Abstract:

A graded ethanol precipitation technique was employed to obtain xylan from the alkaline hydrogen peroxide-extracted corncob liquid. The results of single factor test showed that in the alkaline hydrogen peroxide solution of 1% H₂O₂ and 5% NaOH with the reaction temperature of 50℃, reaction time of 16 h, and liquid-solid ratio of 20:1(mL:g), the yield of xylan could reach 83.15%. And the effects of vacuum freezing and drying methods on the properties of xylan were investigated. Hemicellulose monosaccharide composition was determined by high performance ion chromatography, and hemicellulose was analyzed and characterized by FT-IR, TG, ¹H NMR, ¹³C NMR and GPC. The results showed that all fractions were composed of xylose, glucose, arabinose, etc., mainly composed of L-arabinose-(4-O-methyl-D-glucuronic acid) xylan; the degrees of branching(w(arabinose)/w(xylose)) were 0.17 to 0.52, and it increased as the volume fraction of ethanol increased. The drying method had a great influence on the relative molecular weight of the product. The weight average molecular weights(M_w) of vacuum freeze-dried xylan were 108 533 to 197 752, and the vacuum dried M_w were 41 231 to 47 242.Among the 12 fractions obtained by the two kinds of drying method, the dispersion coefficients were 1.172 to 1.517, and 11 of them had the dispersion coefficient of less than 1.5, which were uniformly distributed low-dispersion xylan.

Key words: hemicelluloses, xylan, low dispersion, relative molecular weight