Cholesterol-Lowering Effects of Rice Bran and Rice Bran Oil Fractions in Hypercholesterolemic Hamsters

Cereal Chem. 69(5):485-489 The effects of temperature of extraction and fractionation of rice bran significantly lower plasma and liver cholesterol and triglycerides were oil were evaluated alone or in combination with defatted rice bran (DFB) observed in those fed an FFB diet than in those fed a CC diet. A diet to determine the effects on their cholesterol-lowering potential in hyperconsisting of DFB in combination with degummed-dewaxed rice bran cholesterolemic hamsters. Diets containing full-fat rice bran (FFB), DFB oil resulted in significantly lower liver cholesterol levels than did the CC plus rice bran oil (extracted at 4 or 540C), and 540C-extracted rice bran diet, whereas DFB alone, rice bran oil extracted at either temperature, oil fractions (gum, wax, and degummed-dewaxed oil) at levels found or DFB plus gum or wax fractions were not significantly different from in FFB were fed to 23-day-old hamsters. All diets contained 10% total the respective corn oil controls. Only FFB lowered both plasma and dietary fiber, 9% fat, and 3% nitrogen. After 21 days, liver weights and liver cholesterol in hamsters. The data suggest that some of the cholesterolplasma and liver cholesterol and plasma triglycerides were significantly lowering properties of FFB are present when DFB is recombined with higher in animals fed a diet of 0.3% cholesterol with cellulose (CC) than degummed-dewaxed rice bran oil, but some active components appear in animals fed a cholesterol-free cellulose diet. In cholesterol-fed hamsters, to be either lost or are deactivated in the fractionation process. Hypocholesterolemic properties of rice bran, rice bran oil (RBO), and/ or their fractions have been observed in animal and human studies (Ayano et al 1980; Ishibashi and Yamamoto 1980; Suzuki 1982; Sharma and Rukmini 1986, 1987; Seetharamaiah and Chandrasekhara 1988, 1989; Raghuram et al 1989; Hegsted et al 1990; Kahlon et al 1990, 1991; Nicolosi et al 1991). Plasma and liver cholesterol lowering by full-fat rice bran (FFB) (stabilized or parboiled) and reductions in total liver cholesterol by defatted rice bran (DFB) plus RBO have been reported in hamsters (Kahlon et al 1990, 1991). Studies in rats have shown significant cholesterollowering effects with 10% RBO or its fractions, such as unsaponifiables (Sharma and Rukmini 1986, 1987), oryzanol (Seetharamaiah and Chandrasekhara 1988, 1989), or wax (Ishibashi and Yamamoto 1980). However, 10% RBO did not affect serum or hepatic lipids in rats (Edwards and Radcliffe, 1991). Hypocholesterolemic effects in rats were observed with hemicellulose (Aoe et al 1989) or insoluble fiber from DFB (Ayano et al 1980). Nicolosi et al (1991) reported the cholesterol-lowering effects of rice oil in monkeys; however, a 50% rice bran diet was not effective in treating hypercholesterolemic monkeys (Malinow et al 1976). In human studies, the consumption of 100 g of rice bran per day resulted in significant plasma cholesterol reductions (Hegsted et al 1990). Similar effects were observed when hyperlipidemic patients replaced customary cooking oil with RBO (Raghuram et al 1989). The addition of unpolished rice to a hypercholesterolemic diet resulted in significantly lower cholesterol elevations in humans (Suzuki 1982). Elsewhere, the consumption of 30 g of rice bran per day (Ranhotra et al 1989), 60 g of rice bran per day (Kestin et al 1990), or the use of brown rice rather than polished rice (Miyoshi et al 1986) had no significant hypocholesterolemic effects in humans. Previously reported data from our laboratory (Kahlon et al 1991) indicated that the cholesterol-lowering potential of FFB was not completely realized when hamsters were fed DFB and RBO (extracted at 540C) recombined in the ratio found in FFB. The cholesterol-lowering activity of FFB may be attributable to the presence of certain fiber and/or lipid components in their native state or in a specific proportion. The extraction of FFB at a lower temperature may result in the retention of cholesterol'Western Regional Research Center, U.S. Department of Agriculture, Agricultural Research Service, 800 Buchanan Street, Albany, CA 94710. 