1,721,003 research outputs found
Cynara cardunculus a novel substrate for solid-state cellulases production and sugar hydrolysates
No full textSecond generation sugars represent a versatile platform for the production of both biofuels and chemicals. Both costs and ready availability of well balanced cellulase preparations are among the major constraints in the enzymatic saccharification yet. Solid state fermentation (SSF), using agro-industrial residues as substrates, offers a big potential for the containment of the cellulase production costs. In this research work, artichoke thistle (Cynara cardunculus), a perennial herbaceous Mediterranean species has been evaluated as a low cost substrate for the production of both cellulases and sugar hydrolysates. Results from this study showed that C. cardunculus spent biomass represents an optimal low cost substrate for the solid-state production of cellulolytic enzymes from A. tubingensis. The optimized use of this enzymatic cocktail enabled the attainment of hydrolysis yields that did not differ significantly from those obtained with benchmark commercial enzymes. © 2018 ETA-Florence Renewable Energies
Bioethanol production from mixed sugars by Scheffersomyces stipitis free and immobilized cells, and co-cultures with Saccharomyces cerevisiae
No full textBioethanol can be produced from several biomasses including lignocellulosic materials. Besides 6-carbon sugars that represent the prevalent carbohydrates, some of these feedstocks contain significant amounts of 5-carbon sugars. One common limit of the major part of the xylose-fermenting yeasts is the diauxic shift between the uptake of glucose and xylose during the fermentation of mixed syrups. Thus, optimized fermentation strategies are required.In this paper the ability of Scheffersomyces stipitis strain NRRLY-11544 to ferment mixed syrups with a total sugar concentration in the range 40-80. g/L was investigated by using mono cultures, co-cultures with Saccharomyces cerevisiae strain Bakers Yeast Type II and single cultures immobilized in silica-hydrogel films. The experimental design for the fermentations with immobilized cells included the process analysis in function of two parameters: the fraction of the gel in the broth and the concentration of the cells loaded in the gel. Furthermore, for each total sugars level, the fermentative course of S. stipitis was analyzed at several glucose-to xylose ratios.The results indicated that the use of S. stipitis and S. cerevisiae in free co-cultures ensured faster processes than single cultures of S. stipitis either free or immobilized. However, the rapid production of ethanol by S. cerevisiae inhibited S. stipitis and caused a stuck of the process.Immobilization of S. stipitis in silica-hydrogel increased the relative consumption rate of xylose-to-glucose by 2-6 times depending on the composition of the fermentation medium. Furthermore the films performances appeared stable over three weeks of continuous operations. However, on the whole, the final process yields obtained with the immobilized cells were not meaningfully different from that of the free cells. This was probably due to concurrent fermentations operated by the cells released in the broth. Optimization of the carrier characteristics could improve the performances of the process with immobilized cells. © 2013 Elsevier B.V
Hydrolysis of Corn Stover by Talaromyces cellulolyticus Enzymes: Evaluation of the Residual Enzymes Activities Through the Process
No full textThe obtainment of sugars from lignocellulosic residues represents a sustainable and versatile platform for the production of a number of bio-based products. Cellulases are a family of enzymes which can effectively hydrolyze the biomass polysaccharides at mild conditions. Cellulolytic fungi belonging to the genera Trichoderma and Aspergillus are the most commonly source of commercial cellulases used so far. More recently, Talaromyces cellulolyticus was also scored as a promising cellulases producer. In comparison to the Trichoderma and Aspergillus systems, Talaromyces enzymes have been less investigated. The present research dealt with the conversion of steam-pretreated corn stover by commercial blend of T. cellulolyticus enzymes with respect to the common blends. The paper also investigated the stability of the enzyme preparation and tested the use of additives (namely Tween 80, Tween 20, and BSA) to improve the enzymes performances and the hydrolysis efficiency. The results indicated that, at the same process conditions, T. cellulolyticus cellulases were more effective and yielded 20% more sugars compared to control blends. Furthermore, the cellulase components displayed a synergistic interaction with hemicellulases. The results indicate that cellulases from T. cellulolyticus are less affected by the high dry matter consistency and the use of additives could increase the total activity by around 50% and β-glucosidase capacity by 10–15%
Bioethanol production from steam-pretreated corn stover through an isomerase mediated process
