The Effect Of Transglutaminase On The Characteristics Of Sour Goat Milk Curd And The Quality During Storage Period

The nutritional value of goat milk is rich and it is praised as "the king of milk." The unique flavor and high nutritional value of goat milk yogurt are well-loved by consumers.However,when goat milk is made to yogurt,many defects easily occurred,such as poor curdability,prolonged coagulation time and easy precipitation of whey,affecting the quality of goat milk yogurt.The use of transglutaminase(TG),cross-linking milk proteins,can effectively improve milk coagulation characteristics.In this paper,goat milk was treated by TG,and we studied the gel properties of fermented goat milk,the quality of set-type and stirred-type goat milk yogurt,which provided a theoretical basis for the development of goat milk yogurt.The first part is the effect of TG on the coagulation characteristics of goat milk yogurt.We studied the effects of TG treatment on the coagulation time,acidity,viscosity and gel properties of goat milk yogurt.The results showed that TG treatment had no significant effect on the acidity during goat milk yogurt fermentation,but shortened the coagulation time;the viscosity of goat milk yogurt increased with the increase of TG concentration during fermentation;when the goat milk yogurt coagulated,TG treatment had an effect on the hardness,cohesiveness and viscosity of goat milk yogurt,which improved the texture characteristics of the gel,and promoted the coagulation of goat milk;goat milk yoghurt treated by TG had significantly higher water holding capacity than control during coagulation;we can see from the microstructure that the higher the concentration of TG treatment,the more dense the three-dimensional network structure of goat milk yogurt,which is conducive to the formation of acid gel;SDS-PAGE electrophoresis showed that ?-casein and a-lactalbumin significantly cross-linked after added TG.The second part is the effect of TG on the quality of set-type goat milk yogurt.We studied the effects of TG treatment on the acidity,water holding capacity,texture properties,flavor substances,lactic acid bacteria and sensory characteristics of set-type goat milk yogurt during storage.The results showed that TG treatment had no significant effect on the acid production ability of lactic acid bacteria during storage;TG treatment had no significant effect on Lactobacillus bulgaricus and Streptococcus thermophilus;TG treatment significantly improved the firmness and viscosity of set-type goat milk yogurt during storage,and the firmness and viscosity increased significantly with the increase of TG concentration.The TG concentration had no significant effect on the springiness of yogurt.The cohesiveness of yogurt can influence smoothness in the mouth.TG had a significant effect on the cohesiveness of the yogurt,increasing the mouthfeel of the yogurt;the TG treatment significantly improved the water holding capacity of set-type goat milk yogurt during storage;the TG treatment inhibited the formation of flavor substances in the yogurt;sensory characteristics analysis showed that TG treatment can increase the taste of goat milk yogurt.The third part is the effect of TG on the quality of stirred-type goat milk yogurt.We studied the effects of TG treatment on the acidity,viscosity,water holding capacity,flavor substances,lactic acid bacteria and sensory characteristics of stirred-type goat milk yogurt during storage.The results showed that the TG treatment reduced the acidity during storage;it had no significant effect on Lactobacillus bulgaricus,but can inhibited Streptococcus thermophilus;TG inhibited the formation of flavor substances of yoghurt;TG treatment significantly increased viscosity and the water holding capacity of goat milk yogurt during storage;TG treatment also improved the sensory characteristics of the stirred-type goat milk yogurt and enhances the taste.