Influence of Growth Temperature on the Amounts of Tocopherols, Tocotrienols, and γ-Oryzanol in Brown Rice

Brown rice is a valuable source of lipid-soluble antioxidants including ferulated phytosterols (i.e., γ-oryzanol), tocopherols, and tocotrienols. To evaluate the impact of temperature on the accumulation of these compounds, seeds from six different rice lines grown to maturity in replicate greenhouses in Gainesville, FL, were analyzed. The lines represented Oryza sativa indica, O. sativa japonica, and Oryza glaberrima of different origins. Temperatures were maintained near ambient at one end of each greenhouse and at approximately 4.5 °C above ambient at the other end. γ-Oryzanols, tocopherols, and tocotrienols were extracted from whole seed (i.e., brown rice) and analyzed by HPLC. Tocotrienols and tocopherols varied widely between lines but changed only slightly with respect to temperature. In general, the proportions of α-tocotrienol and/or α-tocopherol increased at elevated temperature, whereas γ-tocopherol and γ-tocotrienol decreased. Six γ-oryzanol peaks, identified on the basis of absorbance maxima at 330 nm and HPLC−mass spectrometry, were quantified. The most abundant component was 24-methylenecycloartanyl ferulate, present at 40−62% of total. Its levels increased 35−57% at elevated temperature in five of six lines, accounting for most of the change in total γ-oryzanol. The results suggest that the physiological action of individual ferulated phytosterols should be investigated because their relative proportions in γ-oryzanol can change.

Keywords: Antioxidant; climate change; temperature; tocopherols; tocotrienols; oryzanol; Oryza sativa; Oryza glaberrima