NMR and methylation analysis of hemicellulose purified from corn bran.

Corn bran hemicellulose was extracted from de-oiled and de-starched corn bran using 0.3 M alkali at 120 °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 (ara f), xylose (xyl p) and galactose (gal p) with the following linkage: t-ara f , 17.09%; 1,3-ara f , 12.43%; t-xyl p , 16.13%; 1,4-xyl p , 11.57%; 1,3,4-xyl p , 26.02%; 1,2,3,4-xyl p , 10.46%; t-gal p , 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: t-xyl p , 1,2,3,4-β-D-xyl p, t-α-L-ara f , 1,2-α-L-ara f and 1,4-β-D-xyl p. Several other linkage fragments were also deduced: t-ara f →2-ara f →2- O -(1,3,4-xyl), t-ara f →2-ara f →3- O -(1,2,4-xyl), t-ara f →2-ara f →3-ara f, and t-gal→2-ara. Image 1 • Purified corn fibre gum (PCFG) was extracted from corn bran. • Major monosaccharides in PCFG were arabinose, xylose, and galactose. • Glyosidic linkages in PCFG were identified by NMR and methylation analysis. • Monosaccharide sequence was determined by partial hydrolysis and NMR. [ABSTRACT FROM AUTHOR]