Acacia senegal and Acacia seyal are important agroforestry cash crops indigenous to several countries of sub-Saharan Africa, including Nigeria. The gum exudate produced by these species is termed gum Arabic which is an approved food additive (E414), primarily used as an emulsifier. In the current study, the molecular structure, composition and biophysical properties of gum samples harvested from mature trees of Acacia senegal at two specific ecolocations in Nigeria (NG1 and NG2), have been investigated together with two previously characterised gum samples harvested from A. senegal and A. seyal originating from Sudan. The monosaccharide sugar composition analyses have shown that the A. seyal gum had a lower rhamnose and glucuronic acid content than the A. senegal gum, but had higher arabinose content. No significant difference was observed between the sugar composition of the A. senegal gums from Sudan and Nigeria. The total protein content of the Nigerian gum samples were significantly higher than recorded for the Sudanese samples. The principal amino acids present in all the gum samples are hydroxyproline, serine, aspartame, threonine and proline which is in agreement with literature values. The hydrodynamic size of the molecules present in the gums was studied using dynamic light scattering and it was found that molecular association occurred in solution over time which was inhibited in the presence of an electrolyte. The comparison of droplet size distribution for emulsions prepared with A. senegal (NG1) and A. seyal gum samples showed that A. senegal sample was a better emulsifier than the A. seyal. Multilayer adsorption of the samples onto polystyrene latex particles was observed, which resulted in an increase in thickness of the adsorbed layer as a consequence of the interaction between the protein and carbohydrate within the molecules adsorbed on the emulsion surface. Preliminary analyses of the gums using transmission electron microscopy showed the presence of varied macromolecules, ranging in size from ~12 - ~60 nm. Immuno-gold negative staining (using JIM8 monoclonal antibody) indicated clear labelling of arabinogalactan-proteins present in the gums harvested from A. senegal, the labelling of the A. seyal sample was inconclusive. In summary, the data presented represents the first detailed comparison of the structure, composition and physicochemical characteristics of Nigerian Acacia gum exudates versus Sudanese samples (main global supplier) which have shown that gum obtained from Nigerian sources is a viable alternative to ensure future supply of this valuable natural resource.

Cereus triangularis est un cactus non endémique de la sous-famille des Cactoïdées très présent dans le nord de Madagascar. Ses cladodes sont utilisées sous la forme de décoctions dans la pharmacopée Malgache. Bien que riche en hydrocolloides comme la plupart des cactus appartenant à cette sous famille il n’est pas exploité pour la production de polysaccharide. Notre travail a donc consisté à définir les conditions d’extraction des polysaccharides hydrosolubles des cladodes de cette plante, à en identifier la structure, à en caractériser les propriétés physico-chimiques et à explorer des voies enzymatiques pour leur dégradation en oligomères et/ou en polymères de faibles masses molaires. Nos travaux ont conduit à l’identification d’un arabinogalactane de type I de haute masse molaire. Ce polysaccharide est constitué d’une chaîne principale de galactane de type β-(1,4)-D-GalP substituée en position 3 par des groupements T-α-L-Araƒ-(1, ou des chaînes latérales d’arabinanes. Le comportement rhéologique de ce galactane est typique des polymères rheofluidifiants ayant des propriétés de gel faible. La mise en œuvre de dégradations enzymatique à l’aide d’une galactanase fongique a conduit à l’obtention de fractions de plus faibles masses molaires que celles des polymères natifs qui ont pu être testées avec succès pour leurs propriétés prébiotiques. / Cereus triangularis is a non endemic cactus belonging to the sub-family of Cactoideae, well represented in the north of Madagascar. Its cladodes are used in food decoction as a traditional medicine in Madagascar. Even if the hydrocolloid content of this cactus is high as observed with other ones from the same sub-family, it is not exploited for the production of polysaccharides. In this study we have defined an extraction procedure to collect the soluble polysaccharide from the cladodes of this cactus and characterized the structure of it before to investigate its physico-chemical properties and to degrade it into oligosaccharides using enzymes. Structural analyses have revealed that this polysaccharide is a type I arabinogalactan with a high molecular weight. It is mainly composed of a galactan backbone of β-(1,4)-D-GalP substituted at position 3 by T-α-L-Araƒ-(1, or arabinan chains. The rheological properties of this galactan are characteristic of a pseudoplastic fluid with a weak gel behavior. Its enzymatic degradation using a fungal galactanase led to the production of oligomers and low molecular weight polysaccharides which have been successfully tested as prebiotics.

No description available.

No description available.

No description available.

No description available.

