The antioxidant activities of vitamin E (alpha-tocopherol, alpha-tocotrienol, gamma-tocopherol, and gamma-tocotrienol) and gamma-oryzanol components (cycloartenyl ferulate, 24-methylenecycloartanyl ferulate, and campesteryl ferulate) purified from rice bran were investigated in a cholesterol oxidation system accelerated by 2,2′-azobis(2-methylpropionamidine) dihydrochloride. All components exhibited significant antioxidant activity in the inhibition of cholesterol oxidation. The highest antioxidant activity was found for 24-methylenecycloartanyl ferulate, and all three gamma-oryzanol components had activities higher than that of any of the four vitamin E components. Because the quantity of gamma-oryzanol is up to 10 times higher than that of vitamin E in rice bran, gamma-oryzanol may be a more important antioxidant of rice bran in the reduction of cholesterol oxidation than vitamin E, which has been considered to be the major antioxidant in rice bran. The antioxidant function of these components against cholesterol oxidation may contribute to the potential hypocholesterolemic property of rice bran.
Separations of lipid antioxidants, tocopherols (T) and tocotrienols (T3), on octylsilica (OS), octadecylsilica (ODS), phenylsilica, or silica were studied by capillary electrochromatography (CEC)-UV detection. The homologues and isomers of the vitamin E-active compounds were best separated with an OS column. CEC with an ODS column tended to yield broad peaks with poor resolution. Among the various mobile phases evaluated, [acetonitrile-methanol (64:36)]-[25 mM tris(hydroxymethyl)aminomethane, pH 8] (95:5) eluent systems produced the most satisfactory results. Under these conditions, a baseline separation of an 11-component mixture was obtained with elution order similar to that observed in reversed-phase HPLC: deltaT3 > (gamma+beta)T3 > alphaT3 > epsilonT > (delta+zeta2)T > (gamma+beta)T > alphaT > alphaT-acetate. CEC of the antioxidant acetates led to separations inferior to those of the parent compounds. Effects of CEC experimental variables (e.g., mobile phase solvents and buffers, stationary phases and electric field) on analyte separations were assessed in the context of resolution factors and retention factors.
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