Effect of thermal treatment on the molecular-level interactions and antioxidant activities in β-casein and chlorogenic acid complexes

The interaction between beta-casein (beta-CN) and chlorogenic acid (CA) following treatments at 25, 65, 100, and 121 degrees C and their effects on the antioxidant capacity of resultant complexes were investigated. Fluorescence spectroscopy indicated that CA bound to beta-CN mainly via hydrophobic interactions, and thermal treatment at 121 degrees C weakened the binding affinity. Circular dichroism showed that CA and thermal treatment did not affect the secondary structure of beta-CN. Fourier transform infrared spectroscopy indicated that, except for excessive CA, CA did not cause a significant change in the vibrational wavenumber of the amide II of beta-CN. According to the results of matrix-assisted laser desorption and ionization tandem time-of-flight mass spectrometry and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, no covalent bond was observed in the complexes formed between beta-CN and CA after thermal treatments. Assessments of antioxidant capacity indicated a synergistic effect observed between beta-CN and CA in FRAP and an antagonistic effect in ABTS. After 30 min of thermal treatment at 65 degrees C, beta-CN-CA complexes exhibited rather strong antioxidant capacity. These results support the use of CA in functional dairy beverages and maintaining their antioxidant capacity by modulating processing conditions.

Automated summary

The study found that chlorogenic acid binds to beta-casein mainly through hydrophobic interactions, with thermal treatment reducing the binding affinity between them but not affecting the secondary structure of beta-casein. Additionally, no covalent bond was observed in the complexes formed, and a synergistic effect was observed between beta-casein and chlorogenic acid in the assessment of antioxidant capacity in FRAP, while an antagonistic effect was seen in ABTS.