Differences in the intracellular lipids of sake yeast in main mash seeded respectively with two kinds of seed mash: Kimoto and sokujo-moto

Abstract

In sake brewing, yeast cells grown in the traditional seed mash ( kimoto) are enriched in palmitic acid, and those in the popular seed mash ( sokujo-moto) are enriched in linoleic acid. Lipid composition of yeast in the main mash seeded with respective seed mash was determined. The amount of intracellular phospholipids (PLs) of yeast showed little change throughout the fermentation period, while intracellular triglyceride (TG) content decreased dramatically during the growth phase in the main mash. In the main mash seeded with sokujo-moto, the linoleic acid content of intracellular phosphatidyl ethanolamine (PE) was reduced from 30.6% of the original seed mash yeast to 6–9%, whereas the content of intracellular phosphatidyl choline (PC) was merely reduced from the original 48.4% to 26–30% during fermentation. Moreover, even after 4–5 generations of growth in the main mash, the percent of linoleic acid in PC did not notably decrease. The intracellular TG of seed mash yeast is therefore supposed to be a major source of linoleic acid in the early stage of growth in main mash. On the other hand, linoleic acid content in PLs of yeast were detectable only in low quantities (5–10%) during the fermentation of main mash seeded with kimoto as well as that seeded with kimoto (5.5%). Since there was no increase in linoleic acid content, the main mash during rapid growth phase seemed to be deficient in linoleic acid and, therefore, the digestion of raw materials, which contains large amounts of linoleic acid, failed to actively proceed. The ratio of PC PE of the cells was 0.67 in kimoto, and 1.62 in sokujo-moto. The same sort of difference in the PC PE ratio was also seen between the corresponding main mash. The presence of linoleic acid increased the PC PE ratio at the stationary phase of growth, and was decreased in the presense of 16% ethanol. Thus, kimoto could be differentiated from sokujo-moto on the basis of fatty acid composition in PC and by the PC PE ratio of the yeast in the main mash.