1,721,135 research outputs found
Role of gamma-Aminobutyric Acid as a Source of Nitrogen and Succinate in Wine
No full textAm. J. Enol. Vitic. ISI Document Delivery No.: 533YD Times Cited: 2 Cited Reference Count: 41 Bach, Benoit Sauvage, Francois-Xavier Dequin, Sylvie Camarasa, Carole Amer soc enology viticulture DavisInternational audienceSaccharomyces cerevisiae can make use of a nonproteogenic amino acid, gamma-aminobutyric acid (GABA), one of the various nitrogen sources present in grape juice. The effect of this amino acid on yeast fermentation kinetics and by-product formation in winemaking was investigated. The GABA content of musts ranged from 2 to 580 mg/L as a function of variety, year, and geographic origin of the grapes. The gamma-amino acid content may account for up to 20% of the assimilable nitrogen in grape juice. The commercial wine yeast efficiently metabolized exogenous GABA during wine fermentation. The assimilation of this gamma-amino acid increased yeast growth, fermentation rate, and glycerol production, but only when nitrogen was limiting. Results demonstrate that GABA can act as a source of succinate in wine, regardless of the total nitrogen content of the Must. During fermentation, succinate is primarily produced from sugars via the reductive and oxidative branches of the tricarboxylic acid cycle. The yield Of succinate from GABA ranged from 0.75 to I mol succinate/mol GABA as a function of yeast genetic background. Up to 50% of succinate in wine may be derived from GABA, depending on the initial concentration in grape juice. These results provide new insight into GABA metabolism and offer an opportunity to improve the control of wine acidity
Better exploitation of metabolic and enzymatic potentialities of Torulaspora delbrueckii and Metschnikowia pulcherrima for the production of aromas during alcoholic fermentation
No full textAu cours de fermentations spontanées, de nombreuses levures indigènes de la flore du moût de raisin sont impliquées dans les premières étapes du procédé de vinification. Ces levures, peu adaptées aux fortes concentrations en éthanol et aux limitations en oxygène, sont par la suite remplacées par S. cerevisiae dont la présence est nécessaire au bon déroulement de la fermentation. Néanmoins, les levures non-Saccharomyces peuvent contribuer de façon positive à la qualité organoleptique des vins. L'objectif général de cette thèse est d’apporter de nouvelles connaissances sur la physiologie de Torulaspora delbrueckii et Metschnikowia pulcherrima, deux levures non-Saccharomyces distribuées par la société Lallemand, afin de mieux exploiter leurs potentialités en fermentation œnologique, notamment pour la production d'arômes. Une première partie du projet a été dédiée à l’étude du métabolisme de T. delbreuckii et M. pulcherrima, tout d’abord en déterminant leurs performances fermentaires et leur production d’arômes en utilisant différentes sources d’azote. Des propriétés spécifiques à T. delbreuckii et M. pulcherrima ont été identifiées au niveau de la capacité de consommation des composés azotées et du profil de formation des arômes, même si de façon globale, l’incidence de la nature de la source d’azote est similaire à celle de S. cerevisiae. Le devenir de certains acides aminés dans le réseau métabolique a ensuite été élucidé par des approches de traçage isotopique, montrant une gestion différente des acides aminés par les deux levures non-Saccharomyces : vers la biosynthèse des protéines pour T. delbreuckii et vers la formation d’alcools supérieurs pour M. pulcherrima. La deuxième partie du projet a porté sur l’étude des levures non-Saccharomyces en fermentation séquentielle avec S. cerevisiae, en fonction de la disponibilité en nutriments. Des variations dans la réponse de la production des arômes fermentaires et variétaux (thiols) aux teneurs en sucre, azote et lipides ont été mises en évidence entre les deux modalités d’inoculation séquentielle et des fermentations de S. cerevisiae en souche pure, qui s’expliquent par des interactions entre S. cerevisiae et les levures non-Saccharomyces et leurs particularités métaboliques. Enfin, l’intérêt de l’utilisation de levures non-Saccharomyces a été évalué en moût naturel, montrant la contribution positive de ces levures sur le profil aromatique des vins. Les connaissances apportées dans ce projet permettront de définir des stratégies de gestion de la fermentation utilisant au mieux les propriétés de T. delbreuckii et M. pulcherrima pour produire des vins présentant une typicité aromatique marquée.During spontaneous fermentations, many indigenous yeasts from the grape must flora are involved in the first steps of the winemaking process. These yeasts, poorly adapted to high ethanol concentration and limited oxygen availability, are later overcome by S. cerevisiae, required to complete the fermentation. Nevertheless, non-Saccharomyces yeasts may positively contribute to the organoleptic quality of wines. The main objective of this project is to provide a new knowledge on the physiology of Torulaspora delbrueckii and Metschnikowia pulcherrima, two non-Saccharomyces yeasts distributed by Lallemand SAS, to better exploit their potentialities during wine fermentation in particular for the production of aromas. The project was first focused on investigating T. delbrueckii and M. pulcherrima metabolisms, determining their fermentation performances and aroma production using various nitrogen sources. Strain-specific properties in terms of capability to consume the different nitrogen compounds and to synthetize volatile compounds were revealed, although the overall incidence of the nature of the nitrogen source was close to that of S. cerevisiae. The fate of some individual