Structure and quantity of fructan oligomers in oat (Avena spp.)

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Abstract
SUMMARY: Fructan in oat had previously been separated and quantified according to size class. To determine structure, fructan oligomers with a degree of polymerization (DP) of 3–5 were separated and purified by HPLC using a combination of ion exchange and reversed‐phase chromatography. Linkage analysis was performed on purified oligomers using gas chromatography, mass spectroscopy of partially methylated alditol acetates. DP 3 isomers consisted predominantly of 1‐kestose and neokestose. Three DP 4 isomers were based on neokestose and one of the 3 isomers contained 2,6‐linkages. In addition, the seven DP 5 isomers purified were also based on neokestose with two isomers containing 2,6‐linkages exclusively, three with 1,2‐linkages exclusively and two with both 2,6‐and 2,1‐linkages. A fructan fraction obtained by ethanol precipitation had an average DP of 12–3 and consisted exclusively of neokestose‐based isomers with 2,6‐linkages and no branching. Standard curves were obtained with the 13 purified oligomers and the curves were used to quantify oligomers in 49 oat accessions from five species. On a fresh weight basis the fructo‐oligomer in highest concentration in all but 3 of the accessions was 6G,6‐kestotetraose (F2‐6F2‐6G1‐2F).