The Correlation between Structural and Antigenicity Changes of Goat Casein by Heat Treatment
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Abstract:
The heat treatment of α-casein (α-CN) and β-casein (β-CN) in goat milk was explored by circular dichroism, fluorescence spectroscopy and other methods to analyze the effects of their structure and antigenicity. The results showed that with the increase of the heat treatment temperature of the casein, the natural structure of α-CN and β-CN was destroyed, caused molecular cross-linking or aggregation, and changed the molecular weight. The content of free carbonyl in the molecule increased. At 134 ℃, the carbonyl content increased by 134.72% and 110.98%, respectively. The free sulfhydryl content decreased continuously. The maximum fluorescence absorption intensity of the hydrophobic probes increased by 50.38%, and 9.61%, respectively. The temperature rise caused hydrophobic groups or disulfide bonds to be exposed, resulting in increasing hydrophobicity of the proteins. Circular dichroism results showed that the degree of curl or elastic structure in the secondary structure undergoes complex transformation, which changes the spatial structure of the protein. α- spirals were increased, β- turns and irregular curls were decreased. The antigenicity of casein decreased with increased temperature. After simulated gastrointestinal digestion, the antigenicity was reduced by 80.63% and 84.12%, respectively, at 134 ℃. Therefore, heat treatment can reduce the antigenicity of goat milk casein. And the change of antigenicity are inversely proportional to the change of free carbonyl content of protein. In addition, it is also positively correlated with the content of irregular curls and β-turns in the secondary structure.
