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Proteins in white wines: their interaction with tannins and aroma compounds
Full text linkProteins in white wines have several potential effects which can be related to their interactions with other wine components. In particular the interaction with the low quantity of tannins present in white wine should be involved in protein haze formation, as suggested previously. Moreover it is possible that wine proteins are involved in binding aroma compounds, as it is known for several proteins in other food systems. The knowledge on these aspects is however very scant, mainly regarding the forces involved in the interactions as affected by the fine molecular structure of the interacting compounds. This PhD thesis research project is aimed to study in depth these aspects, which can help to improve the quality of white wines
Proteins in White Wines: Their Interaction With Tannins And Aroma Compounds
Full text linkThe presence of protein in white wines represents a major problem for the wine industry mainly due to the fact that proteins generate haze in the bottled white wines. Protein instability, which results in wine haze formation, is due to some grape PR-Proteins that thanks to their intrinsic resistance survive the vinification process, pass into the wine where cause the appearance of undesirable haze and deposits, leading to rejection by consumers. Protein hazing of white wines is considered to be a three-step process, involving protein denaturation followed by aggregation into colloidal particles able to scatter the visible light and make the wine turbid. Because of the complexity and the variability of the wine matrix, the factors and mechanisms involved in this process are still largely unknown. Commonly, winemakers prevent haze formation by removing the proteins through the use of bentonite. However, this treatment causes loss of wine and, being unspecific, also the removal of some aroma compounds. It has been calculated that the total cost deriving from bentonite treatments corresponds to a worldwide total amount of 1 billion dollars per year. Therefore, basic and applied research is still needed to solve the problem of protein haze formation in white wines.
Firstly, the present thesis faces the problem of the impairment of aroma due to bentonite fining. In particular, the study arises from a previous investigation which suggested the existence of an interaction between proteins and aroma compounds. In this context, the interaction of the main wine protein VVTL1 with some fatty acid ethyl esters (FAEE), which are important fermentative aroma compounds has been investigated. Due to the difficulty to determine this interaction at the molecular level, Synchrotron Radiation Circular Dichroism (SRCD) has been used to study the secondary structure of the wine protein as affected by the interactions with FAEE having different chain lengths. Subsequently, the research continued with the investigation of the role played by tannins in the phenomena leading to protein instability of white wines. To this purpose, the effects of several polyphenols (deriving from wine and not) on the stability of VVTL1 has been investigated using SRCD. In parallel, the capability of tannins to react with the proteins over time in bottled wine has been evaluated by Dynamic Light Scattering (DLS) studies in a model wine system. In addition, the thermal stability of two purified proteins, which are representative of the major classes of proteins in white wine (i.e. a class IV Chitinase and the VVTL1), has been investigated by Differential Scanning Calorimetry (DSC) in the presence of the tannins purified from wine at different times after bottling. Finally, the last part of the research focuses on the possibility to produce good quantities of grape proteins in pure form starting from the in vitro culture of berry pulp tissues. These proteins can be used for molecular and functional characterisation. In particular, with this technique it is possible to label the proteins by cultivating the cellular tissues in the presence of N15 which allows the study of their fine structure and interactions by spectroscopic methods
Proteins in white wines: their interaction with tannins and aroma compounds - Oral Presentation
No full textThis presentation concern only a part of the PhD project. In particular the interactions between white wine tannins and proteins. The effects of tannins purified eight months after bottling from full-filled bottle and half-filled bottle on proteins were studied via reconstitution experiments in model wine. Contrarily to that purified few days after bottling, the tannins obtained after eight months show interaction with proteins already at room temperature, especially the ones from half-filled bottles. These data suggest an evolution of tannins reactivity in bottle, highlighting a fundamental role of oxygen. The study allowed clarifying the mechanisms of protein precipitation in bottled white wines
UTILIZZO DEL CHITOSANO ANIMALE NELLA CHIARIFICA DEI VINI E DEI MOSTI
Full text linkPROVE DI CHIARIFICA SU SCALA DI LABORATORIO DI MOSTO E DUE VINI BIANCHI E ROSSI. CONFRONTO DEL CHITOSANO ANIMALE CON ALCUNI PRODOTTI REPERIBILI IN COMMERCI
ARE THE ETHYL ESTERS ABLE TO INTERACT WITH WINE PROTEINS?
No full textThe loss of wine aroma is generally associated to a direct binding of aroma compounds with bentonite. Recently it has been demonstrated that ethyl esters removal by bentonite was increased in the presence of proteins, suggesting the existence of additional interactions. In order to understand if there is a direct association between ethyl esters and wine proteins, the effects induced by these volatile molecules on VVTL1 structure were analyzed by Synchrotron Radiation Circular Dichroism (SRCD) and fluorescence. Although VVTL1 was not strongly affected by ethyl esters and the tryptophan residues were not involved, the data indicate the existence of an interaction between ethyl esters and the proteins
Spectroscopy reveals that ethyl esters interact with proteins in wine
No full textImpairment of wine aroma after vinification is frequently associated to bentonite treatments and this can
be the result of protein removal, as recently demonstrated for ethyl esters.
To evaluate the existence of an interaction between wine proteins and ethyl esters, the effects induced
by these fermentative aroma compounds on the secondary structure and stability of VVTL1, a Thaumatinlike
protein purified from wine, was analyzed by Synchrotron Radiation Circular Dichroism (SRCD) spectroscopy.
The secondary structure of wine VVTL1 was not strongly affected by the presence of selected
ethyl esters. In contrast, VVTL1 stability was slightly increased by the addition of ethyl-octanoate, -
decanoate and -dodecanoate, but decreased by ethyl-hexanoate. This indicates the existence of an interaction
between VVTL1 and at least some aroma compounds produced during fermentation. The data suggest
that proteins removal from wine by bentonite can result in indirect removal of at least some aroma
compounds associated with th
The Secondary Structure of a Major Wine Protein is Modified upon Interaction with Polyphenols
Full text linkPolyphenols are an important constituent of wines and they are largely studied due to their antioxidant properties and for their effects on wine quality and stability, which is also related to their capacity to bind to proteins. The effects of some selected polyphenols, including procyanidins B1 and B2, tannic acid, quercetin, and rutin, as well as those of a total white wine procyanidin extract on the conformational properties of the major wine protein VVTL1 (Vitis vinifera Thaumatin-Like-1) were investigated by Synchrotron Radiation Circular Dichroism (SRCD). Results showed that VVTL1 interacts with polyphenols as demonstrated by the changes in the secondary (far-UV) and tertiary (near-UV) structures, which were differently affected by different polyphenols. Additionally, polyphenols modified the two melting temperatures (TM) that were found for VVTL1 (32.2 °C and 53.9 °C for the protein alone). The circular dichroism (CD) spectra in the near-UV region revealed an involvement of the aromatic side-chains of the protein in the interaction with phenolics. The data demonstrate the existence of an interaction between polyphenols and VVTL1, which results in modification of its thermal and UV denaturation pattern. This information can be useful in understanding the behavior of wine proteins in presence of polyphenols, thus giving new insights on the phenomena that are involved in wine stability
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
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