Thesis (Ph. D.)--Columbia University, 1928. / Vita. Bibliography: p. 24.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Includes bibliographic references.

Gum arabic is a natural gummy exudate from acacia trees and exhibits natural built-in variations commonly associated with hydrocolloids. This study is concerned with the determination of factors which could influence its properties and functionality. These factors include origin (location, soil type, rainfall), different collections, age of the trees and storage condition. Previous studies acknowledged the influence of some of these factors but somehow lack providing definitive answers to questions being asked by the end user and required for the development of Gum arabic industry in Sudan. Local knowledge as well as the various stages of gum collection and processing were reviewed in order to provide a clear background and the justification for the experimental design. In this study samples were collected from six plantations located in the west and east regions in Sudan. Samples were collected from trees of different age (5, 10, 15 and 20 years old) and also from different picking interval (1-4). Each sample was divided into three portions (UK, Khartoum and Port Sudan) and stored for 5 years in order to determine the effect of the respective location. Various analytical parameters (% loss on drying, Optical rotation, % protein, intrinsic viscosity, molecular weight and molecular weight distribution) were measured to fully characterise the gum samples and to determine their functionality (emulsification). The results obtained for all samples were consistent with those previously reported in the literature (see Chapter 4). The only exception, identified in a number of samples from the western region, is the high proportion (~30%) of high molecular weight fraction termed arabinogalactan-protein complex (AGP). The results clearly demonstrated significant variations between plantations located in western region compared with the eastern region. However, the variations between the plantations within the same region are statistically not significant. High values of % protein, viscosity, Mw and % AGP were obtained from the 1st pick, from both regions, and then significantly decreased thereafter to the fourth pick. Samples from west region in Sudan, from 1st and 2nd pick and from tree age (15) years gave the highest viscosity, molecular weight, % AGP and superior emulsification performance compared to other samples from different tree ages. The regression statistical analysis for the physiochemical properties correlation with emulsification performance demonstrated the role of % AGP to be the most influential factor followed by viscosity. The major finding of this study is the effect of storage condition on the properties and functionality of Acacia senegal. An increase in the molecular weight for all stored samples (for 5 years) irrespective of region was evident and statically significant. However, this increase was more prominent for samples from the western region compared to the eastern region. The AGP fraction was increased by the storage treatment up to 40% in Port-Sudan, 20% in Khartoum-Sudan and 15% in UK. The result clearly demonstrated that the temperature and humidity are the crucial factors to induce the natural maturation process in acacia gums. Statistical analysis (linear regression) suggested statistically significant models and equations to predict and explain the variations in the physiochemical and functional properties based on the environmental factors, picking set and age of the tree.

Thesis (Ph.D.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references (ℓ. 135-169)

Thesis(M.S.)--Auburn University, 2006. / Abstract. Includes bibliographic references.

