Rozprawy doktorskie na temat „Gelation”

Chiroptical, rheological and thermodynamic studies have been undertaken to investigate temperature-induced changes in the ý molecular organisation of gelatin. From the results obtained, a unified model for gelation and melting has been developed, and tested using Monte Carlo computer simulation. The temperature at which gelatin gels are formed has a major influence on the properties of the resulting network, with higher curing temperatures conferring increased thermal stability. In particular, gels formed by sequential curing at two different temperatures show biphasic melting. This is explained in terms of a temperature-dependence of helix length within the junction zones of the gel, and quantified by considering end-effects in the thermodynamics of helix stability. Measurements of 'initial slope' kinetics, performed over a broad concentration range, showed first-order kinetics at low gelatin concentrations, while at higher concentrations a second-order process was also evident. The results are interpreted as triple-helix nucleation at metastable 'hairpin turns' in one chain (bringing two chain segments into close proximity) together with a third strand from either the same chain (first order) or a different chain (second order). From simple geometric considerations, the maximum length of intermolecular helices ( which contribute to the gel network) is greater than that of twasted 9 intramolecular structures, giving a qualitative explanation of the increased strength of gels formed by precuring at higher temperatures (where only long helices are stable) over those quenched directly to low temperature. Monte Carlo simulation incorporating an initial assumption that helix propagation is rapid and proceeds to geometric limits gave unrealistic helix lengths and simulated melting profiles, and was replaced by the assumption that cis-trans isomerisation of peptide bonds is the controlling factor in helix propagation. Using the latter assumption, most aspects of the observed behaviour were successfully reproduced using program variables set within realistic ranges or, where possible, fixed at experimentally-determined values. In particularg the co-operativity of the simulated melting process was critically dependent on the value of a parameter x (the number of triplet units within each helix incapable of participating in bonding, due to end-effects), with a value of x=1 giving the best fits with experiment (consistent with accepted bonding patterns for the collagen triple helix). Other key parameters were the midpoint temperature for melting of the parent collagen, which gave best agreement when set at 37-38"C, and t6e proportion of cis peptide residues present in disordered gelatin chains, with an optimum lower limit of 0.15. Using these values, the simulation reproduced, with excellent precision, the helix fraction and melting profile of gels formed over a wide range of quench temperatures, and gave an acceptable approximation to the form of reaction progress curves obtained for helix formation. The biphasic melting of samples held at intermediate temperature before final quenching was also modelled realistically.

The role of hydrophobic substituents on the gelation mechanism of highly esterified pectin and the cellulose derivatives methylcellulose and hydroxypropylmethylcellulose (HPMC) has been explored by monitoring the behaviour of the amphiphilic polysaccharides in varying combinations of an ethylene glycoVwater solvent. The gelling ability (mechanical spectroscopy, visual observation) of very highly esterified (- 100%) pectin in high concentrations of ethylene glycol (>60%) is greatly reduced, however, the polymer still undergoes conformational ordering (CD, OR). A model for gel formation involving a two stage process has been proposed, comprising adoption of the ordered structure stabilised by hydrogen bonding between OH groups of contiguous polysaccharide chains, followed by (or coincident with) aggregation of the ordered sequences by 'hydrophobic' clustering of the fundamental structural subunits to form the three dimensional gel network. It has been found that ethylene glycol promotes the fIrst stage (ordering) but is antagonistic to the second (aggregation). The reversibility (mechanical spectroscopy) of the thermo-gelling cellulose derivatives can be largely abolished in the presence of ethylene glycol (40% for methylcellulose, 10% for HPMC), attributed to solubilisation of the proposed ordered 'bundle' structure at low temperatures removing the enthalpic advantage (DSC) of gel melting. The increased sensitivity of HPMC to modification of the solvent environment is due to the presence of the polar hydroxypropyl substituent causing an inceptive destabilisation of the 'bundle' structure. It is suggested that gelation is driven by the entropic advantage of melting-out 'cages' of structured water surrounding the hydrophobic groups giving rise to intermolecular 'hydrophobic' aggregation.

