Use of objective imaging systems to assess subjective grain appearance traits important to the USA rice industry

Background and objectives Milled rice grain appearance traits, including chalk, determine its grade, price, and marketability. These appearance traits are evaluated visually (VI) in the United States by officially trained inspectors and at commercial mills. Digital imaging systems (IS) provide an alternative means to objectively and rapidly measure these traits. The goals of this study were to compare chalk values determined by VI and IS and to identify IS parameters that are associated with the five grain appearance traits commonly assessed by the US rice industry. Findings Milled rice chalk determined by three VI methods used by commercial mills, a rice export company, and government inspectors, and three IS, WinSeedle, SeedCount, and S21, differed significantly. However, all six methods agreed on ranking of the best and worst of 20 US cultivars for chalkiness. Multiple linear regression analyses identified quality parameters from each IS that are associated with-bran streaks, chalk, kernel color, uniformity length, and appearance overall as determined by commercial mills. Conclusions IS can rapidly quantify rice grain appearance traits but agree with subjective ratings for chalkiness only when differences are extreme. Subjective grain appearance traits as determined by commercial mills appear to be based on several parameters detected by IS. Significance and novelty IS demonstrated that discolored kernels and grain chalkiness are the major factors explaining differences in overall appearance of US long-grain varieties as subjectively assessed by commercial mills.