从阿拉伯胶水解液中结晶分离L-阿拉伯糖

阿拉伯胶水解液经结晶法提纯制备出粗L-阿拉伯糖.研究了时间、温度、pH值和溶剂对L-阿拉伯糖结晶率和纯度的影响,得到了由阿拉伯胶水解液中结晶分离L-阿拉伯糖适宜的工艺条件.该方法操作简便,生产效率高,易于工业化生产.     

L-阿拉伯糖研究进展

L-阿拉伯糖是一种新兴的低热量功能性糖,在自然界中,广泛存在于玉米皮、甜菜根、阿拉伯胶等中。L-阿拉伯糖在血糖、血脂的调节方面有广阔的前景。本文综述了L-阿拉伯糖的制备方法,并介绍了L-阿拉伯糖的性质,展望了L-阿拉伯糖生产的发展趋势。     

酸催化水解阿拉伯胶制备L-阿拉伯糖工艺

阿拉伯胶是提取制备L-阿拉伯糖的理想原料,对阿拉伯胶进行酸催化水解可获得含L-阿拉伯糖、D-半乳糖、L-鼠李糖的反应液,优化酸水解条件使水解液中L-阿拉伯糖的含量和收率均达到最佳水平,是保证后续分离纯化工艺稳定性及产品品质的关键。利用单因素实验考察了反应时间、酸浓度、反应温度、固液比等因素对水解工艺的影响,获得了影响酸水解反应的关键因素及适宜的水解条件。结果表明:温度对L-阿拉伯糖的生成速率有明显影响。经优化,当固液比为1:10 (g/ml)、100℃、0.1 mol·L^-1 H₂SO₄水解90 min或90℃、0.1 mol·L^-1 H₂SO₄水解200 min,水解液中L-阿拉伯糖的相对纯度分别达85%和87%,水解收率高达85%。     

阿拉伯糖催化制取L-核糖的工艺研究

本文对L-阿拉伯糖差相异构反应生成L-核糖进行了实验研究;通过正交试验分析确定了最佳阿拉伯糖转化条件:PH值2.5、反应温度95℃、钼酸铵加入量0.5%、糖液浓度15%,L-阿拉伯糖的转化率达16.9%。     

L-核糖的生物合成及其在药物中的应用

L-核糖是一种重要的药物中间体。综述了以核糖醇及L-阿拉伯糖为原料的L-核糖的生物合成方法,介绍了L-核糖在L-核苷类药物、糖缀合物、寡核苷酸中的应用进展。     

供求平台

求购维生素D3、L-脯氨酸；求购L-阿拉伯糖、D-半乳糖；求购二甲基砜；求购乙酰螺旋霉素；求购盐酸四环素；求购氯糖……     

兴安落叶松阿拉伯糖基半乳聚糖化学结构的研究

木粉在室温下用冷水所得到的提取液，经离心除去沉淀后首先用聚酰胺柱纯化，然后再用乙醇沉淀而制得高纯度阿拉伯糖基-半乳聚精（AG），HPLC分析表明AG聚糖D-半乳糖和L-阿拉伯糖组成，其摩尔比为7．41：1。高碘酸盐消耗为1．12摩尔，甲酸生成量为0．53摩尔，数值与文献值基本一致。13C－NMR研究表明：AG聚糖主链由1～3连接的β-D-吡喃型半乳糖基构成，每个主链半乳精基C—6上有两个或一个1-6连接的β-D-吡喃型半乳糖基和3（2）-O-α－L-呋喃型拉伯糖基-L-呋喃型阿拉伯糖。     