In this study the heat-induced gelation of two (readily available) proteins, which contain disulphide bonds, has been investigated over a range of protein concentrations in the presence and absence of the presence of the reductant, dithiothreitol at neutral pH. The proteins selected in this study were: β-Lactoglobulin and bovine serum albumin. These proteins have different number of disulphide bonds and possess different protein secondary structures. The influences of the reductant and protein concentration on their heat-induced gelation were explored to see whether the proteins were able to form protein hydrogels and that the mechanical properties of the resulting protein hydrogels were controllable. The tilting test tube method revealed that both proteins formed macroscopic hydrogels, at protein concentrations above the critical gelation concentration and that the critical gelation concentration was constantly lower in the presence of the reductant. Micro-DSC revealed that both proteins had completely denatured upon heating and that the denaturation temperature and enthalpy were significantly lower in the presence of the reductant. IR spectroscopy revealed that both proteins undergo major secondary structure transitions that resulted in the formation of fibers that are rich in β-sheet structure upon heating and that the protein lost some secondary structure before any heating and gained more β-sheet structure in the presence of the reductant. Both proteins had partially denatured before any heating in the presence of the reductant and that β-LG underwent aggregation that was accompanied by the loss of native β-sheet structure and the formation of intermolecular β-sheet structure, while that BSA underwent aggregation that was accompanied by the loss of native α-helix structure and the formation of intermolecular β-sheet structure. Cryo-TEM revealed that both proteins formed fibers (10 nm in diameter) that exist as single entities at low protein concentrations and become entangled into macroscopic networks, at protein concentrations above the critical gelation concentration and that more fibers and denser macroscopic networks were formed in the presence of the reductant. Oscillatory rheology revealed that both proteins formed macroscopic networks exhibit viscoelastic behaviour and that their elastic modulus had increased in the presence of the reductant and with increasing protein concentration.

In the first stage of the investigation, the effect of high levels of sugars (mixture of 50% sucrose with 35% glucose syrup) on agarose (0.7 wt%) was characterized by low amplitude oscillatory measurements of storage modulus (G'), loss modulus (G") and loss tangent (tan δ) as well as large deformation techniques. Samples were prepared at 90°C, and measured immediately, or after storage at 5°C. The combined Williams-Landel-Ferry (WLF)/free volume theory was used to derive the glass transition temperature, the fractional free volume, and the thermal expansion coefficient of the glass. Solution of high concentrations of sucrose crystallizes, but addition of the polymer encourages intermolecular interactions, which transform the mixture into a high viscosity glass. The mechanical properties of glucose syrup follow WLF behavior in the glass transition region and revert to an Arrhenius type prediction in the glassy state. Measurements on sugar samples and agarose-sugar mixtures were resolved into a basic function of temperature alone and a basic function of frequency (time) alone. The former traces the energetic cost of vitrification, which increases sharply with decreasing temperature. The latter, at long time scales, is governed by the infinite molecular weight of the agarose network. In the region of short times, the effect of free volume is active regardless of the sample composition. In a continuation of investigating the significance of polymer-cosolute interactions, the effect of sucrose, glucose, fructose, sorbitol, xylitol, glycerol and ethan-1,2-diol on gelation of high methoxy pectin was studied under different experimental conditions. The main changes in procedure in comparison with the work on agarose were: (i) the polymer concentration was increased from 0.7 to 1.0 wt%, (ii) the mixtures prepared at pH 4 and subsequently acidified to pH 3, rather than being prepared at neutral pH, (iii) the cosolute concentration was varying from 50 to 65 wt% and (vi) the mixtures were studied through rheology, calorimetry and optical rotation. The samples were prepared at 95°C and changes in storage modulus (G') and loss modulus (G") during cooling to 5°C, heating to 90° and re-cooling to 5°C, at 1°C/min, were measured at 1 rad s⁻¹ and 0.5% strain. In all cases, the onset temperature for gelation during cooling and the moduli recorded at 5°C increased with increasing concentration of cosolute. However, both values were substantially lower for the liquid cosolutes than for mixtures with solid cosolutes at the same concentrations. The difference is attributed to inhibition of pectin-pectin interactions by pectin-cosolute interactions, which in turn are inhibited by cosolute-cosolute interactions. On heating there was an initial reduction in modulus, with the same temperature-course as the increase on cooling; for the solids, this was followed by an increase attributable to hydrophobic association of methyl ester substituents. No such increase was seen with the liquid cosolutes, but DSC studies showed two reversible thermal transitions in all cases, one over the temperature-range of the initial gelation process on cooling and the other coincident with the increase in modulus on heating in the presence of solid cosolutes. The absence of any detectable increase in modulus on heating with the liquid cosolutes is atttributed to accumulation of cosolute around the polymer chains promoting hydrophobic association between methyl ester groups on the same chain, or within clusters of chains, with, therefore no contribution to network structure. At high concentrations of the solid cosolutes, the increase in modulus on heating was followed by a decrease at higher temperature; this was attributed to excessive aggregation, and was reflected in lower moduli on subsequent re-cooling to 5°C, in contrast to the enhancement in gel strength after heating and cooling observed at lower concentration of the same cosoutes. In the presence of fructose as cosolute, calorimetric studies showed an intense endotherm followed immediately by an intense exotherm on heating. These transitions occurred over approximately the same temperature-range as initial gelation on cooling and increased in magnitude with increasing concentration of the sugar. The displacement of both transitions to progressively higher temperature as the rate of heating was increased was much greater than anticipated from a simple thermal lag, indicating that the undelying structural changes are slow. The proposed interpretation is that fructose is capable of site-binding to pectin in both the ordered and disordered state.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 69-71).
