Preparation and characterization of hen egg proteins-soybean protein isolate composite gels

The physicochemical properties, rheology, texture, water state and microstructure of gels formed from different ratio of egg proteins and soybean protein isolate were investigated. Results showed that composite solution that contained 75% egg proteins had the highest protein surface hydrophobicity while the biggest solubility was found when the proportion of egg proteins was 25%. Solid content and total sulfhydryl groups content before centrifugation increased as the proportion of egg proteins raised while total sulfhydryl groups content after centrifugation had less fluctuations because of the changes of protein solubility. Egg proteins-soybean protein isolate composite solutions had various growth ratio of G' during different stages of solution-gel transition process, suggesting the composition of the solutions affected the molecular interactions and then changed the gelling properties. Besides, composite gels that contained the whole egg had higher hardness and lower springiness than those gels that contained egg yolk. The gel hardness after 50% addition of the whole egg and egg yolk was about 561% and 329% of the original gel strength while the gel springiness was 0.91 and 0.94, respectively. From results of microstructure, egg yolk-soybean protein isolate composite gels possessed denser gel network, which may be related with higher solid content of egg yolk. Conversely, the whole egg-soybean protein isolate composite gels showed rigid fiber network with holes, leading to better water mobility, higher hardness and lower springiness.