Recently, ethyl carbamate (ECA) having a carcinogenic activity has been found in wine, sake, liquors and spirits. For the purpose of prducing a sake which does not contain urea, a precursor of ECA, arginase-deficient mutants were isolated from sake yeast strain Kyokai No.7 (K-7) by a mutation technique using CAO plate. The isolation rate of arginase-deficient mutants from K-7 was much lower than those from K-9 and K-10. The reason was investigated with respect to
CARI gene structure, medium constitution, and culture conditions. It was considered that gene conversion rate of K-7 was lower than those of K-9 and K-10. Sake brewing tests (Total rice 200 g, 100 kg, and 5, 400 kg) using mutants isolated from K-7 and parent strain showed that there is no difference in their fermentation profile and that resulted sake had almost the same sensory and general components except for urea. No urea was detected in the sake brewed with arginase-deficient mutants from K-7 and no ECA was formed after storage for 4 months at 30°C.
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