Gelation Property of Alcohol-Extracted Soy Protein Isolate and Effects of Various Reagents on the Firmness of Heat-Induced Gels

Gelation property, thermal property, protein subunits distribution, and molecular forces involved in gelation of alcohol-extracted soy protein isolate were investigated using texture analyzer, differential scanning calorimeter, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and various reagents. Results showed that salts and pH played important roles in gel firmness, and a power law relationship between gel firmness and protein concentration was observed. The effects of various reagents revealed that disulfide bonds play a major role in soy protein gel formation, while the involvement of electrostatic interactions, hydrogen bonds, and/or hydrophobic interactions also occurred in gel networks. Thermal analysis indicated that both alcohol-extracted soy protein isolate and commercial soy protein isolate (isoelectric precipitation) have undergone serious denaturation, while the gel firmness of alcohol-extracted soy protein isolate was significantly greater than that of commercial soy protein isolate. Sodium dodecyl sulfate polyacrylamide gel electrophoresis image showed that there was almost no difference for protein subunits among alcohol-extracted soy protein isolate, commercial soy protein isolate, and soy powder. Hence, as an alternative environmental friendly extraction method, alcohol-extraction of soy protein isolate has a great prospect to replace presently applied isoelectric precipitation method.