The molecular weight of lignin extracted from lignocellulosic biomass is an important factor in determining its valorization in industrial processes. Herein, this work aims to explore the extraction of high molecular weight and bioactive lignin from water chestnut shells under mild conditions. Five kinds of deep eutectic solvents were prepared and applied to isolate lignin from water chestnut shells. The extracted lignin was further characterized with element analysis, gel permeation chromatography, and Ultraviolet-visible and Fourier-transform infrared spectroscopy. The distribution of pyrolysis products was identified and quantified with thermogravimetric analysis—Fourier-transform infrared spectroscopy and pyrolysis-gas chromatograph-mass spectrometry. The results showed that choline chloride/ethylene glycol/p-toluenesulfonic acid (1:1.8:0.2 molar ratio) exhibited the highest fractionation efficiency for lignin (84.17% yield) at 100 °C for 2 h. Simultaneously, the lignin showed high purity (90.4%), high relative molecular weight (37,077 g/mol), and excellent uniformity. Furthermore, the aromatic ring structure of lignin remained intact, consisting mainly of p-hydroxyphenyl, syringl, and guaiacyl subunits. The lignin generated a large number of volatile organic compounds during the depolymerization process, mainly composed of ketones, phenols, syringols, guaiacols, esters, and aromatic compounds. Finally, the antioxidant activity of the lignin sample was evaluated with the 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay; the lignin from water chestnut shells showed excellent antioxidant activity. These findings confirm that lignin from water chestnut shells has a broad application prospect in valuable chemicals, biofuels and bio-functional materials.

The high cellulose content of pine sawdust causes it to be highly valued as an excellent source for biorefining. However, the complicated interaction between lignin and cellulose presents an obstacle to the successful utilization of pine sawdust. The process of breaking down lignin has become essential for effectively using pine sawdust. The objective of the investigation was to explore the lignocellulolytic enzymes activity and its effect on lignin degradation by strain MP-132. A culture medium with pine sawdust as the solo carbon source was investigated. The performance of lignocellulose breakdown was evaluated through determining the activity of the lignocellulolytic enzymes. Fourier-transform infrared spectroscopy and thermogravimetric analyzer were used to investigate the changes in the structure and appearance of the degraded pine lignin. The maximum activities of lactase, lignin peroxidase, cellulase, and xylanase secreted by strain MP-132 reached 55.97 U/L, 142.6 U/L, 2.92 U/mL, and 2.08 U/mL, respectively. On day 15th, the degradation rates of cellulose, hemicellulose, and lignin were 28.78%, 32.9% and 30%, respectively. After treatment with strain MP-132, significant changes in the lignin structure have been observed in pine sawdust. These findings indicate that Raoultella ornithinolytica MP-132 exhibits potential as an alternative candidate for the lignocellulosic bioenergy industry.