RICE BY‐PRODUCTS: COMPARATIVE EXTRACTION AND PRECIPITATION OF NITROGEN FROM U.S. AND SPANISH BRAN AND GERM

The nitrogen (N/) extractability of several rice (Oryza sativa L.) bran samples was similar with 63, 65 and 67% of the N extracted at pH 9 from Spanish and U.S. bran and U.S. Protex (hexane-extracted bran), respectively. Moist heat treatment, 95–100°C, of Spanish bran diminished N extractability with 21–22% extracted at pH 9 and 10. Although particle size reduction had little effect upon N extractability of heat treated bran, Wiley-(20-mesh) and ball-milling the Spanish rice germ increased N extraction to 57 and 79%, respectively, at pH 9 compared with 34% for the unmilled germ. With all by-products studied nearly optimum extraction was attained at pH 9 with little or no increase observed at pH 10. Classical fractionation of the Spanish brans resulted in H2O-, 5% NaCl-, 60% EtOH-, and 0.4% NaOH-soluble fractions in ratios of 40:21:3:36 and 26:14:5:56 for the untreated and heat treated samples, respectively. Precipitation and recovery of N was optimized when sodium hexametaphosphate (0.1–0.5%) was used in conjunction with HCl. Points of maximum N precipitation were pH 5 for Protex, and pH 4 for U.S. and Spanish brans and germ, in extracts which had been centrifuged at 650 ° G to remove fibrous residue and starch.