Interaction between β-lactoglobulin and chlorogenic acid and its effect on antioxidant activity and thermal stability

The impact of β-lactoglobulin (β-lg) on antioxidant properties of chlorogenic acid (CGA) and the stability of their complexes under different thermal treatments were explored in this study. At lower temperature (below 60 °C), the interactions between CGA and β-lg were hydrophobic, hydrogen bonding and other non-covalent interactions. Increasing temperature promoted covalent bonds between CGA and β-lg because of the changes in the secondary structure and the unfolding of the structure accompanied by the exposure of hydrophobic groups and amino acids in β-lg molecules. Covalent and non-covalent β-lg-CGA complexes retarded the loss of antioxidant properties of CGA and maintained β-lg-CGA solution stability, as determined by centrifugal acceleration experiments, ABTS free radical scavenging and ferrous ion reduction experiments. The fluorescence intensity, circular dichroism, molecular weight, particle size distribution, potential size, amino and sulfhydryl content and electrophoresis distribution were measured to understand the type and strength of the interaction between β-lg and CGA. This interaction significantly increased the antioxidant activity of CGA compared to sole CGA solutions by the results of the ABTS scavenging capacity and FRAP measurements. Concurrently, the thermal stability of β-lg in solutions was enhanced through β-lg-CGA covalent and non-covalent complex interaction with heat treatment. This research provides the foundation for the application of β-lg and CGA in healthy food to retard thermal denaturation of β-lg and loss of antioxidant activity.