Molecular insights into the anti-browning effect of protocatechualdehyde.

Combined Inhibition of Polyphenol Oxidase by Oxyresveratrol and Epigallocatechin Gallate: A Natural Anti-Browning Strategy for Fresh-Cut Pears

Polyphenol oxidase (PPO) is a key enzyme responsible for enzymatic browning in fresh-cut fruits and vegetables, severely compromising their quality and shelf life. This study aimed to investigate the combined inhibitory mechanism of oxyresveratrol (OXY) and epigallocatechin gallate (EGCG) on PPO through multi-spectroscopic analyses, molecular docking, TEM, and XRD, with the goal of developing a natural and effective anti-browning strategy for fresh-cut fruits. The results showed that the optimal combined effect was achieved at an OXY:EGCG ratio of 1:2, where the inhibition rate was significantly enhanced by 43.72% and 14.36% compared to using OXY or EGCG single treatment, respectively. The combined treatment exhibited enhanced chelation capacity of copper ion and DPPH radical scavenging activity, and enhanced hydrogen-bonding interactions while lowering binding energy, exhibiting characteristics of mixed inhibition kinetics. Structural characterization showed that the combined treatment drastically reduced the enzyme’s fluorescence intensity to 39.81% of that of the native enzyme, induced rearrangements in α-helix and random coil structures, triggered obvious protein aggregation, and weakened the intensity of crystal diffraction peaks. Importantly, the combined treatment effectively delayed browning in fresh-cut pear slices, demonstrating its practical application potential. These findings provide a promising natural combined approach for controlling enzymatic browning and extending the shelf life of fresh-cut produce.

Design, synthesis and anti-browning mechanistic study of Trolox derivatives with dual antioxidant and tyrosinase inhibitory properties.

To obtain molecules with dual activities of antioxidant effect and tyrosinase inhibition, a new series of Trolox derivatives (5a-5g) were constructed by incorporating thiosemicarbazone moieties into Trolox based on the molecular hybridization principle. In vitro antioxidant and tyrosinase inhibition assays showed that compound 5a exhibited better antioxidant activity than Vitamin C, and its tyrosinase inhibitory activity was 11 times that of kojic acid. Structure-activity relationship analysis revealed that Trolox and thiosemicarbazone moiety in 5a were crucial for its antioxidant and tyrosinase inhibitory activities. Kinetic assays identified 5a as a reversible mixed-type inhibitor. Furthermore, the mechanism underlying tyrosinase inhibition was elucidated using copper ion chelation, fluorescence quenching, CD spectroscopy, and molecular docking. The mechanism study indicated that 5a interacted with tyrosinase through copper chelation, hydrogen bonding, and hydrophobic interactions, thereby reducing the enzyme activity. Furthermore, 5a could prevent browning in fresh-cut potatoes through its antioxidant and anti-tyrosinase activities.

Polyphenol Oxidase Inhibition for Browning Control in Fruit and Vegetable Products: Molecular Mechanisms, Computational Screening, and Natural Inhibitors

Enzymatic browning, primarily catalyzed by polyphenol oxidase (PPO), is a major cause of postharvest losses and quality degradation in fresh-cut fruit and vegetable processing. To control this browning, conventional methods such as sulfite treatment and thermal inactivation have been widely used, yet they increasingly face safety, sensory, and regulatory concerns. Because of this, more attention has been directed toward natural PPO inhibitors from agro-industrial by-products as safer, value-added alternatives. However, current knowledge of PPO inhibition mechanisms and rational inhibitor discovery remains fragmented across the literature, limiting the development of effective and sustainable anti-browning approaches. To address this gap, this review presents an integrated framework that covers (i) the structural and kinetic basis of PPO catalysis at the binuclear copper active site; (ii) the mechanistic classification of reversible and irreversible inhibitors, together with kinetic characterization using IC50, Ki, and nonlinear regression approaches; (iii) computational screening strategies, including molecular docking and molecular dynamics simulations as modern tools for predicting enzyme–inhibitor interactions and prioritizing candidate inhibitors; and (iv) the potential of agro-industrial by-products as renewable sources of natural PPO inhibitors for extending the shelf life of fresh-cut produce. Through this framework, this review provides an integrated perspective to support the rational evaluation and future development of effective, sustainable PPO inhibitors for food processing.

Elucidating the Antiglycation Potential of Plumbagin Against Methylglyoxal-Induced Glycation of Bovine Liver Catalase.

These findings highlight plumbagin as a potent multifunctional compound capable of mitigating MGO-induced glycation, and highlight plumbagin as a potent multifunctional compound capable of mitigating MGO-induced glycation.

Antioxidant Activity and HepG2 Cytoprotection of Water-Soluble Chili Pepper Polyphenols

Inhibitory Effects of Grape Seed Extract and Epicatechin on Malondialdehyde-Mediated Protein Lipoxidation.

Malondialdehyde (MDA) is one of the principal and most studied reactive carbonyl species derived from polyunsaturated fatty acid peroxidation. This aldehyde is a chemically reactive molecule and should not be considered merely as a marker of lipid peroxidation. Its interaction with proteins, commonly termed protein lipoxidation, modifies protein structure and functions, thus extending the hazards of lipid peroxidation. In this study, a simplified model mimicking MDA-mediated protein oxidation in bovine serum albumin (BSA) was established to simulate protein lipoxidation in food systems. Grape seed extract (GSE, 50-200 mg/L) and epicatechin (EC, 145-580 mg/L) significantly inhibited MDA-mediated protein lipoxidation in BSA, as evidenced by a marked decrease in lipofuscin-like fluorescence and confirmed via Western blot analysis of MDA-protein adduct formation. Nevertheless, concentration-dependent dual effects were observed by protein conformational changes (reduced sulfhydryl, surface hydrophobicity, and altered microstructure) at high concentrations of GSE and EC, although they exhibited potent inhibitory effects in MDA-mediated protein lipoxidation. HPLC quantification demonstrated that GSE scavenged 10-60% of MDA while EC scavenged 70-95%, indicating their direct contribution to MDA removal. Molecular docking simulations further implied a possible binding mode in which EC associates with BSA more favorably (lower free energy) than MDA, which may competitively block the sites accessible to MDA. Collectively, these findings support a mitigation strategy in which phenolic nucleophiles can be employed to counteract MDA-mediated protein lipoxidation.