Flocculation characteristics of an isolated mutant flocculent Saccharomyces cerevisiae strain and its application for fuel ethanol production from kitchen refuse

A stable mutant flocculent yeast strain of Saccharomyces cerevisiae KRM-1 was isolated during repeated-batch ethanol fermentation using kitchen refuse as the medium. The mechanism of flocculation and interaction with the medium was investigated. According to sugar inhibition assay, it was found that the mutant flocculent strain was a NewFlo phenotype. Flocculation was completely inhibited by protease, proteinase K and partially reduced by treatments with carbohydrate-hydrolyzing enzymes. Flocculation ability showed no difference for pH 3.0–6.0. Furthermore, the mutant flocculent yeast provided repeated-batch cultivations employing cell recycles by flocculation over 10 rounds of cultivation for the production of ethanol from kitchen refuse medium, resulting in relatively high productivity averaging 8.25 g/L/h over 10 batches and with a maximal of 10.08 g/L/h in the final batch. Cell recycle by flocculation was fast and convenient, and could therefore be applicable for industrial-scale ethanol production.