酶法水解超级稻秸秆木聚糖制备低聚木糖的工艺研究

本文以超级稻秸秆为原料,碱溶液抽提法得到粗木聚糖,然后酶水解,制备低聚木糖。对酶解条件进行了优化,并采用高效液相色谱法对木聚糖酶解液主要组分进行了分析。结果表明,正交试验优化的最佳酶解条件为温度50℃、pH5. 0、加酶量4%,在该试验条件下低聚木糖得率为13. 5%。酶解液组分分析发现,其主要组分为木二糖和木三糖,只有少量的单糖,该结果有利于后续低聚木糖的纯化,符合低聚木糖制备的要求。     

真菌分解玉米芯生产低聚木糖的研究

从53种真菌中筛选出3株能分解玉米芯木聚糖并产生低聚木糖的菌株。摇瓶发酵的适当条件为：基质含木聚糖提取物5％,蛋白胨0.1％、尿素0.1%,温度32℃,摇床转速180r／min,培养时间48h,木二糖相对于木聚糖的转化率最高为52．2％;直接用固体玉米芯接种培养所选菌种,加水保温,分解玉米芯中的木聚糖生产低聚木糖,在适宜的条件下木二糖相对于玉米芯的最高转化率为8％。     

低聚木糖分离纯化的研究进展

综述了低聚木糖分离纯化的研究进展。低聚木糖是一种非消化性寡糖 ,能选择性增殖肠道内双歧杆菌 ,可广泛应用于食品工业和饲料工业。低聚木糖的分离纯化技术主要包括层析分离技术 (包括凝胶过滤层析、离子交换层析和吸附层析 )和膜分离技术 (包括超滤、纳滤和反渗透 )。低聚木糖的提纯主要采用膜分离技术和层析分离技术 ,低聚木糖单一组分的分离主要采用凝胶过滤层析和吸附层析     

蔗渣制备低聚木糖的有机酸预处理条件研究

采用有机酸法水解制备蔗渣低聚木糖,通过单因素实验、正交试验研究了甲酸-乙酸比例、温度、水解时间、固液比等因素的影响,以水解率、总糖收率和聚糖收率为考察指标,得到有机酸法水解蔗渣制备低聚木糖的最优预处理条件为甲酸∶乙酸=9∶1、水解温度100℃、水解时间60min、固液比1∶7,在此条件下蔗渣水解率为47.78%,总糖收率20.57%,聚糖收率11.88%。HPLC检测结果显示:水解物中木二糖含量为17.69%,木三糖为11.23%,更高聚合度聚糖所占比例为29.42%,木糖为36.78%。半纤维素有机酸水解物可进一步通过木聚糖酶水解、分离制备低聚木糖。研究结果可为蔗渣制备低聚木糖新工艺提供科学依据。     

高效液相色谱法同时测定保健食品中低聚果糖和低聚木糖

目的 建立高效液相色谱法同时测定保健食品中低聚果糖(包括蔗果三糖、蔗果四糖及蔗果五糖)和低聚木糖（包括木二糖、木三糖、木四糖、木五糖、木六糖及木七糖）的含量。方法 采用键合有酰胺官能团杂化填料的色谱柱,以乙腈和水为流动相,利用亲水保留色谱机制（HILIC）实现对低聚果糖和低聚木糖各单体的有效分离,结合示差检测以外标法定量。该方法同时利用木糖对低聚木糖各单体转换系数进行定量。结果 低聚果糖和低聚木糖各单体线性关系良好,相关系数均大于0.998,平均加标回收率为95%以上,具有较高的准确度和良好的重现性。结论 高效液相色谱法由于采用木糖对照品转换定量低聚木糖含量,减少低聚木糖各单体标准品在日常工作中的使用量,进而降低检测成本。该方法经济可靠,测定结果准确,适合于添加有低聚果糖和低聚木糖的功能性产品检测。     

黑曲霉木聚糖酶的底物特异性和低聚木糖生产

对黑曲霉（Ａｓｐｅｒｇｉｌｌｕｓ ｎｉｇｅｒ）木聚糖酶进行了纯化研究,结果表明,经Ｓｅｐｈａｄｅｘ Ｇ－１００和ＤＥＡＥ－ＳｅｐｈａｄｅｘＡ－５０分离后,获得三个组分,称为Ｘ１、Ｘ２、Ｘ３。它们经ＰＡＧＥ电泳分析均为单一组分。对Ｘ１、Ｘ２、Ｘ３的相关性质,特别是底物特异性也作了研究,纯酶Ｘ３组分或部分纯化的酶可用于生产低聚木糖,产品得率为１０％。     

