Treatments of heating and ultrasound improve the inhibition of gallocatechin gallate on tyrosinase.

Abstract

Gallocatechin gallate (GCG), a catechin of tea polyphenols, possesses inhibitory ability against tyrosinase, but few studies have reported how common processing methods affect it. In this research, the influence of heating and ultrasound treatments on the inhibition of GCG against tyrosinase was explored by ultraviolet-visible absorption, fluorescence spectroscopy, high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry. Both heating and ultrasound treatments of GCG alone improved GCG's inhibitory ability against tyrosinase compared with the untreated, and a combination of heating and ultrasound treatment (100 °C, 20 min + 630 W, 20 min) further decreased the relative tyrosinase activity to 26.8%. The treated GCG exhibited a stronger fluorescence quenching effect on tyrosinase, but did not have any influence on the static quenching mechanism. Compared to the untreated GCG, the binding constants of treated GCG by heating, ultrasound and their combination with tyrosinase significantly increased, but the number of binding sites was still approximately one and the main driving force of the treated GCG was still hydrophobic interaction. After treatments of heating, ultrasound and their combination, the composition of GCG solutions was changed. The enhanced inhibition of treated GCG on tyrosinase may be due to partial conversion of GCG into epigallocatechin-3-gallate (EGCG) and gallic acid (GA), which may cooperate with GCG to better inhibit the enzyme activity. This study has provided some valuable information for the application of catechins against tyrosinase in food processing and cosmetic industry. © 2022 Society of Chemical Industry.