A rapid procedure for analyzing rice bran tocopherol, tocotrienol and G-oryzanol contents

Authors: Chen, Ming Hsuan; Bergman, Christine

Submitted to: Journal of Food Composition and Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2003
Publication Date: 4/1/2005
Citation: Chen, M., Bergman, C.J. 2005. A rapid procedure for analyzing rice bran tocopherol, tocotrienol and g-oryzanol contents. Journal of Food Composition and Analysis. 18:139-151.

Interpretive Summary: Rice bran contains phytochemicals such as tocopherol, tocotrienol and gamma-oryzanol fractions that reportedly have positive effects on human health. The tocotrienol-rich rice bran fraction, in a human study, lowered total serum cholesterol and improved the ratio of LDL cholesterol to HDL cholesterol. The gamma-oryzanol fraction extracted from rice bran, when tested in animal feeding studies, lowered total serum cholesterol, had anti-inflammatory activity, and had a tumor inhibitory effect. These health benefits suggest that brown rice, rice bran and its extracts have potential to be used in or as functional foods. Studies have shown that the contents of these phytochemicals in rice bran vary among southern US cultivars. Thus, breeding cultivars for higher contents of these phytochemicals is feasible and beneficial. Methods that can rapidly and reliably extract and quantify phytochemical contents in rice bran or whole grain are necessary for the plant breeding process. The method presented here is a simplified one-step extraction method and allowing the extract to be directly analyzed with decreased effort and time. The consistency and recovery of this method is comparable with other available methods and is suitable for screening a large number of rice varieties.

Technical Abstract: Tocopherol, tocotrienol and gamma-oryzanol are phytochemicals with antioxidant activities and other additional health benefits. Their contents and isomer ratios in rice bran vary among southern US cultivars suggesting that breeding for higher contents or a favorable ratio of these phytochemicals is feasible and beneficial. Methods that can rapidly and reliably extract and quantify their contents in rice bran or whole rice kernel are necessary for the breeding program. A simple, one-step equilibrium extraction procedure coupled with reversed-phase (RP) HPLC is presented here. The one minute equilibrium extraction at a 1:60 (w/v) rice bran to methanol ratio recovered 92 to 102 percent of the target phytochemicals relative to those of repeated, non-saponified, direct solvent extraction methods. At this 1:60 ratio of bran to solvent, isopropanol and methanol are superior extraction solvents relative to hexane. The modified, HPLC mobile-phase gradient with 10 percent of aqueous phase (1 percent of acetic acid) during the first three minutes eliminates all the methanol-soluble interfering compounds. In conclusion, this extraction method has advantages over the currently available methods due to its speed, no special extraction instrumentation is needed; and the extraction solvent, methanol, is compatible with subsequent quantification via RP-HPLC.