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Physicochemical Properties of Rice Endosperm Proteins Extracted by Chemical and Enzymatic Methods

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

Rice proteins are nutritional, hypoallergenic, and healthy for human consumption. Efficient extraction with approved food-grade enzymes and chemicals are essential for commercial production and application of rice protein as a functional ingredient. Rice endosperm proteins were isolated by alkali, salt, and enzymatic methods and evaluated for extractability and physicochemical properties. Alkali (RP_A) and salt (RP_S) methods extracted 86.9 and 87.3% of proteins with 65.9 and 58.9% yield, respectively. The enzymatic methods with Termamyl (RP_ET) and amylase S (RP_EA) extracted 85.8 and 81.0% proteins with 85.2 and 86.2% yield, respectively. Enthalpy values of RP_A (1.79 J/g), RP_S (1.22 J/g), RP_ET (nondetectable), and RP_EA (0.17 J/g), determined by differential scanning calorimetry, demonstrated that the varying level of denaturation of proteins depends on the method of extraction. Surface hydrophobicity data supported this observation. Alkali- and salt-extracted proteins had higher solubility and emulsifying properties than those of enzyme-extracted proteins. Comparatively, more favorable protein composition, lower surface hydrophobicity, higher solubility, and a lower degree of thermal denaturation of alkali- and salt-extracted proteins contributed to higher emulsifying and foaming properties than those of enzyme-extracted proteins; therefore, alkali- and salt-extracted proteins can have enhanced functional use and a potential starting material for preparing tailored rice protein isolates.