FACTORS AFFECTING THE INCREASE OF INOSITO L CONTENT OF YEAST-CELLS INSAKE MASH

In sake brewing, the supply of inositol to the sake mash is markedly l imited due to the polishing of the rice used. Additionally, free inosi tol in polished rice is further decreased during the steeping process. In the present study, free inositol in the supernatant of sake mash d ecreased until very little could he detected because of its uptake by yeast in the early period of the fermentation. Contrastingly, bound in ositol was not utilized by yeast directly, and was not converted into a free form by either phytase or the enzyme extracted from koji. Under such an inositol-limited condition, the number of yeast cells was low er and their size was larger than when inositol was fully supplied. Th e inositol-limited condition also resulted in a low inositol content i n yeast cells in the early period of the sake fermentation. The inosit ol content of yeast cells in sake mash in which an ordinary yeast stra in (INO1) was used increased gradually, and exceeded the level of yeas t fully supplied with inositol in the final period of the fermentation . The total amount of inositol in the sake mash also increased during the fermentation. On the other hand, the inositol content of the cells in sake mash made with an inositol-requiring strain (ino1) increased little during the fermentation. These results showed that the increase in the inositol content of yeast in the final period of sake fermenta tion was mainly due not to uptake from the raw materials but to biosyn thesis by the yeast itself. This finding was supported by the inductio n of inositol-1-phosphate synthase activity under inositol-limited con dition.