Purification and identification of rice bran oil fatty acid steryl and wax esters

Fatty acid steryl esters (FASE) and wax esters (WE) of rice bran oil (RBO) have potential applications in cosmetic, nutraceutical, and pharmaceutical formulations. FASE and WE were extracted from RBO by a modified Soxhlet extraction using hexane as the solvent. FASE and WE were then separated by storage in acetone at 10°C for 24 h. The FASE fraction was further purified by silica gel column chromatography. The contents and compositions of FASE and WE, as well as their saponified products, were identified by CC and CC-MS. The identification of FASE and WE was carried out by comparing the retention time of GC peaks and mass spectral analysis with standards synthesized in our laboratory. FASE and WE accounted for ca. 4.0% of crude RBO, of which 2.8-3.2% and 1.2-1.4% are FASE and WE, respectively. GC-MS of FASE showed five major peaks. Major FA in the FASE fraction were linoleic acid and oleic acid, which were esterified with 4-desmethyl, 4-monomethyl, and 4,4-dimethyl sterols. The contents of 4-desmethylsterol, 4-monomethylsterol, and 4,4-dimethylsterol esters in crude RBO were 76.1, 8.7, and 15.1%, respectively. WE of RBO consisted of both even and odd carbon numbers ranging from C₄₄ to C₆₄. The major constituents were saturated esters of C₂₂ and C ₂₄ FA and C₂₄ to C₄₀ aliphatic alcohols, with C₂₄ and C₃₀ being the predominant FA and fatty alcohol, respectively. The advantages of using a modified Soxhlet extraction over column chromatography are less solvent usage and larger sample size per batch with shorter operation time.