Purification and structural characterization of calcium hydroxide isolated arabinoxylans derived from bran, spent grain and sorghum grains.

The calcium hydroxide extractable polysaccharides isolated from bran, spent grain and sorghum grains were
separated on diethylaminoethyl-cellulose column into five sub-fractions each, by eluting successively with
different eluents. These fractions differed in their yield, uronic acid contents and composition of neutral sugars as
well as phenolic acids. The major fractions (0.1 M ammonium carbonate eluted) were resolved into a single peak
each on Sephacryl S-400 and their homogeneity was ascertained by HPSEC. Ferulic acid was the major phenolic
acid (19.84–29.32 mg/100 g) bound to arabinoxylan-(AX) type polysaccharides. The molecular weights were
found to be 126.6 kDa for bran and spent grain, and 223.9 kDa for sorghum grains AX. The structural characterization
of the purified polysaccharides, carried out by 13C NMR, 1H NMR, FTIR, periodate oxidation, Smith
degradation and optical rotation analysis, indicated their backbone to be 1,4-β-D-xylan (optical rotation ranged
from – 4.0 to – 7.8), substituted mainly at O-2 or O-3 and/or both by α-L-arabinose residues. As evident from the
determination of colour characteristics and high thermostability (T0 > 200 ◦C), these polysaccharides can be
used in the preparation of fibre-rich foods including bakery products.