玉米芯木聚糖的提取及其相对分子质量分布研究

通过碱性过氧化氢溶液提取玉米芯半纤维素,单因素试验结果表明：在1% H₂O₂、5% NaOH的碱性过氧化氢溶液中,反应温度50℃、反应时间16 h、液固比为20：1（mL：g）,木聚糖得率可达83.15%。采用梯度乙醇分级沉淀法进行半纤维素的分离实验,考察了真空冷冻和烘干方式对产物性能的影响。采用高效离子色谱测定半纤维素单糖组成,并用FT-IR、TG、¹H NMR、¹³C NMR和GPC对半纤维素进行分析与表征。结果表明：各级分由木糖、葡萄糖、阿拉伯糖等组成,玉米芯中半纤维素主要由L-阿拉伯糖-（4-O-甲基-D-葡萄糖醛酸）木聚糖构成;支化度（w（阿拉伯糖）/w（木糖））为0.17~0.52,且随着乙醇体积分数的增加而变大。干燥方式对产物的相对分子质量影响很大,真空冷冻干燥的木聚糖重均相对分子质量（M_w）为108 533~197 752,真空干燥的M_w为41 231~47 242;2种干燥方式所得12种级分中,分散系数为1.172~1.517,其中11种产物分散系数小于1.5,为分布均一的低分散度木聚糖。

Extraction and Relative Molecular Mass Distribution of Corncob Xylan

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.