Polyphenol Oxidase from Dendrobium officinale Flowers: Characterization and Browning-Promoting Mechanism

Polyphenol oxidase (PPO) triggered browning during the
storage
and processing of Dendrobium officinale flower (DoF), impairing their nutritional and aesthetic
qualities. This study aimed to investigate the enzymatic properties
and enzymatic browning mechanisms of PPO in DoF,
providing a theoretical foundation for developing effective strategies
to inhibit enzymatic browning. PPO with high purity was obtained by
ammonium sulfate precipitation and ion-exchange chromatography, further
identified by electrophoresis and LC-MS/MS. The PPO exhibited optimal
activity at 35 °C and pH 6.5, while ascorbic acid, glutathione,
and L-cysteine significantly inhibited its activity
and furanones demonstrated potential inhibitory effects. Moreover,
caffeic acid, identified as the most active PPO substrate in DoF, was determined to be the primary contributor to browning.
Molecular docking revealed that caffeic acid exhibited stronger interactions
with PPO compared with other phenolic compounds, which further revealed
the substrate selection mechanism of PPO and the molecular basis of DoF browning.