Construction of a Tannase-Immobilized Magnetic Graphene Oxide/Polymer Nanobiocatalyst with Enhanced Enzyme Stability for High-Efficiency Transformation of Tannins

Highly efficient biotransformation of natural compounds into sustainable biochemical products has attracted great attention. The integration of nanoscience and biotechnology provides attractive solutions for this purpose. Herein, we report the fabrication of a nanobiocatalyst employing a magnetic graphene oxide/polymer nanocomposite as a robust carrier for immobilizing the tannase enzyme, which catalyzes the bioconversion of tannin into gallic acid and glucose. Attributed to the covalent immobilization and propitious interface properties of the coated polymers comprising polyethylenimine and sodium hyaluronate, the nanobiocatalyst is stable without compromising the enzymatic activity. The nanobiocatalyst exhibits 91.8% activity of original tannase and a high enzyme bound amount of 356.8 mg g–1. The stability tests at variable temperatures (30–80 °C) and under pH conditions (4.0–9.0), various inhibitors, and a long-term storage process (25 days) reveal that the heterofunctional support and surface microenvironment facilitate better stability, adaptability, and tolerance ability of the nanobiocatalyst modified with a multicomponent polymer in comparison to the free enzyme and the nanobiocatalyst modified with the monocomponent polyethylenimine. The nanobiocatalyst maintains 94.2% of its initial activity after 10 consecutive uses and is 100% recoverable by applying an external magnet. Moreover, the nanobiocatalyst is used to hydrolyze 96.5 and 95.1% tannins in extracts from Chinese Torreya grandis testa and cake, respectively. These results establish the practicability of magnetic graphene oxide-based supports for immobilizing tannase and the promising application of immobilized tannase for efficient tannin hydrolysis.