投喂低聚木糖对草鱼肠道菌群的影响

投喂添加0.1%、0.2%、0.4%和0.6%低聚木糖的基础饲料56 d, 对草鱼(Ctenopharyngodon idellus)肠道菌群进行了研究。分别在投喂前(0 d)和投喂后的第14、28、42 和56 天取样, 对草鱼肠道大肠杆菌(E. coli)、气单胞菌(Aeromonas)和双歧杆菌(Bifidobacterium)数量进行了分析。结果表明: 基础饲料中添加不同浓度的低聚木糖对草鱼肠道菌群有一定影响, 大肠杆菌数量在28 d 达最低值, 其中0.4%组减少的幅度最大, 与对照组比较显著减少(P<0.05); 气单胞菌数量均有减少但与对照组比较差异并不显著; 双歧杆菌数量均有增加, 其中0.4%组在第14 天时差异显著(P<0.05)。因此, 饲料中添加0.4%低聚木糖效果最佳, 有利于草鱼肠道菌群保持健康的状态。     

低聚木糖对模拟失重大鼠肠道微生态的影响

目的 研究低聚木糖对模拟失重大鼠肠道微生态的影响。方法 采用大鼠尾部悬吊法模拟失重。32只雄性SD大鼠随机分为4组,每组8只：FC组（地面对照组,饲喂基础饲料）,FS组（地面处理组,饲喂添加低聚木糖的饲料）,SC组（尾吊对照组,饲喂基础饲料）。SS组（尾吊处理组,饲喂添加低聚木糖的饲料）,实验21d,SC和SS组解除尾吊继续观察。实验21d。采用选择性培养基对大鼠粪便肠杆菌、肠球菌、类杆菌、双歧杆菌以及乳杆菌进行定量测定。结果 SC组与FC组相比,双歧杆菌数量减少,肠杆菌和肠球菌数量增加;FS组比FC组双歧杆菌数量增加显著,肠杆菌和肠球菌有不同程度的减少,SS组比SC组双歧杆菌数量增加显著,肠杆菌和肠球菌也有不同程度的减少。类杆菌和乳杆菌变化不明显。尾吊解除期,SS组双歧杆菌数量比SC组更快恢复到正常水平。结论 低聚木糖可促进尾吊大鼠肠道益生菌主要是双歧杆菌的增殖,一定程度上促进由于模拟失重造成肠道微生态失调的平衡,并对条件致病菌具有一定的抑制作用。     

酶法制备低聚木糖中木二糖的提纯与色谱鉴定

半纤维素经木聚糖酶水解得到混合的低聚木糖,用葡聚糖凝胶柱SephadexG-10层析分离后,出现四个组分峰,经高效液相色谱分析鉴定,其中3号峰为木二糖纯组分峰.结果表明:利用φ2.5 cm×120 cm凝胶柱,以蒸馏水为流动相,流速为10ml/h,在室温下,可以分离出高纯度的木二糖.     

碱法前处理对小麦麸皮酶解制取低聚木糖的影响

以小麦麸皮为原料,用不同浓度NaOH溶液进行预处理后结合微波消解制取低聚木糖。小麦麸皮以料液比1:10,经NaOH浓度2.5%,温度60℃,时间为2.5小时前处理及微波处理后酶解24h的样品中,低聚木糖提取率高到达22.79%.     

The effect of maltose on dextran yield and molecular weight distribution

Dextran synthesis has been studied since the Second World War, when it was used as blood plasma expander. This polysaccharide composed of glucose units is linked by an α-1,6-glucosidic bond. Dextransucrase is a bacterial extra cellular enzyme, which promotes the dextran synthesis from sucrose. When, besides sucrose, another substrate (acceptor) is also present in the reactor, oligosaccharides are produced and part of the glucosyl moieties from glucose is consumed to form these acceptor products, decreasing the dextran yield. Although dextran enzymatic synthesis has been extensively studied, there are few published studies regarding its molecular weight distribution. In this work, the effect of maltose on yield and dextran molecular weight synthesized using dextransucrase from Leuconostoc mesenteroides B512F, was investigated. According to the obtained results, maltose is not able to control and reduce dextran molecular weight distribution and synthesis carried out with or without maltose presented the same molecular weight distribution profile.     

