Abstract: Defatted soy flakes were washed with aqueous alcohol and the resultant material was extracted with water to prepare soy protein isolate (SPI-A) with improved functional properties in comparing with the conventional soy protein isolate(SPI-C)extracted directly from the alkaline low-denatured soy flakes. Gelling property was determined by rheometer at the protein concentration of 12% (W/W) while the gel fracture force of SPI-A was 385.4g, substantially higher than that of SPI-C (85.4g). Emulsifying and foaming stability were also found to be improved through alcohol washing. High performance size exclusion chromatography showed that when SPI-A and SPI-C were both eluted around the same time, the laser light scattering analysis indicated that SPI-A solution contains particles with larger hydrodynamic radius than SPI-C, suggesting that SPI-A forms larger protein aggregates with more flexible structure whereas SPI-C forms smaller and more compacted aggregates.

Key words: soy protein isolate, ethanol, functionality, gelation, HPLC, light scattering