Wood hemicelluloses are fundamental components of plant secondary cell walls, together with cellulose, pectins and lignin. Hemicelluloses represent a complex and heterogeneous family of polysaccharides that share with cellulose a beta-(1,4) backbone of pentose and hexose building blocks. However, unlike cellulose, hemicelluloses are decorated with a wide pattern of neutral sugar and uronic acid substitutions, and can be further substituted by <i>O</i>-acetyl moieties. In softwoods, acetylated galactoglucomannan represent the main hemicellulose component (between 15-25% of the total composition), whereas arabinoglucuronoxylan is present in lower amounts (7-15%). We believe that the molecular heterogeneity of hemicelluloses modulates the hydration and the intensity of their interactions with cellulose microfibrils and lignin in woody tissues. However, the interplay amongst cell wall components and the structural nature of their interactions on the biomechanical integrity and functionality of secondary cell walls are still controversial.<br/>In this study we have implemented sequential extraction of hemicelluloses from spruce softwood using subcritical water in buffered conditions without prior delignification. This enables the cascade isolation of the mannan and xylan components based on their extractability and recalcitrance in spruce lignocellulose. The time evolution of the extraction was monitored in terms of composition and molecular profiling of the extracted hemicelluloses using glycomic approaches, integrating enzymatic depolymerisation with advanced chromatographic and mass spectrometric techniques. Different populations of mannans and xylans in spruce with distinct molecular motifs have been identified based on their extractability. This structural information is complemented by the use of molecular dynamic (MD) simulations of selected mannan and xylan motifs and their interaction with cellulose microfibrils. The implications of the molecular structure of spruce hemicelluloses on the interactions with cellulose and lignin will be discussed, towards the design of a structural model of the supramolecular architecture of softwoods.

Spruce hemicelluloses (galactoglucomannan and arabinoglucuronoxylan): Interplay with cellulose and lignin in softwoods

2019 Spring National Meeting

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