In-situ annotation of carbohydrate diversity, abundance, and degradability in highly complex mixtures using NMR spectroscopy

Many functions of carbohydrates depend on the detection of short structural motifs, approximately up to hexasaccharide length, by receptors or catalysts. This study investigates the usefulness of state-of-the-art 1H–13C nuclear-magnetic-resonance (NMR) spectroscopy for characterizing the diversity, abundance, and degradability of such short structural motifs in plant-derived carbohydrates. Assignments of carbohydrate signals for 1H–13C NMR spectra of beer, wine, and fruit juice yield up to >130 assignments in situ, i.e. in individual samples without separation or derivatization. More than 500 structural motifs can be resolved over a concentration range of ~103 in experiments of a few hours duration. The diversity of carbohydrate units increases according to power laws at lower concentrations for both cereal and fruit-derived samples. Simple graphs resolve the smaller overall contribution of more diverse but less abundant motifs to carbohydrate biomass. Susceptibility to enzymatic degradation is probed simultaneously for hundreds of structural motifs to reduce uncertainties in the identification of motifs and to probe enzyme specificity with assigned motifs. Several properties of fundamental biotechnological importance can thus be assessed in situ by heteronuclear NMR methods.