Academic literature on the topic 'Physicochemical Approach'

Les préoccupations grandissantes concernant la santé et l’environnement rendent la demande en ingrédients naturels toujours plus forte. Parallèlement, les fournisseurs d’ingrédients naturels tentent de rendre les procédés d’extraction plus performants, plus sûrs, moins consommateurs en énergie et en ressources non-renouvelables. Les hydrotropes, capables de solubiliser des composés hydrophobes dans l’eau, constituent une alternative prometteuse aux solvants organiques, souvent dérivés du pétrole, potentiellement explosifs et émetteurs de composés organiques volatiles. Afin de développer un nouveau procédé d’extraction hydrotropique efficace à base d’amphiphiles biosourcés, nous nous sommes intéressés à la compréhension des cinétiques et des phénomènes physico-chimiques impliqués dans l’extraction de l’acide carnosique (AC), un puissant antioxydant phénolique présent dans le romarin et la sauge officinale. L’extraction de l’AC par des hydrotropes modèles de type éthers de polyéthylène glycol a permis de démontrer l’efficacité et la compétitivité de l’extraction hydrotropique par rapport à une extraction conventionnelle utilisant un solvant. Des relations structure/propriétés physico-chimiques/efficacité ont été établies, puis généralisées aux hydrotropes biosourcés à base de glycérol (éthers de butyle, pentyle, et isopentyle) ou de sucres comme le xyloside d’amyle qui a été sélectionné par la suite pour son efficacité, sa biodégradabilité et sa disponibilité. L’optimisation des conditions d’extraction à l'aide de plans d'expériences a permis de doubler la quantité d’AC récupéré dans l’extrait sec. Pour finir, différentes techniques de précipitation de l’AC contenu dans des solutions hydrotropiques ont été comparées afin de faciliter sa récupération. Parmi elles, l’addition d’eau comme anti-solvant s’est révélée la plus efficace pour précipiter l’AC extrait du romarin. Sur la base de la composition et de l’aspect du précipité obtenu selon différentes conditions de précipitation, nous avons finalement pu établir un mécanisme visant à expliquer les différentes étapes de la précipitation hydrotropique<br>The growing concerns for health and environment makes the demand for natural ingredients ever higher. At the same time, natural ingredients manufacturers are trying to design effective, safer and less energy-costly extraction processes while avoiding the use of non-renewable resources. Hydrotropes are able to solubilize hydrophobic compounds in water, and constitute a promising alternative to organic solvents, which are often derived from petroleum, potentially explosives and producers of volatile organic compounds. To design a new effective hydrotropic extraction process using biobased amphiphiles, we investigated the physical chemical and kinetic phenomena governing the extraction of carnosic acid (CA), a powerful phenolic antioxidant that occurs in rosemary and sage. The CA extraction using alkyl polyethylene glycols ethers as model hydrotropes demonstrated the efficiency and the competitiveness of hydrotropic extractions compared to conventional solvent extractions. Quantitative Structure/properties relationship (QSPR) studies were established and generalized to biobased hydrotropes including butyl or pentyl glycerol ethers, and sugar-based hydrotropes such as amyl xyloside, which was further selected for its efficiency, biodegradability and commercial availability. The optimization of the extraction conditions led to double the CA recovered in the dry extract. Finally, different techniques have been investigated to precipitate CA from a hydrotropic solution. Among them, the addition of water as an anti-solvent appears as the more effective for precipitating CA from rosemary extract. Finally, the comparison of the precipitate composition and aspect obtained using various precipitation conditions led us to establish a mechanism explaining the different steps of the hydrotropic precipitation

The development of sensors assays for comprehensive characterisation of biological samples and effective minimal-invasive diagnostics is highly prioritised. Last decade this research area has been actively developing due to possibility of simultaneous, real- time, in vivo detection and monitoring of diverse physicochemical parameters and analytes. The new approach which has been introduced in this thesis was to develop and examine an optical diagnostic assay consisting of a mixture of environmental-sensitive fluorescent dyes. The operating principle of the system has been inspired by electronic nose and tongue devices which combine nonspecific (or semispecific) sensing elements and chemometric techniques for multivariate data analysis. The performance of the optical assay was based on the analysis of the spectrum of selected dyes with discreet reading of their emission maxima. The variations in peaks intensities caused by environmental changes provided distinctive fluorescence patterns, which could be handled similar to the signals collected from nose/tongue devices. The analytical capability of the assay was engendered by changes in fluorescence signal of the dye mixture in response to changes in pH, temperature, ionic strength and the presence of oxygen. Further findings have also proved the ability of optical assay to estimate development phases and to discriminate between different strains of growing cell cultures as well as identify various gastrointestinal diseases in human. This novel fluorescence-based diagnostic tool offers a promising alternative to electrochemical systems providing high sensitive measurements with broad dynamic range, easy, inexpensive measurements and the possibility of remote sensing and extreme assay miniaturisation. Additionally it does not require reference signal. This new approach can impact on a number of applications such as routine minimal- invasive diagnostics for medical samples, biomedical analysis, pharmaceutical or cosmetic research, quality control and process monitoring of food or environmental samples.

