The water holding capacity and storage modulus of chemical cross-linked soy protein gels directly related to aggregates size

Abstract

Relationships between the size of particles and the water holding capacity or storage modulus of chemical-induced soy protein gels were investigated in the present study. Heat-induced protein aggregates with different sizes ranging from 92.7 to 525.2 nm were obtained by heating the protein mixtures of varying β-conglycinin/glycinin (7S/11S) ratios at 100 °C for 30 min, then they were cross-linked by glutaraldehyde to form the gels. Larger aggregates were formed at lower 7S/11S ratio, and the ratio of the aggregates in protein suspensions increased from 35.7% to 65.6% when the 7S/11S ratio decreased from 5:0 to 0:5. Reducing SDS-PAGE showed that basic polypeptides of 11S played an important role in the forming of larger particles. Scanning electron microscope results revealed that coarser gel networks with larger pores were formed when larger aggregates were participated in forming a gel. The water loss rate increased from 8.2% to 33.3% as the 7S/11S ratio decreased from 5:0 to 0:5, and a positive correlation between the size of particles and the water loss rate of gel network was found, which could be attributed to coarser gel structure formed by larger aggregates. However, a negative relationship between the size of protein aggregates and the storage modulus of gels was observed, due to that more cross links were induced by glutaraldehyde when smaller protein particles were present in gel network.