清酒に関する酵素の研究

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It is believed that in sake, isoamyl acetate is one of the key components of sake flavor. It has been reported that isoamyl acetate is formed by alcohol acetyltransferase (AATase). When we think about the formation of isoamyl acetate, we suggest that the concentration of isoamyl alcohol and the activity of AATase must affect the yield of isoamyl acetate, because acetyl-CoA, another source for the formation of isoamyl acetate, is contained in the cells of Sacchaomyces cervisiae. We have studied the AATase activity, and we found that in industrial production, the AATase activity increased at the early period of the main fermentation and decreased gradually thereafter. From the data obtained, the AATase activity is very unstable to a rise of temperature, and one of the main reasons for the low temperature operation in ginjo-fermentation is to keep the activity of AATase at a desirable level. By considering the above results and the biosynthesis of isoamyl alcohol, we isolated mutants of Saccharomyces cerevisiae from sake yeast that produce sufficient isoamyl acetate in our laboratory. It is also believed that in sake, ethyl caproate is one of the key components of the sake flavor. There have been no report about the synthesis and hydrolysis of ethyl caproate. We have studied the activity of sake yeast in the synthesis and hydrolysis of ethyl caproate. The results obtained are as follows : 1) The esterase of Saccharomyces cerevisiae for ethyl caproate synthesis was separated into three fractions (S-I, II, III) by Sepharose 6B gel filtration. 2) There were differences in the localization of esterase and alcohol acyltransferase (AACTase) in the cells. Therefore, there are two pathways for the formation of ethyl caproate, through esterase and through AACTase. There is a report about esterase in p-nitrophenyl acetate hydrolysis but no report about ethyl caproate synthesis and hydrolysis. We have studied the activity of koji in the synthesis and hydrolysis of ethyl caproate. The results obtained are as follows : 1) Koji had three kinds of esterase in ethyl caproate synthesis, hydrolysis, and p-nitrophenyl acetate hydrolysis. 2) Aspergillus oryzae RIB 647 had all extracellular and intracellular activities when cultured on YEPD liquid medium. 3) The esterase in ethyl caproate synthesis was separated into two fractions (I, II) by Sepharose 6B gel filtration. 4) These fractions of esterase in ethyl caproate synthesis were not always the same as those for ethyl caproate hydrolysis in the position of elution. Sake yeast and koji have esterase and AACTase. We have studied the role of yeast and koji for the formation of ethyl caproate in moromi (unrefined sake). It became clear that sake yeast formed ethyl caproate in moromi and taht koji did not esterize caproic acid and ethanol in moromi but was supplementary in the formation of ethyl caproate. Both yeast and koji hydrolyzed ethyl caproate. Added caproic acid was changed to ethyl caproate only by esterase, not by AACTase. In moromi the activities of esterase and AACTase on yeast were constant. When caproic acid was added to moromi at the early period or at the later period, ethyl caproate increased in proportion ot the quantity of the added caproic acid. Thereby, we found that the limiting factors in ethyl caproate formation were caproc acid or caproly-CoA.
社団法人日本生物工学会の論文
1989-03-25

清酒に関する酵素の研究

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