Determination of polyol profiles in human urine by capillary gas chromatography

A new rapid capillary gas chromatographic method is described for the profile analysis of urinary polyols as their trifluoroacetyl derivatives. Ten urinary polyols: erythritol, threitol, fucitol, ribitol, arabinitol, xylitol, mannitol, glucitol, galactitol and myo-inositol were completely determined for the first time. Iditol was newly found in normal urine. Urinary polyols were verified by gas chromatography/mass spectrometry.     

Effect of detoxification of dilute-acid corn fiber hydrolysate on xylitol production

Four different detoxification methods were evaluated for the production of xylitol from corn fiber dilute-acid hydrolysate using Candida tropicalis. Although C. tropicalis could ferment the dilute partially neutralized hydrolysate to xylitol in low yields (0.1 g/g), it could not ferment the concentrated hydrolysate. Overliming, calcium hydroxide neutralization, neutralization combined with activated charcoal, and overliming combined with activated charcoal methods were used to improve the fermentation of the concentrated hydrolysates. The partial neutralization combined with activated charcoal treatment was the most effective method with respect to xylitol yield and productivity. The highest xylitol yield (0.4 g of xylitol/g of xylose) was obtained for the highest concentration of hydrolysate (three times the original) that had been treated with calcium hydroxide and activated charcoal. The corresponding productivity was 0.23 g/(L x h). Overliming caused reduction in xylitol yield.     

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 % 。     

淀粉与木糖醇共混物的性能

淀粉与木糖醇共混物的性能于九皋，郑华武（天津大学化学系天津３０００７２）关键词淀粉，木糖醇，共混，热塑性研究具有环境条件下可降解的塑料已成为国内外专家学者广泛关注的研究课题。淀粉具有类似高聚物的分子结构，但由于分子量大，分子之间的亲合力强，很难加工成...     

Chromatographic determination of some biomarkers of liver cirrhosis and hepatocellular carcinoma in Egyptian patients

Metabolomics has been shown to be an effective tool for disease diagnosis, biomarker screening and characterization of biological pathways. A total of 140 subjects were included in this study; urine metabolomes of patients with liver cirrhosis (LC, n = 40), patients with hepatocellular carcinoma (HCC; n = 55) and healthy male subjects (n = 45) as a control group were studied. Gas chromatography/mass spectrometry‐based urine metabolomics profiles were investigated for all participants. Diagnostic models were constructed with a combination of marker metabolites, using principal components analysis and receiver operator characteristic curves. A total of 57 peaks could be auto‐identified of which 13 marker metabolites (glycine, serine, threonine, proline, urea, phosphate, pyrimidine, arabinose, xylitol, hippuric acid, citric acid, xylonic acid and glycerol) were responsible for the separation of HCC group from healthy subjects. Also, eight markers metabolites (glycine, serine, threonine, proline, citric acid, urea, xylitol and arabinose) showed significant differences between the LC group and healthy subjects. No significant difference was detected between HCC and LC groups regarding all these metabolites. Metabolomic profile using GC–MS established an optimized diagnostic model to discriminate between HCC patients and healthy subjects; also it could be useful for diagnosis of LC patients. However, it failed to differentiate between HCC and LC patients.     

Catalytic Deoxygenation of Xylitol to Renewable Chemicals: Advances on Catalyst Design and Mechanistic Studies

Xylitol is commonly known as one of the top platform intermediates for biomass conversion. Catalytic deoxygenation of xylitol provides an atomic and energetic efficient way to produce a variety of renewable chemicals including ethylene glycol, 1,2‐propanediol, lactic acid and 1,4‐anhydroxylitol. Despite a few initial attempts in converting xylitol into those products, improving catalyst selectivity towards C?O and C?C cleavage reactions remains a grand challenge in this area. To our best knowledge, there is lack of comprehensive review to summarize the most recent advances on catalyst design and mechanisms in deoxygenation of xylitol, offering important perspective into future development of xylitol transformation technologies. Therefore, in this mini‐review, we have critically discussed the conversion routes involved in xylitol deoxygenation over solid catalyst materials, the nanostructures of supported metal catalysts for C?H, C?C and C?O bond cleavage reactions, and mechanistic investigation for xylitol conversion. The outcome of this work provides new insights into rational design of effective deoxygenation catalyst materials for upgrading of xylitol and future process development in converting hemicellulosic biomass.     

溴代季戊四醇的气相色谱法分析

采用ＢＰＸ－７０毛细管色谱柱对季戊四醇的－溴代、二溴代和三溴代产物进行了分离和定量分析,用内标法定量,本糖醇为内标物。该方法快速、简便、准确。     

Thermus thermophilus木糖异构酶与木糖醇的分子对接及模型分析

在1BXB结构基础上, 通过分子对接方法构建木糖异构酶与抑制剂木糖醇的复合物模型, 为合理设计解除木糖醇对木糖异构酶的抑制及进一步揭示木糖醇对该酶抑制机理提供参考.     

