Preparation and Characterization of Water-soluble Hemicellulose (Arabinoxylan) from Wheat Bran

Abstract

Water-soluble hemicellulose (WSH) extracted from wheat bran by homogenizing with dilute (0.2M) NaOH solution was purified by ultrafiltration and ion-exchange resins. The yield of the final product (WSH) was 7.6% of the bran. The molecular weight distribution of WSH, which was determined by gel filtration chromatography on size-exclusion HPLC, showed that the WSH consisted of polysaccharides of wide molecular weight distribution with a peak of around 350000 dalton. The analysis of sugar composition. showed that the WSH was a highly substituted arabinoxylan in which the ratio of arabinose to xylose was 0.91. The viscosity of the aqueous WSH solution was exponentially correlative to the WSH concentration. WSH was unstable on the condition of low pH (pH 3 and 5) and high temperature (80-100°C), but it was stable at higher pH (pH 9), even at high temperature (80-100°C). It was also shown that WSH had a unique characteristic, a sustained release function, which had never been demonstrated in other polysaccharides such as starch and cellulose. By this function, the tablet comprising bromphenol blue with in a matrix of WSH could gradually release this substance into the solution as the tablet was being dissolved in the aqueous phase. The effect was observed even with a tablet of a mixture containing only 20% WSH with 80% cellulose.