Structural Features of Arabinoxylans Extracted with Water at Different Temperatures from Two Rye Flours of Diverse Breadmaking Quality

Abstract

The water extractable (WE) arabinoxylans from two rye flours differing in baking quality were studied following sequential extraction with water at 4, 40, and 100 °C. Ammonium sulfate fractionation of the resulting WE fractions and subsequent analysis revealed substantial differences in the structure of the isolated materials. Furthermore, it allowed us to identify the factors contributing to arabinoxylan water extractability. Our results provide compelling evidence for the existence of separate polymers in rye WE arabinoxylans with different substitution degrees, ranging from quantitatively dominating, lowly substituted populations (arabinose to xylose ratio, Ara/Xyl ∼ 0.5) to comparatively less abundant, highly substituted analogues (Ara/Xyl ∼ 1.3). Generally, arabinoxylan water extractability was governed by the relative proportion of lowly and highly branched structures. A gradually increasing proportion of highly substituted populations was observed from cold to hot WE fractions. This was associated with the lower proportion of monosubstituted xylopyranosyl residues in the backbone, the higher proportion of disubstituted xylopyranosyl residues, and the higher level of substitution with feruloyl residues. Notable differences in the ratio of phenolic compounds to arabinose residues were observed between corresponding polymers isolated from rye flours of high and low baking quality, whereas the differences in their molecular weights were much less pronounced. Keywords: Rye flour; water extractable arabinoxylan; cell wall components; fractionation; arabinoxylan structure