Submitted to the faculty of Indiana University In partial fulfillment of the requirements for the degree Master in Bioinformatics In the School of Informatics, Indiana University, December 2004 / The aggregation rate of B-Lactoglobulin (BLG) was studied using turbidimetry and dynamic light scattering in the range 5.8<pH,3.5 at a fixed ionic strength of 4.5 mM, and in the range 4.5 - 500mM NACl at a fixed pH of 5.0. The initial slope of turbidity vs time curve was used to define an initial rate. The highest initial rates of aggregation were observed in the pH range 4.50 to 4.75 but the increase in aggregation rate when the pH was reduced from 5.0 to 4.69 was large compared to its decrease when the pH was reduced from pH 4.69 to 4.20; i.e. the dependence of initial rate on pH was highly asymmetric. The rate of aggregation at pH 5.0 strongly increased with decrease in ionic strength I from 100 to 4.5 mM and was found to be nearly linear with 1/ I. QELS measurements at pH 5.22 and 5.40 at I = 4.5mM revealed that particle size increased with time. Eventual appearances of bimodal distributions showed fast and slow modes corresponding to the BLG dimer and to hydrodynamic diameter 100-800 nm. Measurements at 4.0 and 4.2 indicated the consumption of dimers in the first few minutes to form higher order aggregates. Electrostatic modeling via Delphi was used to visualize the electrostatic poetnetial around the BLG dimer in order to elucidate the pH and ionic strength dependence of BLG aggregation rates. The aggregation process appears to comprise firstly an initial fast consumption of dimer, whose dependence on pH and I arises from the interaction of the positive and negative domains of interacting dimers; and secondly, the slow formation of much larger aggregates with relatively little sensitivity to pH and I. The open-ended nature of BLG aggregation is thought to arise from the asymmetry of the dimer charge distribution in the range 4.2<pH<5.2. Polyanions appear to inhibit aggregation. However, the role of polyanions in minimizing BLG aggregation was observed immediately after the addition of polyanioin to the protein. / Bioinformatics

Orientador: Carlos Alberto Gasparetto / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-03T18:07:35Z (GMT). No. of bitstreams: 1 Guimaraes_DanielaHelenaPelegrine_D.pdf: 1470612 bytes, checksum: ba6feee7cf8f1d21e4fb3eb2315b6ebb (MD5) Previous issue date: 2003 / Resumo: Este é um trabalho sobre a incrustação de proteínas de origem animal, b-lactoglobulina e ovoalbumina, sobre superfícies cilíndricas aquecidas, comuns nos equipamentos de tratamento térmico e de concentração por evaporação. A incrustação é um fenômeno de transferência de massa que é uma função da solubilidade dessas proteínas. Para descrever a cinética da incrustação foi desenvolvido um algoritmo de cálculo que teve como subsídio a solubilidade das proteínas. A solubilidade foi determinada experimentalmente na faixa de 40-60°C, incluindo a dependência do pH na faixa de 3,5 a 7,8 para a b-lactoglobulina e 6,0 a 9,0 para a ovoalbumina. O algoritmo foi desenvolvido para aplicação no interior de tubos cilíndricos permitindo um modelo matemático unidimensional, mais simples devido à simetria. O sistema de equações foi resolvido pelo método de diferenças finitas com a aplicação de um algoritmo desenvolvido na linguagem Fortran 77. Os resultados mostram que a solubilidade protéica depende da temperatura e do pH da solução e que a cinética de incrustação é dependente da temperatura do fluido e da sua vazão mássica. O tempo necessário para o decréscimo de 30% no raio interno do tubo foi menor para maiores valores de temperatura e vazão. A deposição das proteínas foi mais acentuada na região de entrada do tubo / Abstract: This is a research work on b-1actoglobulin and ovalbumin fouling over cylindrical heated surfaces, present on heat transfer equipments and evaporators. Fouling is a mass transfer phenomenon which is a function of protein solubility. To describe fouling kinetics an algorithm was developed based on the protein solubility. The protein solubility was determined experimentally in the range of 40-60°C, including dependence with pH in the range of 3.5-7.8 for b-1actoglobulin and 6.0-9.0 for ovalbumin. The algorithm was developed for cylindrical tubes thus leading to a less complex one-dimensional mathematical model, due to symmetry. The system of equations was solved by the finite differences method with an algorithm developed in Fortran 77 language. Experimental results showed that protein solubility depends on the solution temperature and pH and the fouling kinetics was dependent on the fluid temperature and flow rate. The time needed for 30% decrease on the tube internal radius was smaller for higher values of both temperatures and flow rate. Protein deposition was more intense in the tube entrance / Doutorado / Doutor em Engenharia de Alimentos

