相对分子质量对木聚糖结晶能力的影响

The Effects of Molecule Weight on the Crystallization Ability of Xylan

利用木聚糖酶非均相处理木聚糖,通过控制酶解时间制备出了不同相对分子质量的木聚糖样品(X0~X6),并使用质量分数2%或4%的NaOH溶液对酶处理木聚糖进行分散或溶解,再经乙醇沉淀得到经碱液处理的木聚糖样品。通过对酶处理的木聚糖以及进一步经碱液处理的木聚糖进行X射线衍射(XRD)分析,重点探讨了相对分子质量对木聚糖结晶能力的影响。研究发现:非均相的木聚糖酶处理2.5 h,重均相对分子质量(M_(w))降至25 700,数均相对分子质量(M_(n))为5 400,多分散指数(PDI)为4.73;之后,随着酶处理时间的进一步延长,木聚糖M_(w)变化不大,M_(n)继续下降,PDI继续升高。非均相的木聚糖酶处理以及进一步的非均相碱液(2%NaOH溶液)处理可以破坏木聚糖的水合晶结构,使其XRD特征峰的峰强变弱,结晶度降低。将不同相对分子质量的酶解木聚糖进行均相碱液处理,完全溶解于4%NaOH溶液,重新沉淀后的木聚糖XRD谱图显示木聚糖水合晶完整的结晶结构能够再度形成,且结晶度与未处理木聚糖相比变化较小,说明非均匀地降低木聚糖相对分子质量对其结晶能力没有明显影响。

Using heterogeneous xylanase treatment on xylan,xylan samples(X0-X6)with different molecular weights were prepared by controlling the time of enzymatic hydrolysis.The enzyme treaeted xylans were dispersed/dissolved by 2%or 4%NaOH solutions and then re⁃precipitated by ethanol to prepare the alkali treated xylans.The effects of molecular weight on the crystallization ability of xylan were studied through X⁃ray diffraction(XRD)analyses on the enzyme treated and alkali treated xylan samples.The results showed that the weight average molecular weight(M_(w)),number average molecular weight(M_(n))and polydispersity index(PDI)of xylan decreased to 25700,5400 and 4.73,respectively,after heterogeneous xylanase treatment for 2.5 h.Then,with the further extension of enzymatic treatment time,the M_(w) of xylan changed slightly,while M_(n) decreased further,resulting in the increase of the PDI.It was found that the structure of xylan hydrate crystals was destroyed by heterogeneous xylanase treatment and subsequent heterogeneous alkali(2%NaOH solution)treatment,leading to the weakening of XRD peaks and the crystallinity decrease of xylan.Xylans with different molecule weights obtained by xylanase treatment were completely dissolved in 4%NaOH solution to prepare homogeneous solution.After re⁃precipitation,the XRD analysis showed that the complete crystalline structure of xylan hydrated crystal could be formed again,with almost unchanged crystallinity compared to that of unmodified xylan,indicating that heterogeneous reduction of the molecular weight of xylan had little influence on its crystallization ability.