水热抽提玉米芯半纤维素结构变化及对酶解行为影响

为提高富含木聚糖的农业废弃物再利用-高效制备低聚木糖，该研究以玉米芯为原料，通过水热预处理结合乙醇分级沉淀获得不同组分半纤维素，并利用分子质量测定、糖基结构及红外表征了半纤维素组分的基本特征，研究了半纤维素结构变化及对酶解效果的影响。结果显示，当利用3倍体积的乙醇分离半纤维素时，木聚糖的得率达到最大为48.67%,醇沉获得的各木聚糖组分由木糖、葡萄糖、甘露糖等组成；分支度(木糖/阿拉伯糖)为6.61～16.10,木聚糖的沉淀主要受到木聚糖的分子质量和分支度2个因素的影响。以不同组分进行酶促反应动力学实验结果表明，分子质量分布系数较小同时分支度最小的组分，其K_m及V_max分别为(5.43±0.31) mg/mL和(154.9±2.33) U/mg,表现出的催化适应性明显高于其他组分，此结果显示分子质量及分支度可能是影响酶解效率的关键因素。     

苹果膳食纤维中半纤维素的化学组成

采用碱法和二甲亚砜法从苹果膳食纤维中提取出4种半纤维素,分别命名为半纤维素A、B、C和E,通过红外分析和电镜扫描对其化学组成和表面微观结构进行了研究。结果表明:苹果膳食纤维中半纤维素由木葡聚糖(半纤维素A)、木聚糖1(半纤维素B)和木聚糖2(半纤维素C)以及半乳甘露聚糖(半纤维素E)等组成,4种半纤维素的表面微观各不相同,木聚糖1颗粒表面呈规则的晶形外观,具有成晶性;木葡聚糖颗粒表面具有很多颗粒状结构,具有一定的成晶性;木聚糖2和半乳甘露聚糖颗粒表面呈不规则形状,不具有成晶性。     

添加半纤维素对硫酸盐浆回收性能的影响

研究了在未干硫酸盐浆中加入低木聚糖、杨木半纤维素和玉米芯半纤维素。探讨添加半纤维素对硫酸盐浆回收性能的影响。研究结果表明，低木聚糖、杨木半纤维素和玉米芯半纤维素均能提高纸张的强度。还能提高回收纸的强度，当添加2％的木聚糖、1．6％的硫酸铝、抄纸时pH为4．5所得的纸张性能提高最多，纸张的紧度增加24．55％，耐折度增加500％，撕裂指数增加29．01％。抗张指数增加30．01％，耐破指数增加44．07％，散光系数下降17．25％。电镜分析表明加入木聚糖可增加纸张及回收纸中的纤维结合强度。     

以玉米芯为原料酶法制备低聚木糖的研究

以玉米芯为原料,在固液比1：10,NaOH 质量浓度4%,50℃条件下处理24h,木聚糖提取率为91．0%。利用木聚糖酶降解木聚糖制备低聚木糖,确立了最佳酶解工艺条件为：50℃,pH 4．8,木聚糖底物质量浓度 3．0%,每克底物的木聚糖酶用量为50IU,反应时间0．5h。在上述反应条件下,产品平均聚合度为3．61,低聚木糖得率为91．2%。该研究结果在可再生半纤维素资源利用方面具有重要的意义。     

基于碱性H2O2法分级分离竹材半纤维素的结构特性

为探讨竹材半纤维素的高效利用,研究竹材纤维原料碱性过氧化氢法分级分离所得三级半纤维素的结构特性.结果表明:一级半纤维素中含有少量木质素,二级与三级半纤维素的纯度很高;3种半纤维素都是木聚糖型半纤维素,其组成中木糖含量高达50%左右;三级半纤维素均为无定形的非晶体,随着分离级数增加,半纤维素的分子链段趋向均匀,半纤维素的...     

再生半纤维素酶解法制备低聚木糖的工艺优化

采用膜分离提取再生纤维素纤维废液中的半纤维素,确定了工艺参数及半纤维素组成。半纤维素经过酶水解制备低聚木糖,通过正交试验确定了酶水解的工艺参数,分析并测定了低聚木糖的组成和产品应用性能指标。结果表明,选择浓缩倍数为3.5倍时,半纤维素的提取率可达到85%,半纤维素中木糖含量可达79.2%。确定了酶水解的工艺参数,pH为5,酶解温度为55℃,酶解时间为7 h,其低聚木糖得率可达到36.2%。所得低聚木糖的主要成分为木四糖、木三糖、木二糖和木糖,占比可达90.7%。产品性能指标满足饲料级低聚糖干粉国家标准要求,具有很好的应用价值。     

