Arabinans and galactans are complex pectic polysaccharides, which greatly influence the physicochemical and physiological properties of plants and plant-based foods. Conventional methods to characterize these challenging polymers are based on derivatization and/or unselective chemical cleavage of the glycosidic bonds of the polysaccharides, resulting in partial loss of essential information such as anomeric configuration. Here, endo-arabinanase and endo-galactanase were used to selectively cleave pectic arabinans and galactans. The liberated oligosaccharides were purified and characterized by LC-MS and one- and two-dimensional NMR spectroscopy resulting in known but also several previously unknown pectic structural elements. For the routine analysis of pectin hydrolysates by HPAEC-PAD, incubation conditions, chromatographic parameters, and relative response factors of the isolated pectic oligosaccharides against an internal standard were determined. The applicability of the method was demonstrated by analyzing different well-characterized plant cell wall materials. It was demonstrated that the developed method yields additional information about pectic arabinan and galactan structures that is not obtained from conventional methods such as methylation analysis.
Keywords: HPAEC-PAD; dietary fiber; oligosaccharide profiling; pectic arabinans and galactans; pectins; plant cell wall constituents; screening; selective enzymatic hydrolysis.