Quantitative structural elucidation of original lignins in different varieties of waste Gleditsia sinensis Lam. pods

Abstract

Obtaining new materials, industrial chemicals, and energy from the conversion of agricultural and forestry biomass to fill the gap of non-renewable fossil energy has become a growing trend. As a waste biomass, the G. sinensis pods (GSP) after saponin extraction are always discarded due to lack of industrial/high value-added utilization. Herein, in order to lay a foundation for the selection of pretreatment strategies of GSP and the valorization of GSP lignin, the lignins from the different varieties of GSP were isolated by double enzymatic method and quantitatively characterized. Results indicated that GSP lignin was of the GS-type (S/G, 1.1–1.4) and the interunit linkages were mainly β-O-4′ linkage, along with a certain amount of carbon-carbon linkages (≈35/Ar). L1 showed higher β-O-4′ linkage content (61.3/100 Ar) and relative molar mass (12190 mol/g). Some atypical lignin units, such as cinnamyl aldehyde end-group, cinnamyl alcohol end-groups, and ferulates, were also revealed in GSP lignins. Finally, the potential molecular structure graphs of the GSP lignin were depicted on the basis of the quantitative results. Overall, comprehensive research of the structural characteristics of GSP lignin is essential for efficiently deconstructing GSP and transforming the utilization of the cell wall components.