Xylose-lysine model systems: The effect of pH on the volatile reaction products

Aqueous molal solutions of xylose and lysine (initial pH 4–9) were refluxed either with control of the pH at 5–0 or without pH control (final pH 2–6). Analysis by gas chromatography (GC) and GC-mass spectrometry resulted in the identification of 58 and 28 compounds, respectively, from the two systems. Furans were the main reaction products in both systems and 2-furfural alone comprised 522 and 999 g kg^?1 of the volatiles, respectively, from the systems with final pH values of 5–0 and 2–6. Maintaining the pH at 5–0 resulted in a higher yield and greater numbers of nitrogen-containing compounds, and monocyclic pyrroles, pyridines and 2,3-dihydro-l H-pyrrolizines were identified only in that system. Aliphatic compounds, alicyclic compounds, benzene derivatives. l-(2–furfuryl)pyrroles and pyrazines were also identified. This investigation is the first report of the formation of 2.3-dihydro-l H-pyrrolizines in a model system containing lysine as the amino compound; a possible mechanism is proposed.     

嗜单宁管囊酵母木糖酒精发酵的研究

综合利用丰富、廉价且可再生的农作物秸秆资源生产酒精的研究已经渐渐成为全球范围的热点之一。文章研究了嗜单宁管囊酵母木糖酒精发酵的发酵性能,分离、筛选、驯化培养出一株高效木糖酒精发酵菌株 g-13,在最适条件下其木糖酒精发酵的转化率为 0.446 g/g(酒精/消耗的糖),为发酵秸秆纤维水解液中的戊糖生产燃料酒精提供菌种支持。     

木糖生产中废旧活性炭再生条件初步研究

木糖生产中水解液脱色的粉末活性炭,使用后脱色性能下降很快,不能重复利用,致使木糖生产成本高。为此,采用了先盐酸处理、后高温活化的方法,对废旧炭进行了处理,同时考察了盐酸浓度、活化温度、活化时间等因素的影响。结果表明:用质量分数8%的盐酸处理,900℃高温活化5 h,活性炭的脱色性能恢复至新炭的86%,能重新用于水解液脱色。     

强碱树脂在木糖应用中存在的问题及解决方法

木糖是一种在化工、食品等领域有着广泛用途的五碳糖,工业生产是用稀强酸将玉米芯中含有的大量多缩戊糖分解为单个的木糖分子,然后通过离子交换除盐、脱色,精制提取,但在强碱离子交换柱中,木糖分子容易被部分催化异构转化为阿拉伯糖,使得木糖纯度下降,结晶困难。考察了强碱树脂再生浓度、淋洗终点pH值、交换温度以及流速对木糖分子异构的影响,得出最佳的交换工艺条件:再生剂浓度为2%、淋洗终点pH值为7.5、交换温度20℃,流速为1BV/h。     

Anaerobic fermentation of xylose by pichia stipitis: The effect of forced cycling of ph

Xylose fermentation by Pichia stipitis was examined using a two-stage batch process. The cells were first grown aerobically on D-xylose (5 g/L), whereafter additional xylose (10 g/L) was added and fermented during anaerobic conditions (T=30°C). The optimum pH value for a fermentation with constant pH was found to be 4.5 (maximum specific ethanol production rate 0.21 g/(g h). Forced square wave cycling of the pH between 4 and 5, and 3.5 and 5.5 (cycle time 30 min) during the fermentation stage resulted in a fermentation rate lower than the maximum rate, but with unchanged ethanol yields.     

Theoretical examination of the mechanism of aldose-ketose isomerization

Two mechanisms for an aldose–ketose isomerization havebeen examined using high level ab initio and semiempirical molecularorbital methods. The proton transfer pathway via an enediolintermediate is shown to be favored in the absence of a metalion, while the hydride transfer pathway becomes favored in thepresence of a metal ion. Our calculations explain why the protontransfer pathway is operative in most aldose–ketose isomerizationreactions. These calculations also provide further support forthe previously proposed metal ion-mediated hydride transfermechanism for xylose isomerase.     

脱色树脂在木糖脱色中的应用

介绍了脱色树脂在木糖液中的脱色性能，同时提出了脱色树脂脱色的最佳工艺条件。并且脱色树脂应用于木糖液脱色，既简化了生产工艺，又降低了工人的劳动强度，具有较好的现实意义。     

荞麦蛋白-木糖接枝物的制备及性质

通过美拉德反应对荞麦蛋白进行改性,对荞麦蛋白-木糖接枝物的制备及其性质进行研究。在湿热条件下,利用美拉德反应制备荞麦蛋白-木糖接枝物。通过正交试验优化接枝物的制备条件,荞麦蛋白与木糖按1∶5的质量比、在50℃下反应120min,接枝度可达到49.24%。性质测定表明,接枝物的溶解度较荞麦蛋白提高了约25%,乳化性提高了约30%,乳化稳定性提高了约11%。     

利用木糖的耐高温产酒精酵母菌的筛选

从5种土壤和植物叶片上分离到24株酵母菌株。分别对它们的耐高温、木糖利用和产酒精能力进行了测定。从中筛选到4株能在45℃下生长良好，能够利用木糖的产酒精酵母菌株。     

Conversion efficiency of glucose/xylose mixtures for ethanol production using Saccharomyces cerevisiae ITV01 and Pichia stipitis NRRL Y‐7124

BACKGROUND: Efficient conversion of glucose/xylose mixtures from lignocellulose is necessary for commercially viable ethanol production. Oxygen and carbon sources are of paramount importance for ethanol yield. The aim of this work was to evaluate different glucose/xylose mixtures for ethanol production using S. cerevisiae ITV‐01 (wild type yeast) and P. stipitis NRRL Y‐7124 and the effect of supplying oxygen in separate and co‐culture processes. RESULTS: The complete conversion of a glucose/xylose mixture (75/30 g L^?1) was obtained using P. stipitis NRRL Y‐7124 under aerobic conditions (0.6 vvm), the highest yield production being Y_p/s = 0.46 g g^?1, volumetric ethanol productivity Q_pmax = 0.24 g L^?1 h^?1 and maximum ethanol concentration P_max = 34.5 g L^?1. In the co‐culture process and under aerobic conditions, incomplete conversion of glucose/xylose mixture was observed (20.4% residual xylose), with a maximum ethanol production of 30.3 g L^?1, ethanol yield of 0.4 g g^?1 and Q_pmax = 1.26 g L^?1 h^?1. CONCLUSIONS: The oxygen present in the glucose/xylose mixture promotes complete sugar consumption by P. stipitis NRRL Y‐7124 resulting in ethanol production. However, in co‐culture with S. cerevisiae ITV‐01 under aerobic conditions, incomplete fermentation occurs that could be caused by oxygen limitation and ethanol inhibition by P. stipitis NRRL Y‐7124; nevertheless the volumetric ethanol productivity increases fivefold compared with separate culture. Copyright © 2011 Society of Chemical Industry