Variation in the Degree of <scp>d</scp>-Xylose Substitution in Water-Extractable European Durum Wheat (<i>Triticum </i><i>durum </i>Desf.) Semolina Arabinoxylans

Abstract

Durum wheat (Triticum durum Desf.) semolina water-extractable arabinoxylan (TWEAX) (yield 0.28%, arabinose-to-xylose ratio (A/X) 0.62) was fractionated by a stepwise increase in ethanol concentration (up to 65%). The A/X ratios of the resulting fractions varied between 0.42 and 0.80. With increasing ethanol concentrations, increasing A/X ratios went hand in hand with a relative increase of low molecular weight compounds, indicating that high molecular weight compounds with a low A/X ratio are preferentially precipitated from alcohol/water mixtures. 1H NMR showed that, whereas in TWEAX the levels of unsubstituted xyloses (X0), monosubstituted (X1), and disubstituted (X2) xyloses were 63.1%, 11.8%, and 25.1%, respectively, fractions that precipitated with increasing ethanol concentrations had decreasing levels of X0. Simultaneously, the level of X1 decreased equally until it leveled of at ca. 10%. Concomitantly, the level of X2 increased. The levels of X0, X1, and X2 varied between 69.7% and 53.4%, 18.2% and 10.7%, and 12.2% and 35.9%, respectively. Keywords: Arabinoxylans, durum wheat, semolina, Triticum durum Desf.