Probing the structural details of xylan degradation by real-time NMR spectroscopy.

The biodegradation of abundantly available cell wall polysaccharides has recently received much attention, not least because cell wall polysaccharides are substrates for the human gut microbiota and for environmentally sustainable processes of biomass conversion to value-added compounds. A major fraction of cereal cell wall polysaccharides consists of arabinoxylans. Arabinoxylan and its degradation products are therefore present in a variety of agro-industrial residues and products. Here, we undertook to track the structural details of wheat arabinoxylan degradation with high resolution NMR spectroscopy. More than 15 carbohydrate residues were distinguished in the substrate and more than 20 residues in partially degraded samples without any sample cleanup. The resolution of a plethora of structural motifs in situ permits the readout of persisting structures in degradation processes and in products. Reaction progress was visualized for the biodegradation of arabinoxylan by different crude microbial enzyme preparations. The direct observation of structural details in complex mixtures containing arabinoxylan fragments is significant, as such structural details reportedly modulate the health-promoting functions of arabinoxylan fragments.