Le bénéfice de l’encapsulation des molécules bioactives a séduit les industries agroalimentaires depuis plusieurs décennies. Plus récemment des études ont montré la capacité de protéines alimentaires de charge opposée à s’assembler en microsphères par coacervation complexe. La compréhension des forces gouvernant le processus de coacervation entre protéines et l’influence exercée par la présence de bioactifs demeurent des prérequis pour l’utilisation des coacervats complexes comme agent d’encapsulation. Dans ce contexte, l’objectif de mon projet de thèse a été de comprendre le mécanisme de coacervation complexe entre la ¿-lactoglobuline (¿-LG) chargée négativement, et la lactoferrine (LF) chargée positivement, en absence et en présence de petits ligands. La LF a présenté une coacervation préférentielle avec le variant A de la¿¿-LG qui se distingue du variant B par la substitution de 2 acides aminés. Au niveau moléculaire, deux sites de fixation de la ¿-LG sur la LF ont été identifiés.En outre, par la mesure d’une part des coefficients de diffusion rotationnel et d’autre part de la cinétique de diffusion des entités moléculaires constituant les coacervats, il est suggéré que ces derniers sont formés à partir de -LG libre¿¿de pentamère, LF(-LG2)2, ainsi que des entités plus larges, (LF-LG2)n. Afin d’évaluer l’effet de la présence de petits ligands sur la coacervation complexe entre la -LG et la LF, des ligands modèles (ANS et acide folique) ont été utilisés. Dans les conditions expérimentales testées ces deux ligands n’ont pas d’affinité pour la -LG, mais après interact / Encapsulation of bioactives has been used by the food industries for decades and represents a great potential for the development of innovative products. Given their versatile functional properties, milk proteins in particular from whey have been used for encapsulation purposes using several encapsulation techniques. In parallel, recent studies showed the ability of oppositely charged food proteins to co-assemble into microspheres through complex coacervation. Understanding the driving forces governing heteroprotein coacervation process and how it is affected by the presence of ligands (bioactives) is a prerequisite to use heteroprotein coacervates as encapsulation device. In this context, the objective of my thesis work was to understand the mechanism of complex coacervation between -lactoglobulin (-LG) and lactoferrin (LF) in the absence and presence of small ligands. The conditions of optimal ¿-LG - LF coacervation were found at pH range 5.4-6 with a molar excess of ¿-LG. RemarkabAt molecular level, the presence of two binding sites on LF for -LG was evidenced. Moreover, the heterocomplexes such as pentamers LF(-LG2)2 and quite large complexes (LF-LG2)n were identified as the constituent molecular species of the coacervate phase. To evaluate the -LG - LF complex coacervation in the presence of small ligands, models of hydrophobic (ANS) and hydrophilic molecules (folic acid) were used. Although under the experimental conditions tested the small ligands did not interact with -LG, both interacted with LF inducing its self-association into nanoparticles. High relati

Les protéines et les polysaccharides constituent avec les lipides les principaux ingrédients de l’alimentation et lui confèrent à la fois ses propriétés de nutrition et de texture. Une tendance actuelle de l’industrie agroalimentaire est d’élaborer des aliments plus sains c'est-à-dire moins gras et moins salés. A ce titre, les polysaccharides sont des agents detexturation efficaces lorsqu’ils sont utilisés seuls ou en combinaison avec des protéines. Le développement de nouveaux produits alimentaires nécessite donc de rationaliser et mieux comprendre les propriétés physico-chimiques des solutions et des gels mixtes à base de protéines et de polysaccharides. Au cours de ce travail de thèse, nous avons étudié des mélanges de protéines globulaires (la β-lactoglobuline: β-lac) et de polysaccharide (le κ-carraghénane: κ-carr). Ce dernier provient d’algues et, en solution, il conduit à des gels au dessous d’une température critique qui dépend de la nature du sel ajouté. Le κ-carr est un additif important dans l’industrie alimentaire et plus particulièrement comme texturants des produits laitiers. Il est donc essentiel de comprendre les interactions qu’il développe avec les protéines du lait comme la β-lac.L’objectif de ce travail est d’étudier la structure et les propriétés mécaniques d’agrégats ou de gels de β-lac mélangés avec du κ-carr et d’étudier leur influence sur la gélification de ce dernier. Nous nous sommes plus particulièrement intéressés à la sensibilité des mélanges aux ions calcium. Des agrégats protéiques ont été formés soit