Potentialities of Yeast Strains to be Used as Freeze-Drying Starters for the Production of Traditional Sorghum Beer in Côte d’Ivoire

Freeze-drying is a well-known dehydration method widely used to preserve microorganisms. In order to produce freeze-dried yeast starter culture for the brewing purpose of African traditional sorghum beer, we tested tolerance to ethanol stress and evaluated the relative expression level of genes TIF 11 and YJL144W encoding the hydrophilins. Among the strains tested, the best viability rate to ethanol stress (7.5% ethanol (v/v)) was found with Saccharomyces cerevisiae F12–7 and Candida tropicalis C0–7 respectively with 95% and 80%. For Saccharomyces cerevisiae strains, the strain F12-7, which had distinguished itself from other strains in previous tests, the TIF11 and YJL144W genes were the least expressed. For C. tropicalis strains, the statistical analyzes of the relative expression levels from the Tukey test revealed no difference between the strains for the 2 genes (P> 0.05).