Influence of hot-water extraction on ultrastructure and distribution of glucomannans and xylans in poplar xylem as detected by gold immunolabeling

Pre-extraction of hemicelluloses from lignocellulosic feedstock has been a research focus during the last decade within the context of lignocellulosic biorefineries. In this study, the effect of hot-water extraction (HWE) on the topochemistry and ultrastructure of poplar wood (Populus sp.) was investigated based on scanning electron microscopy (SEM) and transmission electron microscopy (TEM) paired with immunogold labeling of the hemicelluloses. The cell walls of HWE wood (HWEW) differ significantly in their ultrastructure from neat wood, i.e., there are many distorted cells and agglomerations of lignin and extractives agglomerations in the cell lumina. Results of immunogold labeling indicate that different types of hemicelluloses are extracted at different stages and both their concentration and distribution within the wood cell wall layers are affected by the HWE. Hemicelluloses more closely associated with lignin appear to be more easily removed by HWE. Lignins are also extracted partially and altered. Results provide a holistic view of chemical and ultrastructural changes including the associated changes in hemicelluloses and lignin distribution in HWEW. The obtained data could be helpful to understand better the mechanical properties and adhesion related issues of HWEW for wood composite production.