Evaluation of cellulase recycling strategies for the hydrolysis of lignocellulosic substrates

Recycling of cellulases should lower the overall cost of lignocellulosiic bioconversion processes. In this study, three recycling strategies were evaluated to determine their efficiencies over five successive rounds of hydrolysis. The effect of lignin on recycling was examined by comparing water-washed, steam-exploded birch (WB; 32% lignin) and WB which had been further extracted with alkali and peroxide (PB; 4% lignin). When the cellulases were recovered from the residual substrates after partial hydrolysis of both substrates, the recovered cellulase activity toward the mixture of fresh and residual substrates decreased after each recycling step. When the cellulases in the supernatants were also recycled, up to 20% more activity could be recovered. In both of these cases, the recovered activities did not correspond to the activities expected from the amount of cellulase protein recovered during recycling. The best recovery was obtained when the cellulases were recovered from both the residue and the supernatant after complete hydrolysis of the PB substrate. In this case, all of the originally added cellulase activity could be recovered for four consecutive hydrolysis rounds. However, when the same recycling strategy was carried out using the WB substrate, the recovered cellulase activity declined quickly with each recycling round. In all three of the recycling strategies, lower cellulase activities were recovered from the substrates with higher lignin contents. (c) 1995 John Wiley & Sons, Inc.     

Structure of Ovarian Asterosaponin-1 in the Starfish Asterias amurensis

Cultured crown gall cells of Catharanthus roseus Don (Vinca rosea L.) was found to contain brassinosteroids. These were identified as brassinolide and castasterone by GC/MS. This is the first conclusive identification of endogenous brassinosteroids in cultured cells.     

Lignocellulose biodegradation: Fundamentals and applications

Lignocelluloses are the building blocks of allplants and are ubiquitous to most regions ofour planet. Their chemical properties make it asubstrate of enormous biotechnological value.The basic chemistry of cellulose,hemicellulose, and lignin has a profound effecton lignocellulose tertiary architecture. Theseintricate associations constitute physical andchemical barriers to lignocellulose utilizationand biodegradation in natural and man-madeenvironments. Overcoming these barriers is thekey to unlocking the commercial potential oflignocellulose. Understanding lignocellulosedegradation under natural conditions forms thebasis of any lignocellulose-based application.A variety of microorganisms and mechanisms areinvolved in the complete biodegradation oflignocellulose in natural environments rangingfrom soil and rumen ecosystems to the termitehindgut. The primary objective oflignocellulose pretreatment by the variousindustries is to access the potential of thecellulose and hemicellulose encrusted by ligninwithin the lignocellulose matrix. Currentworking technologies based on the principles ofsolid-state fermentation (SSF) are brieflyreviewed. The use of unsterile lignocellulosicsfor bioremediation purposes holds promise forcost-effective environmental clean-upendeavors. Novel lignocellulose-basedapplications have found functionality intextile, biological control, and medicalresearch fields and might be exploited there inthe near future. Ultimately, lignocellulosewill probably accompany man to his voyages intospace for interest in this field isintensifying. Therefore, proper management oflignocellulose biodegradation and utilizationcan serve to improve the quality of theenvironment, further man's understanding of theuniverse, and ultimately change local economiesand communities.     

Sustainable liquid biofuels from biomass: the writing's on the walls

Domination of the global biosphere by human beings is unprecedented in the history of the planet, and our impact is such that substantive changes in ecosystems, and the global environment as a whole, are now becoming apparent. Our activity drives the steady increase in global temperature observed in recent decades. The realization of the adverse effects of greenhouse gas emissions on the environment, together with declining petroleum reserves, has ensured that the quest for sustainable and environmentally benign sources of energy for our industrial economies and consumer societies has become urgent in recent years. Consequently, there is renewed interest in the production and use of fuels from plants. The 'first-generation' biofuels made from starch and sugar appear unsustainable because of the potential stress that their production places on food commodities. Second-generation biofuels, produced from cheap and abundant plant biomass, are seen as the most attractive solution to this problem, but a number of technical hurdles must be overcome before their potential is realized. This review will focus on the underpinning research necessary to enable the cost-effective production of liquid fuels from plant biomass, with a particular focus on aspects related to plant cell walls and their bioconversion.     

