Effects Of Different Carbohydrates On The Heat Aggregation Behavior Of Protein From Goat Milk And Quality Of Dairy During Storage

In this paper,the goat milk of Laoshan dairy goat was selected as the experimental raw material.0.2% trehalose,0.2% chitooligosaccharides(COS)and 0.05% pectin were added to milk then pasteurized and partially pasteurized + spray drying.Heat denaturation temperature,microstructure(including average variable,Zeta potential,turbidity and secondary structure),functional characteristics(including emulsifying ability index,EAI;emulsifying stability,ES,foaming capacity,FC and foaming stability,FS)of goat milk protein Stability)and the quality of pasteurized milk,pasteurized fermented goat milk during storage were observed to measure the effect of those additives.According to DSC,the heat denaturation temperature of fresh goat milk was about 132 ℃.After adding 0.2% trehalose,0.2% COS and 0.05% pectin,the variation temperature increased to 135 ℃,139 ℃ and 144 ℃ respectively.Through SDS-PAGE gel electrophoresis,it was found that the addition of two kinds of heat processing and the addition of three kinds of sugar caused the denaturation of milk protein to varying degrees.In terms of average particle size,in the pasteurization group,the addition of the three carbohydrates increased average particle size significantly(P <0.05),the level of impact from high to low was: pectin> COS> trehalose.In the pasteurization + spray drying group,the order of the average change from large to small was trehalose>COS> pectin.As far as Zeta potential was concerned,in pasteurization group,the addition of trehalose and pectin has no significant effect on the stability of goat milk protein.The addition of COS decreased the stability of protein significantly(P <0.05);in the pasteurization + spray drying group,the addition of trehalose decreased the stability of protein significant(P <0.05),the addition of COS and pectin has no significant effect on the stability of the milk protein.The change trend of turbidity was basically similar to the average particle size.In terms of secondary structure,the regular conformation ratio of the secondary structure in raw milk protein was about 60%.The secondary structure were damaged to vary degrees with the addition of three carbohydrates.In pasteurization group,the addition of trehalose,COS and pectin increased the irregular conformation of milk protein,and the effect from high to low was: trehalose> COS> pectin.In the pasteurization + spray drying group,trehalose,COS and pectin could all protect the regular structure of goat milk protein,and the protective effect was ranked from large to small: COS> trehalose> pectin.In terms of functional characteristics,compared with the control group,after pasteurization,the EAI decreased significantly while the ES and FC increased significantly(P<0.05);in the spray drying group,the FC was small Increase;the FS does not change significantly.After pasteurization + spray drying treatment,the EAI decreased while the ES and FS increased significantly(P<0.05).In the pasteurization group,pectin increased EAI significantly,and trehalose increased ES significantly increased.COS significantly increased FC,and trehalose and pectin significantly increased the FS(P<0.05).In the spray drying group,the spray drying treatment significantly reduced the EAI and significantly increased the ES and FS(P<0.05).COS significantly increased the EAI and FC,and trehalose significantly increased the FC and ES(P<0.05).If good interface characteristics and stability were expected,in the pasteurization group,the addition of COS mades the milk protein have good emulsification and foaming properties.In the spray drying group,trehalose could make the milk protein have good emulsification and foaming properties.During the storage period of pasteurized milk,in the Meilan reduction test,the addition of pasteurization,trehalose,and chitooligosaccharides could extend the freshness by 2 days,and pectin can extend by 1 day.The appearance of the addition of three carbohydrates to the phenomenon of alcohol-positive milk was also consistent with the Meilan reduction test.The three carbohydrates had no obvious protective effect on the protein content of pasteurized milk during storage.Pasteurization,trehalose and chitosan can maintain the p H of goat milk.All three carbohydrates can slow down the decline of soluble solids.During the storage period of the pasteurized goat milk,trehalose,COS and pectin had a certain stabilizing effect on the p H of the pasteurized goat milk,and the effect from high to low is: trehalose>chitosan > pectin.Pasteurization,trehalose and COS could all inhibit post-acidification,and COS had a stronger effect.All three carbohydrates can improve the water holding capacity of pasteurized fermented milk,and it was relatively stable during storage.At the end of the storage period,the water holding capacity from high to low was: trehalose>COS>pectin.