Water-soluble arabinoxylans from a Canadian western red spring flour (
cv. Laura) were fractionated by a graded ammonium-sulphate-precipitati
on technique into five fractions obtained at 55% (F55), 60% (F60), 70%
(F70), 80% (F80), and 100% (F100) saturation with (NH4)(2)SO4. The yi
elds of the fractions (based on the total material recovered) were 37.
5%, 22.3%, 23.6%, 11.9%, and 4.7%, respectively. The relative amount o
f Xylp residues doubly substituted at C-2 and C-3 with Araf increased
from F55 to F100, whereas the amount of mono- and unsubstituted Xylp r
esidues decreased in the same order. The presence of short Araf chains
was more pronounced in F100 than in other samples. The content of fer
ulic acid was highest in F55. Fractions F55 and F100 were degraded wit
h purified endo-beta-xylanase from Trichoderma viride. The hydrolysate
fragments were separated, quantified (Bio-Gel P-2, HP-SEC), and chara
cterized (H-1-NMR and methylation analysis). F55 appeared to be built
up from three structurally different regions. The first region, I-55 (
15%), was of relatively high DP and was high in terminal arabinose dou
bly linked to xylose residues at C-3 and C-2. The second region, II55
(40%), contained high amounts of terminal arabinoses linked to xylose
residues at C-3. The third region, III55 (45%), contained high amounts
of contiguously unsubstituted and C-3 monosubstituted xylose residues
. Fraction F100 was built up mainly from the highly substituted region
I-100 (75%), enriched in C-2,3 di- and C-2 monosubstituted xylose res
idues as well as in short arabinose side chains. Region III100 (18%) c
ontained a high proportion of unsubstituted xylose residues; however,
the amount of disubstituted xylose residues in this region was still h
igher than that of monosubstituted residues.