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.

High-purity gamma-oryzanol was obtained from crude rice bran oil using a normal-phase preparative scale HPLC. A reverse-phase HPLC method was used for separating the individual components of gamma-oryzanol present in rice bran oil. Ten fractions were isolated and collected using the reverse-phase HPLC method, and their structures were identified. Identification was accomplished using GC/MS with an electron impact mass spectrum after components were transformed into trimethylsilyl ether derivatives. The 10 components of gamma-oryzanol were identified as Delta(7)-stigmastenyl ferulate, stigmasteryl ferulate, cycloartenyl ferulate, 24-methylenecycloartanyl ferulate, Delta(7)-campestenyl ferulate, campesteryl ferulate, Delta(7)-sitostenyl ferulate, sitosteryl ferulate, compestanyl ferulate, and sitostanyl ferulate. Three of these, cycloartenyl ferulate, 24-methylenecycloartanyl ferulate, and campesteryl ferulate, were major components of gamma-oryzanol.

The effects of solvent-to-bran ratio (2:1 and 3:1, w/w), extraction temperature (40 and 60~ and time (5, 10, 15, 20, and 30 rain) were studied for hexane and isopropanol extraction. Increasing the solvent-to-bran ratios and extraction temperature increased the amounts of crude oil, vitamin E and oryzanol recovered for both solvents. An extraction time of 15 min was sufficient for optimum crude oil, vitamin E, and oryzanol extraction. Preheated isopropanol (3:1 solvent/bran ratio and 60~ extracted less crude oil (P < .05) but more vitamin E (P < .05) and similar amounts of oryzanol (P > .05) relative to preheated hexane. The data suggest that isopropanol is a promising alternative solvent to hexane for extraction of oil from stabilized rice bran.

Rice bran was extruded at 110, 120, 130, and 140ЊC with post extrusion holding times of 0, 3, and 6 min and stored at ambient temperatures for 1 yr. Holding time had no effect (pϾ0.05) on hydrolytic stability whereas 110ЊC was slightly less effective in maintaining hydrolytic stability. Increased holding times reduced (pϽ0.05) total vitamin E content. Oryzanol concentration was lower (pϽ0.05) only after 6 min holding time. Oryzanol was relatively more stable to extrusion temperatures than vitamin E. The highest retentions of total vitamin E and oryzanol were found in raw rice bran during storage. Increased extrusion temperatures reduced the retention of vitamin E and oryzanol during storage.

Whole rice contains several fat‐soluble phytochemicals such as tocopherols, tocotrienols, and γ‐oryzanol which have been reported to possess beneficial health properties. This study was conducted to determine whether brown rice belonging to indica and japonica subspecies were distinguishable from each other regarding the concentration of these compounds by analyzing 32 genotypes. The fat‐soluble compounds were analyzed by normal‐phase HPLC in a single run. The variability of the compounds analyzed was high, but the mean content of γ‐oryzanol across all samples was significantly higher (P < 0.01) in japonica (246.3 mg/kg) than in indica rice (190.1 mg/kg). Similar differences were found for total vitamin E contents which were 24.2 mg/kg in japonica and 17.1 mg/kg in indica rice, respectively. In japonica rice, α‐tocopherol, α‐tocotrienol, and γ‐tocotrienol were the most abundant homologs, while in indica rice the most abundant were γ‐tocotrienol, α‐tocopherol, and α‐tocotrienol. A significant Pearson coefficient (0.80, P < 0.001) between α‐tocopherol and α‐tocotrienol levels was found, independent of the subspecies. Both compounds were positively correlated to total tocols and γ‐oryzanol contents. Although more studies are needed to evaluate the interference of growing rice in different environments and multiple years, the present study provided information on natural variations of the vitamin E isomers and the γ‐oryzanol contents in different rice genotypes.

No abstract

The soy isoflavones daidzin, glycitin, and genistin were purified from defatted soy flour using preparative-scale reverse-phase HPLC. The stabilities of the three isoflavones at different heating temperatures were investigated. Daidzin, glycitin, and genistin were lost at a rate of 26, 27, and 27% of their original concentration, respectively, after 3 min at 185 degrees C. At 215 degrees C, decreases of daidzin, glycitin, and genistin were 65, 98, and 74% after 3 min and 91, 99, and 94% after 15 min, respectively. The order of the thermal stabilities, from lowest to highest, was glycitin, genistin, and daidzin. Acetyl daidzin and acetyl genistin, daidzein, glycitein, and genistein were produced during heating at temperatures above 135 degrees C. The rate of binding of an acetyl group to form acetyl daidzin and acetyl genistin from daidzin and genistin was higher than the rate of loss of a glucoside group to form daidzein and genistein. However, acetyl daidzin and acetyl genistin decreased sharply at temperatures above 200 degrees C, while daidzein, glycitein, and genistein were relatively stable over 30 min. The stability of daidzein was higher than that of glycitein or genistein.

Organic solvents were compared with supercritical CO 2 relative to efficiency for extracting lipid and γ-oryzanol from rice bran. A solvent mixture with 50% hexane and 50% isopropanol (vol/vol) at a temperature of 60°C for 45-60 min produced the highest yield (1.68 mg/g of rice bran) of γ-oryzanol among organic solvents tested. The yield of γ-oryzanol without saponification was approximately two times higher (P < 0.05) than that with saponification during solvent extraction. However, the yield (5.39 mg/g of rice bran) of γ-oryzanol in supercritical fluid extraction under a temperature of 50°C, pressure of 68,901 kPa (680 atm), and time of 25 min was approximately four times higher than the highest yield of solvent extraction. Also, a high concentration of γ-oryzanol in extract (50-80%) was obtained by collecting the extract after 15-20 min of extraction under optimized conditions. Paper no. J9443 in JAOCS 77, 547-551 (May 2000).KEY WORDS: Supercritical fluid extraction, rice bran, γ-oryzanol.γ-Oryzanol is an important fraction, along with tocotrienols and other unsaponifiables, relative to the hypocholesterolemic effects of rice bran oil (1-4). Since γ-oryzanol is readily dissolved in organic solvents, hexane has typically been used in extraction of γ-oryzanol from rice bran (5-7). However, all components of γ-oryzanol contain an alcohol group in the ferulate portion, which gives rise to a relatively high polarity. These components may also be soluble in more polar solvents, such as isopropanol and ethyl acetate, as well as nonpolar solvents, such as hexane or heptane. The polarity of extraction solvent may significantly affect the extractability of γ-oryzanol from rice bran. The effects of various solvents on the yield of γ-oryzanol in extraction have not been reported. Another unclear factor in extraction is the effect of saponification on the efficiency of extraction. In previous studies, saponification was performed prior to the solvent extraction (5-7). Saponification, which is important for reducing interfering lipids and for breaking down the matrix of rice bran for improved recovery of extraction, may have a negative effect on the extraction of γ-oryzanol. It is possible that the ester bond between the ferulate and triterpene components of γ-oryzanol is cleaved under alkali conditions. This could result in the decomposition of γ-oryzanol and decrease the yield of extraction. The effect of saponification on the yield of γ-oryzanol in solvent extraction has not been reported. Supercritical fluid extraction (SFE) of lipid has received attention as an alternative to organic solvent extraction and has been shown to be an ideal method for extracting certain lipids (8-13). Carbon dioxide is changed to its supercritical fluid state beyond the supercritical point (73 atm, 31°C). Supercritical CO 2 extraction is nontoxic, nonflammable, and simple in operation when compared with traditional extraction using solvents. These advantages may make supercritical carbon dioxide extraction ideal in the food and pharmaceutic...