Native Lignin Isolation Facilitated by Cellulase Desorption

Isolating lignin in its native form is essential to understand the lignin chemistry involved in the processing pathway. However, native lignin, due to its heterogeneous aromatic structures and spatial entanglement with carbohydrates, is challenging to separate quantitatively. Cellulase hydrolysis, a mild and effective treatment, allows lignin to be separated in its solid form. However, nonspecific adsorption of cellulases onto lignin during the enzymatic hydrolysis leads to protein contamination, thus interferencing with characterization and quantification of lignin. Addressing is crucial for obtaining high-quality lignin. In this study, this issue is addressed by adopting an alkaline-buffered solution to effectively remove cellulase residues from enzymatic lignin. The efficiency and extent of cellulase desorption were qualitatively and quantitatively analyzed, while the impact of buffer treatment on lignin composition and structure was evaluated in detail. The isolated lignin exhibited over 97% yield, with a carbohydrate content of approximately 5%. The lignin-derived monophenol yield from alkaline nitrobenzene oxidation exceeded 40 wt %, approaching the theoretical maximum yield from native lignin. Furthermore, a simplified purification process achieved nearly 99% purity, resulting in the production of a high-molecular-weight native lignin. The alkaline buffer treatment provides a straightforward and effective method to improve the native lignin isolation with high yield and purity.