Fractionation of wheat bran carbohydrates

Abstract

AbstractA procedure for the fractionation of wheat bran carbohydrates with an emphasis on non‐starchy polysaccharides is described. After a complete extraction using a chloroform‐methanol (2:1) solvent, bran was destarched using amyloglucosidase and extracted using ammonium oxalate. Then delignification by sodium chlorite followed by hot water extractions was applied. Small quantities of water‐soluble hemicellulosic polymers containing glucose, xylose, arabinose with lesser amounts of galactose and mannose were removed by these three steps. The remaining holocellulose (of a low protein content) was extracted using 1M sodium hydroxide, and hemicelluloses A1 and B1 were separated from the extract. Hemicellulose A1 (5.4% of native bran) was determined to be a xylan containing smaller proportions of arabinose and glucose, whereas hemicellulose B1 (12.6% of native bran) was a complex mixture of several types of polysaccharides, the major one being a highly branched arabinoxylan. Hemicelluloses A4 and B4, obtained by 4M sodium hydroxide extraction of the residue after 1M sodium hydroxide treatment, had lesser amounts of arabinose compared with the respective fractions from the preceding step. For hexoses, higher proportions of mannose and glucose were found. α‐Cellulose residue retains 19.8% of pentosans.