The effect of agar on rheological properties and thermal stability of rennet-induced casein micelle gel

Effects of agar on the rheological property and heat stability of casein micelle gels induced by rennet were investigated. The interactions between casein micelle and agar were investigated. Electrostatic interactions between casein micelle and agar were not observed. The movement of agar characteristic bonds indicated the hydrogen bond interaction existed in the casein micelle/agar mixture. The addition of agar promoted the casein micelles aggregation and decreased the rennet coagulation time (RCT) and the storage modulus (G'). The strip-like network microstructure changed into a sheet-like network after the addition of agar. The composite gels were present as a bicontinuous phase structure. The agar and protein were both present as continuous phases. The addition of 0.5% agar increased the water holding capacity (WHC) from 63.30% to 92.44% and decreased the gel hardness from 73.41 g to 60.57 g. The protein digestion rate of gels increased after agar addition during gastric digestion. The WHC increased from 35.20% to 83.56% and the microstructure of gels improved by the addition of 0.5% agar after heating at 80 °C for 30 min. In conclusion, the WHC and thermal stability of the gels improved after the addition of agar.