纤维素酶水解及其在能源与环境保护中的应用

纤维素酶的利用是扩大纤维素应用领域和高值化利用纤维素的一条可行的新途径。本文综述了纤维素酶的来源、纤维素酶的结构和组成、纤维素酶解机理及影响因素、纤维素酶在能源及环境保护方面的应用。     

纤维素酶协同作用蛋白质的研究进展

纤维素酶是木质纤维素原料降解的关键成本因素,综述了近年发现的一些与纤维素酶具有协同作用的蛋白质,及这些蛋白质的基本性质及协同作用的可能机理,以期望降低工业转化过程中纤维素酶的使用成本,并展望了木质纤维素制取燃料乙醇的发展前景。     

纤维素改性研究进展

综述了近年来纤维素改性的进展情况。纤维素预处理往往是纤维素改性的第一步,包括物理化学等方法。纤维素改性物主要包括纤维素酯类、醚类及接枝共聚物,介绍了近年来其化学改性的方法进展。纤维素的生物改性主要应用于造纸行业,利用纤维素酶、半纤维素酶等处理纸浆。细菌纤维素的改性方法包括细菌发酵时的生物改性及纤维素提纯之后的化学改性。最后展望了纤维素改性的应用前景。     

纤维素酶的研究进展

综述了纤维素酶的发展近况及研究进展,介绍了纤维素酶水解结晶纤维素的机制、反应的协同作用及碳水化合物结合组件在反应中所起的作用,并对纤维素酶的研究趋势进行了展望。     

纤维素酶的研究进展

综述了纤维素酶的发展近况及研究进展,介绍了纤维素酶水解结晶纤维素的机制、反应的协同作用及碳水化合物结合组件在反应中所起的作用,并对纤维素酶的研究趋势进行了展望。     

青藏高原地区纤维素分解菌研究进展

简单概述了纤维素分解机制及影响其分解速率的相关因素，详细综述了在青藏高原特殊环境下纤维素分解菌的研究进展，对来自于自然环境中及高原世居动物消化系统中的纤维素分解菌进行了介绍，随后对纤维素酶在各个行业中的应用进行了阐述。最后针对其发展前景进行展望，为高原地区纤维素酶的开发利用提供理论基础。     

纤维素可及性对木质纤维酶水解影响的研究进展

纤维素的可及性是纤维原料中与纤维素酶结合且能够被酶处理的结合位点量,与纤维原料中的粒径和孔隙度有关,纤维素的可及性是影响纤维素酶水解的关键因素。综述了当前纤维素可及性的测定方法,包括氮吸附法、水银压入法、溶质排斥法、蛋白质吸附法、Simons法等,总结了通过提高纤维素可及性来实现高效生物转化的预处理技术,并给出当前生物乙醇转化的可能研究方向。     

超声波对纤维素酶活性影响的研究进展

木质纤维素酶解生成可发酵糖,是生物乙醇生产的关键步骤,超声波处理可提高纤维素酶的活性,强化酶解,增加葡萄糖和乙醇的产率。综述了超声波强化纤维素酶解的应用,超声波处理对纤维素酶空间结构以及纤维素酶解动力学和热力学的影响。分析了超声波对纤维素酶活性的负面影响,并提出了进一步深入研究的方向。     

生物产纤维素酶研究进展

纤维素酶是降解纤维素最有效的生物催化剂.自然界存在很多产纤维素酶的生物.综述了纤维素酶的类别、族属、结构;产纤维素酶的原生动物、后生动物及微生物菌种(细菌、真菌、放线菌等);目前已发现的编码纤维素酶的基因及其表达;纤维素酶的主要作用机理等方面的研究进展,并就今后的研究方向及重点提出了建议.     

