6,7-Dimethoxy-3H-Quinazolin-4-One as a dual-function inhibitor of polyphenol oxidase and bacteria: biological evaluation, mode of action, and anti-browning studies

Abstract

This research investigated the inhibitory effect and mechanism of 6,7-dimethoxy-3H-quinazolin-4-one (DMQ) on polyphenol oxidase (PPO) and bacteria (Escherichia coli and Staphylococcus aureus), as well as its anti-browning properties on fresh-cut apples. The findings demonstrated that DMQ potently inhibited PPO activity with an IC₅₀ of 98 ± 3 μmol L⁻¹. Subsequently, the inhibitory mechanism of DMQ against PPO was elucidated through enzyme kinetics, fluorescence analysis, as well as computer molecular simulation. The results revealed that the interaction between DMQ and PPO led to structural elongation and relaxation of the enzyme, and influenced the microenvironment of amino acid residues at the binding region. These changes modified secondary structure and molecular conformation of PPO, ultimately resulting in the reduction of catalytic activity. Antibacterial experiments demonstrated that DMQ exhibited remarkable antibacterial properties by enhancing cell membrane permeability in E. coli and S. aureus, contributing to cellular contents leakage and bacterial cell death. Furthermore, DMQ delayed the enzymatic browning of fresh-cut apples by controlling phenolic metabolism. In particular, it was confirmed by cytotoxicity and stability tests that DMQ was safe at experimental concentrations and had good thermal stability and photostability. These discoveries offered a theoretical framework for the potential application of DMQ in food preservation.