No full textAgricultural by-products such as corn stover are considered strategic raw materials for the production of second-generation bioethanol from renewable and non-food sources. This paper describes the conversion of steam-pretreated corn stover to ethanol utilising a multi-step process including enzymatic hydrolysis, isomerisation, and fermentation of mixed hydrolysates with native Saccharomyces cerevisiae. An immobilised isomerase enzyme was used for the xylose isomerisation along with high concentrations of S. cerevisiae. The objective was to assess the extent of simultaneity of the various conversion steps, through a detailed analysis of process time courses, and to test this process scheme for the conversion of lignocellulosic hydrolysates containing several inhibitors of the isomerase enzyme (e.g. metal ions, xylitol and glycerol).The process was tested on two types of hydrolysate after acid-catalysed steam pretreatment: (a) the water soluble fraction (WSF) in which xylose was the largest carbon source and (b) the entire slurry, containing both cellulose and hemicellulose carbohydrates, in which glucose predominated.The results indicated that the ethanol concentration rose when the inoculum concentration was increased in the range 10-75g/L. However, when xylose was the largest carbon source, the metabolic yields were higher than 0.51gethanol/gconsumed sugars probably due to the use of yeast internal cellular resources. This phenomenon was not observed in the fermentation of mixed hydrolysates obtained from the entire pretreated product and in which glucose was the largest carbon source. The ethanol yield from biomass suspensions with dry matter (DM) concentrations of 11-12% (w/v) was 70% based on total sugars (glucose, xylose, galactose). The results suggest that xylulose uptake was more effective in mixed hydrolysates containing glucose levels similar to, or higher than, xylose.Analysis of the factors that limit isomerase activity in lignocellulosic hydrolysates excluded any inhibition due to residual calcium ions after the detoxification of the hemicellulose hydrolysates with Ca(OH)2. By contrast, most of the enzyme activity ceased during the fermentation of the entire slurry after steam explosion, probably due to synergistic inhibition effects of various fermentation co-products. © 2014 Elsevier B.V
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Conversion of raw glycerol and cardoon hydrolysate into single cell oil by oleaginous yeasts
No full textThe interest in the bio-based products, namely biofuels and chemicals, has increased in recent years often driven by global concerns about the depletion of the fossil resources and environmental implications. The biomass residues and waste streams from several origins could represent sustainable feedstocks to produce both bioenergy and bio-based products. Microbial oils can be used in a number of oil-based processes, including biodiesel, lubricants, bioplastics production. Their economic feasibility depends on the growing substrates. In order to achieve a feasible production of microbial bio-oils, low-cost substrates are necessary. Aim of the present work was the conversion of un-detoxified hydrolysates of cardoon and raw glycerol from the biodiesel production by Cryptococcus curvatus to develop a cost–effective microbial production of oils. The growth and the lipid production of the oleaginous yeast was assessed at different C/N in batch cultures. The lipids accumulation during the process was monitored through the Nile Red spectrofluorometric analyses. Composition of raw glycerol resulted more inhibitory than cardoon hydrolysate so that no yeast growth was observed above the C/N ratio threshold of 65. The maximum C. curvatus lipid content were 67.2% and 43.7% (g lipids/g cell dry biomass produced %) on cardoon hydrolysate and raw glycerol respectively. The FAME profiles revealed the predominance of fatty acids, namely palmitic, stearic, oleic and linoleic acid, in different percentages depending on the carbon source and on the carbon-to-nitrogen ratios used. The data indicated that the fatty acid compositions depends not only on the C/N ratio but also on the specific carbon source leading to different features and potential applications for the industrial production of renewable chemicals
Arundo donax refining to second generation bioethanol and furfural
Full text linkBiomass-derived sugars are platform molecules that can be converted into a variety of final products. Non-food, lignocellulosic feedstocks, such as agroforest residues and low inputs, high yield crops, are attractive bioresources for the production of second-generation sugars. Biorefining schemes based on the use of versatile technologies that operate at mild conditions contribute to the sustainability of the bio-based products. The present work describes the conversion of giant reed (Arundo donax), a non-food crop, to ethanol and furfural (FA). A sulphuric-acid-catalyzed steam explosion was used for the biomass pretreatment and fractionation. A hybrid process was optimized for the hydrolysis and fermentation (HSSF) of C6 sugars at high gravity conditions consisting of a biomass pre-liquefaction followed by simultaneous saccharification and fermentation with a step-wise temperature program and multiple inoculations. Hemicellulose derived xylose was dehydrated to furfural on the solid acid catalyst in biphasic media irradiated by microwave energy. The results indicate that the optimized HSSF process produced ethanol titers in the range 43–51 g/L depending on the enzymatic dosage, about 13–21 g/L higher than unoptimized conditions. An optimal liquefaction time before saccharification and fermentation tests (SSF) was 10 h by using 34 filter paper unit (FPU)/g glucan of Cellic® CTec3. C5 streams yielded 33.5% FA of the theoretical value after 10 min of microwave heating at 157◦ C and a catalyst concentration of 14 meq per g of xylose
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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