植物/微生物源活性蛋白协同纤维素酶水解木质纤维素的研究进展

综述了微生物源活性蛋白(水解酶和酶促因子)和植物源活性蛋白(水解酶和酶促因子)分别应用于木质纤维素-糖平台的研究进展,总结了植物/微生物源活性蛋白协同纤维素酶水解木质纤维素的作用机制,并对由植物/微生物源活性蛋白组合构建经济高效的纤维素酶水解体系进行了展望。     

纤维素酶法水解的研究现状及展望

纤维素是地球上最丰富的天然高分子化合物,可以通过水解的方法将其转化为为人类生产生活服务的能源、食物及化工原料。而早期水解纤维素主要采用酸水解法,但由于要求条件高,产率低, 以及对环境存在污染,现已被淘汰。近年来,随着生物技术的迅速发展以及具有催化高效性的酶的研究,人们开始试图利用纤维素酶来水解纤维素,以期达到充分利用的目的。作者就纤维素酶法水解的研究进展及应用作了简要的概述。     

Structural features of native cellulose gels and films from their susceptibility to enzymic attack

The reaction of enzymic hydrolysis has been used as a probe to evidence the different structural features of bacterial native cellulose gels and films synthesized from different carbon sources. The gels were found to be more hydrolyzable than were the films, both in terms of reaction extent and of initial reaction rate, by factors increasing with temperature. For instance, a cellulose gel synthesized from glucose showed at 50°C a hydrolysis yield twice as much as that of the corresponding film, thus revealing, in the former case, a higher level of substrate accessibility and enzyme penetrability. It has been suggested that the increase of gel accessibility with temperature can be associated with a corresponding lowering of the amount of structured water close to the polymer chains in the gel. The significant decrease of susceptibility to enzymic attack observed in going from the cellulose film obtained from glucose to that obtained from xylose has been related to the markedly lower value of specific surface area estimated in the latter case. Likely, in the film obtained from xylose, densely packed microfibrils occur that are scarcely accessible to enzyme. In some cases, the reaction progress has been followed by SEM analysis. Microcrystalline cellulose has been also considered for comparison.     

Sequential acid and enzymic hydrolysis of sugar beet pulp

Fermentable sugars from beet pulp were obtained in a two-stage hydrolytic process. The first stage involved mild acid treatment to hydrolyze the hemicellulose, producing a pentose-rich syrup and a cellulose-rich fraction. The second stage was the enzymic saccharification of the cellulose fraction with fungal cellulases to produce a glucose-rich syrup. The acid hydrolysis stage was evaluated to optimize the type of acid, acid concentration, temperature and reaction time. Solubilization was markedly temperature-dependent, whereas the specificity of hemicellulose degradation depended on the type of acid utilized. The effects of different reaction times, enzyme-to-substrate ratios and particle sizes on the enzymic stage were studied. Both saccharification rate and the extent of final conversion to glucose were markedly affected by the enzyme-to-substrate ratio. Sugars recovered from the enzymic degradation of cellulose were partially fermented by Saccharomyces cerevisiae ATCC 4126.     

氨预处理对大豆秸秆纤维素酶解产糖影响的研究

为了提高大豆秸秆酶解产糖能力, 以利于从大豆秸秆中提取生物降解性塑料的原料 ?? 乳酸, 对大豆秸秆纤维素预处理过程的影响因素进行了探索,对预处理前后大豆秸秆的物理结构变化、化学成分变化及预处理条件对大豆秸秆酶水解产糖的影响进行了研究。研究结果表明,粉碎结合氨处理对大豆秸秆酶水解影响较大,较适宜的预处理条件为大豆秸秆粉碎至 140 目,10%氨水处理 24h。经过预处理后大豆秸秆纤维素含量提高 70.27%, 半纤维素含量下降 41.45%, 木质素含量下降 30.16%, 有利于大豆秸秆酶解产糖。     

Factors affecting the enzymic susceptibility of alkali and acid pretreated sugar-cane bagasse

Acid and alkali pretreatments were studied to identify those factors which are critical in determining the susceptibility of a lignocellulosic substrate (bagasse) to enzymic hydrolysis. The different effects of each treatment on the structure of the bagasse affected the subsequent susceptibility to enzymic attack in different ways. The acid treatments appeared to act by disrupting the lignin structure, probably by hydrolysing the carbohydrate chains attached to the lignin, as well as the lignin itself. The attack on the carbohydrate content removed outlying material in the cell wall (i.e. hemicellulose and amorphous cellulose) to expose a ‘core’ of more resistant regions. The alkali treatments appeared to produce a more open structure by penetrating the inner layers and selectively removing hemicellulose molecules as well as breaking some lignin—carbohydrate bonds. The different treatments resulted in structural changes which were found to affect the hydrolysis mechanism.     

