Oxidative Stability of Bran Lipids from Rice Variety [Oryza sativa (L.)] Lacking Lipoxygenase-3 in Seeds

Abstract

Lipoxygenase-3 (LOX-3) is the major component among isozymes in rice seeds. Using the Thai rice variety Daw Dam, which lacks LOX-3 in its seed, and the Japanese rice varieties Koshihikari and Koganemochi, which have normal LOX-3 activity, the oxidative stability of lipids in rice bran fractions during storage at 4 and 37 °C was studied. Free fatty acid content in lipids differed between storage temperatures and peroxide value (POV) differed among varieties. Differences among varieties and between storage temperatures in carbonyl value (COV) in lipids were observed. The amounts of free linoleic and linolenic acids did not differ among varieties during storage at either temperature. POV and COV in Daw Dam were lower, however, than in the other two varieties. These results suggest that the peroxidation of unsaturated fatty acids occurs at lower levels in the Daw Dam bran fraction than in the varieties with LOX-3 in their seed. The effect of this lack of LOX-3 as it relates to rice grain stability is discussed. Keywords: Bran lipid; carbonyl compound; free fatty acid; lipoxygenase-3; peroxide; rice