The availability of new technologies supplied life scientists with large amounts of experimental data. The data sets are large not only in terms of the number of observations, but also in terms of the number of recorded features. One of the aims of modeling is to explain a given phenomenon in possibly the simplest way, hence the need for selection of suitable features. We extended a Monte Carlo-based approach to selecting statistically significant features with discovery of feature interdependencies and used it in modeling sequence-function relationships in proteins. Our approach led to compact and easy-to-interpret predictive models. First, we represented protein sequences in terms of their physicochemical properties. This was followed by our feature selection and discovery of feature interdependencies. Finally, predictive models based on e.g., decision trees or rough sets were constructed. We applied the method to model two important biological problems: 1) HIV-1 resistance to reverse transcriptase-targeted drugs and 2) post-translational modifications of proteins. In the case of HIV resistance, we were not only able to predict whether the mutated protein is resistant to a drug or not, but we also suggested some new, previously neglected, mutations that possibly contribute to drug resistance. For all these mutations we proposed probable molecular mechanisms of action using literature and 3D structure studies. In the case of predicting PTMs, we built high accuracy models of modifications. In comparison to other methods, we were able to resolve whether the closest neighborhood of a residue (the nanomer) is sufficient to determine its modification status. Importantly, the application of our method yields networks of interdependent physicochemical properties of amino acids that show how these properties collaborate in establishing a given modification. We believe that the presented methods will help researchers to analyze a large class of important biological problems and will guide them in their research.