羧甲基纤维素取代均一性的研究

羧甲基纤维素(钠盐,以下简称CMC)是一种重要的水溶性聚电解质。本文在传统溶媒法的基础上,采用乙醇作溶剂的两段加碱法新工艺制备CMC。研究表明,在低浴比(乙醇/纤维素=2.5—3.0)条件下,采用新工艺制得取代度约0.9,粘度(2％水溶液)为900—1000mPa·s,具有较高取代均一性和良好性能的CMC。用酶水解的方法,通过还原值测定,对CMC的取代基沿分子链的分布进行了表征;并对CMC的一些性能进行了测定,同时对其热稳定性进行了研究。     

Production of triglycerides enriched in long-chain n-3 polyunsaturated fatty acids from fish oil

Processes that combine enzymic and physical techniques have been studied for concentrating and separating eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish oil.Candida rugosa lipase was used in hydrolysis reactions to concentrate these acids in the glyceride fraction. By controlling the degree of hydrolysis, two products have been obtained, one enriched in total n-3(∼50%), the other enriched in DHA and depleted in EPA (DHA∼40%, EPA∼7%). The glyceride fraction from these reactions was recovered by evaporation and converted back to triglycerides by partial enzymic hydrolysis, followed by enzymic esterification. Both reactions were carried out withRhizomucor miehei lipase. DHA-depleted free fatty acids from aC. rugosa hydrolysis were fractionated to increase the EPA level (∼30%) and re-esterified to triglycerides by reaction with glycerol andR. miehei.     

Model for Continual Depolymerization of Biomass Catalyzed by Dilute Sulfuric Acid

Ethanol fuel from biomass is conventionally produced via the hydrolysis of biomass catalyzed by acid. In this paper, it is understood that the degree of polymerization of cellulose is randomly distributed and that the rupture of β‐1,4‐glucosidic bonds during acidic hydrolysis of cellulose is a process of continual depolymerization. From this perception, a model is established for the continual depolymerization of cellulose catalyzed by acid. Meanwhile, analog computation resulted in the activation energy and the reaction rate constant related to the rupture of β‐1,4‐glucosidic bonds. The established model is highly validated by test runs and thus assumed as a model that can be used to describe the depolymerization route taken in acidic hydrolysis of cellulose. The calculated activation energy and rate constant for the rupture of β‐1,4‐glucosidic bonds correspond to the rule of acidic hydrolysis of cellulose. Investigation of the model is of great significance in further studies on the hydrolysis mechanism of cellulose.     

Effect of ball milling on the hydrolysis of microcrystalline cellulose in hot‐compressed water

Ball milling leads to a considerable reduction in cellulose particle size and crystallinity, as well as a significant increase in the specific reactivity of cellulose during hydrolysis in hot‐compressed water (HCW). Cryogenic ball milling for 2 min also results in a significant size reduction but only little change in cellulose crystallinity and specific reactivity during hydrolysis. Therefore, crystallinity is the dominant factor in determining the hydrolysis reactivity of cellulose in HCW while particle size only plays a minor role. Ball milling also significantly influences the distribution of glucose oligomers in the primary liquid products of cellulose hydrolysis. It increases the selectivities of glucose oligomers at low conversions. At high conversions, the reduction in chain length plays an important role in glucose oligomer formation as cellulose samples become more crystalline. An extensive ball milling completely converts the crystalline cellulose into amorphous cellulose, substantially enhancing the formation of glucose oligomers with high degrees of polymerization. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

The heterogeneous character of the dilute acid hydrolysis of crystalline cellulose. III. Kinetic and X-ray data

Thirteen prehydrolyzed samples of cellulose, including native, mercerized, and regenerated materials were hydrolyzed in 1% and 1.5% sulfuric acid at 160, 170, and 180°C. Pseudo first-order rate constants and weight average degrees of polymerization were determined for each sample. For all cellulose samples, data from several experiments were used to determine the dependence of the rate of hydrolysis on sulfuric acid concentration. The results obtained in this study indicate that Sharples' end-attack model is consistent with kinetic data for the hydrolysis of cellulose II samples, but is not applicable to the hydrolysis of cellulose I samples. X-ray diffraction analyses indicated that, for native and mercerized cellulose samples, structural changes during dilute acid hydrolysis are not significant. However, data for rayon indicated that such changes may need to be taken into account in analysis of the reaction kinetics.