No abstract

The characterization, anti-tyrosinase activity, cytotoxicity against B16 mouse melanoma cells, antioxidant, and DNA damage protection activities of condensed tannins purified from Vigna angularis seeds were reported.

The activities of ellagic acid in inhibiting mushroom tyrosinase and cell proliferation were evaluated in this research. The results of enzyme kinetics indicated that ellagic acid could effectively inhibit tyrosinase activity. The value of the semi‐inhibitory rate (IC50) was 0.2 ± 0.05 mM. Ellagic acid inhibited tyrosinase activity in a reversible manner and was a mixed tyrosinase inhibitor. Furthermore, ellagic acid had a good inhibitory effect on the proliferation of mouse melanoma B16 cells and could induce apoptosis. The results acquired from fluorescence spectroscopy revealed that the interaction of ellagic acid with tyrosinase depended on hydrogen bond and electrostatic force. In addition, computational docking showed that ellagic acid interacted with amino acid residues of tyrosinase (Asn19 and Lys372) by hydrogen bond and produced electrostatic interaction with amino residue Lys18. Practical applications In the present research, the antityrosinase mechanism of ellagic acid and its effect on mouse melanoma cells were investigated. This study suggested that ellagic acid had a strong inhibitory activity against tyrosinase and cell proliferation,which laid an experimental foundation for the development of new drugs and whitening products. The combined multispectral methods used in this research can be applied to the screening of other antityrosinase inhibitors, further promoting the development and utilization of tyrosinase inhibitors.

Tyrosinase (polyphenol oxidase) is the key enzyme of enzymatic browning in fruits and vegetables. In this research, the impact of ascorbic acid on tyrosinase and its anti‐browning effect on fresh‐cut Fuji apple were investigated. Ascorbic acid had a dual effect on tyrosinase with a half inhibitory concentration (IC50) of 13.40 ± 0.05 µM. Fluorescence assay demonstrated that ascorbic acid interacted with tyrosinase in a dynamic contaction caused by Förster’s resonance energy transfer (FRET) and induced a conformational change of the enzyme. Thermodynamic analysis, copper interaction, and molecular docking further confirmed that ascorbic acid could chelate the copper ions located in active center and interact with amino acid residues of tyrosinase via hydrophobic interaction. In addition, ascorbic acid prevented the browning of fresh‐cut apples by increasing APX activity and inhibiting PPO and POD activities which reduce the oxidation of total phenolics and flavonoids. Practical applications The present study demonstrated that ascorbic acid had a strong inhibitory activity against tyrosinase (IC50 = 13.40 ± 0.05 µM) and anti‐browning activity against fresh‐cut Fuji apple. It could delay the browning degree of apple juice, increase APX activity, inhibit PPO and POD activities, and reduce the oxidation of total phenolics and flavonoids. These findings provided a basis for the feasible application of ascorbic acid on the preservation of fruits.