Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2007
Publication Date: 8/29/2007
Citation: Britz, S.J., Prasad, P., Moreau, R.A., Allen Jr, L.H., Kremer, D.F., Boote, K.J. 2007. Influence of growth temperature on the amounts of tocopherols, tocotrienols, and y-oryzanol in brown rice. Journal of Agricultural and Food Chemistry. 55:7559-7565.
Interpretive Summary: Rice is the most important grain crop in the world and, although grown in tropical or warm climate regions, it is generally grown in climates near its optimum temperature. Rising global temperatures are therefore a concern. Tocopherols, tocotrienols, and gamma-oryzanol are classes of fat-soluble compounds found in rice bran with anti-oxidant activity that may be important for the adaptation of rice seeds to environmental stress and that may also be involved in the ability of rice bran oil to lower blood cholesterol levels. Therefore, it is important to determine if increases in temperature affect the amounts of these compounds. Six lines of rice from North America, Europe, Asia, and Africa were grown to maturity in greenhouses at ambient or elevated temperature (+5 deg. C). The lines represented 2 different species of cultivated rice, Oryza sativa and O. glaberrima, as well as both the indica and japonica ecotypes of O. sativa. The content of tocopherols and tocotrienols differed widely between lines but were not greatly altered by temperature. Gamma-oryzanol, on the other hand, increased 30-40% in 4 of the 6 lines with increased temperature. Most of the increase resulted from changes in 2 components, cycloartenol ferulate and 24-methylene-cycloartanol, which belong to a class of plant sterols thought to be relatively ineffective in cholesterol control but which are good anti-oxidants. Thus, the change in gamma-oryzanol composition may be good for plants but not helpful for people seeking alternate sources of healthy fats in their diets. This information should be useful for plant scientists and breeders as well as nutritional scientists and policy makers.
Technical Abstract: Brown rice is a valuable source of lipid-soluble antioxidants including ferulated phytosterols (i.e., gamma-oryzanol), tocopherols, and tocotrienols. To evaluate the impact of temperature on the accumulation of these compounds, we analyzed seeds from 6 different rice lines grown to maturity in replicate greenhouses in Gainesville, FL. The lines represented Oryza sativa indica, O. sativa japonica, and O. glaberrima of different origins. Temperatures were maintained near ambient at one end of each greenhouse and at approximately 4.5 deg. C above ambient at the other end. Gamma-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 alpha-tocotrienol and/or alpha-tocopherol increased at elevated temperature, while gamma-tocopherol and gamma-tocotrienol decreased. Six gamma-oryzanol peaks, identified on the basis of absorbance maxima at 330 nm and HPLC-mass spectrometry, were quantified. The most abundant component was 24-methylene cycloartanyl ferulate, present at 40-62 percent of total. Its levels increased 35-57 percent at elevated temperature in 5 of 6 lines, accounting for most of the change in total gamma-oryzanol. The results suggest that the physiological action of individual ferulated phytosterols should be investigated, since their relative proportions in gamma-oryzanol can change.