Full Length Research Paper

Flocculation phenomenon of a mutant flocculent Saccharomyces cerevisiae strain: Effects of metal ions, sugars, temperature, pH, protein-denaturants and enzyme treatments

Kedong Ma¹*, Minato Wakisaka¹, Kenji Sakai² and Yoshihito Shirai¹

¹Department of Biological Functions and Engineering, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Kitakyushu, Fukuoka 808-0196, Japan.

²Department of plant resources, Graduate school of Bioresource and Bioenvironmental sciences, Kyushu University, Fukuoka 812-8581, Japan.

*Corresponding author. E-mail: mkedong@yahoo.co.jp. Tel: +81936956060. Fax: +81936956070

Accepted 11 January, 2010

   Abstract

The flocculation mechanism of a stable mutant flocculent yeast strain Saccharomyces 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.