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

Abstract

The present study was aimed to select strains of Saccharomyces cerevisiae and Candida tropicalis based on their ability to tolerate ethanol toxicity and to evaluate the expression level of he hydrophillins encoding genes TIF 11 and YJL144W to express encoding for hydrophilins. Freeze-drying is a popular dehydration method for preserving 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). It is concluded that before freeze-drying starter production other investigations are needed in order to evaluate yeast performance. Also, the pathogenicity of Candida tropicalis strains will be studied for the using potentially non-pathogen strains.