The viability of yeast preservation on protease production during sorghum wort fermentation

Abstract

The routine preservation of microorganisms promotes a complete depression of cell viability, stability and metabolic activity. In this study, Saccharomyces uvarum preserved under various conditions, was successfully reactivated within a relatively short time. The oils selected for preservation demonstrated higher cell viability and survival of yeast cells at cell count per mL of 2×10⁶ cfu/mL Yeast cells preserved in 15 % glycerol in liquid-nitrogen all showed good survival rates and reactivation with 11 × 10⁶ cfu/mL after 2 months. Saccharomyces uvarum was pitched in sorghum wort of two varieties (white & red) and fermentation was allowed to proceed. Results showed that protesse production was higher in red sorghum with yeast preserved in olive oil, mineral oil and corn oil. Production was optimal with isolate preserved under mineral oil and corn oil for 2, 4, 6 and 8 days during fermentation of white sorghum. The highest ethanol content of 27.8 % to 26.1 % was recorded with isolate preserved in mineral oil at room tempertaure for the white sorghum variety, with olive oil having the least yield of 15 %. Higher yield in both wort varieties was generated in the red sorghum wort fermented with yeast preserved in all oils at room temperature. Generally, there was better ethanol yield, cell viability and no apparent decrease in catalytic activity upon preservation , with yeast cells preserved at refrigerated temperature for the white sorghum and room temperature for the red sorghum. Preservation of yeasts cultures in mineral oil and corn oil provided better survival during storage period. Therefore, the use of some traditional methods for yeast culture preservation may be proposed.

Keywords: Saccharomyces uvarum, preservation, protease, viability and sorgum wort