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Title: Phytochemicals and antioxidant capacity in rice brans of different color

Author
item Min, Byungrok
item McClung, Anna
item Chen, Ming Hsuan

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2010
Publication Date: 2/1/2011
Citation: Min, B., McClung, A.M., Chen, M.H. 2011. Phytochemicals and antioxidant capacity in rice brans of different color. Journal of Food Science. 76:C117-126.

Interpretive Summary: Rice bran is an under-utilized byproduct of the rice milling process, which has potential as a rich source of valuable health promoting compounds. The health promoting compounds of bran include phytochemicals that are in the lipophilic, hydrophilic and the insoluble, cell wall-bound fractions. These phytochemicals are antioxidants and can account for the health benefits that are associated with the consumption of whole grain, such as the reduced incidence of chronic diseases and various inflammatory diseases. Thus, rice bran and its extract have potential application as health promoting ingredients in functional foods. In addition, with increasing concern about the safety of synthetic antioxidant usage, there has been increasing interest in the use of natural antioxidants from plant extracts as an alternative. Rice bran extract has been proven as an effective natural preservative in various food systems such as meat, refined oil, and dough. The food application of the rice bran extract can also append its health beneficial value to food products. We determined the amounts of lipophilic, solvent-extractable, and insoluble-bound phytochemicals and their antioxidant capacities, as measured by DPPH radical scavenging capacity, oxygen radical absorbance capacity, and iron chelating capacity assays from eight rice varieties differing in bran pigment. Concentration ranges of tocols, the sum of homologs of tocopherols and tocotrienols, and gamma-oryzanols were 319.67 - 443.73 and 3861.93 - 5911.12 ug per g bran, respectively. All rice brans had higher phenolics in the bound form than did blueberry and broccoli. Red and purple rice brans had three to 25 times higher total phenolic and flavonoid concentrations and total antioxidant capacity than did blueberry, broccoli, or light-colored rice bran. These results indicate that red and purple rice brans are natural sources of hydrophilic and lipophilic phytochemicals for use in quality control of various food systems as well as for nutraceutical and functional food application. The results further suggested that we should further take full advantage of the natural genetic resources in the USDA National Small Grains Collection, which contains over 18,000 rice accessions collected from around the world that vary widely in bran color, for enhancing these health-promoting phytochemicals in new rice varieties.

Technical Abstract: Rice bran, a by-product of the rice milling process, contains most of the phytochemicals of whole grain rice, but has been under utilized. Phytochemicals in rice bran are present in lipophilic, hydrophilic, and insoluble-bound forms. However, little information is available regarding the differences in phytochemical profiles and antioxidant capacities of rice brans of different color. This study aimed at determining the amounts of lipophilic, solvent-extractable (free), and insoluble-bound phytochemicals and their antioxidant capacities, as measured by DPPH radical scavenging capacity, oxygen radical absorbance capacity (ORAC), and iron chelating capacity assays, from eight rice varieties differing in bran pigment: one white, two light brown, two brown, one red, and two purple. Free and bound phytochemicals and their antioxidant capacities in broccoli and blueberry were also determined for comparison. Concentration ranges of tocols (sum of homologs of tocopherols and tocotrienols) and gamma-oryzanols were 319.67-443.73 and 3861.93-5911.12 ug per g bran, respectively. Total anthocyanin concentration in purple rice bran (IAC600; 33.68 mg kuromanin equivalents per g dry weight basis) was four times higher than that in blueberry. Total proanthocyanidin concentration was the highest in red rice bran (IITA119; 22.61 mg catechin equivalents per g dry weight basis) and small in other rice brans, broccoli, and blueberry (0.09 - 1.31). Red and purple rice brans had three to 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 of red and purple rice brans also had 1.2 - three times higher bound phenolic and flavonoid concentrations and total antioxidant capacities than that of light-colored rice bran. These results indicate that red and purple rice brans are natural sources of hydrophilic and lipophilic phytochemicals for use in quality control of various food systems as well as for nutraceutical and functional food application.