The inhibitor of tyrosinase activity in black rice bran was investigated. The methanol extract from black rice bran was re-extracted with hexane, chloroform, ethyl acetate, or water. The ethyl acetate extract had the most potent inhibition against tyrosinase activity by 80.5% at a concentration of 0.4 mg/mL. Inhibitory compound in the ethyl acetate fraction was isolated by silica gel column chromatography, and identified as protocatechuic acid methyl ester (compound 1) by GC, GC-MS, IR, and 1H and 13C NMR spectroscopy. Compound 1 inhibited 75.4% of tyrosinase activity at a concentration of 0.50 micromol/mL. ID(50) (50% inhibition dose) value of compound 1 was 0.28 micromol/mL. To study the structure-activity relationship, protocatechuic acid (2), vanillic acid (3), vanillic acid methyl ester (4), isovanillic acid (5), isovanillic acid methyl ester (6), veratric acid (7), and veratric acid methyl ester (8) were also assayed.

The components of the volatile oils from the straws of Oryza sativa L. (Onshinomai, Asamurasaki, Hinohikari) were analyzed by capillary GC/GC-MS. The quantification of volatile compounds in the oils was made by the internal standard method, using palmitic acid as reference substance. Palmitic acid was the most abundant component in these samples, followed by hexahydrofarnesyl acetone and phytol.

In the evaluation of the carcinogenicity or mutagenicity caused by environmental chemicals, it is quite important to determine factors present in our environment that may affect these activities. With the development of techniques for detecting possible environmental carcinogens and mutagens (1), it has been shown that ordinary diets contain many kinds of mutagens and antimutagens. Abstract: A methanol extract from black rice bran showed a suppressive effect of the SOS-inducing activity on the mutagen 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (furylfuramide) in the Salmonella typhimurium TA1535/pSK1002 umu test. The methanol extract was reextracted with hexane, chloroform, ethylacetate, butanol and water. The ethylacetate fraction showed a suppressive effect. Suppressive compounds in an acidic fraction of the ethylacetate fraction were isolated by silica gel column chromatography and identified as vanillic acid (1) and protocatechuic acid (2) by GC, GC/MS, IR and 1 H and 13 C NMR spectroscopy. Compounds 1 and 2 suppressed the furylfuramide-induced SOS response in the umu test. Compounds 1 and 2 suppressed 37.7 and 44.5% of the SOS-inducing activity on furylfuramide at a concentration of 1.20 mmol/mL. These compounds were assayed with other mutagens, 4-nitroquinolin 1-oxide (4NQO) and N-methyl-N -nitro-N-nitrosoguanidine (MNNG), which do not require liver metabolizing enzymes. In addition, compounds 1 and 2 were assayed with aflatoxin B 1 (AfB 1 ) and 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), which require liver metabolizing enzymes. These compounds showed suppressive effects of the SOS-inducing activity against furylfuramide, 4NQO, MNNG, AfB 1 and Trp-P-1. To research the structure-activity relationship, veratric acid (3) as a similar compound of 1 and methyl esters of 1,2 and 3 (1Me, 2Me and 3Me) were also assayed with all chemical mutagens. Compounds 1Me, 2Me and 3Me exhibited stronger suppressive effects of the SOS-inducing activity against all chemical mutagens than 1,2 and 3.

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