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Influence of Kernel Maturity, Milling Degree, and Milling Quality on Rice Bran Phytochemical Concentrations

¹United States Department of Agriculture, Agricultural Research Service, Rice Research Unit, 1509 Aggie Drive, Beaumont, TX 77713. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of a product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that also can be suitable. ²University of Nevada Las Vegas, Las Vegas, NV 89154. ³Corresponding author. Phone: 409-752-5221 ext. 2242. Fax: 409-752-5720. E-mail: bergman5@UNLV.nevada.edu

Rice bran is a rich source of phytochemicals including tocopherols (T), tocotrienols (T3), and γ-oryzanol that have purported positive effects on human health. The screening of germplasm to determine the genetic diversity influencing contents of these compounds requires knowledge of how sample preparation influences concentrations of the phytochemicals in rice bran. Obtaining this knowledge was the objective of this study. Cultivars with different milling qualities were all milled to different degrees. The differences in bran removal among cultivars decreased as the milling time increased. Samples that were milled for 30 and 40 sec (milled to the degree of 0.23–0.44% surface lipid content [SLC]) showed no significant differences in T and T3 concentrations in the bran within cultivars. Bran starch concentration affected the rankings of cultivars based on phytochemical contents. Expression of the γ-oryanol concentration in bran after subtracting starch reduced the concentration differences resulting from differences in degree of milling (DOM). Bran from the mature thin kernels had phytochemical contents similar to that of the mature thick kernels milled for 30 sec. The immature thin kernels had significantly lower contents of most of the bran phytochemicals than did the mature kernel fractions.