Preparative separation of γ-oryzanol from rice bran oil by silica gel column chromatography

gamma-Oryzanol is considered to be an important fraction in rice bran oil. Due to the low concentration levels (1-3%) of gamma-oryzanol in crude rice bran oil (CRBO), isolation and purification would be necessary before practical usage. This study developed an efficient and easy-to-scale-up chromatographic separation method for the production of gamma-oryzanol. First, the CRBO was prepared using a Soxhlet extractor operated under an optimal extraction condition (using 130 mL of hexane for 2 hr per 15 g rice bran). The extraction yield was 16-18% (w/w) and the purity of gamma-oryzanol was 2.4-3.0% (w/w). Then gamma-oryzanot in the CRBO was purified by preparative elution chromatography under the normal phase mode. Column operation was optimized by using a silica gel column packed with small particles (12 mum) and operated by a three-step gradient elution mode, where the mobile phase composition of hexane/ethyl acetate was from 90 : 10 or 85 : 15 to 50 : 50 v/v to pure ethyl acetate. The injection amount was increased as large as possible but had to be within its solubility limit (about 30-35 wt/vol%). The system performance achieved was as follows: the recovery of gamma-oryzanol was about 90 + %, the purity of gamma-oryzanol was up to 90-98% (the ratio of concentration was about 30 + % times), but the productivity was only about 10 mg per injection, which needs to be further increased by scaling-up the column system.