Characterization of hemicelluloses of sugar beet roots grown in Morocco

Hemicelluloses, extracted by means of concentrated alkali (1 M, followed by 4 M sodium hydroxide) from alcohol-insoluble, pectin-free residue of Moroccan sugar beet samples, obtained by using l M NaOH were collected twice in 1996 (Early and Late samples). The hemicellulose extracts were precipitated by aqueous ethanol at 50 and 75%, giving three fractions P50, P75 and S (supernatant), each aqueous ethanol fraction represented approximately one-third of the initial material. The supernatants were mostly arabinose (271-339 m g-1 and 115-164 mg g-1, for the 1 M and the 4 M extracts, respectively). Proteins were present in the supernatants and P75 fractions. Glucuronic acid and diferulic acid were present in some samples. Fractionation of P50 and P75 on DEAE Sepharose gave initial fractions containing fucose, xylose and glucose (xyloglucans). The fractions from P75 were rich in mannose and glucose (glucomannans). Those fractions that were retained were rich in xylose and arabinose but also glucose (up to 40-45 mol%) in the case of the Late season samples. The material that could only be eluted from the DEAE column by 0.5 M sodium hydroxide was mostly composed of xylose (74-80 mol%). Methylation analysis of these fractions showed the characteristic structure of xylans.