Journal
JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
Volume 63, Issue 2, Pages 707-715Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jf505283x
Keywords
Amaranthus hypochrondriacus; dietary fiber; cell wall; arabinans; galactans; oligosaccharides; NMR; arabinopyranose; methaylation analysis
Funding
- Office of the Vice President for Research
- Medical School
- College of Biological Science
- NIH
- NSF
- Minnesota Medical Foundation
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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 alpha-(1 -> 5)-linked l-arabinopyranose units. In addition, it was evidenced that galactans from amaranth seeds are composed of beta-(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.
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