Selection of non-foaming mutants from sake yeast

Abstract

Most sake yeasts form high froth in sake mash during fermentation. Non-foaming mutants were isolated from Kyokai No.7, a most popular strain of Saccharomyces cerevisiae used for sake brewing, by the froth flotation method and the cell agglutination method. In the froth flotation method, normal froth forming cells were adsorbed on the surface of air bubbles and removed with them from cultured broth by aeration. A small portion of resiudal broth was inoculated into another fresh medium and the cultured broth was again aerated to remove normal cells. Non-foaming mutants were accumulated in the cultured broth after several repetition of the culturing and bubbling procedures. In the agglutination method, the normal froth-forming cells were agglutinated with cells of a strain of lactobacilli, B-47, at pH 3.0. In this paper, two other agglutination methods for selecting non-foaming mutant from sake yeast were further developed. It was found that normal froth-forming cells were agglutinated with sucrose palmitate or with celite at pH 3.0. It was inferred that yeast cells are agglutinated with sucrose palmitate by some surface chemical activities such as hydrophobic interaction and that celite acts electrostatically with yeast cell because yeast cell is charged positively, while celite is charged negatively at pH 3.0. Nonfoaming mutants of Kyokai No.9 were isolated by the sugar ester agglutination method and that of Kyokai No.6 and No.8 were isolated by the celite agglutination method at high frequencies.
Soaps such as Na-palmitate and Na-stearate were also found to be as efective as the sugar ester for agglutinating the normal yeast cells. Mineral powders such as montmorillonite, powders of cation exchangers such as cellulose phosphate or strongly acidic ion exchange resin were effective for agglutinating the normal cells. Solution of K-polyvinyl sulfate, Na-lauryl sulfate, Amaranth and 1-anillinonaphthalene-8-sulfonate were also effective.