摘要
本文围绕低聚木糖生产的主要工艺，对汽爆法提取玉米芯木聚糖的条件、卷须链霉菌(Streptomyces cirratus)D-10木聚糖酶合适的酶解条件以及酵母精制低聚木糖酶解液进行了研究。主要内容和结论如下：
1．关于汽爆法提取玉米芯木聚糖，在时间和固液比固定的条件下，压力与木聚糖提取率和木质素的溶出率都呈正相关，而D．P．值随着压力的增加先达到一个最高值后下降；在压力和固液比固定的条件下，反应时间越长，木聚糖提取率和木质素的溶出越高，而D．P．值随反应时间的增加不断下降，当反应时间达到一定程度，D．P．值低于2，表明维压时间过长，木聚糖过度降解，反而不利于木聚糖的提取；在压力和反应时间固定下，随固液比的增加，木质素的溶出也不断增加，而木聚糖提取率和D．P．值都是先上升后下降，综合得出1：20的固液比是较合适的固液比。
2．关于卷须链霉菌(Streptomyces cirratus)D-10木聚糖酶酶解，研究玉米芯汽爆液，碱提玉米芯木聚糖酶解的合适条件。得出80U／100mL，酶解6h和60U／g，酶解8h是卷须链霉菌D-10木聚糖酶酶解玉米芯汽爆液和碱提玉米芯木聚糖的合适条件。研究表明汽爆法提取的玉米芯木聚糖比碱提玉米芯木聚糖的水解率高，酶用量相对少，因此汽爆法相对于碱提法是较优的方法。
3．关于酵母精制低聚木糖的研究，针对微生物发酵法精制低聚木糖的特点，筛出一株具有消耗木单糖、阿拉伯糖而不消耗木二糖特性的酵母，并利用该酵母精制汽爆法提取的玉米芯木聚糖酶解液，研究该酵母精制低聚木糖液合适的精制条件，结果表明10％的接菌量，培养48 h是合适的精制条件。精制结束时，经TLC分析，酶解液中的木糖、阿拉伯糖几乎全部被去除，木二糖和木三糖没有明显变化，最终得到以木二糖和木三糖为主要成分的低聚木糖液。
This study covers the researches on the extraction of corncob xylan by steam-explosion, the optimal condition of Streptomyces cirratus D-10 xylanase hydrolyzing steam-exploded corncob and purifing the hydrolyzed steam-exploded corncob by yeast, The conclusions are as follows:
1.The effects of explosion pressure, reaction time and ratio of corncob with water on the extraction rate of xylan, the soluble value of lignin and the degree of polymerization of xylan were investigated. It is found that explosion pressure and extraction rate of xylan are positive correlation, while with the pressure increasing, the D.P. increases firstly and then decreases; The longer the reaction time is, the more the extraction rate of xylan and lignin; The D.P. will decrease with the increasing reaction time, however, excess reaction time will lead to the excess degration of xylan. With the increase of ratio of corncob with water, the amount of lignin increases, while the amount of xylan and the D.P. increases firstly and then decreases. It is concluded that optimal ratio of corncob with water is 1 : 20.
2.The optimal conditions of Streptomyces cirratus D-10 xylanase hydrolyzing steam-exploded corncob and alkali-extracted corncob xylan were studied. It is obtained that 80 U/ 100 mL of the enzyme concentration hydrolyzing for 6 h and 60 U/g of the enzyme concentration hydrolyzing for 8 h are the optimal conditions of the Streptomyces cirratus D-10 hydrolying the steam-exploed corncob and alkali-extracted corncob xylan, respectively. It is shown that the xylanase is more effective on the steam-exploed corncob than on the alkali-extracted corncob xylan, and steam-exploed corncob is a more suitable substrate for Streptomyces cirratus D-10 xylanases to prepare xylooligosaccharides.
3.In this study, we also selected an yeast, which can metabolize selectively xylose and arabinose, but can not degrade xylobiose. Xylose and arabinose in the hydrolysate of the steam-exploded corncob are fully consumed with 10 % inoculation at 48 h, while the mount of the xylooligosaccharides don't change notably. After purification by the yeast, the main compontents of the hydrolysate of the steam-exploded corncob are xylobiose and xylotriose.
引文
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