Thermal Polymerization Modification Of Whey Protein Concentrate And Its Application In The Set Yogurt

Polymerized whey protein has a higher viscosity,and it can be used in food processing as a thickener,which was of great significance to improve the texture and water holding capacity of the food.The effects of heat treatment temperature,heat treatment time and protein concentration on physicochemical properties of polymerized whey protein concentrate(PWPC)and polymerized heat-stable whey protein concentrate(PHSWPC),and the effect of the addition amount of PWPC and PHSWPC on the physicochemical properties,water holding capacity(WHC),syneresis,texture,sensory evaluation,microstructure,rheological properties and the stability during storage of set yogurt were investigated.The results are as follows:The free thiol contents and Zeta-potential of whey protein concentrate polymer(PWPC)and heat stable whey protein concentrate polymer(PHSWPC)all reduced and then increased,however,the surface hydrophobicity increased and then reduced,turbidity,particle size and viscosity increased with the increase of heat treatment temperature,protein concentration and treatment time.The results of intrinsic fluorescence spectra showed that the tertiary structure of PWPC and PHSWPC changed.When the WPC and HSWPC at a concentration of 12%(w/v)were heated at85 °C for 30 min,the free thiol contents and the Zeta-potential reached the lowest,were 17.75 ±0.49,16.63 ± 0.28 ?mol/g and-27.50 ± 0.65,-29.23 ± 0.71 mV,respectively.The rheological properties show that the PWPC and PHSWPC were a kind of viscous fluid,and presented a shear thinning fluid properties.With the increase of the addition amounts of 12%(w/v)PWPC and PHSWPC(85 ? for30min),the content of protein of set yogurt gradually increased,and the titratable acidity after post fermentation,viscosity and firmness of set yogurt gradually increased,but the titratable acidity on fermentation end point was not significant difference(P(29)0.05),WHC increased and then decreased,however,syneresis was opposite.The WHC was significantly increased by 14.60% and 16.97%,respectively,and the syneresis was significantly decreased by 14.60% and 16.97%,respectively,(P<0.05),when the addition amounts of PWPC and PHSWPC was 16%.The titration acidity,viscosity and hardness of set yogurt with 16% PWPC,16% PHSWPC and 0.1% pectin were all lower than that of the control,as well as the decrease rate of the WHC and syneresis during storage period.The network structure of the set yogurt with 16% PWPC,16%PHSWPC and 0.1% pectin were more compact and uniform compared to the control,and the network structure of the set yogurt with 16%PHSWPC was the most compact.Comparing the control,the set yogurt with 16% PHSWPC presented the highest viscosity,followed by 16% PWPC and 0.1% pectin.The rheological properties of all the set yogurt samples showed a typical shear thinning fluid properties,were non-newtonian fluid.Hence,PWPC and PHSWPC can be used as protein-based thickener in set yogurt to improve the quality of yogurt and maintain the stability of yogurt during storage.The application of polymerized whey protein in the food industry is of great significance for improving the comprehensive utilization of whey protein.