Novel Kefir yeast having remarkable sugar utilization. Part I. Identification and fermentation character of Kefir yeast.

Abstract

A novel yeast KY-5 was isolated from Danish Kefir grains grown in skimmed milk and identified as Torulopsis holmii by the morphological, physiological and chemical method with analyses of its electrophoresis, coenzyme Q system and DNA base composition. Glucose, galactose, mannose and sucrose were fermented by the yeast, but lactose was not fermented. An inductive period was not required for galactose fermentation, even though the yeast was cultivated in a glucose medium. On the other hand, an inductive period was necessary for fructose fermentation. The yeast preferentially metabolized galactose in a glucose and galactose mixed medium. According to Warburg respirometric analyses of the intact cell, protoplast cell and cell free extract of the yeast, the remarkable sugar utilization might be dependent on constituent enzymes involved in the sugar intake and metabolism. The enzymes seemed to be quite different from those of usual yeasts.