FUNCTIONAL PROPERTIES AND NUTRITIONAL QUALITY OF ALKALI- AND HEAT-TREATED SOY PROTEIN ISOLATE

Alkali and heat are increasingly utilized in food processing. This study was conducted to evaluate specific functional and nutritional properties of alkali- and heat-treated soy protein isolate (AHSPI) and the relationship between these properties. High pH (12.0) and temperature (100C) increased protein solubility of the isolate from 47 to 99.5% and emulsifying activity index from 74 to 184 m²/g. The values for in vitro protein digestibility (IVPD), computed-protein efficiency ratio, and IVPD-corrected amino acid score of AHSPI were not significantly (P>0.05) affected at pH 8.0 or 10.0, but were reduced At pH 12.0. At pH 12.0, lysinoalanine content significantly (p<0.05) increased from 0.39 to 1.22 g/100g protein as temperature was increased from 40 to 100C. Improvements in functional properties of soy proteins can be obtained through combined alkali and heat treatments. However, very high pH and temperature should be avoided to maintain nutritional quality of the proteins.