2 The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. American Association of Cereal Chemists, Inc., 1992. lowering components in the DFB and/ or RBO. Distribution of wax and gum fractions between DFB and RBO also would be altered when FFB is extracted at a lower temperature. This study was conducted to investigate the cholesterol-lowering effects of rice bran defatted at low (40C) or high temperature (540C), RBO extracted at low or high temperature, and RBO fractions (gum, wax, and degummed-dewaxed oil) extracted at 540C combined with defatted rice bran at levels found in FFB. The test animals were hypercholesterolemic hamsters. MATERIALS AND METHODS Male, 23-day-old Syrian golden hamsters (Simonsen Laboratories, Gilroy, CA) were kept individually in wire-bottom cages in a controlled environment (20-22°C, 60% rh, 12-hr light and dark cycles). Animals were assigned by selective randomization to 11 groups of 10 animals each, with treatment diets and water provided ad libitum for the 21-day feeding period. Feed consumption was measured twice a week and animals were weighed once a week. All animal procedures described were approved by the Animal Care and Use Committee of the Western Regional Research Center, USDA, Albany, CA, and conformed to the principles in "Guide for the Care and Use of Laboratory Animals" (Committee on Care and Use of Laboratory Animals 1985). Stabilized rice bran (Randall et al 1985) obtained from a local milling company was extracted by soaking the rice bran with six changes of hexane at a mean temperature of 40C for lowtemperature extraction and 540 C for high-temperature extraction. The lower temperature was obtained by mixing frozen rice bran with chilled hexane in a 40C room. The higher temperature resulted from pouring boiling hexane (650 C) over rice bran preheated to the same temperature and allowing the mixture to stand for 10 min (mean temperature 540C). Hexane was removed from the oil by distillation. A portion of oil extracted at 54°C was heated to 60°C with 1% added water, left overnight at room temperature, and then centrifuged at 20,000 X g for 20 min at 200 C to obtain the gum fraction. Degummed oil was refrigerated (4°C) for four days and centrifuged at 20,000 X g for 20 min at 40C to obtain the wax fraction. The dry matter contents of the gum and wax obtained were 96.2 and 94.9%, respectively. Defatted brans were desolventized by aerating overnight and heating at 1 10°C for 20 min. The original moisture content was maintained by adding water. Diet ingredients were analyzed for total dietary fiber (Prosky et al 1988), crude fat (AOAC 1990, method 920.39C), and nitrogen (Kjeldahl procedure). The composition of the full-fat and defatted rice brans is presented in Table I. All diets were formulated to contain 10% total dietary fiber, 9% fat, and 3% nitrogen. RBO fractions were incorporated in Vol. 69, No. 5,1992 485 the diets at the same concentration at which they were present in the crude oil in the FFB diet. Corn oil was used as the supplementary source of fat. The composition of the diets is shown in Table II. Two diets were cholesterol-free and contained either 10% cellulose (C) or 50% stabilized, full-fat rice bran (RB). The remaining diets contained 0.3% cholesterol and either 10% cellulose (CC); 10% cellulose plus 9% rice bran oil extracted at 540C (CCRO54); 10% cellulose plus 9% rice bran oil extracted at 4 C (CCRO4); 50% stabilized, full-fat rice bran (FFB); 41% defatted rice bran, 4 C (DFB4); 42% defatted rice bran, 540C (DFB54); or 42% defatted rice bran, 540C, plus either 0.9% rice bran oil gum (DFBG), 0.2% rice bran oil wax (DFBW), or 7.9% degummed-dewaxed rice bran oil (DFBO-WG). All diets were stored at 4° C. After 21 days, the animals were fasted for 16 hr and anesthetized with CO2 for sample collection. Blood was drawn by cardiac puncture using ethylenediaminetetraacetic acid dipotassium salt (0.3 mg/ ml plasma) as the anticoagulant and centrifuged at 1,300 X g for 20 min at 40C to obtain plasma. Livers were excised, rinsed with water, blotted, weighed, and kept on dry ice. Livers and plasma aliquots were stored at -70'C. Plasma samples were analyzed by enzymatic colorimetric procedures for cholesterol (Sigma diagnostic kit 352, Sigma Chemicals, St. Louis, MO) and triglycerides (Gilford diagnostic kit 232422, Gilford Systems, Oberlin, OH). Plasma values were determined using standard curves obtained by running several concentrations of calibrators TABLE I Composition of Rice Bran Fractions Total Dietary Fibera Nitrogen" Fatc (% dry (% dry (% dry Moisture Fraction matter) matter) matter) (%) Rice bran 19.91 2.17 17.96 6.88 Defatted rice bran (40C) 24.22 2.56 1.18 6.83 Defatted rice bran (540C) 24.11 2.59 0.44 7.47 aAnalyzed by the procedure of Prosky et al (1988). bAnalyzed by the Kjeldahl procedure. c Analyzed by ether extraction (AOAC 1990, method 920.39c). corresponding to the respective kits. Aliquots of liver were extracted by the procedure of Folch et al (1957) and analyzed for cholesterol and triglycerides as described previously (Kahlon et al 1990), using Sigma kit 352 for cholesterol and Sigma kit 405 for triglycerides. Liver values were determined from standard curves obtained by running National Bureau of Standards reference materials (cholesterol, SRM 911b; tripalmitin, SRM 1595) through the procedures as described for the samples. All samples were analyzed in triplicate. Data were statistically analyzed using Duncan's new multiple range test (Steel and Torrie 1960). A value of P < 0.05 was considered as the criterion of significance.