Effect Of Heat Treatment On Emulsification And Stability Of WPC And WPI Thermal Polymerization

The effects of heating temperature(70, 75, 80, 85 and 90℃), protein concentration(8, 9, 10, 11 and 12%), heating time(15, 30, 45, 60 and 90 min) and p H(3, 6, 7, 8 and 9) on the thermal polymerization of whey protein concentrate(WPC) and whey protein isolate(WPI) were investigated in this present study. This study mainly evaluated the formation of main forces(free thiol) of whey protein thermal polymerization, the main feature(viscosity and Zeta potential) and the functional properties of thermal polymerization products(foamability and emulsibility), and further analyzed the microstructure and molecular weight distribution of whey protein thermal polymerization using the method of transmission electron microscopy(TEM) and electrophoretic. The results are showed as following:The results of the study showed that the free thiol group content and Zeta-potential of whey protein concentrate polymer(PWPC) and whey protein isolate polymer(PWPI) were first reducing and then increasing with the increase of heat treatment temperature, protein concentration, treatment time and p H, however the viscosity was increasing. The results of intrinsic fluorescence spectra showed the structure of PWPC and PWPI changed. Emulsifying activity, emulsion stability, foaming capacity and foaming stability increased and then decreased. When protein was heated at 10% concentration under p H 7, 85℃ for 30 min, free sulfydryl group and Zeta-potential of PWPC and PWPI reached the minimum. Meanwhile, emulsifying activity, emulsifying stability, foaming capacity and foaming stability reached maximum. Contents of free thiol of PWPC and PWPI decreased by 58.83% and 57.05% compared with those of WPC and WPI. Zeta-potential value decreased by 107.46% and 117.32%. Emulsifying activity decreased by 15.55% and 27.64%. Emulsion stability increased by 137.06% and 60.67%. Foaming capacity increased by 64.07% and 47.02%. Foaming stability increased by 89.09% and 61.58%, respectively.Additionally, the study found that content of free thiol groups, EAI and ESI of PWPI were significantly higher than those of PWPC under the same experimental conditions(P < 0.05). When protein was heated at 10% concentration under p H 7, 85℃ for 30 min, content of free sulfhydryl group, emulsifying activity, emulsion stability, foaming capacity and foaming stability of PWPI were higher 88.89%, 153.92%, 87.39%, 5.71% and 5.29% compared with those of PWPC, respectively. While Zeta-potential value of PWPI was 12.82% lower than that of PWPC.The results of TEM showed that WPC and WPI formed the network structure after thermally polymerized and PWPI had denser network structure. The SDS-PAGE electrophoretic patterns of PWPC and PWPI showed that the band intensity of α-lactalbumin and β-lactoglobulin reduced, suggesting whey protein was thermally polymerized.Hence, emulsifying activity and emulsifying stability of PWPC and PWPI increased significantly and PWPI had better emulsifying activity and emulsifying stability. PWPC and PWPI could be used in food processing as emulsifier agent, which was of great significance to expand utilization of whey protein in all fields.