NMR and methylation analysis of hemicellulose purified from corn bran

Corn bran hemicellulose was extracted from de-oiled and de-starched corn bran using 0.3M alkali at 120 degrees C. Following neutralization, ethanol (75%) precipitation, dialysis, protein digestion, re-precipitation in ethanol, and freeze-drying, purified corn fiber gum (PCFG) was obtained in overall yield of 45.96%. PCFG gave a single peak by high performance size exclusion chromatograph, and had average molecular weight of 296 kDa. Monosaccharide composition, methylation, and GC-MS analysis indicated that PCFG was comprised of three monosaccharides, arabinose (araf), xylose (xylp) and galactose (galp) with the following linkage: t-araf, 17.09%; 1,3-araf, 12.43%; t-xylp, 16.13%; 1,4-xylp, 11.57%; 1,3,4-xylp, 26.02%; 1,2,3,4-xylp, 10.46%; t-galp, 6.37%. Partial acid hydrolysis suggested that arabinofuranose sugar residues were substituted onto a 1,4-linked xylan backbone. Extensive 1D and 2D NMR spectroscopy was used to identify and confirm the following linkages: txylp, 1,2,3,4-beta-D-xylp, t-alpha-L-araf, 1,2-alpha-L-araf and 1,4-beta-D-xylp. Several other linkage fragments were also deduced: t-araf -> 2-araf -> 2-O-(1,3,4-xyl), t-araf -> 2-araf -> 3-O-(1,2,4-xyl), t-araf -> 2-araf -> 3-araf, and t-gal -> 2-ara.