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Influence of water activity and molecular mobility on peroxidase activity in glucose and maltodextrin solution
No full textMaltodextrins influenced the enzymatic activity in aqueous solutions by affecting the water activity (a w) and mobility as described by viscosity and T'g. In diluted solutions, viscosity being equal, (1) maltodextrin with dextrose equivalents (DE) of 33 was more effective than glucose in limiting horseradish peroxidase (HRP) activity; (2) an increase in the maltodextrin chain length from DE 33 to DE 8.7 did not further limited enzymatic activity; (3) the maltodextrin with the highest chain length (DE 2.5) determined the highest enzyme inhibition. In general, the increase of molecular weight negatively affected the HRP activity by increasing the viscosity and T'g (decreasing molecular mobility) but it positively affected the a w and, in some cases, this compensated the HRP activity inhibition. In concentrated solutions (apparent viscosity ≈ 40 mPa s) the HRP activity decreased with the increase of the maltodextrin molecular weight, and it showed a dependence on T'g which could be described by a William, Landel and Ferry (WLF)-type equation. On the contrary, in the solution added with the maltodextrin with the highest chain length (DE 2.5) the HRP activity was much higher than that predicted by the WLF-type equation. The maltodextrin with DE 2.5 contains intact starch fragments and in water forms a suspension. In such a discontinuous system, the viscosity in the vicinity of the protein is lower than the bulk viscosity, and thus, the enzyme activity is higher than expected. Moreover, since T'g is a property of the soluble phase, it does not explain the mobility in discontinuous system
Influence of water activity and system mobility on peroxidase activity in maltodextrin solutions
No full textMaltodextrins influenced the enzymatic activity
in aqueous solutions by affecting the water activity (aw) and
mobility as described by viscosity and T’g. In diluted
solutions, viscosity being equal, (1) maltodextrin with
dextrose equivalents (DE) of 33 was more effective than
glucose in limiting horseradish peroxidase (HRP) activity;
(2) an increase in the maltodextrin chain length from DE 33
to DE 8.7 did not further limited enzymatic activity; (3) the
maltodextrin with the highest chain length (DE 2.5)
determined the highest enzyme inhibition. In general, the
increase of molecular weight negatively affected the HRP
activity by increasing the viscosity and T’g (decreasing
molecular mobility) but it positively affected the aw and, in
some cases, this compensated the HRP activity inhibition.
In concentrated solutions (apparent viscosity≈40 mPa s) the
HRP activity decreased with the increase of the maltodextrin
molecular weight, and it showed a dependence on T’g
which could be described by a William, Landel and Ferry
(WLF)-type equation. On the contrary, in the solution
added with the maltodextrin with the highest chain length
(DE 2.5) the HRP activity was much higher than that
predicted by the WLF-type equation. The maltodextrin with
DE 2.5 contains intact starch fragments and in water forms a
suspension. In such a discontinuous system, the viscosity in
the vicinity of the protein is lower than the bulk viscosity,
and thus, the enzyme activity is higher than expected.
Moreover, since T’g is a property of the soluble phase, it
does not explain the mobility in discontinuous systems
Influence of water activity and molecular mobility on peroxidase activity in salt and sorbitol-maltodextrin systems
No full textSolvent composition, system mobility and viscosity play a central role in the regulation of enzymatic activity.The aim of this study was to investigate the individual and combined effect of water activity (aw), bulk viscosity and glass transition temperature (T’g) on the activity of horseradish peroxidase (HRP) in buffered solutions. For this purpose, the water activity of the solutions was modulated using both a ionic (sodium chloride) and a non-ionic (sorbitol) ligand and viscosity changed upon the addition of maltodextrin.In viscous solutions characterized by different compositions, the effectiveness of a solute in the inhibition of the HRP activity was dependent both on the chemical properties of the solution, as described by aw, and on the mobility of the system, as described by the inverse of viscosity and T-T’g. Viscosity was the most important factor in the inhibition of HRP activity in solutions characterized by the same T’g value, but when T’g was changed, due to changes in the solutes composition, the latter became a key factor in the regulation of the enzyme activity. In salt-maltodextrin systems the water activity reduction limited HRP activity with higher efficiency at low viscosities whilst in sorbitol–maltodextrin systems, characterised by different T’g values, the aw lowering by sorbitol addition resulted in the increase of HRP activity depending on its effect on T’g.[...
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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