Structure and physicochemical properties of β-glucans and arabinoxylans isolated from hull-less barley

Abstract

The molecular characteristics of β-glucans and arabinoxylans from selected hull-less barleys were examined following their sequential extraction with water (45 and 95 °C), Ba(OH) 2, Ba(OH) 2/H 2O, and NaOH which resulted in five distinct fractions designated as WE45, WE95, Ba(OH) 2, Ba(OH) 2/H 2O, and NaOH, respectively. Both water-extractable fractions consisted mainly of β-glucans but up to 20% of arabinoxylans were found in WE45 of normal and high amylose barley varieties. Analysis of the water-extractable β-glucans, indicated differences in molecular features (weight average molecular weight ( M w), β-(1→4) to β-(1→3) linkage ratios, and amounts of cellulosic regions along the β-glucan chain) between WE45 and WE95, and among β-glucans from different cultivars. The variation observed in the viscoelastic behaviour of WE45 and WE95 fractions confirmed differences in the molecular weight among water-extractable β-glucans derived from various barley cultivars. Differences in the structure of arabinoxylans from the various fractions and cultivars were also observed. Water-extractable arabinoxylans (WE45 and WE95 fractions) had significantly lower xylose to arabinose (Xyl p/Ara f) ratios (1.47 and 1.52) than those extracted with Ba(OH) 2 (1.70), implying a greater degree of branching in the more readily soluble fractions. Small varietal differences in molecular weight ( M w), root mean square radius ( R g), and polydispersity ( M w/ M n) among Ba(OH) 2 fractions correlated with the substitution pattern of the xylan backbone.