Effect Of Calcium Salt On Thermal Stability And Functional Properties Of Goat Milk Protein

In this project,goat milk was used as a test material to analyze the distribution of calcium salts in the micelle phase and whey phase under pH and heat treatment conditions.The changes of milk calcium and calcium chloride on the thermal stability of goat milk protein were discussed.The effects of calcium salt on the stability of goat milk casein micelles were studied systematically.The changes of calcium salt addition on liquid milk quality and storage characteristics and the functional characteristics of goat milk protein were discussed.This paper optimizes the processing conditions and storage stability of calcium goat milk products,and provides theoretical basis for the further study of calcium functional dairy products,the expansion and application of goat milk and the industrial production.(1)Studies on calcium content in goat milk under different pH and heat treatment conditions showed that the soluble calcium content in the whey phase decreased significantly with the increase of temperature at 65? and above(P<0.05),while the soluble calcium content in the whey phase increased significantly with the decrease of pH at pH between 6.9-4.9(P<0.05).It was found that the addition of calcium and the removal of calcium decreased the thermal stability of milk protein.The degree of transformation from regular structure to irregular structure of goat milk protein with milk calcium addition of 0.6 g/L and 1.0 g/L and calcium chloride addition of 0.4 and 1.0 g/L in heat treatment was higher than that in the heat treatment group without calcium,and the removal of calcium reduces this degree of transformation.(2)Casein(CN)with different calcium salt content was obtained by Ultra high speed centrifugation.The study of the stability of casein micelles by calcium salts found that the addition of milk calcium and calcium chloride caused the reduction of the casein content in the supernatant of the goat milk after ultra high speed centrifugation,and the contents of casein in the supernatant of goat milk with different calcium removal increased significantly.The hydration rate of casein micelle added with different calcium salts decreased significantly(P<0.05),and the hydration rate of casein micelle with decalcification rate of 8.54% and above increased significantly(P<0.05).Compared with fresh goat milk casein,the particle size of goat milk casein with decalcification rate of 8.54% and above decreased significantly(P<0.05).The absolute value of Zeta potential of casein micelles with 0.6 g/L milk calcium and above and casein micelles with 0.4 g/L calcium chloride and above significantly decreased(P<0.05),and the Zeta potential of casein micelles with decalcification rate 42.70% increased significantly(P<0.05).The turbidity of casein micelles with 0.4 g/L-0.8 g/L milk calcium and 0.2 g/L-0.8 g/L calcium chloride was significantly increased(P<0.05),while that of decalcified casein micelles was significantly decreased(P<0.05).The addition and removal of calcium salt make the secondary structure content of casein micelle in goat milk change from regular structure to irregular structure.These results indicate that the addition of calcium salt promoted the transfer of free casein to casein micelles in varying degrees,while the removal of calcium caused the dissociation of casein micelles and the increase of free casein.(3)The study of liquid milk quality and storage stability by adding calcium salt found that the centrifugal precipitation rate of pasteurized goat milk increased significantly when the amount of milk calcium was 0.6 g/L or above(P<0.05),while the centrifugal precipitation rate of pasteurized goat milk with different calcium chloride content increased first and then decreased with the increase of calcium content,and the highest centrifugal precipitation rate was 2.5% when the amount of calcium chloride was 0.6 g/L.The pH of goat milk with different calcium salt addition decreased significantly after pasteurized treatment and during storage(P<0.05).The addition of milk calcium and calcium chloride increased the content of soluble solids in the pasteurized milk.According to sensory analysis,when the amount of calcium chloride added is 0.2 g/L-1.0 g/L,the sensory score of its pasteurized goat milk is lower than that of the same amount of milk calcium.Therefore,the effect of milk calcium is significantly better than calcium chloride as a source of pasteurized high-calcium goat milk.(4)For high calcium acid goat milk,it was found that in the same storage time,the water holding capacity of goat milk added with different milk calcium and calcium chloride increased significantly during storage 1-5 d(P<0.05).The pH of goat milk with 0.6-0.8 g/L of milk calcium during storage 1-7 d increased significantly(P<0.05)and the acidity decreased significantly(P<0.05).The pH of goat milk with 0.6-1.0 g/L of calcium chloride during storage 1-5 d increased significantly(P<0.05)and the acidity decreased significantly(P<0.05).These results indicate that the addition of milk calcium and calcium chloride promotes the formation of the gel structure of acid goat milk.(5)The functional properties of goat milk protein were studied by removing calcium salt,and it was found that the removal of calcium changed the foaming properties,emulsifying properties and solubility of goat milk protein in varying degrees.