The Effect Of Transglutaminase Treatment On The Thermal Stability Of Goat Milk

Goat milk is rich in nutrients and easy to be digested and absorbed by the human body,and is favored by consumers.However,goat milk protein is unstable,and protein precipitation is prone to occur during heat treatment,which affects the development of goat milk products.In order to solve the problem of low heat stability of goat milk,this paper studied the effect of transglutaminase(TGase)on the heat stability of fresh goat milk,and then provided a basis for the production and development of goat milk products.The first part is the effect of preheat treatment on heat stability of goat milk catalyzed by transglutaminase.The effect of TGase on the heat stability of goat milk by preheat treatment was studied.The results showed that the heat coagulation time(HCT)of goat milk increased significantly(P<0.05)with the increase of preheated temperature and processing time.Preheating goat milk at the temperature of 60-70 C for 60 min or 80-90? for 30 min could completely inactivate the natural TGase inhibitor in goat milk.Preheat treatment could denature whey protein in goat milk.Meanwhile,the degree of whey protein denaturation increased with the increase of treatment temperature,which was beneficial to the cross-linking of milk protein by TGase.The existence of natural TGase inhibitor in goat milk was confirmed by further sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE).The preheat treatment could induce the increase of the degree of cross-linking of ?-casein in goat milk under the action of TGase,which prevented the dissociation of ?-casein from casein micelles to further improve the heat stability of goat milk.The second part is the effect of TGase treatment on the heat stability of goat milk.The heat stability of goat milk induced by transglutaminase(TGase)was studied,and the cross-linking of goat milk protein and dissociation of casein were analyzed by SDS-PAGE to study the influence of TGase on heat stability of goat milk.The results showed that TGase treatment had no effect on the pH of goat milk.The viscosity and effective particle size of goat milk increased with the increase of processing time.TGase treatment significantly(P<0.05)increased the HCT of goat milk.The higher concentration of TGase used and longer time treated,the higher heat stability of goat milk achieved.The heat stability of goat milk reached the highest when the TGase treated temperature was 50?.TGase treatment could change the HCT-pH curve of goat milk from pattern of A to B,and the heat stability of goat milk improved with the increase of pH.It is further confirmed by SDS-PAGE that TGase treatment could promote the cross-linking of protein in goat milk and then inhibit the degree of?-casein dissociation,thereby improving the heat stability of goat milk.The third part is the effect of stable salt on the heat stability of TGase-treated goat milk.The effects of disodium hydrogen phosphate,sodium dihydrogen phosphate,sodium pyrophosphate,sodium tripolyphosphate and sodium citrate on the heat stability of goat milk treated by TGase were studied.The results showed that disodium hydrogen phosphate,sodium pyrophosphate,sodium tripolyphosphate and sodium citrate could significantly(P<0.05)improve the heat stability and pH of TGase-treated goat milk,while sodium dihydrogen phosphate reduced the heat stability and pH of TGase-treated goat milk.The stable salt affected the heat stability of goat milk by its own action and regulating the pH of goat milk.When the pH of goat milk was certain(pH 6.7),the effects of five stable salts on the stability of goat milk were different.It was:sodium tripolyphosphate>sodium pyrophosphate>sodium citrate>disodium hydrogen phosphate>sodium dihydrogen phosphate,of which sodium tripolyphosphate had the most significant effect.