Removal of off-flavour-causing precursors in soy protein by concurrent treatment with phospholipase A2 and cyclodextrins

A simple mild process to remove phospholipids in soy protein isolate has been developed. The method includes two steps: A 5% soy protein isolate solution is concurrently treated with 0.5-1.5 μkat phospholipase A2/g protein and 10 mmol/l β-cyclodextrin for 4 h at 43 °C, pH 8.0; secondly, soy protein is separated from the treated solution by precipitating at pH 4.5. The treatment removed more than 92% of the off-flavour precursors in SPI. Comparing α-, β-, and γ-cyclodextrins, α-cyclodextrin was more effective (>95% removal of precursors) than β-cyclodextrin, while γ-cyclodextrin essentially had no effect. Under accelerated storage conditions at 45 °C for 90 days, the rate of hexanal production in the treated SPI was 12-times slower than that in the untreated SPI. The treatment lowered the thermal denaturation temperature and enthalpy of denaturation of soy proteins but not its solubility, indicating that the treatment caused some structural changes in soy proteins.