Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 20, 2010
Publication Date: February 22, 2010
Citation: Min, B., Mcclung, A.M., Chen, M. 2010. Phytonutrients in rices of different bran color. 33rd ice Technical Working Group Meeting Proceedings, Feb. 22-25, 2010. CD ROM. Technical Abstract: The consumption of the whole grain has been linked to the reduced incidence of chronic (cancer, diabetes, cardiovascular disease) and various inflammatory diseases. The phytonutrients/antioxidants contained in the whole grain, specifically in the bran layer, contribute to these health benefits. Rice bran is a rich source of lipophilic antioxidants, including tocopherols, tocotrienols, and '-oryzanols. Many studies have reported that these lipophilic phytochemicals have strong antioxidant capacities and show various health-beneficial effects, including reduction of total plasma cholesterol, increase of HDL cholesterol level, and prevention of cancer and cardiovascular disease. In addition, the simple phenols extracted from light brown colored rice have a potential chemopreventive effect. Studies have shown that the majority of phenolic compounds in cereals are actually bound to cell-wall components and cannot be extracted by solvents. These bound phenolic compounds can be liberated by digestive enzymes and micro-flora in the colon providing their health-protective effects on site and/or to other body parts after absorption. A recent study showed that, in an animal model system, diets supplemented with the cell wall-bound fraction of rice bran reduce hypertension, hyperlipidemia, and hyperglycemia. Recent interest has been focused on pigmented rice, and especially on the purple and red colored bran rice varieties because of their abundance of anthocyanins and proanthocyanidins, respectively. These sub-groups of phenolics have strong antioxidant capacities related to health-promoting potentials such as obesity prevention, anti-cardiovascular disease, anti-inflammation, and anti-cancer effects. The objective of this study was to comprehensively determine the profiles of lipophilic, hydrophilic (free), and insoluble, bound phytochemicals in different colored rice brans (1 white, 2 light brown, 2 brown, 1 red, and 2 purple). Three antioxidant-capacity assays based on different mechanisms were used for evaluating the antioxidant capacity of the hydrophilic (free) and insoluble-bound fractions: the DPPH radical scavenging capacity, the oxygen radical absorbance capacity (ORAC), and the iron chelating capacity. Concentration ranges of tocols (sum of homologs of tocopherols and tocotrienols) and '-oryzanols were 319-443 and 3861-5911 µg/g bran, respectively. The total anthocyanin concentration in purple rice bran (IAC600; 33.68 mg kuromanin equivalents/g dry wt basis) was 4 times higher than that in blueberry (P<0.05) (dry wt basis). Total proanthocyanidin concentration was the highest in red rice bran (IITA119; 22.61 mg (+)-catechin equivalents/g dry wt basis) (P<0.05) and small in other rice brans, broccoli, and blueberry (0.09-1.31). Red and purple rice brans had 3-25 times higher total phenolic and flavonoid concentrations and total DPPH radical capacity, and ORAC (sum of those in free and bound phenolic fractions) than did blueberry, broccoli, or light-colored rice bran. The bound phenolic fraction accounted for more than 45% of total hydrophilic ORAC antioxidant capacity in bran of the light color bran rice. The bound phenolic fraction of red and purple rice brans had higher bound phenolic and flavonoid concentrations and total antioxidant capacities than that of light-colored rice bran (P<0.05). Converting the concentration of anthocyanins in bran to cooked rice (without accounting for any cooking effect), the purple rice of IAC600 would contain 170 mg of total anthocyanins in 100 grams of cooked rice versus 124 mg/100 g in fresh blueberry. In conclusion, whole grain rice is an excellent food source with well balanced macro and micro-nutrients and phytonutrients, and the red and purple rices are exceptionally high in phytonutrients, with levels comparable to blueberry, the dietary phytonutrient yardstick. Whole grain rice merits increased use as table rice and in nutraceutical and functional food applications.