The influence of kernel maturity, milling degree and milling quality on rice bran phytochemical concentrations

Authors: Chen, Ming Hsuan; Bergman, Christine

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2004
Publication Date: 1/1/2005
Citation: Chen, M., Bergman, C.J. 2005. The influence of kernel maturity, milling degree and milling quality on rice bran phytochemical concentrations. Cereal Chemistry 82(1):4-8.

Interpretive Summary: Rice bran is a rich source of phytochemicals, such as tocopherols, tocotrienols, and gamma-oryzanol, that have positive effects on human health. The screening of germplasm to determine the genetic diversity of these compounds requires knowledge of how sample preparation influences concentrations of the antioxidants in rice bran. Obtaining this knowledge was the objective of this study. Cultivars with different milling qualities were all milled to different degrees. Bran starch concentration significantly affected the rankings of phytochemical contents of cultivars when samples with a wide range of grain characteristics, i.e. milling quality, were compared. A high degree of milling reduced the differences in bran removal among cultivars with different milling qualities. Samples that were milled for 30 or 40sec (milled to the degree of 0.23 to 0.44 percent surface lipid content) showed no significant differences in bran concentrations of tocopherols and tocotrienols within cultivars. Subtracting starch from bran reduced the differences in bran gamma-oryanol concentration that were resulting from differences in milling degree. Bran from the mature-thin kernels had similar antioxidant contents as that of the mature-thick kernels milled for 30 sec. The immature-thin kernels had significantly lower contents of most of the bran antioxidants than mature kernel fractions.

Technical Abstract: Rice bran is primary considered to be a byproduct of the rice milling process. However, it contains phytochemicals, such as the vitamin E isomers and gamma-oryzanol, which reportedly have positive effects on human health. We are in the process of studying the genetic diversity of these phytochemicals using a set of germplasm collected across six continents. A rapid extraction method has been developed and will be used for the quantification of these phytochemicals. However, information is lacking, despite its equal importance, as to how sample preparation affects the levels of these phytochemicals in rice bran. That is the focus of this study. We determined that milling rice to a higher degree reduced the differences in bran removal among cultivars with different milling qualities. Phytochemical concentration in the bran should be expressed as an equal starch basis for their comparison among cultivars. Immature, green kernels should be removed prior to milling. These criteria will be used to prepare the diverse set of germplasm for study.