Preparation Of Polymerized Whey Protein And Its Application In Fermented Goat Milk

Polymerized whey protein（PWP）is prepared from whey protein after proper modification,which has outstanding functions,but its application and development are insufficient.Fermented goat milk is rich in nutrition and easy to absorb,but its unique smell limits the development and promotion of the product.The purpose of this experiment was to prepare a PWP with high viscosity but no gel state by heat-induced modification of whey protein,so that it has good thickening effect.Then the effects of PWP on the physicochemical properties,curd and flavor of fermented goat milk were investigated in order to provide theoretical basis for the intensive processing of whey protein and the quality optimization of fermented goat milk.The research contents were as follows:（1）Influence of modification conditions on PWP characteristics.Taking the viscosity and water-holding capacity of PWP as indicators,the preparation process of PWP was optimized.It was found that the modification conditions of PWP suitable for dairy products were protein concentration of 10%,pH of 7,heating temperature of 80℃and Ca²⁺concentration of 20 mmol/L.At this time,the viscosity and water-holding capacity of PWP were 854±5.78 m Pa.s and 55.8±0.01%respectively,reaching the expected target values.（2）Basic characteristics of PWP and its preliminary application in fermented goat milk.The viscosity,water retention,texture and microstructure of PWP before and after modification were tested.It was found that after thermal modification,the basic characteristics of whey protein were significantly improved.The viscosity and water retention were increased by 14.33 and 2.35 times,respectively,and the microstructure was more compact.Then different amounts of PWP were applied to fermented goat milk.It was found that when the amount of PWP was 0.6%,the fermented goat milk had appropriate viscosity,water retention and sensory scores,and 0.6%was determined as the appropriate supplemental level of PWP.（3）Effect of PWP on the quality characteristics of fermented goat milk.Using blank samples as control,the effects of PWP on the physicochemical properties,total number of viable bacteria,curd properties and flavor of fermented goat milk during fermentation and post-ripening were investigated.It was found that the fermented goat milk supplemented with PWP increased the acid production rate,the viable bacteria count was higher,the viscosity and water retention capacity were increased by 320 m Pa.s and 5%,respectively,and the microstructures were more compact and uniform.PWP could reduce the odor and bitterness of fermented goat milk,enrich the flavor composition of samples,and significantly improve the overall quality characteristics of fermented goat milk.（4）Effect of PWP on storage quality of fermented goat milk.The changes of physical and chemical properties,total number of viable bacteria,histological status and flavor quality of fermented goat milk during storage were investigated.It was found that during storage,fermented goat milk showed slightly acidification,decreased viable bacteria,histological status and flavor quality.Adding PWP can slow down the decline of viscosity and texture quality of fermented goat milk,and maintain higher viable bacteria count and flavor characteristics.