Condensed tannins from <i>Potentilla fruticosa</i> calyx as a potent tyrosinase inhibitor: mechanistic insights and application in fresh-cut asparagus lettuce preservation

Abstract Undesirable enzymatic browning of fruits and vegetables can be controlled by using effective tyrosinase inhibitors. In this study, bioactive tannins purified from the calyx of Potentilla fruticosa (PFTs) showed prominent inhibition on both the monophenolase (IC50 = 134.85 ± 0.04 μg/ml) and diphenolase (IC50 = 118.06 ± 8.30 μg/ml) activities of tyrosinase. Fourier transform infrared spectroscopy (FT-IR) and thiolysis coupled with reverse-phase high performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) revealed that PFTs were oligomeric condensed tannins with (epi)catechin, (epi)catechin gallate, and (epi)gallocatechin gallate as the predominant constitutive units. The inhibition of diphenolase by PFTs was found to be reversible and mixed type, with competitive inhibition being dominant. Integrated fluorescence, FT-IR spectroscopy and molecular docking results further demonstrated that PFTs bound to tyrosinase via hydrophobic interactions and hydrogen bonding, thereby perturbing the microenvironment of amino acid residues and altering the secondary structure of tyrosinase, which consequently led to the loss of enzyme catalytic activity. During storage, the browning of fresh-cut asparagus lettuce was efficiently delayed after treatment with PFTs, suggestive of its possibility as an anti-browning agent. Furthermore, PFTs possessed superior antioxidant efficacy compared to the commercial antioxidant BHT, as evaluated by DPPH, ABTS, and FRAP assays. Taken together, these findings supported the potential application of PFTs in the cosmetic and food preservation industries.