PVA-Hydrogel Entrapped <Emphasis Type="Italic">Candida Guilliermondii</Emphasis> for Xylitol Production from Sugarcane Hemicellulose Hydrolysate

Viable cells of Candida guilliermondii were immobilized by inclusion into polyvinyl alcohol (PVA) hydrogel using the freezing–thawing method. Entrapment experiments were planned according to a 2³ full factorial design, using the PVA concentration (80, 100, and 120 g L⁻¹), the freezing temperature (−10, −15, and −20 °C), and the number of freezing-thawing cycles (one, three, and five) as the independent variables, integrated with three additional tests to estimate the errors. The effectiveness of the immobilization procedure was checked in Erlenmeyer flasks as the pellet capability to catalyze the xylose-to-xylitol bioconversion of a medium based on sugarcane bagasse hemicellulosic hydrolysate. To this purpose, the yield of xylitol on consumed xylose, xylitol volumetric productivity, and cell retention yield were selected as the response variables. Cell pellets were then used to perform the same bioconversion in a stirred tank reactor operated at 400 rpm, 30 °C, and 1.04 vvm air flowrate. At the end of fermentation, a maximum xylitol concentration of 28.7 g L⁻¹, a xylitol yield on consumed xylose of 0.49 g g⁻¹ and a xylitol volumetric productivity of 0.24 g L⁻¹ h⁻¹ were obtained.     

Kinetic Characteristics of Xylitol Crystallization from Aqueous-Ethanolic Solutions

The kinetics of xylitol crystallization from aqueous-ethanolic solutions as a function of the initialsolution supersaturation, solvent composition, temperature was studied. The effect of solvent compositionon the rate of the xylitol bulk crystallization was considered.     

木糖醇的由来及用途

介绍了木糖醇的由来及合成,以及在改善糖尿病症状、治疗肺感染和其他领域中的用途,并展望了木糖醇的发展前景.     

Improvement on <Emphasis Type="SmallCaps">d</Emphasis>-xylose to Xylitol Biotransformation by <Emphasis Type="Italic">Candida guilliermondii</Emphasis> Using Cells Permeabilized with Triton X-100 and Selected Process Conditions

Cells of Candida guilliermondii permeabilized with Triton X-100 were able to efficiently produce xylitol from a medium composed only by d-xylose and MgCl₂·6H₂O in potassium phosphate buffer, at 35 °C and pH 6.5. Under these conditions, the results were similar to those obtained when cofactor and co-substrate or nutrients were added to the medium (about 95 % d-xylose was assimilated producing 42 g/L of xylitol, corresponding to 0.80 g/g yield and 2.65 g/L h volumetric productivity). Furthermore, the permeabilized cells kept the d-xylose assimilation in about 90 % and the xylitol production in approx. 40 g/L during three bioconversion cycles of 16 h each. These values are highly relevant when compared to others reported in the literature using enzyme technology and fermentative process, thereby demonstrating the effectiveness of the proposed method. The present study reveals that the use of permeabilized cells is an interesting alternative to obtain high xylitol productivity using low cost medium formulation. This approach may allow the future development of xylitol production from xylose present in lignocellulosic biomass, with additional potential for implementation in biorefinery strategies.     

Effect of Furfural, Vanillin and Syringaldehyde on Candida guilliermondii Growth and Xylitol Biosynthesis

Xylitol is a five-carbon sugar alcohol with established commercial use as an alternative sweetener and can be produced from hemicellulose hydrolysate. However, there are difficulties with microbiological growth and xylitol biosynthesis on hydrolysate because of the inhibitors formed from hydrolysis of hemicellulose. This research focused on the effect of furfural, vanillin, and syringaldehyde on growth of Candida guilliermondii and xylitol accumulation from xylose in a semi-synthetic medium in microwell plate and bioreactor cultivations. All three compounds reduced specific growth rate, increased lag time, and reduced xylitol production rate. In general, increasing concentration of inhibitor increased the severity of inhibition, except in the case of 0.5 g vanillin per liter, which resulted in a faster late batch phase growth rate and increased biomass yield. At concentrations of 1 g/l or higher, furfural was the least inhibitory to growth, followed by syringaldehyde. Vanillin most severely reduced specific growth rate. All three inhibitors reduced xylitol production rate approximately to the same degree.     

