Covalent binding of β-Lactoglobulin and rosmarinic acid by alkaline and free-radical treatment: Improved thermal stability and antioxidant capability

The aim of this study was to investigate the effect of rosmarinic acid (RA) on the structure and functional characteristics of β -Lactoglobulin ( β -LG) under two different covalent conditions (alkaline and free radical grafting). The successful covalent grafting of RA was predicted by the increase in the molecular weight of the complex, the total phenolic content, and the change in the reactive groups. The structure of the alkaline-modified conjugates gradually tightened with increasing RA concentration, whereas the structure of the free radical-grafted conjugates gradually stretched. Overall, the structure of β -LG became more stable (the number of α-helix and β-sheet rose), effectively enhancing the thermal stability of β -LG. In addition, the introduction of RA improved the interfacial wettability, emulsification, and antioxidant capacity of β -LG. This study provided some theoretical insights into the interactions between proteins and polyphenols.