Immobilization of polyphenol oxidase on chitosan/organic rectorite composites for phenolic compounds removal

Immobilization of Agaricus bisporus Polyphenol Oxidase 4 on mesoporous silica: Towards mimicking key enzymatic processes in peat soils

HYPOTHESIS

The use of immobilized enzyme-type biocatalysts to mimic specific processes in soil can be considered one of the most promising alternatives to overcome the difficulties behind the structural elucidation of riverine humic-derived iron-complexes. Herein, we propose that the immobilization of the functional mushroom tyrosinase, Agaricus bisporus Polyphenol Oxidase 4 (AbPPO4) on mesoporous SBA-15-type silica could contribute to the study of small aquatic humic ligands such as phenols.

EXPERIMENTS

The silica support was functionalized with amino-groups in order to investigate the impact of surface charge on the tyrosinase loading efficiency as well as on the catalytic performance of adsorbed AbPPO4. The oxidation of various phenols was catalyzed by the AbPPO4-loaded bioconjugates, yielding high levels of conversion and confirming the retention of enzyme activity after immobilization. The structures of the oxidized products were elucidated by integrating chromatographic and spectroscopic techniques. We also evaluated the stability of the immobilized enzyme over a wide range of pH values, temperatures, storage-times and sequential catalytic cycles.

FINDINGS

This is the first report where the latent AbPPO4 is confined within silica mesopores. The improved catalytic performance of the adsorbed AbPPO4 shows the potential use of these silica-based mesoporous biocatalysts for the preparation of a column-type bioreactor for in situ identification of soil samples.

Process optimization of polyphenol oxidase immobilization: Isotherm, kinetic, thermodynamic and removal of phenolic compounds

Chitosan/montmorillonite (CTS/MMT) and chitosan‑gold nanoparticles/montmorillonite (CTS-Au/MMT) composites were prepared, characterized through Fourier transformed infrared (FT-IR), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM), and utilized as support for immobilization of polyphenol oxidase (PPO). PPO was immobilized on CTS/MMT (IPPO) and CTS-Au/MMT (IPPO-Au) by physical adsorption, respectively. In order to achieve simultaneous maximization of immobilization efficiency and enzyme activity, the immobilization process parameters were optimized by Taguchi-Grey relational analysis (TGRA) approach. Under the optimal immobilization condition, the immobilization efficiency and enzyme activity reached at 50.16% and 1.46 × 10⁴ U/mg for IPPO, and 63.35% and 3.01 × 10⁴ U/mg for IPPO-Au, respectively. The isotherm, kinetic and thermodynamics of PPO adsorption were investigated in detail. The adsorption process was better explained by Toth isotherm and Fractal-like pseudo second order model, respectively. Intra-particle diffusion and film diffusion were involved in the adsorption process and intra-particle diffusion was not the only rate-controlling step. The adsorption of PPO was exothermic, physical and spontaneous at the investigated temperature range. The immobilized PPO were used to oxidize phenolic compounds. All investigated phenolic compounds showed the higher conversion as catalyzed by IPPO-Au. For both IPPO and IPPO-Au, the conversion of substituted phenols was higher than that of phenol.