Transfer Volumes of Small Peptides from Water to Aqueous Xylitol Solutions at 298.15 K

Densities have been measured by an oscillating-tube densimeter for aqueous solutions of glycylglycine and glycylglycylglycine in aqueous xylitol solutions with xylitol mass fractions ranging from 0 to 0.15 at 298.15 K. Apparent molar volumes and limiting partial molar volumes have been used to calculate the corresponding transfer volumes from water to different concentrations of xylitol + water mixtures. The results are interpreted in terms of the cosphere overlap model.     

Characterization of xylitol dehydrogenase from debaryomyces hansenii

The xylitol dehydrogenase (EC 1.1.1.9) from xylose-grown cells ofDebaryomyces hansenii was partially purified in two Chromatographic steps, and characterization studies were carried out in order to inves tigate the role of the xylitol dehydrogenase-catalyzed step in the regu lation of D-xylose metabolism. The enzyme was most active at pH 9.0–9.5, and exhibited a broad polyol specificity. The Michaelis con stants for xylitol and NAD⁺ were 16.5 and 0.55 mM, respectively. Ca²⁺, Mg²⁺, and Mn²⁺ did not affect the enzyme activity. Conversely, Zn²⁺, Cd²⁺, and Co²⁺ strongly inhibited the enzyme activity. It was concluded that NAD⁺-xylitol dehydrogenase from D.hansenii has similarities with other xylose-fermenting yeasts in respect to optimal pH, substrate specificity, and K_m value for xylitol, and therefore should be named L-iditol:NAD⁺-5-oxidoreductase (EC 1.1.1.14). The reason D.hansenii is a good xylitol producer is not because of its value of K_m for xylitol, which is low enough to assure its fast oxidation by NAD⁺ xylitol dehydrogenase. However, a higher K_m value of xylitol dehydro genase for NAD⁺ compared to theK _m values of other xylose-ferment ing yeasts may be responsible for the higher xylitol yields.     

Production of Xylitol from D-Xylose byDebaryomyces hansenii

Xylitol, a naturally occurring five-carbon sugar alcohol, can be produced from D-xylose through microbial hydrogenation. Xylitol has found increasing use in the food industries, especially in confectionary. It is the only so-called “second-generation polyol sweeteners” that is allowed to have the specific health claims in some world markets. In this study, the effect of cell density on the xylitol production by the yeastDebaryomyces hansenii NRRL Υ-7426 from D-xylose under microaerobic conditions was examined. The rate of xylitol production increased with increasing yeast cell density to 3 g/L. Beyond this amount there was no increase in the xylitol production with increasing cell density. The optimal pH range for xylitol production was between 4.5 and 5.5. The optimal temperature was between 28 and 37°C, and the optimal shaking speed was 300 rpm. The rate of xylitol production increased linearly with increasing initial xylose concentration. A high concentration of xylose (279 g/L) was converted rapidly and efficiently to produce xylitol with a product concentration of 221 g/L was reached after 48 h of incubation under optimum conditions.

     

Factors that affect the biosynthesis of xylitol by xylose-fermenting yeasts

Xylitol is a sweetener with important technological properties like anticariogenicity, low caloric value, and negative dissolution heat. Because it can be used successfully in food formulations and pharmaceutical industries, its production is in great demand. Xylitol can be obtained by microbiological process, since many yeasts and filamentous fungi synthesize the xylose reductase enzyme, which catalyses the xylose reduction into xylitol as the first step in the xylose metabolism. The xylitol production by biotechnological means has several economic advantages in comparison with the conventional process based on the chemical reduction of xylose. The efficiency and the productivity of this fermentation chiefly depends upon the microorganism and the process conditions employed. In this mini-review, the most significant upstream parameters on xylitol production by biotechnological process are described.     

Model compound studies

The influence of other hemicellulosic sugars (arabinose, galactose, mannose, and glucose), oxygen limitation, and initial xylose concentration on the fermentation of xylose to xylitol was in vestigated using experimental design methodology. Oxygen limitation and initial xylose concentration had strong influences on xylitol production by Candida tropicalis ATCC 96745. Under semiaerobic conditions, xylitol yield was highest (0.62 g/g), whereas under aerobic conditions volumetric productivity was highest (0.90g/[L·h]). In the presence of glucose, xylose utilization was strongly repressed and sequential sugar utilization was observed. Ethanol produced from the glucose caused a 50% reduction in xylitol yield when the ethanol con centration exceeded 30 g/L. When complex synthetic hemicellulosic sugars were fermented, glucose was initially consumed followed by a simultaneous uptake of the other sugars. The highest xylitol yield (0.84 g/g) and volumetric productivity (0.49 g/[L·h]) were obtained for substrates containing high arabinose and low glucose and mannose contents.     

新型甜味剂——木糖醇

木糖醇作为新型甜味剂,已得到广泛应用。本文介绍了木糖醇的理化性质、医用价值及木糖醇的生产过程。