Les gommes d’Acacia (AG, E414EC) sont largement utilisées par ses propriétés stabilisantes, émulsifiantes et filmogènes. Le but de ce projet de thèse consiste à caractériser les propriétés interfaciales et émulsifiantes des gommes d’Acacia. Les études des propriétés interfaciales liquide-liquide ont confirmé que l’A. senegal permettait une plus grande diminution de la tension interfaciale et une formation plus rapide de films à l’interface. Ceci est en accord avec sa teneur plus élevée en AGP de masse molaire élevée riche en protéine, la meilleure accessibilité de la partie protéique et la plus grande flexibilité moléculaire par rapport à A. seyal. De même, ces avantages biochimiques et structuraux de l’A. senegal se sont avérés être impliqué dans les propriétés émulsifiantes des gommes. Les résultats d'une approche innovante visant à contrôler la teneur en AGP de masse molaire élevée riche en protéines dans le milieu et la concentration totale de gomme par le mélange de deux fractions bien caractérisées isolées chez A. senegal ont confirmé la synergie fonctionnelle entre la quantité des AGP de masse molaire élevée riche en protéines et la concentration totale en gomme. De plus, en présence de quantités élevées d'AGP de masse molaire élevée riches en protéines, les émulsions étaient stables contre la floculation/coalescence en raison de la forte teneur en protéines permettant une répulsion électrostatique entre les gouttelettes et la viscosité apparente élevée du milieu. Celles-ci étaient en accord lorsque les propriétés émulsifiantes de A. senegal et A. seyal ont été comparées. En effet, A. senegal contient une plus grande quantité d'AGP de masse molaire élevée riches en protéines et d'acides uroniques, et sa dispersion présente une viscosité apparente supérieure à celle d'A. seyal. En outre, lorsque les gommes d'Acacia étaient utilisées sous forme de films séchés, la grande teneur en AGP riches en protéines de masse molaire élevée et la bonne accessibilité des fragments protéiques d'A. senegal permettaient aux films d’avoir une surface homogène lisse avec des propriétés hydrophobes caractéristiques. En revanche, les films de A. seyal étaient irréguliers et constitués d'une organisation répétitive comme de nombreuses grosses particules uniformément réparties sur la surface par rapport au faible degré de ramification, une teneur élevée en arabinose favorisant les liaisons hydrogènes intra et inter moléculaires et une forte capacité d'hydratation chaînes polysaccharidiques de A. seyal. Selon les résultats, cette thèse apporte de nouvelles connaissances sur la relation entre la composition biochimique, les propriétés structurales et physico-chimiques, pour la première fois, dans les deux aspects de la gomme, à savoir sous forme de dispersion liquide et de films séchés.Mots clés : gomme d’Acacia, propriétés interfaciales et émulsifiantes, arabinogalactane-protéines, arômes / Acacia gums (AG, E414 EC) are widely used for its stabilizing, emulsifying and film-forming properties. The aim of this project is to characterize the interfacial and emulsifying properties of Acacia gums. The main results from liquid-liquid interfacial properties study confirmed that A. senegal showed a faster decrease of interfacial tension and a more rapid interfacial film formation. These were in agreement to its greater content of high molar mass-protein AGPs content, the more accessibility of proteinaceous moieties, and the higher molecular flexibility compared to A. seyal. In the same vein, these biochemical and structural advantages of A. senegal were found to be involved in the emulsifying properties of gums. The results from an innovative approach aiming to control high molar mass protein-rich AGPs content in bulk and the total concentration of gum by mixing two well characterised fractions isolated from A. senegal confirmed the functional synergism between the amount of high molar mass protein-rich AGPs and the total gum concentration. Moreover, in the presence of high molar mass protein-rich AGPs in high amount, the emulsion became stable to flocculation/coalescence due to the great protein content allowing electrostatic repulsion between droplets and the high bulk apparent viscosity. These were in agreement when the emulsifying properties of A. senegal and A. seyal were compared. Indeed, A. senegal containing a greater amount of high molar mass protein rich AGPs and uronic acids and its dispersion having a higher apparent viscosity than A. seyal allowing the former to form emulsion with a more stability. Besides, when Acacia gums were used in the form of dried film, the great content of high molar mass protein-rich AGPs and the good accessibility of proteinaceous moieties of A. senegal allowed the smooth homogeneous surface with a hydrophobic characteristic properties of A. senegal dried films. In contrast, A. seyal films was irregular and composed of a repetitive organization as numerous large particle uniformly distributed on surface in the relation to the low degree of branching, high arabinose content favoring intra and inter molecular hydrogen bonding and high hydration ability causing aggregation of polysaccharide chains of A. seyal. According to the results, this thesis brings new knowledge of the relationship between biochemical composition, structural and physicochemical properties, for the first time, across both aspects of gum, i.e. in the form of liquid dispersion and dried films.Keywords: Acacia gums, interfacial and emulsifying properties, arabinogalactan proteins, aroma compounds

