J. Samuel Godber, Zhimin Xu, Maren Hegsted and Terry Walker
Rice bran and its oil contain large concentrations of several compounds that could potentially prevent chronic diseases such as coronary heart disease and cancer. The LSU AgCenter has been actively engaged in identifying, extracting, purifying and evaluating the functionality of several of these compounds. The focus has been on vitamin E, especially the tocotrienols, and oryzanol, which contains a high proportion of phytosterols. Recent efforts have included an evaluation of the potential of supercritical carbon dioxide as a more appropriate extraction medium, use of cell culture to evaluate cellular antioxidant activity, and an evaluation of the potential of oryzanol to reduce bone loss in rats whose ovaries had been removed as a model of postmenopausal women.
Functional foods are defined as foods, or food components, that provide health benefits beyond their nutritional value. Functional foods may reduce chronic diseases such as coronary heart disease or cancer. One of the most well-recognized functional foods is garlic, which has been found to reduce serum cholesterol and possibly prevent certain types of cancer. Oat bran, soy protein and red wine are also viewed as functional foods, to name just a few. For several years, ongoing research in the LSU AgCenter has focused on rice bran as a potential human food ingredient.
Rice bran and antioxidants
Our initial studies with rice bran focused on stabilizing it against lipid degradation that leads to flavor problems. During these studies, we realized rice bran had high levels of both tocopherols and tocotrienols, which comprise vitamin E and act as antioxidants in our body, and also had high levels of a mixture of compounds referred to collectively as oryzanol. Oryzanol components are complex compounds that can act as an antioxidant and can improve solubility in cell membranes and potentially lower cholesterol by competitive inhibition of absorption and synthesis. Our recent efforts have focused on recovery of these compounds from rice bran, especially oryzanol.
Conditions were optimized for the extraction of oryzanol using a process called supercritical fluid extraction (SFE) with carbon dioxide as an extraction solvent. This state-of-the-art extraction process has been suggested as a means to obtain high-value functional components from low-value agricultural byproducts such as rice bran. We demonstrated the viability of this approach because we were able to obtain a highly concentrated extract of oryzanol. We now have a pilot scale extractor that will allow us to scale up the extraction process to demonstrate the commercial potential of this approach.
To evaluate individual components of the oryzanol mixture, we employed a sophisticated separation process using a preparative scale chromatograph. We were able to purify the three major fractions of oryzanol: cycloartenyl ferulate, 24-methylene cycloartanyl ferulate and campesteryl ferulate. Separation conditions were developed that would permit economical purification of these three components.
Rice bran components reduce cholesterol oxidation
The possibility that rice bran components could reduce the effects of oxidation both in food and in our bodies is one of the most exciting aspects of rice bran as a functional food. The causes associated with almost all chronic disease can be traced to the effects of oxidants, both in the environment, including food, and in our bodies. Cholesterol oxidation products have been suggested as a major cause of heart disease. The antioxidant activities of four of the vitamin E and three oryzanol components purified from rice bran were investigated in a chemical model of cholesterol oxidation. All components exhibited significant antioxidant activity in the inhibition of cholesterol oxidation. All three oryzanol components were higher than any of the four vitamin E components.
A second approach to the potential effect of these components on oxidation and cholesterol dynamics has been initiated using cell culture techniques. Cell membrane integrity of living cells was used to test the protective effect of oryzanol compared with the vitamin E component alpha-tocopherol against an oxidizing agent. Oryzanol was found to maintain greater cell survival than alpha-tocopherol, and both were considerably higher than the untreated control.
Rice bran and osteoporosis
Osteoporosis affects more than 20 million older Americans, with the number increasing every year. This bone loss can be greatly reduced with hormone replacement therapy for post-menopausal women. Unfortunately, many women do not to use hormones because of side effects such as increased risk for cancer. This has led to great interest in identifying functional foods that can reduce bone loss naturally.
Ovariectomized rats are used as a model for postmenopausal osteoporosis and typically lose substantial bone mineral density after an ovariectomy. The addition of a 7 percent oryzanol rice bran oil concentrate to the diets of ovariectomized rats was slightly protective in reducing bone loss at several bone sites. This protective effect was strongest for the tibia, where the bone density was 5 percent greater for rats fed rice bran oil concentrate than the control rats. The beneficial effect of the rice bran oil concentrate appeared to be primarily on cortical bone in the long bones, not on the trabecular bone in vertebra. Crystalline oryzanol and crystalline oryzanol dissolved in corn oil had no effect on bone mineral density. This suggests that either the oryzanol as it occurs naturally in rice bran oil is more biologically active than crystalline oryzanol or that something else in the rice bran oil is affecting bone density positively.
Rice bran as a functional food
Rice bran and its oil may be among the most important sources of functional food components available in the world today, considering rice bran’s vast worldwide production and the fact that it is poorly used for human food consumption. Our efforts are revealing potential functional applications for rice bran in human foods. The importance of these efforts is becoming more critical because of the introduction to U.S. markets of margarine and other products, such as Benecol, containing compounds reputed to lower serum cholesterol that are similar to the oryzanol components under study.
Thus, the establishment of the therapeutic potential for specific oryzanol components could lend credence to similar applications with rice bran oil or concentrates.
The potential role of rice bran components in bone health is a critical area of research and expands our potential for reducing osteoporosis with functional foods. More study is needed to identify the active elements in rice bran oil beneficial in reducing bone loss and determine their mode of action. The rice bran oil concentrate appears to act primarily on preserving the slow turn-over cortical bone in the long bones. Other functional foods such as soy protein act on the rapid turnover trabecular bone in vertebrae. This leads to the possibility that the two in combination could provide even greater bone benefits in preserving both cortical and trabecular bone in the elderly to reduce osteoporotic fractures.
(This article appeared in the fall 2002 issue of Louisiana Agriculture.)