Increasing alcohol yield by selected yeast fermentation of sweet sorghum. II. Isolation and evaluation of mutants and wild types for ethanol production

Abstract

Three yeast strains, which gave over 93% sugar conversion efficiency (SCE) in sweet sorghum juice containing 20% total sugar in a previous study, were submitted to 3 and 6% ethylmethanesulfonate (EMS) to induce mutations. Several mutants produced by the EMS treatment and their respective wild types grew well in media containing up to 40% sugar. Some mutants tolerated 2·5% more alcohol than their respective wild types. Saccharomyces cerevisiae IZ 1716 Mutant 10 produced a significantly greater yield of ethanol from sweet sorghum juice containing 26% sugar than the wild type. Under large-scale fermentation, this mutant had an SCE of 89·4% after 36h in sweet sorghum juice containing 28% sugar. The final alcohol concentration reached 13·28% (w/v) after 48h, corresponding to an SCE of 93·57%.