Cereal Chem 47:38 - 42.  |  VIEW ARTICLE
Use of Dye-Binding and Biuret Techniques for Estimating Protein in Brown and Milled Rice.

L. C. Parial and L. W. Rooney. Copyright 1970 by the American Association of Cereal Chemists, Inc. 

Linear regression equations relating colorimetric protein dye-binding and biuret values (absorbance) to Kjeldahl protein content of milled and brown rice were determined. Two dye-binding techniques, based on the reaction of acid orange 12 dye with protein, and modified for single-sample analysis and for multiple- sample determinations, were investigated. The rice samples, representing 45 varieties, ranged from 4.6 to 12.9% protein (% Kjeldahl N x 5.95). Correlation coefficients for milled rice were -0.986 and -0.961 for the single-sample and multiple-sample dye-binding techniques, respectively. For brown rice, corresponding "r" values were -0.969 and -0.984. Correlation coefficients for the biuret test were 0.964 and 0.981 for milled and brown rice, respectively. All four methods of determining protein were employed to analyze both milled and brown samples of 32 varieties of rice from a different crop. Mean protein content of milled and brown rice estimated by the two dye-binding techniques were not statistically significantly different from those obtained by Kjeldahl determinations; whereas statistically higher mean protein values were found with the biuret test. The colorimetric techniques described are satisfactory, rapid, simple, and relatively inexpensive methods for routine use in determining protein in rice-breeding programs.