Tyrosinase inhibitory mechanism of pyrimidine-thiols and their potential application in the anti-browning of fresh-cut apples.

The tyrosinase inhibitory activity and inhibition mechanism of pyrimidine-2-thiol (PT) and pyrimidine-2,4-dithiol (PDT) were investigated. In the anti-tyrosinase activity evaluation assay, PT exhibited 2-fold stronger activity than kojic acid in the presence of L-Tyrosine and L-Dopa, and PDT showed 13 times higher activity than kojic acid, respectively. Kinetic analysis revealed PT and PDT acted as mixed inhibitors. Copper ions chelation, fluorescence quenching, 1H NMR titration, and molecular docking assays manifested PT and PDT could participate in chelation with copper ions in the tyrosinase. Furthermore, UV and CD assay results suggested that PT or PDT could induce conformational changes in tyrosinase. Critically, both compounds delayed fresh-cut apple browning and did not exhibit appreciable toxicity on normal cells. These findings demonstrate that PT and PDT are highly potent, safe, and promising tyrosinase inhibitors, with significant potential as novel anti-browning agents for extending the shelf life of fresh-cut fruits in the food industry.