Made available in DSpace on 2014-08-20T13:44:24Z (GMT). No. of bitstreams: 1 dissertacao_daisy_leticia-ramirez_monzon.pdf: 495372 bytes, checksum: 4109f5d12e44f58ba6cd6d0affc3d675 (MD5) Previous issue date: 2012-02-07 / The soybean (Glycine max L. Max) is one of the main crops grown in Brazil, the second largest world producer. Its evolution has been strongly supported by the development of technologies that allowed the acreage increase. Currently, the use of biotechnology tools aims to contribute to the development of new genotypes with characteristics that can continue increase the production. The identification of genes responsible for characters that can assist in developing varieties with improved seed quality may constitute something innovative. The seed tegument has an important function as for the seeds resistance to deterioration. In this sense, the partial characterization of the protein expression FLA 14 (Arabinogalactan), directly related to the cell wall synthesis in the seed tegument may contribute to the advancement of these studies. The aim of this work was to generate and validate primers capable of quantifying the gene expression of the FLA 14 protein in four soybean genotypes, two with black tegument (TP and IAC 222) and higher lignin content and two with yellow tegument (CD 202 and Potência) and lower lignin content. The plant tissue (tegument) was collected 50 days after the anthesis. In order to obtain the gene expression among genotypes, it was used the qRT-PCR technique, where it was tested four combinations of primers, constructed from sequence models of soybeans ESTs. With the validation results, the primers that were found within the standards were the FLA 14p1, FLA 14p2 and β-Actina. They were all used at the expression studies. The results of the relative expression showed that soybean genotypes with black tegument and higher lignin content express the FLA 14 protein quantitatively superior to the genotypes with yellow tegument and lower lignin content. / A soja (Glycine max L. Merr.) é uma das principais culturas produzidas no Brasil, sendo considerado o segundo maior produtor mundial. Sua evolução foi fortemente amparada pelo desenvolvimento de tecnologias que possibilitaram o aumento da área cultivada. Atualmente o emprego de ferramentas da biotecnologia busca contribuir para o desenvolvimento de novos genótipos com características que possam continuar incrementando a produção. A identificação de genes responsáveis por caracteres que possam auxiliar no desenvolvimento de variedades com melhor qualidade da semente, pode se constituir em algo inovador. O tegumento apresenta uma função importante quanto à resistência das sementes à deterioração. Nesse sentido, a caracterização parcial da expressão do gene da proteína FLA 14 (Arabinogalactano), relacionadas diretamente com a síntese da parede celular no tegumento da semente pode contribuir para o avanço dos estudos. O objetivo do trabalho foi gerar e validar primers capazes de quantificar a expressão gênica da proteína FLA 14 em quatro genótipos de soja, dois desses com tegumento preto (TP e IAC 222) e maior conteúdo de lignina, e outros dois com tegumento amarelo (CD 202 e Potência) e menor conteúdo de lignina. O tecido vegetal (tegumentos) foi coletado aos 50 dias após a antese. Para a análise da expressão gênica entre os genótipos, utilizou-se a técnica de qRT-PCR, onde foram testadas quatro combinações de primers construídos a partir de modelos de sequência de ESTs da soja. Com os resultados da validação, os primers que se encontraram dentro dos padrões foram os FLA 14p1, FLA 14p2 e β-Actina utilizando-se no estudo de expressão. Os resultados da expressão relativa permitiram concluir a expressão do gene da proteína FLA 14 é quantitativamente superior nos genótipos de soja com tegumento preto e conteúdo superior de lignina em relação aos genótipos com tegumento amarelo e menos teor de lignina.

No description available.

Arabinogalactan proteins (AGPs) are proteoglycans heavily substituted by arabinogalactan polysaccharides. These are composed of arabinose and galactose, and minor sugars such as glucuronic acid (GlcA), fucose and xylose. The arabinogalactan polysaccharides do not decorate classical AGPs exclusively, but they can also be found decorating a wide range of proteins. Arabinogalactan proteins have been implicated in many processes of plant development. Recently, AGPs were proposed to bind and store calcium at the plasma membrane. They are extracellular, and are localised mainly at the plasma membrane via a GPI-anchor. They can also be soluble in the apoplast. Their low abundance, chemical similarity and high functional redundancy have hindered their study. My strategy to overcome these difficulties was to study knock-out Arabidopsis thaliana plants of glycosyltransferases that transfer sugars specifically onto AG-polysaccharides. Glucuronic acid makes up about 10% of the arabinogalactan polysaccharide structure in Arabidopsis thaliana cell culture AGPs. Previously, the glucuronic acid transferase A TGLCA T14A, a member of the CAZy Glycosyl Transferase 14 family, was shown to transfer GlcA specifically onto AGPs, and knock-out Arabidopsis plants showed a 30% reduction in [Me]GlcA substitution in AGP-enriched preparations. However, no clear growth phenotype was observed. The characterisation of knock-out plants of other GT14 family members and combinations thereof is described here. Based on previous studies (Lamport and Várnai, 2013), I assayed in vitro the calcium binding capacity of AGP extracts from WT and knock-out plants. The results showed that AGP extracts from knock-out plants can hold less calcium than WT plants in vitro. A wide range of plant growth phenotypes were identified. Growth phenotypes can be explained by changes in the cytoskeleton and deficiencies in calcium signaling. Our evidence suggests links between structural deficiencies of extracellular proteoglycans to extracellular calcium and cytoskeleton. This research has the potential to create a new model system for the study of molecular mechanisms dependent on calcium that drive cell expansion, division and differentiation in plants.