木聚糖酶及其应用研究进展

木聚糖酶是半纤维素的主要一种,它是由β-D-吡喃型木糖单元通过1-4糖苷相连的直链高聚物。分解木聚糖的最主要的酶为β-D-1,4内切木聚糖酶。近十年来,木聚糖酶在饲料、食品、制浆造纸工业中显示了广阔的应用前景。本文重点论述了木聚糖的结构、木聚糖酶的特性及其应用。     

热水预水解对松木及其水解液主要化学成分的影响

研究了热水预水解对松木原料中主要碳水化合物的影响,探讨了阿拉伯糖、半乳糖、葡萄糖、木糖和甘露糖的溶出规律及热水预水解对水解液中各聚糖浓度变化的影响;并研究了170℃水解温度对松木原料的化学组成如聚戊糖、苯-醇抽出物、综纤维素、木素、灰分含量的影响。结果表明,预水解过程中,各种聚糖的溶出速度从快到慢依次是:阿拉伯糖、半乳糖、甘露糖、木糖和葡萄糖,水解过程只有部分半纤维素被降解,大量半纤维素还将依赖后续蒸煮和漂白过程予以除去;在180℃的水解温度下,水解液中各聚糖的浓度随水解时间快速下降,糠醛和羟甲基糠醛的浓度则迅速增加,不利于水解液发酵制备乙醇;随着水解时间的延长,松木聚戊糖、灰分含量逐渐减少;苯-醇抽出物含量逐渐增加;综纤维素含量先快速下降,90 min后基本保持不变;木素含量先减少后又略有增加。     

从笋壳中提取木聚糖研究

竹笋壳是竹笋加工当中的大宗废弃物,是一种极具开发潜力的资源.木聚糖是许多植物细胞壁中半纤维素的主要组分,是由β-1,4木糖苷键连接的以D-木糖残基为主链的复杂分子多聚糖.通过降解木聚糖可以得到功能性食品低聚木糖.本研究以竹笋壳为原料,采用了制备综纤维再碱抽提方法,分析了碱溶液质量分数、固液比、提取温度和提取时间对提取木聚糖得率的影响.碱提取竹笋壳中木聚糖的方法为:碱质量分数为5％,固液比为(g∶mL) 1∶10,提取时间为3h,提取温度为120℃.木聚糖提取率达到原料质量的24.77％.实验结果表明,笋壳中含半纤维素为35.08％,与目前生产低聚木糖的主要原料玉米芯中半纤维素的含量相当,是提取木聚糖的较好资源.本研究为笋壳制备低聚木糖奠定了坚实的基础,也为笋壳资源的综合利用提供了基础数据.     

凝胶过滤色谱法研究酶法生产低聚木糖过程中木聚糖分子结构的变化

以玉米芯为原料的低聚木糖生产包括原料的稀酸预处理，蒸煮和酶法水解等过程，本文采用凝胶过滤色谱研究玉米芯木降糖在整个过程中的分子结构的变化。研究结果表明，在选定的稀酸预处理条件下木聚糖不会降解；蒸煮时木聚糖发生随机降解，蒸煮温度越高，降解程度越大，135℃蒸煮30min，大部分木聚糖已有相当程度的降解，但它们的相对分子质量仍然大于1500，该蒸煮条件可满足低聚木糖生产要求；蒸煮液（连渣）加木聚糖酶水解得到的产品的主要成分为木二糖和木三糖等低聚木糖。     

一种酿酒酵母表达cDNA文库分离纤维质降解酶系基因的方法

目的:建立一种筛选自然界产纤维质降解酶系基因的新方法。方法:对酿酒酵母表达载体pYES2多克隆位点加入真核生物稀有限制性酶切位点SfiI进行改造,利用SMART技术,以大肠杆菌文库为转导,构建了拟青霉(Paecilomyces sp.H28)的酿酒酵母全长cDNA表达文库。结果:利用纤维质-刚果红染色法从文库筛选到多种纤维素和半纤维素降解酶系基因。结论:成功构建了拟青霉的酿酒酵母表达cDNA文库,加快了纤维质降解酶系基因的快速分离,也为其它相关基因的快速分离提供了有益的借鉴。     

Cloning and sequencing the genomic encoding region of copper-zinc superoxide dismutase enzyme from several marine strains of the genus Debaryomyces (Lodder & Kreger-van Rij)

