Sequencing analysis of β-glucan from highland barley with high performance anion exchange chromatography coupled to quadrupole time–of–flight mass spectrometry

Abstract

Highland barley is one of the hull-less barleys that contains high amounts of β-glucan. A detailed sequence analysis is needed to support the application of the β-glucan from highland barley. The β-conformation and 1 → 3/1 → 4 linkages were confirmed using nuclear magnetic resonance (NMR) spectroscopy. Monosaccharide analysis was accomplished with high-performance anion exchange chromatography (HPAEC) coupled to pulsed amperometric detection (PAD) and showed that glucose (G) was the dominant sugar component of this β-glucan. HPAEC-PAD was applied with on-line electrospray ion - to quadrupole time – of – flight mass spectrometry (Q/TOF-MS) to sequence oligosaccharides enzymatically derived from this β-glucan. More than 20 oligosaccharides were observed in the partially digested β-glucan mixture and their degree of polymerization (dp), confirmed by MS analysis, ranged from dp 2 to dp 20. The sequences of oligosaccharide dp2 – dp7 in the digested product mixture were unambiguously determined with MS/MS. Based on the sequence analysis of these oligosaccharides, G1→3G1→4G and G1→3G1→4G1→4G were determined to be the major repeating blocks of this β-glucan, and they were interspersed with homogeneous 1 → 4 linked domains with different lengths. The ratio of 1 → 3 and 1 → 4 linkages in the β-glucan was approximately 1:3.