: Yarrowia lipolytica PII6a, Candida famata MI1a, C. kefyr PII1b, C. sphaerica FII7a, adjunct cultures for cheese production were preserved by freeze-drying. The effect of process parameters and cryoprotective agents on cell survival and stability of growth characteristics was evaluated. Among three lyophilisation protocols, the process with three-step drying at temperatures of -38°C, -20°C and -10°C assured the highest cell viability. The survival of yeast strains in the presence of multicomponent cryoprotective agents containing skimmed milk, trehalose and sodium glutamate in three combinations (MT, MG, MTG) was significantly higher than in the presence of those agents used alone. The best agent for Y. lipolytica, C. kefyr and C. sphaerica appeared to be MT, while for C. famata - MG. Cell viability of yeast strains directly after freeze-drying was in the range of 74-80% and was relatively stable during one-year storage except C. famata. Initial yeast growth patterns were very well preserved in most of the preparations during 6 months of storage.