Inhibition of enzymatic browning in fresh-cut potatoes by 1,3,4-oxadiazole-2-thiol analogs and elucidation of their tyrosinase inhibition mechanism

Abstract

Tyrosinase is the rate-limiting enzyme in enzymatic browning, and its activity is closely related to copper ions at the active site. We hypothesized that 1,2,4-oxadiazole derivatives could chelate copper ions at the active site of tyrosinase, thereby inhibiting its activity. Fourteen 1,3,4-oxadiazole-2-thiols were developed to evaluate Cu²⁺-chelating and anti-tyrosinase effects. Compound 2f (IC₅₀ = 17.7 ± 0.21 μM) had stronger activity than kojic acid (IC₅₀ = 47.7 ± 0.49 μM) as a mixed-type inhibitor. HPLC revealed that 2f inhibited dopaquinone formation, whereas UV/CD spectroscopy showed that 2f induced tyrosinase conformational changes. Fluorescence quenching, Cu²⁺ chelation, and molecular docking analyses confirmed the direct Cu²⁺-binding ability of 2f. In addition, 2f had low cytotoxicity and effectively prevented browning in fresh-cut potatoes. These results confirm our hypothesis that thiol-containing 1,3,4-oxadiazole derivatives inhibit tyrosinase for Cu²⁺ chelation and hydrophobic interactions. The results support their potential as safe, efficient anti-browning agents for fresh-cut produce preservation, addressing industry needs for practical enzymatic browning control.