A simple method for the determination of DNA molecular weight distribution

A method is described for the molecular weight distribution of DNA which is determined from sedimentation-velocity analysis. Knowing the distribution of sedimentation coefficients for a single DNA concentration it is possible to extrapolate such a distribution to infinite dilution of the solute in a simple way. Two versions (using two or three terms of a series) of extrapolating equations are considered and discussed in detail. The sedimentation coefficients distribution calculated from these equations differs only insignificantly with that obtained in a conventional way.     

Process development for the enzymatic hydrolysis of food protein: Effects of pre-treatment and post-treatments on degree of hydrolysis and other product characteristics

An enzymatic process was developed to produce protein hydrolysate from defatted soya protein. Various unit operations were tried, and the effects of pre- and post-treatments on the product characteristics such as degree of hydrolysis (DH), free amino acid content (%FAA) and average molecular weight (MW) were investigated. The use of acid washes showed no difference in %DH. Increasing pH during pre-cooking gave lower %DH. Alkaline cooking made too much insoluble protein, thus the protein yield was too small. A better hydrolysis with more acceptable taste was obtained when the combination of Neutrase/Alcalase/Flavourzyme was used in place of Alcalase/Flavourzyme combination. Untoasted defatted soya was more effective on the proteolysis than toasted one. The MW of the evaporated and spray dried product was higher than that of undried product, due to precipitation of low-solubility components. When the product separation was carried out by ultrafiltration and the product concentration by reverse osmosis, the solubility and the taste of the product were improved. The difference between enzyme hydrolysate and acid hydrolysate was significant in free amino acid composition, especially in tyrosine, phenylalanine, glutamine and asparagine.     

A high molecular weight silk fibroin scaffold that resists degradation and promotes cell proliferation

The regulation of the biodegradation rate of 3D-regenerated silk fibroin scaffolds and the avoidance of premature collapse are important concerns for their effective applications in tissue engineering. In this study, bromelain, which is specific to sericin, was used to remove sericin from silk, and high molecular weight silk fibroin was obtained after the fibroin fibers were dissolved. Afterwards, a 3D scaffold was prepared via freeze-drying. The Sodium dodecyl sulfate–polyacrylamide gel electrophoresis results showed that the average molecular weight of the regenerated silk fibroin prepared by using the bromelain-degumming method was approximately 142.2 kDa, which was significantly higher than that of the control groups prepared by using the urea- and Na₂CO₃-degumming methods. The results of enzyme degradation in vitro showed that the biodegradation rate and internal three-dimensional structure collapse of the bromelain-degumming fibroin scaffolds were significantly slower than those of the two control scaffolds. The proliferation activity of human umbilical vein vascular endothelial cells inoculated in bromelain-degumming fibroin scaffolds was significantly higher than that of the control scaffolds. This study provides a novel preparation method for 3D-regenerated silk fibroin scaffolds that can effectively resist biodegradation, continuously guide cell growth, have good biocompatibility, and have the potential to be used for the regeneration of various connective tissues.     

Effect of molecular weight distribution on the solution properties of sodium hyaluronate in 0.2M NaCl solution

Various molecular parameters, which characterize sodium hyaluronate in 0.2M NaCl solution, were obtained at 25°C by means of the static and dynamic light scattering and low shear viscometry over the molecular weight range of 5.94–627 × 10⁴. Molecular weight distribution was obtained by using the Laplace inversion method of the autocorrelation function of the scattered light intensity and by Yamakawa theory for the wormlike chain with the stiff chain parameters for sodium hyaluronate in 0.2M NaCl (persistence length, chain diameter, molar mass per unit contour length, and the excluded‐volume strength). The molecular weight distribution thus obtained reproduced the solution properties of sodium hyaluronate well. Especially, the intrinsic viscosity showed a good agreement over four orders of molecular weight with Yamakawa theory combined with the Barrett function. Sodium hyaluronate in 0.2M NaCl solution is well expressed by the wormlike chain model affected by the excluded‐volume effect with the persistence length of 4.2 nm. © 1999 John Wiley & Sons, Inc. Biopoly 50: 87–98, 1999     

The solution molecular weight and shape of the bacterial exopolysaccharides amylovoran and stewartan

Amylovoran, the acidic exopolysaccharide (EPS) of Erwinia amylovora, and stewartan, the capsular EPS of E. stewartii, were characterized by analytical ultracentrifugation and by size exclusion chromatography connected to dual detection of light scattering and mass. The average molecular weights of amylovoran and stewartan were determined as 1.0×10⁶ and 1.7×10⁶ Da, with polydispersity values (M_w/M_n) of 1.5 and 1.4, respectively. Based on the sugar composition and their molecular weight, both exopolysaccharides consist of approximately 1000 repeating units per molecule, this suggests a similar mechanism for chain length determination during biosynthesis of EPS in both organisms.     

