Effects of nitrogen fertilization rate on tocopherols, tocotrienols and γ-oryzanol contents and enzymatic antioxidant activities in rice grains.

Tocopherols (Toc), tocotrienols (T3) and γ-oryzanol (GO), major bioactive compounds of rice, are known to possess potent antioxidant activity. In this study, the objective was to determine the effects of nitrogen fertilization rate on contents of Toc, T3 and GO, and activities of enzymatic antioxidants in rice grains. Experiments were conducted on five different levels of nitrogen fertilization. Among the different treatments, grains of 2 N (two-fold of the recommended amount of nitrogen fertilizer) treatment showed the highest total Toc, total T3, α-T3, β-Toc, γ-Toc and γ-T3 levels, whereas 0 N (no treatment) group had the highest GO content. Increasing nitrogen fertilization significantly reduced the rice grain catalase and ascorbate peroxidase, but not the superoxide dismutase activities. Under 0 N and 0.5 N (low N fertilization) treatments, malondialdehyde and HO contents in rice grains were significantly higher than that of other treatments. These results suggest that a two-fold increase in nitrogen fertilization favor the accumulation of Toc and T3 but not GO in rice grains.