Properties of soy protein isolate prepared from aqueous alcohol washed soy flakes

Defatted soy flakes were washed with aqueous alcohol and the resultant material was extracted with water to prepare soy protein isolate (ASPI) with improved functional properties and flavor profile in comparing with the conventional soy protein isolate (CSPI) extracted directly from the low-denatured soy flakes. Gelling property was determined by rheometer at the protein concentration of 12% (w/w) and the gel fracture force of ASPI was 385.4 g, substantially higher than that of CSPI (85.4 g). Emulsifying and foaming stability were also found to be improved through alcohol washing. High performance size exclusion chromatography showed that ASPI and CSPI was eluted around the same time, but laser light scattering analysis indicated that ASPI solution contained particles with larger hydrodynamic radius than CSPI, suggesting that ASPI formed larger protein aggregates with more flexible structure whereas CSPI formed smaller and more compacted aggregates. Off-flavor volatiles were collected by solid phase micro-extraction and analyzed by GC-MS. The results showed that hexanal, acetic ether, pentanal, decanal, 2-pentylfuran and 1-octen-3-ol contents of ASPI were 10 times lower than that of CSPI.