amino acids throughout the metabolic network has been then elucidated using isotopic tracer experiments, showing a different management of the nitrogen resource between the two non-Saccharomyces species: toward the protein biosynthesis for T. delbrueckii and toward the synthesis of higher alcohols for M. pulcherrima. The second part was dedicated to the analysis of the non-Saccharomyces yeasts in sequential inoculation with S. cerevisiae, according to nutrient availability. Substantial variations were found in the response to sugar, nitrogen and lipids content of the production of fermentative and varietal (thiols) aromas between the two modalities of sequential fermentation and S. cerevisiae pure culture, related to interactions between S. cerevisiae and the non-Saccharomyces yeasts and their metabolic specificities. Finally, the benefit of the use of non-Saccharomyces yeasts was assessed in natural must, revealing the positive impact of non-Saccharomyces yeasts on the aroma profile of wines. This knowledge will allow to design fermentation management strategies making best use of T. delbrueckii and M. pulcherrima properties for the production of wines with a strong aromatic character
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
Contribution des interactions entre l’environnement et le génotype à la production d’arômes par les levures non-traditionnelles
Get PDFYeast is used for fermentation in the biotechnology sector and plays a critical role in the production of fermented beverages. The quality of the final product depends on yeast performance and the environmental conditions of fermentation. Combining knowledge on yeast biology and the different fermentation elements allows generation of beverages with new properties and improved processes. Nitrogen is an essential nutrient for yeast, nonetheless, besides the contribution of the nitrogen source to growth, some nitrogen compounds are precursors of volatile molecules that produce aroma. The nitrogen compounds assimilated by yeast are classified as rich or poor nitrogen sources depending on how they support growth. Although Saccharomyces cerevisiae is the most important and most widely used yeast species, other non-traditional yeasts are attracting industrial interest because of the new traits of technological interest that they offer. Saccharomyces uvarum has relevant properties that can be exploited for the production of fermented beverages. Particularly, the cryotolerance and capacity to produce high amounts of volatile compounds offers new opportunities for the fermentation industry. Kluyveromyces marxianus is another food-grade yeast that is of interest for its aroma properties. In S. cerevisiae, nitrogen metabolism is well-understood but less is known about these pathways in non-traditional yeasts, nor whether there are regulatory differences between the yeasts. This thesis explores nitrogen metabolism in non-traditional yeasts and the nitrogen source effect on the metabolome and transcriptome. The main focus was on S. uvarum as this is already used to a certain extent in the fermented beverage sector. First, we established the nitrogen preference of S. uvarum and subsequently performed fermentations with a reference S. uvarum strain in oenological conditions varying the nitrogen source to evaluate the fermentation performance and metabolome. Next, a comparative analysis of gene expression (RNAseq) in ammonium, methionine, phenylalanine and asparagine was performed to determine how the nitrogen source affects the expression of key genes involved in nitrogen metabolism and aroma production in this species. In overall terms, the pathways used by S. uvarum were equivalent to those used by S. cerevisiae but some detail varied. One such detail was a major difference between S. cerevisiae and S. uvarum in use of asparagine, which we found was a preferred amino acid for S. cerevisiae but not for S. uvarum. This was intriguing, in particular because asparagine is the major source of nitrogen in apple juice, where S. uvarum is traditionally used for cider fermentation. This led us to explore the evolution history and functional role of ASP3, a gene involved in asparagine assimilation. Our data on the use of amino acids by S. uvarum highlighted the role of the Ehrlich pathway in interconversion of nitrogen compounds and in generation of precursors of aroma volatiles. As a complement to this work in S. uvarum, we expanded the study of amino acid metabolism to K. marxianus, specifically focusing on expression of the BAT1 gene encoding a branched chain aminotransferase responsible for both synthesis and catabolism of branched chain amino acids. The intriguing aspect of this was that while Saccharomyces spp. possess separate genes for the mitochondrial and cytosolic forms of the enzyme, Kluyveromyces spp. have a single gene that can be used to produce alternative proteoforms for the same purpose. In addition to uncovering a novel mechanism of transcriptional regulation in K. marxianus, the work also provided information to help explain the evolutionary basis for the retention of two copies of the gene in Saccharomyces spp. Overall, the research reported in this thesis demonstrates that exploring the metabolism and characteristics of non-conventional yeasts opens up possibilities to find interesting traits with potential industrial applications. This study increases understanding of the importance of the nitrogen source in fermentation performance and the flavour and aroma production of yeast and broadens the knowledge on S. uvarum, in particular, for applications in the fermented beverage industry
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
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