The stability of polyphenol oxidase in deep eutectic solvents: Insights from spectroscopy and molecular docking

The activity of polyphenol oxidase (PPO) in vitro is susceptible to inactivation, making the stabilization of PPO activity crucially important. This study investigated the stability of PPO in seven types of deep eutectic solvents (DES). The results indicated that DES provides good enzyme stability, with betaine-based DES demonstrating a particularly prominent effect on PPO stability; specifically, enzyme activity was highest when using 60 % (v/v) betaine-glycerol (DES-7). Ultraviolet-visible (UV-vis) and fluorescence spectroscopy results revealed that the binding of DES to PPO induces certain conformational changes, with the fluorescence quenching of PPO by DES-7 attributed to static quenching. Circular dichroism spectroscopy results further indicate that the addition of DES-7 enhances the stability of the α-helix region, significantly increasing the content of α-helix structures in the enzyme protein. Additionally, molecular docking results similarly show that the interaction between DES and PPO leads to conformational changes in PPO, with hydrogen bonds and van der Waals forces identified as the primary binding forces. These findings provide theoretical references for understanding the mechanism of the interaction between PPO and DES, as well as technical support for the industrial application of DES in PPO.