Aroma Formation by Shoyu Yeast Mutants Resistant to Amino Acid Analogues

KUSUMEGI Kazuhiro, IDENAGA Naoki, YOSHIDA Hidetugu

doi:10.6013/jbrewsocjapan1988.92.827

To improve top note of shoyu (soy sauce) flavor, we investigated mechanisms of larger production of aroma components by Zygosaccharomyces rouxii mutants resistant to amino acid analogues and examined shoyu making by them. Three mutants were obtained by 2 or 3 step treatments with etidium bromide and growth on the media containing amino acid analogues. The mutants, grown in the Shoyu-medium containing 0.17% total nitrogen, 10% NaCl, and 10% glucose, formed 1.7 to 2.1 times as high concentration of isoamyl alcohol as the parental strain.But, when grown in the same medium with 1.0% total nitrogen, they formed 30% to 40% lower concentrations of aroma components. In either medium grown with the parental strain or its mutants, acetate esters of higher alcohols were not detected. And the mutants, especially strain RBMK-212, showed smaller amounts of amino acid uptake than the parental strain. We' think that strain RBMK-212 would be released from feed-back inhibition or repression in amino acid biosynthetic pathway, resulting in formation of a large quantity of higher alcohols comparing with the parental strain. In a Shoyu making experiment, each kiageshoyu (raw soy sauce) made by using the 3 mutants individually, was found to contain higher concentrations of 5 higher alcohols than that by the parental strain. Kiage-shoyu made by strain RBMK-212 contained the highest cocentrations (22mg per 1 isobutyl, 45 isoamyl and 14.8β-phenetyl alcohols), and its flavor was evaluated preferable in the sensory test.

Aroma Formation by Shoyu Yeast Mutants Resistant to Amino Acid Analogues

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