Este trabalho consiste no estudo e nas aplicações da dosimetria por Ressonância Paramagnética Eletrônico (RPE). Em uma tentativa de realizar a dosimetria retrospectiva do esmalte dentário através do menor método invasivo possível utilizamos espectrômetros de Ressonância Paramagnética Eletrônico (RPE), operando em Banda - X e Banda - K, visando determinar as condições que poderiam ser usados em casos de exposições acidentais. Primeiro, um pequeno prisma de esmalte foi removido e um almofariz de ágata foi utilizado para triturar este prisma até que as partículas atinjam um diâmetro de cerca de 0,5 mm. Este processo de extração do esmalte resultou em um menor sinal de artefato comparado com a extração de esmalte realizado diretamente com uma broca de abrasão diamantada. A moagem manual do esmalte não leva a qualquer sinal induzido de RPE, enquanto que o uso de uma broca diamantada mesmo em baixa velocidade aparecem rebarbas produzindo um sinal de artefato equivalente ao sinal dosimétrico induzido por uma dose de 500 mGy de radiação gama. Uma massa de 25 mg de esmalte foi removida de um dente molar previamente irradiado in vitro com uma dose de 100 mGy. Esta quantidade de esmalte foi suficiente para detectar o sinal dosimétrico em um espectrômetro de Banda - X padrão. Utilizando a Ressonância Paramagnética Eletrônica (RPE) espectros de goma arábica irradiados com doses entre 0,5 e 5 kGy foram estudados. A relação linear entre a dose absorvida e as intensidades dos espectros de RPE foi observada. Espectros de RPE irradiados de goma arábica apresentaram um decaimento das concentrações relativas dos radicais livres originados pela radiação produzindo pelo menos duas espécies de radicais livres com meia-vida de 3,3 e 125,4 horas. Os resultados das simulações encontradas para estes grupos radicais foram giso = 2,0046; A = 1,2 mT e gx = gy = 2,0062, gz = 2,0025. / In an attempt to make in vitro electron spin resonance (ESR) retrospective dosimetry of the tooth enamel a lesser invasive method, experiments using X-Band and K-Band were performed, aiming to determine conditions that could be used in cases of accidental exposures. First, a small prism from the enamel was removed and ground with an agate mortar and pestle until particles reach a diameter of approximately less than 0.5 mm. This enamel extraction process resulted in lower signal artifact compared with the direct enamel extraction performed with a diamond burr abrasion. The manual grinding of the enamel does not lead to any induced ESR signal artifact, whereas the use of a diamond burr at low speed produces a signal artifact equivalent to the dosimetric signal induced by a dose of 500 mGy of gamma irradiation. A mass of 25 mg of enamel was removed from a sound molar tooth previously irradiated in vitro with a dose of 100 mGy. This amount of enamel was enough to detect the dosimetric signal in a standard X-Band spectrometer. Electron spin resonance (ESR) spectra of irradiated gum Arabic with doses between 0.5 to 5kGy were studied. A linear relationship between the absorbed dose and the intensities of the ESR spectra was observed. ESR spectra of irradiated gum Arabic showed a decay of relative concentrations of free radicals originated by radiation and the production of at least two species of free radicals with half-times: 3.3 and 125.4 hours. The results of spectral simulations for these radical groups were giso= 2.0046; A= 1.2mT and gx= gy= 2.0062, gz= 2.0025.

Gum arabic, a tree exudate, is essentially used for its binding and emulsifying properties. This natural product is a complex mixture of covalently linked proteins and charged polysaccharides moieties, differing in their molecular mass and hydrophobicity. A large body of literature now exists on the structure and interfacial properties of gum Arabic but a comprehensive description of the relationship between interfacial composition, interfacial structuration and emulsion metastability remains elusive. In the literature, gum Arabic is described as a mixture of three fractions: an arabinogalactan rich polysaccharide fraction, a polysaccharide-protein conjugates fraction and a fraction of glycoproteins. The conjugate fraction is thought to be responsible for the emulsifying and stabilizing properties of the gum, with the protein part adsorbing at oil droplets surface and the carbohydrate moieties providing steric repulsion between droplets. In this work, we have investigated the microscopic behavior of the gum species in solution and at oil/water interfaces. The first step was to characterize the structure of gum Arabic species in solution. A twodimensional separation of the gum molecules was performed using size exclusion chromatography followed with by hydrophobic interaction separation, which confirmed the highly heterogeneous composition of the gum. Small angle X-ray and neutron scattering measurements on the gum and its fractions led us to propose a structural representation of the gum conjugated moieties. Then the composition of adsorbed gum Arabic films as compared to gum Arabic solutions has been investigated. An increase in the protein rate of the interfacial film showed the crucial role of the polypeptide moieties on the adsorption. The composition of the adsorbed film was shown to differ from the bulk but remained heterogeneous in size and hydrophobicity. A mass balance revealed a strong dependence between the emulsion formulation (gum concentration and physico-chemical parameters) and the surface concentration, while the composition of the interface was only slightly changed. These results suggest that gum Arabic adsorbing species must adopt conformational changes depending on emulsification conditions. In a third stage, we have addressed the stabilization mechanisms resulting from the adsorption of gum Arabic amphiphilic species. For that purpose, we have developed a method to recover the adsorbed species within an oil-in-water emulsion. This method allowed us to unveil a structuration of the adsorbed film. Species recovered from the interface displayed aggregation, the magnitude of which directly depended on the coverage density and protein rate of the adsorbed film. The metastability of emulsions, stabilized with gum Arabic, increased upon promoting interfacial structuration, i.e. when the aggregation rate of adsorbed species was enhanced. Such behavior has not been reported so far in the literature and we believe that it is a key mechanism of gum Arabic-based on emulsions. Finally, small angle neutron scattering experiments (contrast match between the continuous and dispersed phases) disclosed differences of structuration between two regimes of interface coverage. These observations were discussed in the light of the comparison with the scattering spectra of gum Arabic solutions. To conclude, this thesis revolves around the composition/structuration relationship in gum Arabic-stabilized emulsion stabilized and demonstrates that an original mechanism is at play in this complex system.

