Effect of rice kernel thickness on degree of milling and associated optical measurements

Three cultivars of long-grain rice were milled to three degree of milling (DOM) levels. Inverse linear relationships were established between surface fat concentration (SFC) and Satake milling meter (MM1B) optical DOM measurement values, including whiteness, transparency, and DOM, for the unfractionated head rice within each cultivar. Milled bulk rice for each cultivar was subsequently separated into thickness fractions. Effects of milled rice kernel thickness on SFC and optical DOM measurements were investigated. For a given DOM level, SFC decreased with increasing milled rice kernel thickness up to a thickness of 1.67 mm, after which it remained constant. As the overall DOM level increased, the difference in DOM between thin kernels and thick kernels lessened, implying that thin kernels were milled at a greater bran removal rate than thick kernels. Milled rice kernel thickness significantly (at the 0.05 significance level) affected MM1B whiteness and MM1B transparency in two of the cultivars because of the predominant effects of the thinner kernel fractions. Within each cultivar, MM1B DOM was not significantly influenced by milled rice kernel thickness.