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

Abstract

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.