Elucidating the inhibitory mechanism on polyphenol oxidase from mushroom and melanosis formation by slightly acid electrolysed water.

• Slightly acid electrolysed water (SAEW) inhibited PPO in a mixed-type mode. • SAEW bound to PPO by hydrogen bond and rearranged the secondary structure. • HOCl bound to the active site of PPO to inhibit its enzymatic activity. • SAEW treatment inhibited melanin related compounds formation. It has been revealed that slightly acid electrolysed water (SAEW) could delay enzymatic browning and melanin formation in food. In this work, multi-spectroscopic methods and UHPLC-Q-TOF-MS were combined to study the underlying reason. The reversible mixed-type inhibition mode of HOCl (main components in SAEW) was determined. The ground state complex formation quenched the intrinsic fluorescence of polyphenol oxidase (PPO) and it was stable at lower temperature. The PPO conformational change (transformation from α-helix to β-sheet) induced by SAEW was confirmed by 3D fluorescence and Circular dichroism (CD) spectrum. Moreover, the driving force of the interaction between HOCl and PPO was hydrogen bond, which was validated by the molecular docking result. Besides, the formation of melanin related compounds including dihydroxyphenylalanine (DOPA), dopaquinone, dopachrome, 5,6-dihydroxyindole-2-carboxylic acid (DHICA), 5,6-dihydroxyindole (DHI), and 5,6-indolequinone were significantly inhibited by SAEW treatment. These results demonstrated the potential of SAEW as a PPO inhibitor in the food industry. [ABSTRACT FROM AUTHOR]