New chiral imidazolium ionic liquids from isomannide

New chiral bis and mono-imidazolium ionic liquids derived from isomannide were synthesized. The structural features of the chiral organic cations impart a special arrangement of the chiral cavity. The new chiral chloride salts of isomannide derivatives are pivotal compounds for the synthesis of different organic ionic liquids. After metathesis different anions were associated to the chiral cations providing a new class of chiral ionic liquids.     

The Micromolecular Fibrinogen Derivatives: Fractionation by Ultrafiltration and Cation-Exchange Chromatography

The micromolecular fibrinogen derivatives were fractionated by successive ultrafiltrations through the Araicon membranes UM10, UM2 and UM05 into three fractions which represented approx. 9%, 2% and 1.5% of the weight of fibrinogen. Assuming that the fragments behaved as spherical molecules, fraction 10-2 contained mainly fragments with mol. weights of 1,000–10,000; fraction 2–05 contained fragments with mol. weights of 500–1,000 and the 05 fraction contained fragments with mol. weights smaller than 500. Cation exchange chromatography on the aminex resin Spinco PA-35 at a high sensitivity range indicated that there were 19–21 fragments in the 10-2 fraction, 10–12 fragments in the 2–05 fraction and 20–22 fragments in the 05 fraction. Relative to fibrinogen, all three fractions were poor in amino acids absorbing light at 280 mu. The two larger fractions were able to prolong the thrombin, prothrombin and partial thromboplastin times of plasma and could also delay the generation of plasma thromboplastin.     

Investigations about dissolution of cellulose in the 1-allyl-3-alkylimidazolium chloride ionic liquids

In this work, the 1-allyl-3-alkylimidazolium chloride ionic liquids were synthesized and characterized by increasing carbon atoms (n ≤ 6) of alkyl chains on a cationic 3-imidazole ring. The results indicated that 1-allyl-3-alkylimidazolium chloride with asymmetrical structure on the two sides of a cationic 3-imidazole ring (i.e., n = 1, 2, 6) exhibited alkalinity and lower thermal stabilities, and showed better solubility to the cellulose samples at 60-120 °C than those with symmetrical structures (n = 3, 4). The cellulose samples treated by 20% (w/w) ethylenediamine solution showed better solubility in 1-allyl-3-ethyl, hexyl-imidazolium chloride ionic liquids than that treated with 20% (w/w) NaOH solution at 5 °C for 72 h. XRD and TG analysis indicated that 0 0 2 plane apparent crystallite size as well as thermal stability of the regenerated cellulose samples from the ionic liquids decreased significantly compared with the untreated cellulose samples.     

溶液中木质素和葡萄糖的超滤分离

以木质素和葡萄糖的混合溶液为木质纤维素水解液模型,采用截留相对分子质量为5 000的卷式聚醚砜膜对葡萄糖和木质素进行全回流模式的分离,探讨了木质素和葡萄糖浓度、操作压力、错流速率对通量、木质素和葡萄糖截留率的影响。结果表明:在实验条件范围内,通量随葡萄糖浓度和木质素浓度的增加而降低,并随操作压力、错流速率的增加而增加。木质素截留率不受任何条件的影响,基本稳定在97%。葡萄糖截留率随木质素浓度的增加而增加,并随错流速率的增加而减小。在0.8 g/L的木质素质量浓度条件下,当错流速率从0.12 m/s增加到0.17 m/s时,葡萄糖截留率从14%减小到7.3%。由此可见,在混合溶液的超滤过程中,通过合理选择错流速率,能够改善木质素和葡萄糖的分离。     

纤维素糖化技术的瓶颈与酶活表征

纤维素作为自然界广泛存在的一种可再生资源,是重要的可替代工业原料,因此,纤维素糖化技术研究始终是人类关注的热点问题。针对天然纤维素生物降解研究中所面临的关键性问题,借鉴淀粉糖化技术的研究思路,比较和探讨了影响纤维素生物降解的技术瓶颈和真纤维素酶活性的表征,提出了纤维素生物转化和纤维素酶筛选的新途径。