Copper-zinc superoxide dismutase (SODC) is a cytosolic enzyme which catalyses the dismutation of the superoxide radical. Due to its physiological importance, the encoding genes have been cloned from several species of higher eukaryotes. However, genes from moulds and yeast have not been studied extensively. In this paper, the encoding region of this gene (sod1) has been cloned from several strains of marine yeast belonging to the genus Debaryomyces (dvv sod1, dvy sod1 and dh sod1-61) through genomic DNA-PCR amplification. Fragments of 480-486 nucleotides were obtained, which contain information for products of 153-156 amino acids with calculated molecular masses of 15.8-16.6 kDa. The deduced amino acid sequence shows that D. vanrijiae enzymes present three additional amino acids not closely related to the active site conformation. In addition, in D. vanrijiae var. vanrijiae (strain 020), one histidine residue is apparently replaced by a proline; the incidence and function of other aromatic or heterocyclic amino acids is discussed. Homology and phylogenetic trees were constructed from amino-acid sequence multi-alignment analyses; the interrelationships among fungi are discussed. The sod-1 sequences reported in this paper were deposited in the public data library of the NCBI under Accession Nos AF301019, AF327449 and AF327448.     

Degradability of phenolic acid-hemicellulose esters: A model system

A synthetic model system containing p-coumaric and ferulic acids esterified to hemicellulose was used to study polysaccharide degradability. Oatspelts xylan was fractionated into A_linear, B_linear and B_ranched fractions prior to synthetic esterification with phenolic acids at treatment concentrations of 0, 25, 50, 75 and 100 g phenolic acid per kg hemicellulose. Concentrations of phenolic acids esterified to the hemicellulose fractions were determined by alkaline hydrolysis. In-vitro dry matter disappearance (IVDMD) and degradability of hemicellulose neutral sugars were measured after 48 h ruminal fermentations. Esterification efficiency of the phenolic acids to the hemicellulose fractions was low (0.3 to 13.9%) and greater for p-coumaric than ferulic acid (4.7 vs 3.1%, respectively). Concentration of esterified phenolic acids was negatively correlated with IVDMD for the A_linear and B_branched fractions. Ferulic acid appeared to be more inhibitory to IVDMD than p-coumaric acid. Generally the degradability of the side chain sugars of the hemicellulose fractions was negatively correlated with esterified phenolic acid concentrations. Xylose degradation was only correlated with esterified ferulic acid level in the A_linear fraction. The in-vitro ruminal fermentations resulted in the degradation of the majority of the phenolic acid esters. Analysis of the synthetic phenolic acid-hemicellulose esters by ¹³C NMR and FTIR was unable to prove the presence of monomeric phenolic acid esters. The presence of phenolic acid polyesters was unlikely because of the solubility of the synthetic phenolic acid-hemicellulose esters. The neutral sugar degradation data suggest that esterification of the phenolic acids was limited to sugars with primary hydroxyl groups. While this model system was useful for studying cell wall degradation, future studies must employ model systems in which the chemical constituents being tested accurately model those found in nature.     

Lignin Interaction with Cellulase during Enzymatic Hydrolysis

The conversion of lignocellulosic biomass into biofuels or biochemicals typically involves a pretreatment process followed by the enzyme-catalyzed hydrolysis of cellulose and hemicellulose components to fermentable sugars. Many factors can contribute to the recalcitrance of biomass, e.g., the lignin content and structure, crystallinity of cellulose, degree of fiber polymerization, and hemicellulose content, among others. However, nonproductive binding between cellulase and lignin is the factor with the greatest impact on enzymatic hydrolysis. To reduce the nonproductive adsorption of enzymes on lignin and improve the efficiency of enzymatic hydrolysis, this review comprehensively summarized the progress that has been made in understanding the interactions between lignin and enzymes. Firstly, the effects of pretreatment techniques on lignin content and enzymatic hydrolysis were reviewed. The effects of lignin content and functional groups on enzymatic hydrolysis were then summarized. Methods for the preparation and characterization of lignin films were assessed. Finally, the methods applied to characterize the interactions between lignin and cellulase were reviewed, and methods for decreasing the nonproductive binding of enzymes to lignin were discussed. This review provides an overview of the current understanding of how lignin hinders the enzymatic hydrolysis of lignocellulosic biomass, and provides a theoretical basis for the development of more economical and effective methods and additives to reduce the interaction of lignin and enzymes to improve the efficiency of enzymatic hydrolysis.     

生物质原料的酶解及其在制浆造纸工业中的应用

纤维素、半纤维素和木素是主要的生物质原料,它们对自然界的碳循环是必不可少的.每种聚合物都可被能产生协同作用的酶系的多种微生物降解.不久的将来,基于微生物和酶的新工艺会引起新的环境友好技术.主要介绍了三大生物质原料的生物降解所需要的微生物和酶,对主要酶的作用机制和分子生物学进展也进行了阐述,另外概述了基于木质纤维原料酶水解的生物制浆和生物漂白的研究进展.     