日开发生产阿拉伯糖的新方法

日本Unitika公司开发了一种酶基方法生产L-阿拉伯糖,这是一种低卡罗里增甜剂,该化合物是由甜菜滤糟和其它残渣纤维(如桔子和苹果纤维)多糖用来自曲霉属霉的阿拉伯酶和阿拉伯呋喃糖酶生产。生产L-阿拉伯糖的通常方法涉及半纤维素的酸基分解,半纤维素是由谷纤维、阿拉伯胶和甜菜浆用碱萃取而得,该法除需专门的反应器外,还需中和化学品和处理碱酸废水的副加处理。新方法,滤糟与水和酶在一容器内在40-80℃混和3-24h,含阿拉伯糖的溶液经过滤,用活性炭和离子交换处理提炼,然后蒸发浓缩,生成L-阿拉伯糖结晶,该新方法已经间歇试验证明,公司现正计…     

阿拉伯糖和其他糖类复聚衍生物发展动向

阿拉伯糖和其他糖类结合的复聚衍生物广泛存在于自然界,且对人体健康有重要的生理功能。但自然界并无游离的阿拉伯糖存在,需由人工从阿拉伯糖的复聚衍生物中提取。国内自2008年卫生部批准L阿拉伯糖单糖为新资源食品以来,对阿拉伯糖的功能有较多的报导,但对于阿拉伯糖和其他糖类复聚衍生物的报导较少。为使读者能更多地了解阿拉伯糖、阿拉伯糖和其他糖类复聚衍生物的发展动向,本文对其进行简要介绍。     

苎麻水溶性碳水化合物的分离和分析

用冷、热水分级抽提苎麻水溶性碳水化合物，然后分离出多糖、低聚糖和单糖。苎麻水溶性多糖和低聚糖用酸水解成单糖，再将水解所得的中性糖和酸性糖分别制备成糖腈乙酰酯和二硫缩醛硅烷化衍生物，作气相色谱分析。分析结果表明，苎麻水溶性多糖的糖基主要是D-半乳糖、L-鼠李糖、D-葡萄糖、L-阿拉伯糖、D-甘露糖和D-半乳糖醛酸。此外，尚有少量的L-岩藻糖、L-来苏糖、D-木糖和D-半乳糖醛酸甲酯。苎麻低聚糖的糖基组成与苎麻水溶性多糖的相似。苎麻游离单糖主要有D-赤鲜糖和七碳糖，还有少量的D-半乳糖、L-阿拉伯糖和D-半乳糖醛酸。     

Engineering the substrate specificity of xylose isomerase

Xylose isomerase (XI) catalyzes the isomerization and epimerization of hexoses, pentoses and tetroses. In order to clarify the reasons for the low reaction efficiency of a pentose sugar, L-arabinose, we determined the crystal structure of Streptomyces rubiginosus XI complexed with L-arabinose. The crystal structure revealed that, when compared with D-xylose and D-glucose, L-arabinose binds to the active site in a partially different position, in which the ligand has difficulties in binding the catalytic metal M2. Lys183 has been thought to stabilize the open substrate conformation by hydrogen bonding to oxygen O1. Our results with L-arabinose showed that the substrate stays in a linear form even without a hydrogen bond between Lys183 and oxygen O1. We engineered mutations to the active site of Actinoplanes missouriensis XI to improve the reaction efficiency with L-arabinose. The mutation F26W was intended to shift the position of oxygen O1 of L-arabinose closer to the catalytic metal M2. This effect of F26W was modeled by free energy perturbation simulations. In line with this, F26W increased 2-fold the catalytic efficiency of XI with L-arabinose; the increase was seen mainly in kcat. The mutation Q256D was outside the sphere of the catalytic residues and probably modified the electrostatic properties of the active site. It improved 3-fold the catalytic efficiency of XI with L-arabinose; this increase was seen in both Km and kcat. This study showed that it is possible to engineer the substrate specificity of XI.     

