A rapid procedure for analysing rice bran tocopherol, tocotrienol and γ-oryzanol contents

Abstract

Tocopherols, tocotrienols and γ-oryzanol compounds are phytochemicals with antioxidant activities and potential 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. Methods that can rapidly and reliably extract and quantify their contents in rice bran or whole rice kernel are necessary for breeding programs. A simple, one-step equilibrium extraction procedure coupled with reversed-phase (RP) HPLC is presented here. The one-min equilibrium extraction at a 1:60 (w/v) ratio of rice bran to methanol recovered 92 to 102% 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. A modified, mobile-phase gradient with 10% of aqueous phase for the first 3-min eliminates all the methanol-soluble interfering compounds. This extraction method has the following advantages over the currently available methods: speed, no special extraction instrumentation is needed; and the extraction solvent, methanol, is compatible with subsequent quantification via RP-HPLC.