Interactions between whey soybean protein (WSP) and beta-conglycinin (7S) during the formation of protein particles at elevated temperatures

In this study, the amount, size, calcium sensibility, and composition of heat-induced protein particles in the mixture of beta-conglycinin (7S) and whey soybean protein (WSP) dispersion are compared with those of 7S and WSP dispersion to investigate the interactions between WSP and 7S during heating. The addition of 7S prevents WSP from forming large protein particles which can be precipitated by centrifugation at 10,000g for 10 min. The protein in the heated mixture of 7S and WSP (7S/WSP = 1/1) coagulates at higher calcium concentrations than that in the mixture of heated 7S and heated WSP at a ratio of 1/1. This result strongly indicates that 7S and WSP interact with each other during heating and form complex protein particles which have special surface properties that are different from individual 7S and WSP protein particles. Particle size distribution analysis has also shown that 7S prevents WSP from forming larger protein particles during heating. SDS-PAGE analysis shows that lipoxygenase (LOX), beta-amylase, and lectin of WSP and the beta subunit of 7S tend to form a particulate fraction, while the KTI, alpha, and alpha′ subunits tend to form a soluble fraction. WSP, 7S, and their mixture have been heated at 60, 65, 70, 75, 80, 85, 90, and 95 °C for 10 min, and ultracentrifugation analysis shows that about 77–85% of the protein particles were formed at 65–75 °C in all three dispersions. SDS-PAGE analysis indicates that LOX and β-amylase have been denatured and that they have participated in the formation of protein particles when heated within 65–75 °C, while lectin has begun to participate in particle formation at above 85 °C. It is concluded that WSP plays an evident role in the formation of protein particles in soymilk during heating.