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STUDIES ON NATURAL AND EDIBLE BIOPOLYMERS. ISOLATION, CHARACTERIZATION AND CHEMICAL MODIFICATIONS OF POLY(Γ-GLUTAMIC ACID) (Γ-PGA) FROM BACILLUS SUBTILIS
Get PDFPoly(γ-glutamic acid) (γ-PGA) is a unusual anionic, water-soluble homopolyamide composed of D- and/or L-glutamic acid monomers, connected by amide bonds between α-amino and γ-carboxyl groups, mainly produced by Gram-positive bacteria of the genus Bacillus.
γ-PGA is hygroscopic and water-soluble; in the salt form is able to form gels containing water in more than 3,000 times its weight. It is fairly resistant to hydrolysis, although it is degraded in basic medium at high temperature; it appears to be insensitive to common proteases such as pepsin or tripsin. γ-PGA is completely innocuous and edible. The popular food known as natto in Japan or dan-douchi in China, a soybean fermented compound that contains about 1% of γ-PGA, has formed part of the diet of Asian people for hundreds of years.
Due to its biodegradability and to the intrinsic absence of toxicity as well as to the classification as GRAS (Generally Regarded As Safe) of the main producers, i.e. Bacilli, γ-PGA represents one of the naturally occurring polymers of interest for the production of environmentally friendly derivatives.
Although having been known and even used for industrial applications for a long time, and considerable efforts having been spent in investigating its chemical and biological properties, much lies ahead to be elucidated about this polymer biosynthesis and conformational aspects. In addition, its potential applications appear to be still almost unexploited in the Western world.
This Ph.D. thesis deals with the bioproduction, characterization and derivatization of γ-PGA from Bacillus subtilis in order to obtain novel biomaterials useful for biopackaging, biomolecule immobilization, and as drug carriers. In particular, the problems we have addressed were: the optimization of productivity, by means of genetic engineering technologies; the characterization of the polymer, with regard to its stereochemical composition and molecular weight, which deeply affect its chemical-physical properties and reactivity; the development of effective methodologies for chemical modification of the polymer, in view of preparing derivatives of pharmaceutical and technological interest. Finally, we also established a synthetic approach for the preparation of standard samples with controlled stereochemistry necessary for conformational studies
New Guanosine 5’-Phosphate Derivatives as Flavor Enhancers
No full textUmami (the fifth taste) is an essential element in our appreciation of food and is imparted by monosodium L-glutamate (MSG) and 5’-ribonucleotides such as disodium inosine 5’-monophosphate (IMP) and disodium guanosine 5’-monophosphate (GMP). These compounds are now used extensively as seasonings or condiments to supplement, enhance or round off the flavor of many savory-based processed foods. They are the best flavor enhancers that are in commercial use worldwide (Yamaguchi et al. 1998).
What is perhaps the most interesting property about MSG and 5’-ribonucleotides is their capacity to interact synergistically. This phenomenon of synergism is of the utmost importance, because it provides an opportunity for the food processor to use less MSG in the formulation without affecting flavor quality.
Although a molecular mechanism behind the synergism between MSG and IMP has been recently suggested (Zhang et al. 2008), a number of issues remain to be clarified including the structure/activity relationships (SARs) of 5’-nucleotide-related MSG enhancers. The aim of our current study is to gain further insight into the role played by substituents of the purine nucleus of 5’-ribonucleotides in eliciting a synergism with MSG.
In this regard, we synthesized a number of N2-acyl and N2-alkyl guanosine monophosphates, as shown in Scheme 1, and evaluated them for their capacity to enhance the taste intensity of MSG (Cairoli et al. 2008). Using a panel of tasters and the “Probit” method to make the responses of tasters statistically valid, we found that the synergistic activity of some N2-substituted GMPs was significantly higher than that of GMP and was related to the chain length of the alkyl or acyl substituent as well as to the position of a sulphur atom along the carbon chain
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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