Abstract
The flocculation mechanism of a stable mutant flocculent yeast strainSaccharomyces cerevisiae KRM-1 was quantitatively investigated for potential industrial interest. It was found that the mutant flocculent strain was NewFlo phenotype by means of sugar inhibition test. The flocculation was completely inhibited by treatment with proteinase K, protein-denaturants and carbohydrate modifier. The absence of calcium ions significantly inhibited the flocculation, indicating that Ca2+ was specifically required for flocculation. The flocculation was stable when temperature below 70°C and pH was in the range of 3.0 - 6.0. The flocculation onset of the mutant flocculent strain was in the early stationary growth phase, which coincided with glucose depletion in the batch fermentation for the production of ethanol from kitchen refuse medium. The results are expected to help develop better strategies for the control of mutant flocculent yeast for future large-scale industrial ethanol fermentation. Key words: Kitchen refuse, Saccharomyces cerevisiae, flocculation, lectin-like, newflo phenotype.
Highlights
Flocculation of yeasts is usually described as a phenolmenon wherein cells could aggregate spontaneously and form flocculation which sediment rapidly in culture medium (Miki et al, 1982a)
The flocculation onset of the mutant flocculent strain was in the early stationary growth phase, which coincided with glucose depletion in the batch fermentation for the production of ethanol from kitchen refuse medium
The mutant flocculent yeast strain S. cerevisiae KRM-1 was recently isolated during the repeated-batch fermentation using kitchen refuse as medium
Summary
Flocculation of yeasts is usually described as a phenolmenon wherein cells could aggregate spontaneously and form flocculation which sediment rapidly in culture medium (Miki et al, 1982a). This capacity of yeast cells has been traditionally utilized by the brewing and wine industries and more recently, in continuous ethanol fermentation processes (Ge et al, 2006; Kida et al, 1992; Teunissen and Steensma, 1995; Seong et al, 2006; Nonklang et al, 2009). It is possible that flocculent yeast could be advantageous in industrial fermentation as
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