Journal of Agricultural and Food Chemistry vol:56 issue:24 pages:11914-11919
Color measurements on flour of five raw rice cultivars with different degrees of milling (DOM) showed that red and brown pigments are concentrated in the outer rice layers, i.e. bran and outer endosperm (DOM < 15%). Extinction measurements (lambda 450 nm) of rice extracts showed that yellow pigments are virtually absent in the middle and core endosperm (DOM > 15%). The relation between the extinction values and the yellow color parameter (b*) showed that both are representative for the yellow pigment content of flour from rice with DOM lower than 9%. Determinations of the carotenoid levels in raw brown rice samples indicated that carotenoid levels in raw brown rice are lower than in common nonrice cereals. The major brown rice carotenoids are beta-carotene and lutein (both ca. 100 ng/g), while zeaxanthin levels are lower (ca. 30 ng/g). Regression analyses indicated that yellowness, extinction values, and quantitative carotenoid data are related. b*-Values and contents of total carotenoids (r = 0.70), beta-carotene (r = 0.84), lutein (r = 0.78), and zeaxanthin (r = 0.83) were linearly related. However, extinction values (lambda 450 nm) and contents of total carotenoids (r = 0.92), beta-carotene (r = 0.91), lutein (r = 0.89), and zeaxanthin (r = 0.84) showed the best correlations. The three-step hydrothermal treatment parboiling reduces carotenoid contents of brown rice to trace levels. Consequently, pigments do not contribute to the final color of milled parboiled rice.