La gomme arabique est un exsudat d’arbre qui est essentiellement utilisée pour ses propriétés stabilisantes et émulsifiantes. Ce produit naturel est un mélange complexe de protéines et de polysaccharides liés de façons covalentes, qui différent de part leur masse molaire et leur hydrophobicité. Malgré le grand nombre d’études existantes dans littérature sur la structure et les propriétés interfaciales de la gomme arabique, la compréhension de la relation entre la composition interfaciale, la structuration interfaciale et la métastabilité d’émulsions restent mal comprises à ce jour compliquée. La gomme arabique est classiquement décrite comme un mélange de trois fractions : une fraction riche en polysaccharide (arabinogalactan), une fraction composée de conjugués protéine-polysaccharides et enfin des glycoprotéines. Les propriétés émulsifiantes et stabilisantes de la gomme sont attribuées à la fraction de conjugués dont la partie protéinée s’adsorbe à la surface des gouttes d’huiles et les espèces carbonées apportent des répulsions stériques entre les gouttes. Dans cette thèse, nous avons étudié le comportement microscopique des espèces de la gomme en solution et aux interfaces huile/eau. La première étape a consisté à caractériser la structure des molécules de la gomme en solution. Une séparation bi-dimensionnelle de la gomme a été réalisée par exclusion stérique suivie d’une séparation par affinité hydrophobe, ce qui nous a permis de confirmer la nature très hétérogène de la gomme. Des expériences de diffusion des rayons-X et des neutrons aux petits angles sur la gomme arabique et ses fractions nous ont amené à proposer un modèle structural des espèces conjuguées. Nous avons ensuite étudié la composition de films de gomme arabique adsorbés en émulsion en la comparant avec celle de la gomme en solution. Une augmentation du taux de protéine dans le film interfacial a montré le rôle crucial des espèces polypeptidiques sur l’adsorption. Nous avons observé que la composition du film adsorbé diffère de la gomme en solution mais reste hétérogène en taille et en hydrophobicité. Un bilan massique a révélé une forte dépendance entre la formulation d’émulsion (concentration en gomme et paramètres physicochimiques) et la concentration surfacique alors que la composition de l’interface a très peu changé. Ces résultats suggèrent une modification de conformation des espèces adsorbées en fonction des conditions d’émulsification. Dans un troisième temps, nous nous sommes intéressés aux mécanismes de stabilisation provenant de l’adsorption des espèces amphiphiles de la gomme arabique. Pour cela, nous avons développé une méthode permettant de récupérer les espèces adsorbées dans une émulsion huile dans eau. Cette méthode nous a permis de mettre à jour une structuration du film adsorbé. Les espèces récupérées de l’interface ont montré la présence d’une agrégation, dont l’intensité dépend directement du taux de couverture et du taux de protéine de l’interface. La métastabilité d’émulsions stabilisées par de la gomme arabique est ainsi favorisée par l’augmentation de la structuration interfaciale, i.e. quand le taux d’agrégation des espèces adsorbées augmente. Un tel comportement n’a pas encore été reporté dans la littérature et nous pensons qu’il s’agit d’un mécanisme clef dans le cadre d’émulsions stabilisées par la gomme arabique. Enfin, des expériences de diffusion de neutrons aux petits angles (avec un contraste identique entre les phases continue et dispersée) ont révélé des différences de structuration entre deux régimes de concentration surfacique. Ces observations ont été discutées au regard des spectres de diffusion de la gomme en solution. Pour conclure, cette thèse porte sur la relation entre