Inclusion complex of methyl gallate with hydroxypropyl-β-cyclodextrin, a tyrosinase inhibitor: Preparation, characterization and bioactivity evaluation

Abstract

Tyrosinase inhibitors are crucial in food preservation and hyperpigmentation treatment. In this study, methyl gallate (MG) was shown to exert a potent inhibitory effect towards tyrosinase activity and diminish o-quinone production competitively. This pronounced inhibition was probably associated with the strong capacity of MG to chelate copper ions and the alterations in the microenvironment and secondary structure of tyrosinase caused by MG binding. Unfortunately, the practical application of MG as a tyrosinase inhibitor is limited due to its poor water-solubility. To address this challenge, the inclusion complex of MG with hydroxypropyl-β-cyclodextrin (HP-β-CD) was further prepared. The resulting MG/HP-β-CD inclusion complex (MG/HP-β-CD-IC) exhibited a 1:1 stoichiometric ratio and superior encapsulation efficiency exceeding 80%, with MG solubility up to 217.16 mmol/L. Comprehensive characterization via SEM, FT-IR, XRD, TGA and molecular docking confirmed the successful embedding of MG into the HP-β-CD cavity driven by hydrogen bonding and hydrophobic interactions, and the MG/HP-β-CD-IC displayed an irregular block structure and exceptional thermal stability. Furthermore, in vitro bioactivity evaluation suggested that HP-β-CD inclusion maintained the original antioxidant and anti-tyrosinase activities of MG. These findings offered detailed insights into the mechanism of tyrosinase inhibition by MG and highlighted the great potential of HP-β-CD in improving MG's water-solubility.