生物质提取木糖工艺及木糖检测方法研究进展

木糖作为一种重要的化工原料,在食品、饮料等行业中应用广泛。综述了生物质制备木糖的工艺进展,对木糖检测方法进行了简单阐述。      

木糖母液微生物脱除葡萄糖及回收木糖

木糖生产过程中产生大量的木糖结晶母液。由于其杂糖含量较高，仅通过常规的浓缩，结晶等步骤，很难从中回收得到结晶木糖。本研究采用酵母发酵技术，先脱除木糖母液中的葡萄糖等杂糖，再结合真空浓缩与冷却结晶工艺，可以再析出晶体木糖，收率约25％。微生物脱除葡萄糖技术同样可用于玉米芯水解液中葡萄糖的有效去除，以提高木糖的结晶得率。     

木糖的清洁生产

本文系统论述了清洁生产的起源,在木糖生产中应用的必要性和意义,提出了推行清洁生产是木糖行业发展的必然要求。     

木糖生产工艺的研究进展

综述了木糖的性质、用途、发展状况,着重阐述了木糖的生产工艺及其发展。     

保健食品中低聚木糖含量测定

目的建立一种含有多糖纤维和低聚木糖的保健食品中低聚木糖含量测定的方法。方法用无水乙醇沉淀多糖纤维,将多糖纤维从试样中分离,用12%稀硫酸溶液将试样中的低聚木糖酸解为木糖,10%氢氧化钠溶液调p H至中性,选择适合的糖柱,以木糖为标样,外标法计算低聚木糖的含量(以木糖通过转换系数计)。结果酸解后试样中木糖浓度在0.0378~0.4536 mg/m L的范围内与峰面积的线性关系良好,相关系数r0.999。在3水平不同浓度木糖标准品添加下,木糖的回收率为97.9%。结论该方法操作简便、重现性好,适用于添加了多糖纤维和低聚木糖的保健食品中低聚木糖的含量测定。     

木糖制备技术研究进展

从食品加工下脚料中制备木糖可使农业废弃物得到重新利用,有广泛的应用前景。综述了木糖制备工艺中常见的预处理、木聚糖降解和木糖提纯等制备过程中的研究进展,对国内外的蒸汽爆破预处理,催化水解,分离纯化技术进行了简要的介绍,并提出了展望。     

低聚木糖的生产和应用

由木糖苷组成的低聚糖称为低聚木糖，该糖具有很多功能特性。本文综述了采用化学和酶法等方法由木质纤维材料制取低聚木糖，低聚木糖的精制纯化，以及低聚木糖在食品添加剂方面的应用，其中特别介绍了低聚木糖的保健效果。     

低聚木糖在保健食品中的应用

该文概述了低聚木糖的化学结构和加工特性,对低聚木糖的保健功能进行了重点阐述,并简要说明了低聚木糖的工业制备和在保健食品领域的应用前景。     

低聚木糖的研究进展

低聚木糖是一种功能性低聚糖,在食品、保健品、药品、农业等方面都有重要作用。阐述了低聚木糖的结构性质、功能特性和制备方法,同时也综述了国内外的研究进展和应用。低聚木糖高值化利用的研究和开发将会带来很大的经济效益和社会效益[1]。     

椰壳常压酸水解制备木糖

本文介绍了椰壳常压酸水解制备木糖工艺过程,通过正交试验考察了酸预处理时间、酸浓度、椰壳粉粒度、水解时间等对木糖产率的影响。结果表明:酸浓度与水解时间对木糖产率有显著性影响,酸预处理时间和椰壳粉粒度对木糖产率没有显著性影响,采用0.2mol/L的盐酸,100℃温度下水解6h,木糖产率可达椰壳空气干燥基质量的16%,水解液经脱色脱盐等一系列工艺制备的椰壳木糖纯度达99%以上。     

Saccharomyces cerevisiae engineered for xylose metabolism requires gluconeogenesis and the oxidative branch of the pentose phosphate pathway for aerobic xylose assimilation

Saccharomyces strains engineered to ferment xylose using Scheffersomyces stipitis xylose reductase (XR) and xylitol dehydrogenase (XDH) genes appear to be limited by metabolic imbalances, due to differing cofactor specificities of XR and XDH. The S. stipitis XR, which uses both NADH and NADPH, is hypothesized to reduce the cofactor imbalance, allowing xylose fermentation in this yeast. However, unadapted S. cerevisiae strains expressing this XR grow poorly on xylose, suggesting that metabolism is still imbalanced, even under aerobic conditions. In this study, we investigated the possible reasons for this imbalance by deleting genes required for NADPH production and gluconeogenesis in S. cerevisiae. S. cerevisiae cells expressing the XR-XDH, but not a xylose isomerase, pathway required the oxidative branch of the pentose phosphate pathway (PPP) and gluconeogenic production of glucose-6-P for xylose assimilation. The requirement for generating glucose-6-P from xylose was also shown for Kluyveromyces lactis. When grown in xylose medium, both K. lactis and S. stipitis showed increases in enzyme activity required for producing glucose-6-P. Thus, natural xylose-assimilating yeast respond to xylose, in part, by upregulating enzymes required for recycling xylose back to glucose-6-P for the production of NADPH via the oxidative branch of the PPP. Finally, we show that induction of these enzymes correlated with increased tolerance to the NADPH-depleting compound diamide and the fermentation inhibitors furfural and hydroxymethyl furfural; S. cerevisiae was not able to increase enzyme activity for glucose-6-P production when grown in xylose medium and was more sensitive to these inhibitors in xylose medium compared to glucose.     

