An insight into heat-induced gelation of whey protein isolate–lactose mixed and conjugate solutions: rheological behavior, microstructure, and molecular forces

It is known that protein/sugar conjugates prepared by Maillard reaction (MR) have good gel properties. However, there is not much information about the mechanism of MR on the gel properties of whey protein isolate (WPI). Electrophoresis confirmed the maximum molecular weight conjugate was obtained at incubation for 2 days, and its glycation degree was 82% by O-phthaldialdehyde (OPA) method. At this time, its absorbance at 294 nm and 420 nm increased significantly. The rheological results showed that the conjugate gel had better relative viscoelasticity, higher fracture modulus and mechanical strength, more covalent bonds in the gel structure and higher viscosity at high shear rates than the mixed gel. The total free sulfhydryl groups and relative fluorescence intensity of WPI–Lactose conjugate decreased significantly, indicating the conformation of WPI was altered after MR. Besides WPI–Lactose conjugate gel had a denser and smaller smooth pores microstructure by microcopy analysis.