毛细管区带电泳法分离发酵液中的木糖和木糖醇

 建立了利用毛细管区带电泳分离发酵液中木糖和木糖醇的新方法。研究表明 :采用硼砂缓冲溶液时 ,木糖和木糖醇的分离度随硼砂浓度的增高而加大 ,在室温下硼砂最高浓度为 130mmol/L ;分离度还与溶液的 pH有关 ,在pH 9 5 5处分离度有最大值 ;缓冲液中十六烷基三甲基溴化铵的浓度为 4× 10 -6mmol/L～ 8× 10 -4 mmol/L时对分离度无显著影响 ;在优化的分离条件下 ,木糖和木糖醇可在 6min内基线分离。测定了发酵过程中样品各组分的含量和加标回收率 ,5次测定木糖的相对标准偏差 (RSD)为 1 42 %～ 3 11% ,回收率为 96 0 %～ 10 8 0 % 。     

生物基平台化合物催化转化制备糠醇

糠醇(FOL)作为一种重要且多用途的有机化工原料,可以有效地转化为各种高价值的化学品,如糠醛树脂、脲醛树脂、酚醛树脂、果酸、增塑剂和火箭燃料等。以糠醛(FAL)、木糖和果糖为原料经催化加氢制备FOL的绿色生产工艺,具有良好的应用前景和研究价值。本文系统总结了近年来国内外以FAL、木糖、果糖为原料制备FOL的研究现状,从催化剂类型、催化效率和催化机理等方面对制备FOL的催化剂进行了总结,并在此基础上对催化加氢制备FOL的发展趋势进行了展望,为开发更为新型、高效、绿色、稳定的催化剂体系提供理论指导和有益借鉴。     

Changing flux of xylose metabolites by altering expression of xylose reductase and xylitol dehydrogenase in recombinant Saccharomyces cerevisiae

We changed the fluxes of xylose metabolites in recombinant Saccharomyces cerevisiae by manipulating expression of Pichia stipitis genes (XYL1 and XYL2) coding for xylose reductase (XR) and xylitol dehydrogenase (XDH), respectively. XYL1 copy number was kept constant by integrating it into the chromosome. Copy numbers of XYL2 were varied either by integrating XYL2 into the chromosome or by transforming cells with XYL2 in a multicopy vector. Genes in all three constructs were under control of the strong constitutive glyceraldehyde-3-phosphate dehydrogenase promoter. Enzymatic activity of XR and XDH in the recombinant strains increased with the copy number of XYL1 and XYL2. XR activity was not detected in the parent but was present at a nearly constant level in all of the transformants. XDH activity increased 12-fold when XYL2 was on a multicopy vector compared with when it was present in an integrated single copy. Product formation during xylose fermentation was affected by XDH activity and by aeration in recombinant S. cerevisiae. Higher XDH activity and more aeration resulted in less xylitol and more xylulose accumulation during xylose fermentation. Secretion of xylulose by strains with multicopy XYL2 and elevated XDH supports the hypothesis that d-xylulokinase limits metabolic flux in recombinant S. cerevisiae.     

Activity of xylose reductase from Candida mogii grown in media containing different concentrations of rice straw hydrolysate

Xylose reductase (XR) activity was evaluated in extracts of Candida mogii grown in media containing different concentrations of rice straw hydrolysate. Results of X Ractivity were compared to xylitol production and a similar behavior was observed for these parameters. Highest values of specific production and productivity were found for xylose reductase (35 U/g of cell and 0.97 U/[g of cell·h], respectively) and for xylitol (5.63 g/g of cell and 0.13 g/[g of cell·h]) in fermentation conducted in medium containing 49.2 g of xylose/L. The maximum value of XR:XD ratio (1.82) was also calculated under this initial xylose concentration with 60 h of fermentation.     

RSM analysis of the effects of the oxygen transfer coefficient and inoculum size on the xylitol production by Candida guilliermondii

Biotechnology production of xylitol is an excellent alternative to the industrial chemical process for the production of this polyalcohol. In this work the behavior of Candida guilliermondii yeast was studied when crucial process variables were modified. The K _La (between 18 and 40/h) and the initial cell mass (between 4 and 10 g) were considered as control variables. A response surface methodology was applied to the experimental design to study the resulting effect when the control variables were modified. A regression model was developed and used to determine an optimal value that was further validated experimentally. The optimal values determined for K _La and X ₀ were 32.85/h and 9.86 g, respectively, leading to maximum values for productivity (1.628 g/h) and xylitol yield (0.708 g/g).     