Colloidal gels are viscoelastic materials characterized by the collective behavior of particles that form a space-spanning network. Although the network structure embodies the aggregation process of the particles, the kinetic pathway from a stable suspension to such a complex microstructure remains poorly understood. In this work, we explore the evolution of microscopic structure and dynamics of home-made colloidal particles in the early phase of gelation, by extending the applicability of Differential Dynamic Microscopy (DDM) to non-ergodic media. We demonstrate uncoupled development of the structure and dynamics that reveals an intermediate stage of gel formation, and compare the DDM results with the rheological features of evolving gels. We finally show how understanding the gelation at multiple length and time scales via DDM and rheology opens new ways to tune the mechanical properties of colloidal gels that bear inherent versatility.
by Jae Hyung Cho.
S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2011.
"September 2010." Cataloged from PDF version of thesis.
Includes bibliographical references.
Smart materials, or materials that respond to some stimulus by changing their properties, make up an active area of research in many fields. Light can be considered an especially attractive choice of stimulus because it can be applied with precise spatial and temporal control, and is non-invasive. This thesis explores light sensitive gels and colloids, which could be used as valves in microfluidics devices, as tunable templates for the production of nanoparticles, or as devices for capturing pollutants or delivering drugs. At the basis of the sensitivity to light is the azobenzene chemical group, which isomerizes from cis to trans under visible light and the reverse under UV light. When this group is embedded in the hydrophobic tail of a surfactant, the aggregation properties of the surfactant become light-sensitive. The trans form of the azobenzene surfactant is more likely to form micelles than the cis. When mixed with a hydrophobically modified polymer, these micelles can act as crosslinking sites for a gel network. Upon UV irradiation, the crosslinking is disrupted and the gel transitions to a solution state. NMR methods were used to characterize the micelles and gels, and to understand the steps that control the kinetics in these photoreversible systems. The gelation process can be considered to consist of photoreaction, micelle formation, and possibly polymer relaxation. It was found that the photon flux through the material limits the rate of reaction, which then controls the remaining processes in the system. The photoreaction was studied under varying conditions, including concentration, light intensity, and wavelength. Due to their optical thickness, these materials are possibly better suited for use as thin films. NMR experiments were also used to probe the interactions between the polymer and surfactant. In contrast to surfactant-only solutions, trans-dominated and cis-dominated micelles appeared equally likely to form aggregates with an appropriate polymer. The cis-rich aggregates failed to effectively crosslink the polymer and form a gel. This was confirmed by using diffusion measurements to monitor the size of crosslinked polymer clusters. This cluster growth correlated well with previous rheology results, but the high tendency of cis samples to form aggregates had not been anticipated. It is hypothesized that cisdominated aggregates are too small and unstable to act as crosslinking sites. In an effort to create a wider array of tunable colloids, the azobenzene surfactant was then mixed with a traditional surfactant of opposite charge. Solutions consisting of oppositely charged surfactants have been known to result in unilamellar vesicles, when prepared at appropriate concentrations and mixing ratios. The size, type and number density of the aggregates in this work were found to be controllable through the use of light. Depending on the light conditions, either nanodiscs or vesicles could be observed.
by Sanjoy Sircar.