The evolution of sugar isomerases

L-Arabinosc isomerase (EC 5.3.1.4 [EC] ) catalyzes the isomerizationof L-arabinose to L-ribulose. Here we report on the purification,kinetic mechanism and chemical mechanism of L-arabinose isomerasefrom Escherichia coli. The enzyme catalyzes the isomerizationof L-arabinose to L-ribulose by a proton transfer mechanism,in contrast to xylose isomerase which uses a hydride transfermechanism to perform a similar isomerization. Arabinose isomeraseactivity is metal dependent, although the enzyme can catalyzethe exchange of the proton attached to carbon 2 of arabinosewith the solvent in the absence of metal ion. Manganese(II)is the only metal ion which renders the enzyme active for theisomerization reaction. Arabinose isomerase has high substratespecificity for L-arabinose. The difference in chemical mechanismbetween xylose isomerase and arabinose isomerase suggests thatthese enzymes are not related by convergent evolution. Thiswork also suggests that unless convergent evolution has beendemonstrated, the mechanism of one enzyme may not give any insightinto the mechanism of a second enzyme catalyzing the same reaction     

Determination and correlation of the solubility of L-arabinose and D-galactose in binary solvent mixtures from 278.15 to 333.15 K

L-arabinose and D-galactose could be released during the hydrolysis process of Arabic gum. The development of a crystallization process of L-arabinose is highly dependent on the knowledge of the solubility of both saccharides. In this work, the solubility of L-arabinose and D-galactose in binary mixtures of methanol-water or ethanol-water (mole fraction of water ≤0.5816) was determined at temperatures between 278.15 and 333.15 K by a static equilibrium method. The experimental data correlated well with the modified Apelblat equation, the simplified polynomial empirical equation, NRTL model and UNIQUAC model. Additionally, the thermodynamic properties including the dissolution enthalpy and entropy were obtained from the experimental data. Within the studied temperature range, the dissolution is endothermic and the dissolution process is non-spontaneous.     

The green hydrolysis technology of hemicellulose in corncob by the repeated use of hydrolysate

To achieve green hydrolysis technology of hemicellulose through repeated using hydrolysate,the hydrolysis of hemicellulose in corncob was studied.The influence of repeated use of corncob hydrolysate on concentrations of D-xylose and L-arabinose was investigated.The loss rates of D-xylose in the prepared D-xylose solutions both with and without corncob,and repeated using corncob hydrolysate under identical acidity condition were discussed.The result shows that D-xylose concentration and L-arabinose concentration are all gradually increasing with the growing time of repeated use of corncob hydrolysate.After the fifth repetition,the concentrations of D-xylose and L-arabinose are 196.7 g·L~(-1)and 22.0 g·L~(-1),respectively.Substance inhibiting the degradation of D-xylose is generated during repeated use of corncob hydrolysate,and the production is further proved by the change of D-xylose concentration and the loss rate of D-xylose over heating time.     

Experimental measurement and thermodynamic modeling of binary and ternary solid-liquid phase equilibrium for the systems formed by L-arabinose,D-xylose and water

Solid-liquid phase equilibrium data for binary (L-arabinose-water) and (D-xylose-water) systems at temperatures from (269.85-298.05) K and ternary (L-arabinose-D-xylose-water) system at temperatures of 273.85 K,278.85 K and 284.45 K were measured at atmospheric pressure.The ternary phase diagrams of the systems were constructed on the base of the measured solubility.Two pure solid phases were formed at given temperatures,including pure L-arabinose and pure D-xylose,which were confirmed and determined by the method of Schreinemakers' wet residue.At the same temperature,the crystallization region of L-arabinose was larger than D-xylose's.The acquired solubility data were then correlated using the NRTL model,Wilson model and Xu model.The calculated solubility with the three models agreed well with the experimental values.     

龙葵多糖中单糖组成的色谱研究(Ⅰ)

首次从龙葵(Solanum Nigrum L)的水提取液中得到一水溶性多糖,经纸色谱、硅胶薄层色谱和高效液相色谱分析其全水解液,证明它由D—葡萄糖(93％),L—阿拉伯糖(7％)组成。