Effect of single nutrient limitation of poly-beta-hydroxybutyrate molecular weight distribution in alcaligens europhus

The effect of magnesium and phosphate limitation on the molecular weight distribution of poly-beta-hydroxybutyrate (PHB) in Alcaligens europhus in cotinuons culture has been stuied. Conditions of nitrogen limitation both with glucose excess (above ca. 20 g/L) and without excess were investigated Under N-limitation and glucose excess, M(w) decreases when the magnesium content is decreased below 50% (19.7 mg/L) of the basal medium content; this also results in a broadenng of molecular weight distribution (M(w)/M(n)) from 2 to 5 and a decrease in M(w) fron 2 x 10(6) to 0.9 x 10(6). Below 20% of the basal content of magnesium (7.9 mg/L) these two trends were reversed. This behaviour was not observed in the absence of glucose excess, phshate had virtually no effect on PHB M(w) or its distribution, whereas wih no (or little) glucose excess M(w) of the PHB decreased with phosphate concentrations below 50% of the basal level (0.705 g/L). Hence, in continuous or fed-batch cultures, in addition to nitrogen limitation to alklow for PHB accumulation, it is necesary to control both the addition of glucose (no excess) and also to maintain magnesium limitation (ca. 25% of basal medium level, 9.9 mg/L) and phosphate above 50% of he basal level (0.705 g/L). Thus, when broadening of molecular weight destribution (increase in M(w)/M(n)) is observed at the end of fed-batch culture it is probably caused by phosphate limitation and/or glucose excess. (c) 1995 John Wiley & Sons, Inc.     

低分子肝素的抗炎作用及机制

低分子肝素(low molecular weight heparin, LMWH)除作为抗凝血和抗血栓药在临床上广为应用外,近年来其抗炎活性也颇受重视.LMWH抗炎机制涉及炎症细胞、炎症因子和黏附分子等环节.目前对LMWH的抗炎机制研究还处在初级阶段,但是LMWH独特的性质使其有望成为有效且安全的新型抗炎药物.     

功能性低分子量岩藻多糖的研究进展

低分子量岩藻多糖来源于褐藻,是一类含有硫酸基团的多糖,具有多种生物学功能,如抗凝血、抗病毒、抗血栓、抗肿瘤等功能,因此可被广泛地应用于医药、食品等领域。着重介绍了低分子量岩藻多糖的制备及其生物学功能的研究进展。     

A low molecular weight DNA polymerase from wheat embryos

The study of plant DNA polymerases lags far behind that concerning their animal or yeast counterpart. In this work we describe the first extensive purification to apparent homogeneity, as well as a detailed biochemical and immunological characterization, of a low molecular weight DNA polymerase (DNA polymerase C_I) purified from wheat embryos. The monomeric enzyme is a basic protein having a molecular weight of 52 kDa. Polyclonal antibodies raised in rabbits against DNA polymerase C_I did not inhibit animal DNA polymerases and or wheat DNA polymerase A, whereas wheat DNA polymerases C_II and B were much less affected than the C_I enzyme. Several properties of enzyme C_I were studied. Some known inhibitors of DNA polymerase activity including aphidicolin, phosphonoacetic acid and heparin, did not affect DNA polymerase C_I while the activity of this enzyme was strongly inhibited by ddTTP and N-ethylmaleimide. The polyamine spermine decreased markedly the enzyme activity, while spermidine produced a strong stimulation at the same concentrations that spermine inhibited the enzyme. The best template for this enzyme is poly dA-oligo dT, although polymerase C_I can recognize significantly some synthetic polyribonucleotide templates (poly rC-oligo dG, poly rA-oligo dT) but only at a given protein/template primer ratio. The enzyme is blocked at the amino terminus, thus preventing the automatic sequencing of the protein. The amino acid analysis showed a striking similarity with the animal low molecular weight DNA polymerase . The latter observation, as well as the effect of inhibitors (except N-ethylmaleimide which does not inhibit the animal polymerase) indicate that the DNA polymerase described in this work is a plant DNA polymerase very similar to the low molecular weight animal DNA polymerase , an enzyme believed to be involved in nuclear DNA repair.