[in Japanese]

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[in Japanese]

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We studied the changes in antioxidant activities of Hon-mirin, a traditional Japanese alcoholic seasoning, during storage. Hon-mirin is produced by the saccharification of glutinous rice with rice-koji for 40∼60 days under high alcoholic contents of about 20% at 20～30C. Recently, it was found that amadori-compounds in an amino-carbonyl reaction contribute to antioxidant activities of Hon-mirin in the early stages of storage. In this paper, the contribution of “melanoidin&rdquo color substances-- which are produced in the later stages of the amino-carbonyl reaction in Hon-mirin-- to antioxidant activities was studied. The correlation coefficient between color intensity (OD^430nm) and antioxidant activities (Trolox equivalent（μmol/100ml)) of Hon-mirin was significant at the 1.0% level (r=0.885, n=19). Antioxidant activities of Hon-mirin stored for 3 years more than doubled (1,063.6 Trolox eq.（μmol/100ml)), and that stored for 10 years increased more than 7 times (2,977.7 Trolox eq. (μmol/100ml)) compared with the short term stored Hon-mirin (431.1 Trolox eq. (μmol/100ml)). The relationship whereby antioxidant activities and the color intensity of Hon-mirin increase depending on the storage period was confirmed with Hon-mirin produced by small scale in our laboratory. The numerical value of antioxidant activities per color intensity (Trolox eq./OD^430nm/100) decreased with the storage period of Hon-mirin, and in the purified color substance, that value converged at 1.92∼5.72 (average: 3.55).
The molecular weight of the purified color substances isolated from Hon-mirin stored for 3 years or for 10 years was estimated as 26-43KDa and 34-57KDa, respectively. Molecular weights and antioxidant activities of color substances increased depending on the storage periods of Hon-mirin. It was concluded that melanoidin contributes to the antioxidant activities of stored Hon-mirin.

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To search for an O-methyltransferase gene of koji-mold involved in the conversion of 2,4,6-trichlorophenol (TCP) to 2,4,6-trichloroanisole (TCA, a main cause of a musty/moldy off-odor), we performed gene disruptions in Aspergillus oryzae and screened a disruptant weakened in the conversion ability. First, 76 genes assigned as SAM-dependent methyltransferase or O-methyltransferase were extracted from the Aspergillus oryzae RIB40 genome database. Among them, 34 genes were individually disrupted. Rice-koji was then made using the resulting disruptants in the presence of TCP. The conversion ability of TCP to TCA in the rice-koji of the AO080521000231 disruptant was much lower (12%) than that of non-disrupted transformant while the rice-koji retained sufficient enzyme productivities of α-amylase, glucoamylase, acid carboxypeptidase, and acid protease. These results suggest that AO080521000231 encodes the primary O-methyltransferase involved in the conversion of TCP to TCA.

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