Transglutaminase-set soy globulin-stabilized emulsion gels: Influence of soy β-conglycinin/glycinin ratio on properties, microstructure and gelling mechanism

Abstract

Soy protein-stabilized emulsions or emulsion gels have recently attracted increasing interests in the research of food science. However, the importance of protein composition on the properties and microstructure of the formed emulsion gels is little understood. This paper investigated the influence of varying glycinin/β-conglycinin ratio on the properties, microstructure and gelling mechanism of soy globulin-stabilized emulsion gels, at a constant total protein concentration and oil fraction (6%, w/v, and 0.3), induced by microbial transglutaminase (MTGase; 20U per gram of protein). The enzyme incubation resulted in the gelation of all soy globulin-stabilized emulsions, but the rheological properties, water holding capacity (WHC) and microstructure of the formed emulsion gels considerably varied with glycinin content in the globulin mixtures. Basically, increasing the glycinin content progressively increased the gel stiffness, but significantly decreased the WHC. Confocal laser scanning microscopic observations showed that increasing glycinin content led to the formation of emulsion gel network with a more inhomogenous and porous microstructure. The improvement of the gel stiffness by increasing glycinin content was largely associated with the enhanced flocculation of oil droplets, more proteins entrapped within the network, as well as more importance of covalent cross-links for the gel network at higher glycinin contents. The results confirmed that the properties of MTGase-set soy protein-stabilized emulsion gels can be well modulated by varying the protein composition. The findings are of important relevance for the development of cold-set soy protein-stabilized emulsion gels with targeted properties in the food or other fields.