title: Neutral Pectin side chains of Amaranth (Amaranthus hypochondriacus) contain long, partially branched Arabinans and short galactans, both with terminal arabinopyranoses.
abstract: Amaranth is a pseudocereal of high nutritional value, including a high dietary fiber content. Amaranth dietary fiber was suggested to contain large amounts of neutral rhamnogalacturonan I side chains. In this study, endo-arabinanase and endo-galactanase were used to liberate arabinan and galactan oligosaccharides from amaranth fiber. The liberated oligosaccharides were identified by high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and HPLC-MS(n) using standard compounds, which were isolated from amaranth, sugar beet, potato, and red clover sprouts and characterized by one- and two-dimensional NMR spectroscopy. It was demonstrated that insoluble amaranth arabinans have linear and branched areas, with the O-3 position being the dominant branching point. Minor amounts of branches at position O-2 and double substitution were also found. Amaranth arabinans were also demonstrated to contain terminal α-(1→5)-linked l-arabinopyranose units. In addition, it was evidenced that galactans from amaranth seeds are composed of β-(1→4)-linked d-galactopyranose units, which can also be terminated with l-arabinopyranose units. In direct comparison to structural elucidation of amaranth fiber by using methylation analysis, the advantage of the enzymatic approach over methylation analysis was demonstrated.
authors.affiliation: Department of Food Chemistry and Phytochemistry, Institute of Applied Biosciences, Karlsruhe Institute of Technology (KIT) , Adenauerring 20a, 76131 Karlsruhe, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Wefers
authors.forename: Catrin E
authors.initials: CE
authors.lastname: Tyl
authors.forename: Mirko
authors.initials: M
authors.lastname: Bunzel
mesh_terms: D027721:Amaranthus / Q000737:chemistry*; D004043:Dietary Fiber / Q000032:analysis; D005685:Galactans / Q000737:chemistry*; D015394:Molecular Structure; D010368:Pectins / Q000737:chemistry*; D010936:Plant Extracts / Q000737:chemistry*; D011134:Polysaccharides / Q000737:chemistry*; D012639:Seeds / Q000737:chemistry
chemical_list: D004043:Dietary Fiber; D005685:Galactans; D010936:Plant Extracts; D011134:Polysaccharides; C030080:araban; D010368:Pectins
keywords: Amaranthus hypochrondriacus; NMR; arabinans; arabinopyranose; cell wall; dietary fiber; galactans; methylation analysis; oligosaccharides