Genotype and environment effects on tocopherol, tocotrienol, and γ-oryzanol contents of Southern US rice

Rice bran contains phytochemicals such as E vitamers (i.e., tocopherols and tocotrienols) and the gamma-oryzanol fraction that reportedly may have positive effects on human health. Brown rice, rice bran, and rice bran extracts are therefore attractive candidates for use in the development of functional foods. The objectives of this project were to quantify the effects of genetics versus environment on the tocopherol, tocotrienol, and gamma-oryzanol contents of Southern U.S. rice and to determine associations between the levels of these phytochemicals. Seven rice cultivars grown in four states during two years were studied. Averaged across all samples, the content of alpha-tocotrienol > gamma-tocotrienol > alpha-tocopherol > gamma-tocopherol, and the tocopherols and tocotrienols were 27.5 and 72.5% of the total E vitamer content, respectively. Total E vitamer content ranged from 179 to 389 mg/kg and gamma-oryzanol from 2,510 to 6,864 mg/kg, A low correlation between total E vitamer and gamma-oryzanol contents suggests that to obtain rice bran with high levels of both of these fractions, new cultivars would need to be produced using hybridization and selection. In general, growing environment had a greater effect on E vitamer and gamma-oryzanol levels than did genotype. Therefore, rice breeders selecting genotypes with optimized levels of E vitamers and gamma-oryzanol will need to grow their breeding material in multiple years and locations.