Uncovering the Structure of Lignin from Moso Bamboo with Different Tissues and Growing Ages for Efficient Ambient-Pressure Lignin Depolymerization

Lignin is a complex and heterogeneous biomacromolecule, exhibiting significant variations in its structure based on plant species, growth stages, and tissue types. Uncovering the structure of lignin is crucial for guiding the chemical processing of bamboo and developing an efficient production of monophenols. Herein, the double enzymatic lignin (DEL) was isolated from bamboo with different tissues (parenchyma cells and fiber) and growing ages (1, 5, and 8 years), and the structural heterogeneity of this DEL was characterized. A hydrogen-free green ambient-pressure reductive catalytic depolymerization (ARCD) reaction of DEL aids in understanding the relationships between the molecular composition and the depolymerization performance of the lignin. The results revealed that the predominant interunit linkage of lignin in bamboo is β–O–4 linkages, particularly in parenchyma, with distinct distributions of typical lignin units such as tricin, ferulate (FA), and p-coumarate (pCA) between parenchyma and fibers. The macromolecular structure of lignin had a significant influence on the yield and selectivity for the production of monophenols, with higher yields observed for parenchyma cells. These findings highlight the potential of lignin depolymerization in 5-year-old moso bamboo parenchymal cells, rich in β–O–4 linkages, as a promising feedstock in lignin-first biorefineries. This work provides a valuable example of the selection of high-aryl-ether lignin feedstock for efficient lignin depolymerization and mass production of phenolic compounds.