indépendamment puis mélangés au κ-carr soit directement in situ en dénaturant thermiquement des mélanges κ-carr/β-lac native. Les deuxméthodes de préparation ont été comparées pour des compositions constantes des mélanges. La diffusion de la lumière, la rhéologie et la microscopie laser confocale ont été mises en oeuvre pour étudier la texture des mélanges.La taille et la morphologie des agrégats protéiques dépendent fortement de la concentration en ions calcium ajoutés qui se lient spécifiquement aux protéines. Nous avons montré que les très grands agrégats protéiques formés en présence de calcium conduisent à une microséparation de phase quand ils sont mélangés avec du κ-carr même à très faible concentration. Ainsi, la structure des systèmes mixtes est très sensible à la quantité de calcium en présence. Lesagrégats protéiques renforcent les gels de κ-carr formés en présence de potassium tout comme l’ajout de calcium. Ce renforcement dans le cas des agrégats protéiques est dû au transfert des ions calcium de la β-lac vers le κ-carr. De plus, nous avons montré que la gélification du β-carr induite par des ions potassium continuait à avoir lieu en refroidissantdes mélanges κ-carr/β-lac où cette dernière est dénaturée in situ. Cela conduit à des réseaux interpénétrés qui sont plus forts mécaniquement que la somme des deux réseaux pris individuellement. En conclusion, nous avons montré que la compétition entre la β-lac et le κ-carr pour les ions calcium était le paramètre de contrôle des propriétés texturales desgels mixtes. / Protein and polysaccharide are together with lipids the main ingredients of food and procure both nutrition and texture. A recent tendency in the food industry is to develop more healthy products that contain less fat and salt. The addition of polysaccharides is recognized as a good way to control the texture of food products. The texture of many food products is determined by gelation of either the proteins or the polysaccharides, or both. When both are present, gelation of the protein or the polysaccharide will be influenced by the presence of the other type. Understanding of the physical chemical properties of aqueous solutions and gels containing protein and polysaccharides by themselves and in mixtures is needed for a rational development of novel food products. This thesis describes an investigation of mixtures of the globular protein β-lactoglobulin (β-lg) and the polysaccharide κ-carrageenan (κ-car). κ-car is a polysaccharide isolated from algae that is often used as an additive in food industry. In solution it forms a gel below a critical temperature that depends on the amount and the type of salt. Addition of κ-car can improve the smoothness, creaminess, and body of food products and is often usedmodify the texture of dairy products. Therefore it is important to understand the interaction of κ-car with milk proteins such as β-lg, which is the main protein component of whey. The objective of the present investigation was to study the structure andthe mechanical properties of β-lg aggregates or gels when mixed with κ-car and to study the influence of the former on the gelation of κ-car. The focus was on the sensitivity of the system to calcium ions Protein particles were either formed separately and subsequently mixed with κ-car or formed directly in mixtures of κ-car and native β-lg by heating. The two different methods of preparation were compared with the same composition of polymers. The research presented in this thesis is essentially experimental using scattering techniques and confocal laser scanning microscopy to study the structure and shear rheology to study the dynamic mechanical properties.The size and morphology of protein aggregates formed by heating β-lg is strongly dependent on the concentration of Ca2+ that binds specifically to the proteins. It is shown that larger aggregates formed in the presence of Ca2+ micro-phase separate already at low κ-car concentrations. Therefore the structure of mixed systems is extremely sensitive to the amount of Ca2+ present in the system. The presence of protein aggregates was found to reinforce potassium induced κ-car gels, but it was also found that addition of CaCl2 strengthens potassium induced pure κ-car gels. We show that the reinforcement by addition of protein aggregates is caused by the transfer of a fraction of Ca2+ from β-lg to κ-car. It was shown that potassium induced gelation of κ-car also occurs during cooling heat-set β-lg gels formed in mixtures at higher protein concentrations leading to interpenetrated networks that are stronger than the sum of the individual networks. Themain conclusion of the investigation reported here is that the competition of κ-car and β-lg for calcium ions determines both the structure and the mechanical properties of the mixed systems.