Ph.D.

Des gels des sols et des precipites sont obtenus par hydrolyse et condensation du tetra-n-butoxyde de titane dilue dans le n-butanol. La condensation du precurseur non modifie aboutit toujours a un precipite. La diffusion aux petits angles des rayons x montre que ces precipites sont formes de polymeres denses a surfaces rugueuses. L'inhibition selective de la condensation par des protons ou par des complexes organiques oblige les polymeres a croitre de maniere anisotrope. Quand ces amas atteignent une taille macroscopique, un gel se forme. La structure interne de ces amas varie continument avec le taux d'inhibition. Pour des fortes inhibitions, l'etat final est un sol ou un gel transparent de dimension fractale egale a 2. Pour les taux d'inhibition intermediaires, le gel devient turbide. La precipitation est obtenue quand la dimension fractale atteint 3. Nous montrons que l'etat final de l'agregation est le resultat d'une difference de reactivite des monomeres en fonction de leur environnement. En fonction de cette reactivite, le bain reactionnel change de regime pendant l'agregation et passe de recombinaison de polymeres branches a la precipitation d'objets denses. Ceci explique le role de certains modificateurs chimiques dans le controle des processus d'agregation, en particulier dans le procede sol-gel

Mestrado em Bioquímica - Bioquímica Alimentar
Traditionally, whey protein (WP) gelation requires the application of heat, hence limiting the use of whey protein ingredients as gelling agents in foods sensitive to high temperatures. Acid-induced gelation has been shown to promote whey protein gel formation at room temperature, using acidulants. However, it requires the application of heat in the initial stages of the process to achieve partial denaturation of the protein and the formation of soluble aggregates. Gelation in the presence of weak organic acids at room temperature has been reported for shark myofibrils. Nevertheless, according to the literature, these conditions have not yet been tested in whey proteins. Therefore, the aim of this study was to investigate whey protein gelation at ambient temperature upon addition of weak organic acids (formic, acetic and propionic). The effect of protein concentration, acid concentration, pH and acid type on the sol-gel protein phase behavior was investigated by macroscopic observation. Phase diagrams were established to define the physical state of the WP systems as a function of protein and acetic acid concentration, and pH. Small strain oscillatory rheological measurements were performed in order to characterize the gelation times and the viscoelastic properties of the obtained gels. Differential scanning calorimetry was applied to investigate the denaturation behavior of the WP, under the studied concentration and ionic conditions. Rheological measurements and visual assessment of the prepared samples indicated that all formic, acetic and propionic acids have induced whey protein gelation. However, this process was shown to be highly dependent on protein concentration, acid concentration, pH and acid type, which also seemed to influence the appearance of the final gels. Therefore, increasing protein and acid concentrations resulted in decreased gelation times and led to the formation of increasingly turbid and opaque gels. WPI gelation was also shown to occur more rapidly as the pH increased towards the isoelectric point, promoting the formation of translucent gels which became more turbid at higher values of pH. Lastly, propionic acid was the fastest to induce gel formation, yielding opaquer gels, followed by acetic acid and formic acid which formed clearer gels. DSC results showed a decrease in the denaturation temperature of WP in the presence of the highest acetic acid concentration studied (2.8 mol L-1, pH 3.2) in relation to the protein with no added acid, from 78 to about 58 ºC, indicating the lower thermal stability of the proteins in the presence of high acetic acid concentrations, probably related to changes in the intramolecular interactions stabilizing the proteins and to consequent conformational changes in the proteins upon acid addition.
