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Preparation of Rice Endosperm Protein Isolate by Alkali Extraction

¹Department of Food Science, University of Arkansas, 2650 N. Young Avenue, Fayetteville, AR 72704. ²Corresponding author. Phone: 479-575-4779. Fax: 479-575-6936. E-mail address: nhettiar@uark.edu ³DSM Nutritional Products, Dept. NRD/CF-Nutrition Research & Development and Center Formulation, PO Box 3255, 4002 Basel, Switzerland.

Rice endosperm extraction conditions were optimized by response surface methodology. The optimum alkali extraction conditions were pH 11.0 at 40°C for 3 hr with 8:1 solvent-to-solid ratio. The maximum protein yield was 43.1% at these conditions. As the extraction pH was increased from 9.0 to 12.0, protein extractability and content increased but the solubility and emulsifying properties of the extracted protein decreased. The extracted protein was recovered by either isoelectric precipitation (IEP) or ultrafiltration (UF). Ultrafiltering the supernatant with a 5-kDa hollow fiber membrane concentrated the protein from 1.8 to 16% (dry basis) and the resulting solution was spray-dried to produce a protein concentrate (RP_UF) with 71% protein. Although RP_IEP contained higher protein (86%) than RP_UF (71%), RP_UF showed higher solubility and emulsifying properties. The solubility of RP_UF was higher (37%) than RP_IEP (15%). RP_UF also demonstrated higher emulsion activity (0.414) and stability (22.4 min) compared with the emulsion activity (0.282) and stability (15.5 min) of RP_IEP. Higher solubility and the soluble nonprotein components of RP_UF contributed to higher emulsifying properties than RP_IEP. The UF provided milder extraction conditions with improved emulsifying properties than conventional IEP.