Novel bind-then-release model based on fluorescence spectroscopy analysis with molecular docking simulation: New insights to zero-order release of arbutin and coumaric acid

The present study aimed to systematically investigate the mechanisms of the zero-order release of arbutin and coumaric acid from whey protein concentrate-high methoxyl pectin (WPC-HMP) complex. The morphological analysis was applied to characterize the structure of the complexes, and fluorescence spectroscopy analysis with molecular docking simulation was used to study their binding interactions. The results indicated that porous structure of WPC-HMP with average pore diameter of 29.02 μm had no influence on the release profiles. The binding constant of coumaric acid (8.71 × 10⁴ L/mol) was higher than that of arbutin (2.90 × 10⁴ L/mol) at 298 K, led to the priority in binding order of coumaric acid. The main binding affinities were van der Waals forces and hydrogen bonds for arbutin, but hydrophobic interactions for coumaric acid. The binding interactions also resulted in regular conformational and structural changes of WPC. Moreover, a novel bind-then-release model for arbutin and coumaric acid was developed, revealing the final zero-order release profile is the balance between the competition effect and the diffusion effect.