Izumoring: a novel and complete strategy for bioproduction of rare sugars

Starch, whey or hemicellulosic waste can be used as a raw material for the industrial production of rare sugars. D-glucose from starch, whey and hemicellulose, D-galactose from whey, and D-xylose from hemicellulose are the main starting monosaccharides for production of rare sugars. We can produce all monosaccharides; tetroses, pentoses and hexoses, from these raw materials. This is achieved by using D-tagatose 3-epimerase, aldose isomerase, aldose reductase, and oxidoreductase enzymes or whole cells as biocatalysts. Bioproduction strategies for all rare sugars are illustrated using ring form structures given the name Izumoring.     

Useful byproducts from cellulosic wastes of agriculture and food industry--a critical appraisal

Cellulose, an important cell wall polysaccharide, which is replenished constantly in nature by photosynthesis, goes waste in a lion's share in the form of pre-harvest and post-harvest agricultural losses and wastes of food processing industry. These cellulose wastes have an immense potential to be utilized for the production and recovery of several products and ingredients in food application. In this present study, a wide spectrum of researches in the arena of properties of cellulose, hemicellulose and lignin; their degradation; sources and composition of cellulosic and lignocellulosic wastes of agriculture and food industry; present status of converting them into value-added products of food applications; constraints in their conversions and future prospects therein has been reviewed in details. The study has encompassed production of biomass for various utilization and production and recovery of protein and amino acids, carbohydrates, lipids, organic acids, foods & feeds and other miscellaneous products.     

肠道梭菌在机体能量过度摄入中的作用

肥胖与肠道菌群对能量的过度摄入有密切的关系。目前发现人体肠道中与肥胖有关的细菌主要有厚壁菌门和拟杆菌门细菌,其中梭菌属是厚壁菌门中非常重要而且数量庞大的一类菌。研究表明肠道梭菌属细菌代谢是导致机体能量摄入过度的主要原因之一。此外,肠道菌的多糖水解酶降解膳食纤维产生短链脂肪酸提供机体额外的能量,细菌脂多糖的吸收增多促进机体能量过度摄入,饥饿诱导脂肪因子的表达受到抑制时能量更容易以脂肪的形式蓄积,这些因素均与肥胖的形成有密切关系。但是目前对肠道梭菌在以下几个方面的作用仍未被阐明:1)梭菌是否是多糖水解酶的主要来源;2)多糖水解酶产生的短链脂肪酸对能量摄入的贡献;3)梭菌占优对细菌脂多糖的产生与吸收的影响;以及4)梭菌对FIAF表达的影响等。本文提出了可能的机制,为进一步的研究提供参考。     

Chlorella viruses as a source of novel enzymes

A special advantage has been conferred upon Chlorella cells as tools in biotechnology when viruses (Phycodnaviridae) infecting Chlorella cells were discovered and isolated. The viruses are large icosahedral particles (150-200 nm in diameter), containing a giant, 330-380 kbp long, linear dsDNA genome. Recently, the nucleotide sequence of the 330,740-bp genome of PBCV-1, the prototype virus of Phycodnaviridae, was determined, and up to 702 open reading frames (ORFs) were identified along the genome. The possible genes present include those encoding a variety of enzymes involved in the modification of DNA, RNA, protein and polysaccharides as well as those involved in the metabolism of sugars, amino acids, lipids, nucleotides and nucleosides. Many of these genes are actually expressed during viral infection, with functional enzymes detected in the host cytoplasm or incorporated into the virion. The successful utilization of these viral enzymes as various DNA restriction and modification enzymes (Cvi enzymes) that are now commercially available is well documented. Also noteworthy are virion-associated chitinase and chitosanase activities that have potentially important applications in the recycling of natural resources. The virions of Chlorella viruses contain more than 50 different structural proteins, ranging in size from 10 to 200 kDa. Some of these proteins may be replaced with useful foreign proteins using recombinant DNA technology. The proteins of interest can be recovered easily from the viral particles, and collected by centrifugation after complete lysis of the host Chlorella cells.     

嗜碱性木素降解菌降解能力的初步研究

通过比较不同嗜碱细菌对麦草中木素、纤维素和半纤维素的降解率, 并比较不同菌株的产酶及酶活情况, 筛选出了木素降解能力较强, 而纤维素和半纤维素降解能力相对较弱的嗜碱性木素降解菌。在ｐＨ≈１０－４的条件下培养８ｄ 后, 菌株６ 降解了３２－３７％ 的麦草木素, 而纤维素和半纤维素分别降解了２１－４８％ 和２２－６９％ 。这与其产酶情况基本一致, 该菌株的酶活最高, 分别为ＭｎＰ２７１－３０Ｕ／Ｌ和ＬｉＰ４１－９４Ｕ／Ｌ。