L'huile d'olive est une composante vitale du régime méditerranéen en raison de sa valeur nutritionnelle et économique bien connues. Plusieurs facteurs environnementaux, agricoles et technologiques jouent un rôle important dans la définition de la qualité de l'huile d'olive. Au Liban, des études préliminaires ont montré que certains critères de qualité dépassent les valeurs seuils des normes éditées par le Conseil Oléicole International (COI) pour les huiles d’olive extra-vierges, dont les causes n'ont pas été identifiées. En conséquence, quatre-vingt-seize échantillons d'huile d'olive ont été récoltés sur deux saisons, traités en utilisant différentes méthodes d'extraction et collectés sur huit sites (Akkar, Chouf, Hasbaya, Koura, Tyr, Nabatiyeh, Zgharta et Hermel) à fort potentiel pour l’obtention d’une indication géographique protégée (IGP). Dans cette optique, les huiles extraites et/ou collectées, ont été soumises à une analyse chimique conventionnelle comme suggéré par le COI et à une analyse rapide en utilisant la spectroscopie de fluorescence 3D en mode frontal (3D-FFFS) et la chromatographie en phase gazeuse ultra-rapide (Ultra-Fast GC).Une corrélation entre le profil en acides gras et les conditions pédoclimatiques des principales régions oléicoles du Liban a été constatée. L'altitude, la température et l'humidité relative sont les principaux facteurs d’influence du profil d'acides gras. Les régions libanaises à haute altitude, à température moyenne basse et à faible humidité relative ont une teneur élevée en acide oléique. Les zones à basse altitude, à température moyenne plus élevée et avec une humidité relative plus élevée ont un profil en acides gras caractérisé par les acides linoléique, linolénique, palmitoléique et palmitique. Les facteurs agricoles, en particulier la date de récolte, affectent également les constituants majeurs et mineurs de l'huile d'olive. En effet, l'acidité et les polyphénols totaux étaient fortement influencés par celle-ci. De plus, une modification du profil d'acides gras caractérisée par une teneur en linoléique plus élevée, une teneur en oléique plus faible, une augmentation du ∆7-stigmasténol dépassant la limite fixée par le CIO et la présence de composés malodorants (dont l’éthanol) ont été observés lors de récoltes plus tardives. En outre, deux facteurs technologiques, notamment un stockage inadéquat des fruits et de mauvaises pratiques hygiéniques de fabrication, ont favorisé la lipolyse enzymatique du triacylglycérol du fruit modifiant de manière significative les profils d'arômes et d’acides gras de l'huile d'olive.La 3D-FFFS et l'Ultra-FGC ont toutes deux montré de très bonnes performances. La 3D-FFFS couplée à des techniques chimiométriques a été appliquée sur des qualités hétérogènes et dégradées d'échantillons d'huile d'olive libanaise afin de prédire les principaux paramètres physicochimiques de qualité. Ainsi, vingt-deux modèles de régression MLR basés sur les scores PARAFAC ont été générés, dont la majorité a montré un bon coefficient de corrélation (R&gt;0,7). Un deuxième modèle, utilisant la PLS sur les matrices d'émission-excitation (EEM) dépliées, a conduit à des résultats similaires, avec une légère amélioration par rapport au modèle MLR. D’autre part, l’Ultra Flash GC a permis d’identifier en quelques minutes seulement (&lt; 2 min) l'éthanol, le (E,E)-2,4-décadiénal (défaut organoleptique) et le 1-hexanol (fruité, herbeux) comme principaux volatils caractérisant la variété Soury.Cette étude offre la possibilité d’établir au Liban un plan de contrôle analytique qui lie les aspects environnementaux et les techniques de culture/récolte aux caractéristiques physico-chimiques de l'huile d'olive qui en résultent. Une telle matrice monitorée à l’aide de techniques d'analyse rapide facilitera la vérification de la conformité du produit final aux normes internationales. En outre, ce travail préparera le terrain grâce à une fiche d'identification détaillée pour l'IGP<br>Olive oil is a vital component of the Mediterranean diet, hence Lebanese, owed to its well-known economic and nutritional value. Several environmental, agricultural, and technological factors play an essential role in defining olive oil's quality. In Lebanon, preliminary studies on the quality of extra virgin olive oil have shown that certain quality criteria exceed the International Olive Council's (IOC) standards. However, the causes of such non-conformities have not been clearly identified. Accordingly, ninety-six olive oil samples have been harvested from two seasons, processed using different extraction methods, and collected from eight locations (Akkar, Chouf, Hasbaya, Koura, Tyr, Nabatiyeh, Zgharta, and Hermel). These locations are identified by the European Union to have potentials for Protected Geographical Indications (PGI). In this perspective, and to meet the European framework's requirements, the analyzed oil will be subjected to conventional chemical analysis as suggested by the IOC and to ultra-fast analysis using 3D-front face spectroscopy (3D-FFFS) and ultra-flash gas chromatography (Ultra-FGC).A correlation between the fatty acid profile and the pedoclimatic conditions of the main olive growing regions in Lebanon was noticed. Three main pedoclimatic conditions, altitude, temperature, and relative humidity, were the major influencers and the reason for the distinctive fatty acid profile of the Lebanese olive oil. Lebanese areas with high altitudes, low average temperature, and low relative humidity have high oleic acid content. As for areas with lower altitudes, higher average temperature, and higher relative humidity, the fatty acid profile was characterized by linoleic, linolenic, palmitoleic, and palmitic acids. In addition to the environmental factors, agricultural ones, particularly the harvest date, had affected the chemical constituents of olive oil. The results obtained showed that the harvest date strongly influenced acidity and total polyphenols. A change in the fatty acid profile characterized by a higher linoleic and lower oleic content, an increase in ∆^7-stigmastenol exceeding the limit set by the IOC standards, and a dominating off-flavor compound (ethanol) was noticed as a result of delaying the harvesting time. Besides, two technological factors, particularly improper fruit storage, and bad hygienic practices, significantly affected olive oil’s quality parameters and fatty acid content.3D-FFFS and Ultra-FGC were used in-line with conventional analysis, and they both showed an undeniable performance. 3D-FFFS coupled with chemometric tools, namely multiple linear regression (MLR) applied on parallel factor (PARAFAC) scores and partial least squares (PLS), was tested on inconsistent qualities of olive oil samples to predict quality parameters. Twenty-two MLR models were generated, the majority of which showed a good correlation coefficient (R&gt;0.7). A second model using PLS on the unfolded emission-excitation matrices was also conducted to improve the regression and assess whether the variability can be handled successfully. However, similar results, with a slight improvement over the MLR model, were obtained. As for Ultra Flash GC, it made it possible to identify, in only a few minutes (&lt; 2 min), ethanol, (E,E)-2,4-decadienal (organoleptic defect), and 1-hexanol (fruity, grassy) as the main volatiles characterizing the Soury variety.This study offers the potential to disseminate an analytical control plan that links environmental aspects in Lebanon and cultivation/harvesting techniques to olive oil's resulting physicochemical characteristics. Such a matrix incorporating rapid analysis techniques will facilitate governance over the end product's final quality and, subsequently, conformity to IOC standards. Furthermore, this work will set the ground through a detailed identification fiche for PGI

In many countries water quality is assessed by using indices derived from the presence of macroinvertebrate species. This study aimed to improve the application of one such index (Hindu-Kush Himalaya based index: HKHbios) to rivers and streams in Bhutan. Sampling in a number of different streams showed that there was a strong influence of the monsoon on stream macroinvertebrates, however the month to month and site to site HKHbios scores showed no consistent patterns. Dry season sampling and increased ecological information on a number of macroinvertebrate taxa were identified as areas where water quality assessment in Bhutanese streams could be improved.