1,720,960 research outputs found
Novel biorefining systems for photosynthetic microorganism
Full text linkThis thesis describes research done on novel biorefining systems for microalgae. Following the principles of Green Chemistry, the environmental impact of biomass processing can best be minimized by utilizing many components of the biomass, extracting them with innovative solvents and by getting maximum utility out of any solvent used. Switchable Hydrophilicity Solvents (SHSs) are a new class of solvents able to change their nature from hydrophobic to hydrophilic and vice-versa. In this work a SHS has been used to carry out the fragmentation and extraction of both hydrophobic and hydrophilic molecules from microalgal biomass in the two opposite-hydrophilicity states that the SHS can exhibit, thus bringing about a quite substantial simplification in the biorefining of the matrix and increasing the “useful effect” of the solvent itself that performs a second, complementary biomass extraction task during the regeneration stage. The proposed concept of “Circular Extraction” scheme has been validated with the N,N-dimethyl-cyclohexylamine on the oleaginous microalga Scenedesmus dimorphus, showing an extraction efficiency in the backward-mode of 52 % for proteins, 50 % for carbohydrates, and 93 % for lipids. In the second part of this work, the PCH (1,2-propanediol, choline chloride, water 1:1:1) Natural Deep Eutectic Solvent (NaDES) was used to treat microalgal biomass and carry out the extraction of cellular components, such as lipids, proteins, carbohydrates and photosynthetic pigments (chlorophylls and carotenoids) from the biomass itself. NaDES, i.e. mixtures formed by natural primary metabolites present in all organisms form intermolecular hydrogen bonds and, when mixed in a certain ratio, change their state from solid to liquid forming a eutectic system. Experiments were carried out based on different contact time between biomass and PCH: 24 and 72 hours, with and without pre-treatment with ultrasound. Biomass was shaken together with the PCH solvent in the presence of glass beads to promote the extraction efficiency. The analysis of the extract composition was carried out spectrophotometrically for pigments (chlorophylls and carotenoids), with biochemical assays for proteins and carbohydrates and gravimetrically for the determination of lipids. The results showed the ability of PCH, coupled with the mechanical destruction of cell walls, to solubilize a wide range of polar biomolecules at room temperature, precisely the 49 % of proteins, 46 % of carbohydrates, 15 % of neutral lipids, 16 % of chlorophylls and 32 % of carotenoids. In the last part of the experimental work is introduced and demonstrated the first SHS ever described in the open literature which is based on a natural deep eutectic solvent (NaDES). The innovative solvent system that is disclosed therein is based on natural metabolites, that are intrinsically safe, and on water solution of a hydrophilicity-switching compound whose toxicity is practically nil, therefore also duplicating this as the first finding of a practically bio-safe switchable hydrophilicity solvent. Together, the two findings mark a significant step toward the identification of a destination-neutral biorefining tool for the obtainment of biologic fractions from biomasses with a wide range of potential market applications. We demonstrated the potential of this novel system for fractionating proteins-, carbohydrates- and lipids-containing biomass by following the Circular Extraction biorefining scheme on microalgae. The present finding is quite a substantial step toward intrinsic safety in biomass processing
Extraction and purification of exopolysaccharides from exhausted Arthrospira platensis (Spirulina) culture systems
Full text linkMicroalgal endo and exopolysaccharides (EPS) are attracting increasing interest for their potential applications
in the food, cosmetic and pharmaceutical industries. The standard applications of microbial EPS are as food
coatings, emulsifying and gelling agents, flocculants, hydrating agents etc. They present unique biochemical
properties that make them interesting from the biotechnological point of view. Their physical-chemical
properties are interesting for biomedical applications, since polysaccharides have been demonstrated to
possess inhibitory properties against various types of viruses, bacteria and tumors. The purpose of this work is
to upgrade the exhausted culture media resulting from the cultivation of the cyanobacterium Arthrospira
platensis (Spirulina), in order to extract the exopolysaccharides excreted by the cyanobacterium and test their
exploitation potential in a cosmetic context (a body cream). The study results include: defining the
composition and the productivity of EPS by the Spirulina culture, developing a suitable application method for
the DPPH assay in lipophilic matrices, and evaluation of the antioxidant action of these polymers in the
cosmetic field
Potential of choline chloride - based natural deep eutectic solvents (NaDES) in the extraction of microalgal metabolites
Full text linkIn a typical chemical process, the solvents are widely used for the dissolution of the reagents, to favor the
kinetics and the thermodynamics of a chemical reaction, for the extraction of products, for the separation of
mixtures. However most of the currently used organic solvents are characterized by different properties
harmful to human health and the environment. Among the principles of Green Chemistry are that solvents
should be innocuous to Man and to the Environment (safer solvents) and that the substances used in a
chemical process should be chosen to minimize the potential for chemical accidents (intrinsically safe
processes).
Biorefining, the biomass Era counterpart of oil refining is most likely going to be extraction-based, and thus
heavily solvent-dependent, much as the Oil Era was based on distillation and hence heat-dependent. Ionic
Liquids (ILS) and eutectic mixtures exploited as solvents (DES) are two major classes of solvents that are
making their way in Green Chemistry and, in particular, in biomass processing research.
NaDES ('Natural Deep Eutectic Solvents'), i.e. mixtures formed by natural primary metabolites present in all
organisms, such as sugars, polyols, amino acids, organic acids, derivatives of choline, form intermolecular
hydrogen bonds and, when mixed in a certain ratio, change their state from solid to liquid forming a eutectic
system. The most interesting NaDESs are those in which water is one of a ternary system since the degree of
dilution with water modifies such physical properties of the NaDES as the density, the viscosity, and the
polarity. By modulating the water content the solvation power can be adjusted to specific needs.
In this work, the PCH (1,2-propanediol, choline chloride, water 1:1:1) NaDES was used to treat microalgal
biomass and carry out the extraction of cellular components, such as lipids, proteins, carbohydrates and
photosynthetic pigments (chlorophylls and carotenoids) from the biomass itself.
Three sets of experiments were carried out based on different contact time between biomass and PCH: 24
and 72 hours, with and without pre-treatment with ultrasound. Biomass was shaken together with the PCH
solvent in the presence of glass beads to promote the extraction efficiency. The analysis of the extract
composition was carried out spectrophotometrically for pigments (chlorophylls and carotenoids), with
biochemical assays for proteins and carbohydrates and gravimetrically for the determination of lipids. The
results showed the ability of PCH, coupled with the mechanical destruction of cell walls, to solubilize a wide
range of polar biomolecules at room temperature
Circular extraction. An innovative use of switchable solvents for the biomass biorefinery
No full textThe environmental impact of biomass processing can best be minimized by utilizing many components of the biomass and by getting maximum utility out of any solvent used. A Switchable-Hydrophilicity Solvent (SHS) has been used for a complete extraction of hydrophobic and hydrophilic molecules in the solvent's opposite-hydrophilicity states, thus simplifying microalgal biomass extraction and increasing the solvent usefulness
A novel switchable-hydrophilicity, natural deep eutectic solvent (NaDES)-based system for bio-safe biorefinery
No full textA switchable-hydrophilicity solvent system, consisting of a fatty acid-based natural deep eutectic solvent
(NaDES), complemented by a bio-friendly dilute amine solution, has been introduced. The potential of
the most benign switchable solvent system has been characterised in microalgae biorefining according
to the recently proposed ‘Circular Extraction’ scheme
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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