Effect of Coexistence of Soybean Lecithin on Thermal Gelation of Soybean Protein

Abstract

Effects of commercial soybean lecithin on flow properties of soybean protein-water suspension systems and coagulated gels were studied. Textural properties and geometrical characteristics of heat-induced gels were also investigated. For suspension systems and their heat-induced gels, thixotropy index (TI) decreased with increasing amounts of added lipid, but degree of consistency increased. Hardness of the gels increased with increasing amounts of the lipid under small deformation (20%), but decreased under larger deformation (>60%) in the region above the yield point. Scanning electron microscopic structure of the gels related to textural characteristics. The lipid free gels exhibited a closely packing structure with small globules. On the other hand, lecithin-added gels showed a pumice stone structure. It was revealed that bulkier flocs formed from spherical particles of protein were also responsible for high viscosity of lecithin-added systems. These findings suggested that the topological interactions between morphologically different particles were weakened by the increase of degree of polydispersibility of the lecithin-added systems. Furthermore, it seemed that the intermolecular entanglements and linkage between protein molecules were reduced by addition of polar lipids.