Lignin structural elucidation and compositions investigation of Camellia oleifera fruits collected from various locations

A sufficient understanding of structural characteristics of lignin is essential for the production of biomaterials, bioenergy, and biochemicals from lignocellulosic biomass. Camellia oleifera fruit shell (CFS) is a considerable waste lignocellulosic resource in the camellia seed oil production industry, and contains a large amount lignin. Herein, to understand the structural characteristics of CFS lignin, double enzymatic lignins (DEL) and acid-soluble lignins (ASL) from CFS collected from various locations were separated and thoroughly characterized. Additionally, to synthetically comprehend the difference among the six camellia varieties, the chemical compositions of the camellia fruits were also studied. The results showed that the ASL from XL210 shells showed the highest lignin derivative content (4.15 wt %). All DEL were of the SG-type with low S/G ratios (0.47–0.88) and homogeneous structures (Mw/Mn, 2.00–2.06). The DEL showed a high content of β−O−4 aryl ether linkages (41.89–48.26/100 Ar) and C−C interunit linkages, namely β−β (14.84–26.30/100 Ar) and β−5 (9.61–13.85/100 Ar). DELQD had the highest total phenolic OH content (2.64 mmol/g) among the six DEL. Finally, the structural models of the DEL were depicted. Understanding the chemical compositions of Camellia oleifera fruits and structural characteristics of the CFS lignins would facilitate the optimization of the pretreatment process and the deconstruction of the CFS, and in addition, it would be important for the future comprehensive utilization of Camellia oleifera fruits and the valorization of the CFS.