Effect of Thermal Processing on the Secondary Structure and Antigenicity of Bovine Milk α_s1-Casein

To investigate the effect of thermal processing on the conformation and antigenicity of bovine milk α_s1-casein, the changes in the immunogenicity of α_s1-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 α_s1-casein. The results showed that the α-helix content of α_s1-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 α_s1-casein led to a significant decrease in the antigenicity of α_s1-casein. The icELISA showed that the residual antigenicity of α_s1-casein was the highest after heating treatment at 70—100 ℃for 20 min, while the WB results showed that α_s1-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 α_s1-casein through animal tests.