Successful incorporation of plant-based materials into biorefinery processes is heavily dependent pretreatments which allow economically-sensible access to target compounds. Confocal Raman Microscopy (CRM) offers the unique analytical opportunity to - without any chemical specimen alteration - qualitatively and semi-quantitatively observe the
in muro spatial distribution of structural components
. The effect of hot water pretreatment on the distribution of lignin and cellulose inside the cell walls of
Acer saccharum was studied. Wood chips were transversely microtomed into thin sections of 10 µm. These sections were pretreated in hot water at 160 C for varying lengths of time and then analyzed by CRM. Alternatively, wood chips were pretreated first and then subject to CRM analysis. Raman spectra were obtained by excitation with a polarized laser (λ=532nm) on a LabRam Xplora Confocal Raman Microscope. Spectra were analyzed by the equipmentâs built-in LabSpec software component. Primary component and cluster analyses of the data were also performed to sort data corresponding to morphologically distinct cell wall layers.
The results showed for the first time, that lignin dissolved progressively from the secondary walls and the compound middle lamella regions. Samples where the lignin dissolution was limited by transport within the cell walls were markedly heterogeneous and showed large variations in distributions within the morphologically distinct CML and secondary layers. On the other hand, when thin section samples were subjected to pretreatments, the dissolution of lignin was more uniform, and clear distinctions between the morphological layers were observed. CRM distributions of these cell wall components can provide good data for understanding and modeling the physio-chemical processes occurring in the cell walls under different pretreatment conditions.
