To investigate the effect of thermal processing on the conformation and antigenicity of bovine milk αs1-casein, the changes in the immunogenicity of αs1-casein under different heating conditions were analyzed by indirect competitive enzyme immunosorbent assay (icELISA) and Western blotting (WB) methods, and then the secondary structure changes were analyzed by fluorescence spectroscopy using 8-anilino-1-naphthalenesulfonic acid (ANS) as a probe and circular dichroism spectroscopy to preliminarily reveal the regulatory mechanism of heat treatment on the antigenicity of αs1-casein. The results showed that the α-helix content of αs1-casein significantly decreased after treatment at 80 ℃ for 60 min, 90 ℃ for 10 min or 90 ℃ for 60 min compared with the untreated control, whereas the random coil content increased significantly after treatment at 70 ℃ for 20 min, 80 ℃ for 20 min or 90 ℃ for 20 min. The surface flourescence intensity was the strongest after heating treatment at 70-100 ℃ for 20 min, while the secondary structure changes were not significant under other heating conditions. The conformational changes of αs1-casein led to a significant decrease in the antigenicity of αs1-casein. The icELISA showed that the residual antigenicity of αs1-casein was the highest after heating treatment at 70-100 ℃ for 20 min, while the WB results showed that αs1-casein still had immunoreactive properties under all heating conditions. It is suggested to further reveal the regulatory mechanism of heat treatment on the antigenicity of αs1-casein through animal tests.

In order to investigate the effects of tea polyphenols on the conformation and antigenicity of αs1-casein, epigallocatechin gallate (EGCG) and epigallocatechin (EGC), tea polyphenols with high bioactivity, were used for grafting onto αs1-casein. The conformational changes of αs1-casein were studied by fluorescence, synchronous fluorescence and circular dichroism (CD) spectroscopy, and the changes in the antigenicity of αs1-casein were analyzed by indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and Western blot assay. The results showed that EGC and EGCG both quenched the fluorescence of αs1-casein, and affected the Tyr and Trp residues of αs1-casein. The α-helix and β-sheet contents of αs1-casein increased slightly, and the random coil content decreased slightly. The conformational change of αs1-casein resulted in a significant decrease in the antigenicity of αs1-casein. The effect of EGCG on the conformation and antigenicity of αs1-casein was stronger than that of EGC.