Preparation of Rice Endosperm Protein Isolate by Alkali Extraction

Abstract

ABSTRACT 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.