INFLUENCE OF STRUCTURE ON THE PHYSICOCHEMICAL PROPERTIES OF WHEAT ARABINOXYLAN

A water-soluble arabinoxylan from wheat flour was purified and fractionated by a graded ammonium sulphate fractionation technique. The yields (based on the total amount of the material recovered) of the four polysaccharide fractions obtained at 60% (F60), 70% (F70), 80% (F80), and 95% (F95) saturation with (NH4)2SO4 were 58.8%, 29.2%, 7.6%, and 4.4%, respectively. Monosaccharide. H-1-NMR, and C-13-NMR analyses revealed differences in structural characteristics among the fractions. F60 had the lowest arabinose:xylose ratio (0.58), followed by F70 (0.71), F80 (0.85), and F95 (0.88). The relative amount of Xylp residues doubly substituted at O-2 and O-3 with Araf increased substantially from F60 to F95, whereas the amount of unsubstituted and monosubstituted Xylp decreased in the same order. The content of ferulic acid was much higher in F60 than in the remaining samples: F60 also showed the highest intrinsic viscosity (4.70 dl/g) followed by F70 (4.20 dl/g), F80 (3.16 dl/g), and F95 (1.90 dl/g). Calculated coil overlap parameter values (c*[eta]: 1.20-1.30) were much lower than those of other random coil polysaccharides. implying a rather stiff/extended chain conformation. Oxidative gelation of arabinoxylan fractions was probed by dynamic rheometry. Fraction F60 formed rigid gel networks, as assessed by the storage modulus (G') and tan-delta (G"/G') values, while F70 and F80 exhibited poor gelling capacity. The arabinoxylan fractions were also effective in stabilizing protein foams against thermal disruption in the order of F60 > F70 > F80.