Review: The structure and function of yeast xylose (aldose) reductases

Yeast xylose (aldose) reductases are members of the aldo-keto reductase family of enzymes which are widely distributed in a variety of other organisms. In yeasts, these enzymes catalyse the first step of xylose metabolism where xylose is converted to xylitol. In the past 16 years, xylose reductases from yeasts able to ferment or utilize xylose have been isolated and studied mainly because of their importance in xylose bioconversions. In recent years, genes encoding xylose reductases from several yeasts have been cloned and sequenced. A comparison of the primary sequences of yeast xylose reductases with the much better characterized human aldose reductase and human aldehyde reductase reveals that the yeast enzymes are hybrids between aldo-keto reductases and the short chain dehydrogenases/reductases families of enzymes. Why this is so and its evolutionary significance is presently not known. This short review will critically examine the structure and function information that can be gleaned from the sequence comparison. Several interesting questions arise from the sequence comparison and these can provide fruitful areas for further investigations. © 1998 John Wiley & Sons, Ltd.     

响应面法优化不同型态热带假丝酵母发酵生产木糖醇的工艺

利用Design Expert软件对菌丝型和酵母型热带假丝酵母发酵生产木糖醇实验进行设计及结果分析,建立木糖和木糖醇浓度与4个关键因子(菌型、发酵温度、pH、初始木糖浓度)的二次多项式回归模型,并对模型进行解析。结果表明:菌丝型热带假丝酵母转化木糖为木糖醇的能力高于酵母型;升高发酵温度,有利于木糖转化为木糖醇,而pH升高对转化过程并没有明显促进;发酵液中初始木糖浓度与木糖转化率呈正相关关系;获得最佳发酵工艺条件为菌种采用菌丝型酵母,发酵温度37℃,pH8,初始木糖浓度60mg/mL,此时木糖醇浓度达到17.21mg/mL。     

木糖浓度及补料发酵对树干毕赤酵母乙醇发酵的影响

探究不同浓度木糖及补料对树干毕赤酵母（Pichia stipitis）菌株1K-9发酵木糖产乙醇的影响,提高木糖产乙醇的发酵水平,为扩大规模发酵木糖产乙醇打下基础。结果表明,菌株1K-9先采用10%木糖进行乙醇发酵,36 h补加与10%木糖培养基等体积的20%木糖培养基继续发酵,发酵至108 h时菌数也达到了（12.16±0.07）×108个/mL,较未补料发酵时有所提高;发酵108 h时醪液中残留的木糖含量为（1.03±0.02）g/L,较未补料发酵时有所降低;乙醇含量达到了6.56%vol,较未补料时提高了1.85%vol。因此补料发酵是有效的。     

Effect of soy protein on intestinal absorptive ability of calves by the xylose absorption test

Five calves per group were fed whole milk (control) or one of three milk replacers with one-thrid of the total protein provided by a soy product. Soy products were Promocaf (a commercial soy protein concentrate), an experimental soy flour. After a 24-h fast, calves were fed xylose solution. Urine was collected for 5 h. Jugular blood was sampled at 0, .5, 1, 1.5, 2, 2.5, 3, 4, and 5 h after xylose administration. Xylose tests were weekly on each calf through 5 wk of age. Urinary xylose excretion, as a percentage of xylose fed, was higher in the control group during the last 4 wk than in groups fed milk replacers. Mean urinary xylose excretions during 5 wk from calves sampled 5 h after xylose administration were 12.4, 4.2, 4.2, and 4.3% of xylose administered for calves fed milk, soy flour, soy protein concentrate, and Promocaf, respectively. Mean increases in peak of xylose concentration in plasma were 55.7, 44.4, 42.8, and 45.3 mg/100 ml. Peak values for control calves were higher than those for calves fed soy products at wk 4 and 5. Times required to reach peak value did not differ significantly. Neither xylose concentration of plasma nor urinary xylose excretion differed among the groups fed soy products.     

椰子壳制取D-木糖糖液最佳结晶工艺条件的选择

探索了D-木糖过饱和溶液中浓度、时间、温度、pH值和乙醇溶剂对木糖结晶的影响。由此确定了椰子壳酸水解液中木糖结晶分离的最佳工艺条件。用高效液相色谱仪与红外光谱仪分析结果表明，椰壳水解液分离的木糖结晶样品与标准D-木糖样品的谱图特征峰完全一致。     

Enhancement of xylose uptake in 2-deoxyglucose tolerant mutant of Saccharomyces cerevisiae

Chemical mutation of Saccharomyces cerevisiae using ethyl methane sulfonate was performed to enhance its ability of xylose uptake for ethanol production from lignocellulose under microaerobic condition. Among the appeared mutants, the mutant no. 2 (M2) strain screened using inhibitory effects of 2-deoxyglucose (DOG) showed more than 4-fold high ability in xylose uptake compared with the wild type strain, under the presence of glucose. The catabolite repression by glucose was sufficiently reduced in M2 strain due to its tolerance to the high concentration of DOG (0.5%, wt./vol.). Metabolomic analyses of various sugars in the cell revealed that some of xylose was reduced to xylitol in M2 cell, providing the concentration gradient of xylose and more uptake of xylose. Xylulose-5-phosphate was significantly detected in the crude cell extract from M2 strain, indicating higher metabolic activity in pentose phosphate pathway. This was also confirmed by in vitro analyses of key enzymes involved in glucose and xylose metabolism, such as hexokinase, glucose-6-phosphate dehydrogenase and xylose reductase. Glucose uptake was moderately suppressed in the presence of trehalose-6-phosphate inhibiting the activation of hexokinase, resulting in more uptake of xylose through hexose transport system. To our knowledge, this study is the first report verifying that the mutation technique successfully enhances the xylose uptake by S. cerevisiae, particularly under the presence of glucose.