QUALITY CHARACTERISTICS IN RICE BY NEAR-INFRARED REFLECTANCE ANALYSISOF WHOLE-GRAIN MILLED SAMPLES

Various physical and chemical tests exist to assess the cooking and pr ocessing characteristics of rice. As new lines of rice are developed i n the United States and elsewhere, plant breeders routinely test for a mylose content, alkali spreading value (an indicator of gelatinization temperature), protein content, viscosity properties of the flour-wate r paste, and the appearance of milled grains (whiteness, transparency, and degree of milling). A study was undertaken to determine the exten t to which near-infrared reflectance (NIR) spectroscopy on whole-grain milled rice could be used to measure such characteristics. Samples of U.S. rices (n = 196) from advanced breeders' lines and commercial rel eases, representing conventional and specialty short-, medium-, and lo ng-grain classes, were milled and scanned in the visible and near-IR r egions (400-2,498 nm). Reference chemical and physical analyses were a lso performed on each sample. Results of partial least squares modelin g indicated that reasonably accurate models were attained for apparent amylose content (standard error of prediction [SEP] = 1.3 percentage units; coefficient of determination on the validation set [r(2)] = 0.8 9), protein content (SEP = 0.13 percentage units, r(2) = 0.97), whiten ess (SEP = 0.60 percent reflectance, r(2) = 0.97), transparency (SEP = 0.15 percent transmittance, r(2) = 0.93), and milling degree (SEP = 2 .7 dimensionless units on a 0-199 scale, r(2) = 0.97). To a lesser ext ent, alkali spreading value could be modeled by NIR (SEP = 0.43 units on a 2-7 scale, r(2) = 0.82), however, this accuracy is probably suffi cient for initial screening in breeding programs. Conversely, models f or the five flour paste viscosity properties recorded by a rapid visco analyzer (RVA) were not sufficiently accurate (r(2) < 0.75) to warran t replacement of the RVA procedure with an NIR model. Reducing the sam ple size for NIR scanning from approximately 100 to approximately 8 g did not significantly affect the model performance of any constituent.