Abstract:

To under the effect of physical force on emulsion activity index (EAI) and emulsifying stability (ES) of soybean protein isolates (SPIs) obtained from different varieties of soybeans, various concentrations of NaCl, NaSCN, urea and 1,2-propylene were respetively used to treat SPI for changing its physical force. Results indicated that the increasing concentration of NaCl and NaSCN resulted in an initial increase and a following reduction of EAI of SPI. This suggests that electrostatic interaction was a dominant force and hydrophobic interaction is unfavorable to EAI of SPI. The fact that emulsifying stability was decreased with increasing concentrations of NaCl and NaSCN demonstrates that electrostatic interaction is stronger than hydrophobic interaction. The addition of urea improved the exposure of hydrophobic groups in protein and promoted the increase of EAI of SPI. However, no obvious effect of added urea at different levels on EAI was observed. Furthermore, as 1,2-propylene concentration increased, there was an increase of EAI. Therefore, hydrogen bonding interactions are beneficial to EAI and ES of SPI.

Key words: soybean protein isolate, electrostatic interaction, hydrophobic interaction, emulsion activity, emulsifying stability