丝瓜络炭磺酸的制备及其催化合成糠醛

以丝瓜络为炭源、浓硫酸为磺酸化试剂,制备了丝瓜络炭磺酸催化剂。利用中和滴定、X射线衍射、傅里叶变换红外光谱和热重-差热分析等手段对催化剂进行了表征。以表面酸密度为考察指标,确定了在300℃炭化3h、在80℃下磺化3h为优化的催化剂制备条件,此条件下丝瓜络炭磺酸催化剂表面酸密度可达1.119mmol/g。以木糠水解制备糠醛为探针反应,通过正交实验法考察了催化剂的实际催化活性。结果表明,在水解反应时间2h、水解反应温度200℃和催化剂用量占原料质量10%时,糠醛的平均收率达到78.69%,此时催化剂的催化活性最高。催化剂经第一次循环使用后性能有所下降,但随后的循环使用催化性能稳定。将使用过的催化剂经再磺化,可基本恢复到新制催化剂的催化活性。     

基于光子晶体的物质的量浓度测量研究

利用平面波展开法对二维光子晶体在H极化下的光子带隙进行数值计算。考虑了溶液温度和物质的量浓度对光子带隙的影响。结果表明,以半乳糖和木糖的水溶液作为空气孔中介质材料,当溶液物质的量浓度一定时,光子带隙随溶液温度的变化而改变;而当溶液温度一定时,光子带隙随溶液物质的量浓度发生变化。较高物质的量浓度和较高温度的溶液更容易形成光子带隙。在某些情况下,木糖的光子带隙大于半乳糖的光子带隙。     

离子排斥色谱法同时测定2,3-丁二醇发酵液中的葡萄糖和木糖及各种代谢产物

针对2,3-丁二醇发酵体系,以高交联度磺化苯乙烯-二乙烯基苯共聚物多孔微球为固定相的Aminex HPX-87H离子色谱柱为分析柱,利用示差折光检测器对该体系中的6种代谢产物(2,3-丁二醇、3-羟基丁酮、乙醇、乙酸、甲酸和乳酸)以及2种残留底物葡萄糖和木糖进行了分离.在65 ℃柱温下,以5 mmol/L H2SO4作为流动相,发酵液样品中底物葡萄糖和木糖及2,3-丁二醇等各种代谢产物的线性相关系数均在0.9990～0.9999之间,回收率为98.8%～103.2%,精密度为0.3%～2.1%.在最佳色谱条件下,能够同时测定2,3-丁二醇发酵体系中的残留底物和各种代谢产物的含量,适合于实时定量监测2,3-丁二醇发酵过程.     

Cofermentation of glucose,xylose, and arabinose by mixed cultures of two genetically engineeredZymomonas mobilis strains

Cofermentation of xylose and arabinose, in addition to glucose, is critical for complete bioconversion of lignocellulosic biomass, such as agricultural residues and herbaceous energy crops, to ethanol. A factorial design experiment was used to evaluate the cofermentation of glucose, xylose, and arabinose with mixed cultures of two genetically engineeredZymomonas mobilis strains (one ferments xylose and the other arabinose). The pH range studied was 5.0-6.0, and the temperature range was 30-37°C The individual sugar concentrations used were 30 g/L glucose, 30 g/L xylose, and 20 g/L arabinose. The optimal cofermentation conditions obtained by data analysis, using Design Expert software, were pH 5.85 and temperature 31.5°C. The cofermentation process yield at optimal conditions was 72.5% of theoritical maximum. The results showed that neither the arabinose strain nor arabinose affected the performance of the xylose strain; however, both xylose strain and xylose had a significant effect on the performance of the arabinose strain. Although cofermentation of all three sugars is achieved by the mixed cultures, there is a preferential order of sugar utilization. Glucose is used rapidly, then xylose, followed by arabinose.     

Enzymatic saccharification and fermentation of xylose-optimized dilute acid-treated lignocellulosics

The cellulose reactivity of two lignocellulosic feedstocks, switchgrass and poplar, was evaluated under straight saccharification (SS) and simultaneous saccharification and fermentation (SSF) conditions following dilute sulfuric acid pretreatments designed for optimum xylose yields. The optimum pretreatment conditions, within the constraints of the experimental system (Parr batch reactor), were 1.2% acid, 180°C, and 0.5 min for switchgrass and 1% acid, 180°C, and 0.56 min for poplar. The cellulase enzyme preparation was from Trichoderma reesei and fermentations were done with Saccharomyces cerevisiae. Time courses for SS were monitored as the sum of glucose and cellobiose; those for SSF as the sum of glucose, cellobiose, and ethanol. Percentage conversions under SS conditions were 79.1% and 91.4% for the pretreated poplar and switchgrass feedstocks, respectively. Analogous values under SSF conditions were 73.0% and 90.3% for pretreated poplar and switchgrass, respectively.