Wax extraction and characterization from full-fat and defatted rice bran

Abstract

Rice bran oil (RBO) contains 3-4% waxes (rice bran wax, RBW), which are composed of wax esters (WE), hydrocarbons, and other minor constituents. Saponified rice bran wax esters (RBWE) generate fatty acids, long chain alcohols, and phytosterols. Phytosterols and long chain fatty alcohols (policosanol) are known to reduce serum cholesterol and inhibit hepatic cholesterol synthesis. The yields and RBWE contents of RBO and RBW extracted from full-fat RB (FFRB) and defatted RB (DFRB) were determined using 6 different conditions with Soxhlet and Microwave-assisted extraction (MAE). The compositions of WEs from RBO and RBW were also compared. RBW was obtained from RBO by winterization and solvent fractionation. WEs were separated by chromatographic methods, and analyzed as intact WE using a mass analyzer. After saponification of WE, alcohols, sterols, and fatty acids were analyzed by GC. Crude FFRBO yields were not significantly different among the extraction methods, while MAE (isopropanol, 120°C) showed significantly higher DFRBO yields. DFRBOs had higher concentrations of crude RBW than FFRBOs, and hexane extractions showed higher crude RBW yields. Crude RBW yields from FFRB were higher than from DFRB, while refined RBW yields from FFRB and DFRB were more similar. The refined RBW yields by hexane extractions were much higher than those by isopropanol extractions, and DFRBOs showed higher refined RBW yields than FFRBOs. HPLC results indicated that most WE was contained in RBO raffinate, and around half of the refined RBW consisted of WE. The mass spectra showed that there were more long chain species in WE from RBW. GC results identified C13-C22 fatty acids and the major alcohols in WE from RBW appeared as C32 and C34. Six sterols were identified in WE from RBO. Results indicate that MAE with hexane is more efficient than Soxhlet for RBWE extraction. DFRB appears to have significant RBW content, which would make it an excellent source for potential commercial exploitation. This study established an efficient procedure for WE analysis as well as for alcohol/sterol separations from RBW for further biological experiments.