Mutagenicity and Antimutagenicity of Hydrophilic and Lipophilic Extracts of Thai Northern Purple Rice


Purple rice (Oryza sativa L. var. indica) cv. Kum Doisaket is cultivated in northern Thailand. This studyevaluated the mutagenic and antimutagenic properties of hydrophilic and lipophilic components of purple riceusing the Ames test. The seed and hull of purple rice were extracted with hexane, methanol, ethanol, and water.The methanol extracts had the highest amounts of phenolic acids and flavonoids, while the hexane extractscontained large amount of tocols and γ-oryzanol. None of the extracts were mutagenic in Salmonella typhimuriumstrains TA98 and TA100. The hexane extract of rice hull and the methanol extract of rice seed were stronglyeffective against aflatoxin B1- and 2-amino-3, 4 dimethylimidazo (4, 5-f) quinoline-induced mutagenesis, whileaqueous extracts showed weakly antimutagenic properties. All extracts with the exception of aqueous extractsenhanced the number of revertant colonies from benzo (a) pyrene induced-mutagenesis. None of the extractsinhibited mutagenesis induced by the direct mutagens 2-(2-furyl)-3-(5-nitro-2-furyl)-acrylamide and sodiumazide. The hull extracts showed more potent antimutagenicity than the seed extracts. Based on a chemicalanalysis, γ-oryzanol and γ-tocotrienol in the hull and cyanidin-3-glucoside and peonidin-3-glucoside in the seedare candidate antimutagens in purple rice. The antimutagenic mechanisms of purple rice might be related toeither modulation of mutagen metabolizing enzymes or direct attack on electrophiles. These findings supportedthe use of Thai purple rice as a cancer chemopreventive agent.