Selection and characterisation of high ethanol tolerant Saccharomyces yeasts from orchard soil

Six yeast strains with different levels of ethanol tolerance were isolated from orchard soil. Out of the six isolates, isolate Orc 6 showed the highest ethanol tolerance (20%) while isolates Orc 2 and Orc 11 had15% ethanol tolerance. High level ethanol tolerant Saccharomyces yeast, Orc 6, was investigated for its potential application in ethanologenic fermentations. Data presented in this study revealed that Orc 6 yeast isolate tolerated osmotic stress above 12% (w/v) sorbitol and 15% (w/v) sucrose equivalent of osmotic pressure thus exhibiting superior osmotolerance than the reference production wine yeast strain. Invertase activity was also higher for Orc 6 yeast when grown in both sorbitol and sucrose media. Sorbitol increased yeast sedimentation rate in contrast to sucrose. Generally, the new yeast strain, Orc 6, showed superior fermentative performance compared to the reference production yeaststrain