1,720,961 research outputs found
NMR Reinvestigation of the Caffeine–Chlorogenate Complex in Aqueous Solution and in Coffee Brews
No full textCaffeine complexation by chlorogenic acid (3-caffeoylquinic acid, CAS Number [327-97-9]) in aqueous solution as well as caffeine-chlorogenate complex in freshly prepared coffee brews have been investigated by high-resolution 1 H-NMR. Caffeine and chlorogenic acid self-associations have also been studied and self-association constants have been determined resorting to both classical isodesmic model and a recently introduced method of data analysis able to provide also the critical aggregation concentration (cac). Furthermore, caffeine-chlorogenate association constant was measured. For the caffeine, the average value of the self-association constant determined by isodesmic model ( K i = 7.6 ± 0.5 M −1 ) is in good agreement with the average value ( K a = 10 ± 1.8 M −1 ) determined with the method which permits the determination of the cac (8.43 ± 0.05 mM). Chlorogenic acid shows a slight decreased tendency to aggregation with a lower average value of association constants ( K i = 2.8 ± 0.6 M −1 ; K a = 3.4 ± 0.6 M −1 ) and a critical concentration equal to 24 ± 1 mM. The value of the association constant of the caffeine-chlorogenate complex (30 ± 4 M −1 ) is compatible with previous studies and within the typical range of reported association constants for other caffeine-polyphenol complexes. Structural features of the complex have also been investigated, and the complex conformation has been rediscussed. Caffeine chemical shifts comparison (monomeric, complexed, coffee brews) clearly indicates a significant amount of caffeine is complexed in beverage real system, being chlorogenate ions the main complexing agents
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
Functional characterization of three Coffea arabica L. monoterpene synthases: Insights into the enzymatic machinery of coffee aroma
No full textThe chemical composition of the coffee beverage is extremely complex, being made up of hundreds of volatile and non-volatile compounds, many of which are generated in the thermal reactions that occur during the roasting process. However, in the raw coffee bean there are also compounds that survive roasting and are therefore extracted into the beverage. Monoterpenes are an example of this category, as their presence has been reported in the coffee flower, fruit, seed, roasted bean and in the beverage aroma. The present work describes the isolation, heterologous expression and functional characterization of three Coffea arabica cDNAs coding for monoterpene synthases. RNA was purified from C. arabica (cv. Catuai Red) flowers, seeds and fruits at 4 successive ripening stages. Degenerate primers were designed on the most conserved regions of the monoterpene synthase gene family, and then used to isolate monoterpene synthase-like sequences from the cDNA libraries. After 5'- and 3'-RACE, the complete transcripts of 4 putative C. arabica monoterpene synthases (CofarTPS) were obtained. Gene expression in different tissues and developmental stages was analysed. After heterologous expression in Escherichia coli, enzyme activity and substrate specificity were evaluated in vitro by incubation of the recombinant proteins with geranyl pyrophosphate (GPP), geranylgeranyl pyrophosphate (GGPP) and farnesyl pyrophosphate (FPP), precursors respectively of mono-, di- and sesquiterpenes. The reaction products were characterized by HS-SPME GC-MS. CofarTPS1 was classified as a limonene synthase gene, while CofarTPS2 and 3 showed lower activity with the production of linalool and β-myrcene
A chromosome-scale assembly reveals chromosomal aberrations and exchanges generating genetic diversity in Coffea arabica germplasm
Full text linkIn order to better understand the mechanisms generating genetic diversity in the recent allotetraploid species Coffea arabica, here we present a chromosome-level assembly obtained with long read technology. Two genomic compartments with different structural and functional properties are identified in the two homoeologous genomes. The resequencing data from a large set of accessions reveals low intraspecific diversity in the center of origin of the species. Across a limited number of genomic regions, diversity increases in some cultivated genotypes to levels similar to those observed within one of the progenitor species, Coffea canephora, presumably as a consequence of introgressions deriving from the so-called Timor hybrid. It also reveals that, in addition to few, early-occurring exchanges between homoeologous chromosomes, there are numerous recent chromosomal aberrations including aneuploidies, deletions, duplications and exchanges. These events are still polymorphic in the germplasm and could represent a fundamental source of genetic variation in such a lowly variable species
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
Uniform and Non-Uniform Cellular Automata: Some Issues and Case Studies in Computer Vision
No full textDispelling 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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