Abstract: In this study, changes in the structure and antigenicity of the milk allergenic proteins α-casein (α-CN) and β-casein (β-CN) after ultrasonic treatment were investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, circular dichroism (CD) spectroscopy, fluorescence spectroscopy and enzyme-linked immunosorbent assay (ELISA). The results showed that with the increase of ultrasonic power, the molecular mass of α-CN did not change significantly, β-CN aggregated at 600 W; the carbonyl contents of the two caseins increased, and the free sulfhydryl contents decreased first and then rose after reaching a minimum value at 500 W, while the trend was opposite to that of hydrophobicity. The proportion of α-helical secondary structure was reduced after sonication, and the proportion of random coil initially increased with ultrasonic power up to 500 W and then decreased; this trend was opposite to that of β-sheet content, indicating that ultrasonic treatment could destroy the structure of casein. As the ultrasonic power increased, the antigenicity first increased, reaching a maximum level at 500 W, and then decreased. The hydrophobicity of caseins was positively correlated with changes in random coil content, but negatively correlated with changes in β-sheet content. Sonication could affect protein structure conformation while altering the antigenicity of caseins, which was associated with changes in hydrophobicity and random coil content.

Key words: bovine α-casein, ultrasonic, antigenicity, carbonyl, sulfhydryl, secondary structure, hydrophobicity