Effects of ultrafine grinding time on the functional and flavor properties of soybean protein isolate

Soybean protein isolate (SPI) powders were prepared at different ultrafine grinding time, and the functional and flavor properties of microparticulation SPI were evaluated. With extending ultrafine grinding time, a narrow and uniform particle size distribution in SPI powders was produced. The particle sizes of protein powders at grinding time 0, 2, 4, 6 and 8 h significantly reduced from 217 +/- 16.5-137.5 +/- 10.7 nm, while the absolute values of zeta-potential significantly increased from 25 +/- 0.93-32.4 +/- 117 mV (P < 0.05). The microstructure of SPI at grinding time 0-8 h changed from smooth to irregular. With prolonging the ultrafine grinding processing time, the solubility, foaming and emulsifying properties of SPI powders were improved, the content of alpha-helix, beta-sheet and random coils increased, while beta-turn decreased. Furthermore, the ultrafine grinding time clearly influenced the volatile compounds of SPI powders. The main flavor compounds were aldehydes, alcohols, acids, ketones and alkanes. SPI powders for grinding time 2, 4, 6 and 8 h exhibited the higher total content of volatile compounds compared to that for 0 h. So the ultrafine grinding treatment at appropriate time could affect the functional and flavor properties of SPI.