Antioxidant Activity and Antimutagenicity of Hom Nil Rice and Black Glutinous Rice

Abstract

Raw, cooked and fermented Hom-Nil rice and black glutinous rice (Oryza sativa) extracts were investigated for their antioxidant activity and antimutagenicity. Each rice extract exhibited high antioxidant activity. The antioxidant activity and total phenolic contents of black glutinous rice extracts were higher than that of Hom Nil rice extracts. In addition, antioxidant activity and total phenolic content of fermented rice extract was higher than those of both raw rice extract and the cooked rice extract respectively. These rice extracts were not mutagenic in the Ames test using Salmonella typhimurium strains TA98 and TA100 without metabolic activation at pH 3.0-3.4. After nitrite treatment, rice extracts exhibited their mutagenicity on both tester strains. Their antimutagenicity against nitrite-treated 1-aminopyrene was evaluated. Each rice extract possessed antimutagenic activity. The antimutagenicity of black glutinous rice extracts was higher than that of Hom Nil rice extracts. Fermentation might be a good process to increase the antimutagenicity. The protective effects of these rice extracts might be due to the presence of antimutagenic components that were supposed to be flavonoids which might scavenge of the toxic compounds or/and inhibit bacterial enzyme. Thus, the results from this study make such rice potentially useful in dietary antioxidant and chemoprevention.