composition et structuration dans des émulsions stabilisées par la gomme arabique et démontre notamment un mécanisme original de stabilisation qui joue un rôle important dans ce système complexe. / Gum arabic, a tree exudate, is essentially used for its binding and emulsifying properties. This natural product is a complex mixture of covalently linked proteins and charged polysaccharides moieties, differing in their molecular mass and hydrophobicity. A large body of literature now exists on the structure and interfacial properties of gum Arabic but a comprehensive description of the relationship between interfacial composition, interfacial structuration and emulsion metastability remains elusive. In the literature, gum Arabic is described as a mixture of three fractions: an arabinogalactan rich polysaccharide fraction, a polysaccharide-protein conjugates fraction and a fraction of glycoproteins. The conjugate fraction is thought to be responsible for the emulsifying and stabilizing properties of the gum, with the protein part adsorbing at oil droplets surface and the carbohydrate moieties providing steric repulsion between droplets. In this work, we have investigated the microscopic behavior of the gum species in solution and at oil/water interfaces. The first step was to characterize the structure of gum Arabic species in solution. A twodimensional separation of the gum molecules was performed using size exclusion chromatography followed with by hydrophobic interaction separation, which confirmed the highly heterogeneous composition of the gum. Small angle X-ray and neutron scattering measurements on the gum and its fractions led us to propose a structural representation of the gum conjugated moieties. Then the composition of adsorbed gum Arabic films as compared to gum Arabic solutions has been investigated. An increase in the protein rate of the interfacial film showed the crucial role of the polypeptide moieties on the adsorption. The composition of the adsorbed film was shown to differ from the bulk but remained heterogeneous in size and hydrophobicity. A mass balance revealed a strong dependence between the emulsion formulation (gum concentration and physico-chemical parameters) and the surface concentration, while the composition of the interface was only slightly changed. These results suggest that gum Arabic adsorbing species must adopt conformational changes depending on emulsification conditions. In a third stage, we have addressed the stabilization mechanisms resulting from the adsorption of gum Arabic amphiphilic species. For that purpose, we have developed a method to recover the adsorbed species within an oil-in-water emulsion. This method allowed us to unveil a structuration of the adsorbed film. Species recovered from the interface displayed aggregation, the magnitude of which directly depended on the coverage density and protein rate of the adsorbed film. The metastability of emulsions, stabilized with gum Arabic, increased upon promoting interfacial structuration, i.e. when the aggregation rate of adsorbed species was enhanced. Such behavior has not been reported so far in the literature and we believe that it is a key mechanism of gum Arabic-based on emulsions. Finally, small angle neutron scattering experiments (contrast match between the continuous and dispersed phases) disclosed differences of structuration between two regimes of interface coverage. These observations were discussed in the light of the comparison with the scattering spectra of gum Arabic solutions. To conclude, this thesis revolves around the composition/structuration relationship in gum Arabic-stabilized emulsion stabilized and demonstrates that an original mechanism is at play in this complex system.

Este trabalho consiste no estudo e nas aplicações da dosimetria por Ressonância Paramagnética Eletrônico (RPE). Em uma tentativa de realizar a dosimetria retrospectiva do esmalte dentário através do menor método invasivo possível utilizamos espectrômetros de Ressonância Paramagnética Eletrônico (RPE), operando em Banda - X e Banda - K, visando determinar as condições que poderiam ser usados em casos de exposições acidentais. Primeiro, um pequeno prisma de esmalte foi removido e um almofariz de ágata foi utilizado para triturar este prisma até que as partículas atinjam um diâmetro de cerca de 0,5 mm. Este processo de extração do esmalte resultou em um menor sinal de artefato comparado com a extração de esmalte realizado diretamente com uma broca de abrasão diamantada. A moagem manual do esmalte não leva a qualquer sinal induzido de RPE, enquanto que o uso de uma broca diamantada mesmo em baixa velocidade aparecem rebarbas produzindo um sinal de artefato equivalente ao sinal dosimétrico induzido por uma dose de 500 mGy de radiação gama. Uma massa de 25 mg de esmalte foi removida de um dente molar previamente irradiado in vitro com uma dose de 100 mGy. Esta quantidade de esmalte foi suficiente para detectar o sinal dosimétrico em um espectrômetro de Banda - X padrão. Utilizando a Ressonância Paramagnética Eletrônica (RPE) espectros de goma arábica irradiados com doses entre 0,5 e 5 kGy foram estudados. A relação linear entre a dose absorvida e as intensidades dos espectros de RPE foi observada. Espectros de RPE irradiados de goma arábica apresentaram um decaimento das concentrações relativas dos radicais livres originados pela radiação produzindo pelo menos duas espécies de radicais livres com meia-vida de 3,3 e 125,4 horas. Os resultados das simulações encontradas para estes grupos radicais foram giso = 2,0046; A = 1,2 mT e gx = gy = 2,0062, gz = 2,0025. / In an attempt to make in vitro electron spin resonance (ESR) retrospective dosimetry of the tooth enamel a lesser invasive method, experiments using X-Band and K-Band were performed, aiming to determine conditions that could be used in cases of accidental exposures. First, a small prism from the enamel was removed and ground with an agate mortar and pestle until particles reach a diameter of approximately less than 0.5 mm. This enamel extraction process resulted in lower signal artifact compared with the direct enamel extraction performed with a diamond burr abrasion. The manual grinding of the enamel does not lead to any induced ESR signal artifact, whereas the use of a diamond burr at low speed produces a signal artifact equivalent to the dosimetric signal induced by a dose of 500 mGy of gamma irradiation. A mass of 25 mg of enamel was removed from a sound molar tooth previously irradiated in vitro with a dose of 100 mGy. This amount of enamel was enough to detect the dosimetric signal in a standard X-Band spectrometer. Electron spin resonance (ESR) spectra of irradiated gum Arabic with doses between 0.5 to 5kGy were studied. A linear relationship between the absorbed dose and the intensities of the ESR spectra was observed. ESR spectra of irradiated gum Arabic showed a decay of relative concentrations of free radicals originated by radiation and the production of at least two species of free radicals with half-times: 3.3 and 125.4 hours. The results of spectral simulations for these radical groups were giso= 2.0046; A= 1.2mT and gx= gy= 2.0062, gz= 2.0025.

Metal ions of gum arabic were removed by ion exchange to yield the free acid form. Arabate salts were prepared using monovalent and divalent metal ions. Addition of monovalent metal ions was found to double the viscosity of the gum as compared to the viscosity of the raw gum, and more than triple the viscosity of the free acid form at low solution concentration. At high solution concentration, monovalent ions increase the viscosity of the solution by about 50% over that of the raw gum. Divalent ions failed to increase the viscosity at low solution concentrations, while an increase of 14% over that of the raw gum was observed at high solution concentration. pH's were found to have a significant effect on gum viscosity. Gum arable was blended with four natural gums and one synthetic gum. The results showed that an increase in blended non-arabic gum results in greatly increased viscosity of the mixture, and that increasing gum arabic content results in viscosity reduction. Prediction of blend viscosity on the basis of the concentration of blend constituents was found to be possible, and to result in good agreement with the observed data. Studies of gum arabic trends suggested a relationship between the living conditions of the main producers and production levels. The study also concluded that incentives for quality improvement and for novel. collection and distribution methods need to be devised. The demand analysis shows an important relationship between gum demand, food- industry growth in the U.S.A., and gum price. / M.S.