Tradicionalmente, a gelificação das proteínas do soro do leite requer aplicação de calor, limitando a utilização destes agentes gelificantes em alimentos sensíveis a elevadas temperaturas. É possível a gelificação destas proteínas induzida por ácidos à temperatura ambiente, através do uso de acidulantes, requerendo, contudo, a aplicação de calor numa fase inicial do processo. De acordo com a literatura, foi possível gelificar proteínas miofibrilares de tubarão na presença de ácidos orgânicos fracos. No entanto, não existem registos que indiquem a utilização destas condições para gelificar proteínas do soro do leite. Este trabalho teve como objetivo investigar a gelificação de proteínas do soro do leite, à temperatura ambiente, na presença de ácidos orgânicos fracos (fórmico, acético e propiónico). Os efeitos do tipo e concentração de ácido, concentração de proteína e pH sobre a transição de fase sol-gel foram estudados através da observação macroscópica de amostras em tubos de ensaio. Estabeleceram-se diagramas de fase para as proteínas do soro de leite em meio aquoso acidificado, em função das concentrações de proteína e ácido acético e do pH. Os tempos de gelificação e as propriedades viscoelásticas dos géis obtidos foram caracterizados através de ensaios reológicos dinâmicos a baixa deformação. A desnaturação destas proteínas, sob as diferentes condições em estudo, foi avaliada por calorimetria diferencial de varrimento. Os resultados dos ensaios reológicos e da avaliação visual das amostras indicaram que todos os ácidos estudados induziram a gelificação do isolado de proteínas do soro do leite. Contudo, este processo demonstrou ser altamente dependente da concentração de proteína e de ácido, do pH e do tipo de ácido, fatores estes que também influenciam o aspeto final dos géis. Assim, o aumento da concentração de proteína e de ácido resultou em tempos de gelificação menores e na formação de géis cada vez mais turvos e opacos. A gelificação destas proteínas também aconteceu mais rapidamente à medida que o pH aumentava e se aproximava do ponto isoelétrico, originando géis inicialmente translúcidos que se tornaram mais turvos a pH mais elevado. A formação de géis aconteceu de forma mais rápida na presença de ácido propiónico, seguindo-se o ácido acético e o ácido fórmico. No primeiro caso, foram produzidos géis translúcidos e opacos, enquanto os outros ácidos formaram géis mais transparentes. Os resultados de calorimetria mostraram a diminuição da temperatura de desnaturação do isolado de proteínas do soro de leite, de 78 para 58 ºC, para a concentração de ácido acético estudada mais elevada (2.8 mol L-1, pH 3,2), indicando a influência da presença do ácido na estabilidade térmica das proteínas, provavelmente uma consequência de alterações nas interações intramoleculares e na conformação destas proteínas.

Two models of coagulation are presented: one, a system of coupled partial differential equations and the other microscopic Brownian particles. Both models feature a parameter that represents the tendency of two particles to coagulate at sufficiently close distances. Both models have a phase transition, viewed as the mass clumping together as a gel. Previous work has shown the models are connected, and in here we show that their phase transition to instantaneous gelation is connected as well.

This thesis is focused on the structural and rheological changes in globular proteins when subjected to high pressure processing (HPP), a novel non-thermal food processing technique. Structure-functionality changes associated with thermal processing has been well studied, but little is known for HPP. One of the principal objectives of this thesis was to compare protein structure-functionality relationship between thermal and HP processing. Three groups of proteins of varying complexity and source were studied: beta-lactoglobulin (b-lg), a small well understood protein from cow's milk whey (model system); porcine blood plasma proteins, and soy protein concentrate. Blood is generally considered a waste from the meat industry, plasma is obtained from centrifugation of the blood and is composed mainly of serum albumin and globulins (simplified multi-component system). Soy protein concentrate (SPC) is a complex system of vegetable proteins composed of a varied mix of large glycoproteins. In general, HPP affected protein structure and functionality, but the specific effects depended on the protein characteristics. Pressure-independent parameters, like concentration and pH, exerted a major influence on protein denaturation and influenced the HP-induced gel network formation. For b-lg, significant structural changes were observed at 600 MPa and these correlated to changes in the viscoelastic properties. HP-induced gelation did not follow the classic structural changes observed on thermal gelation. Protein gels of comparable strength were produced by thermal and HPP (conc. ≥ 20 %); the heat induced gels were stiffer than their HP-induced counterparts, the latter only modestly
Cette thèse est concentrée sur les changements structuraux et rhéologiques des protéines globulaires une fois soumise à l'haute pression procès (HPP), une technique non thermique innovatrice de traitement des produits alimentaires. Il y a un ensemble de connaissances impressionnant sur les changements de structure-fonctionnalité liés au procès thermique mais peu est connu pour HPP. Un des principaux objectifs de cette thèse était de comparer le rapport de structure-fonctionnalité entre les deux procédés (haute pression et thermique). Trois groupes de protéines on été étudiés en variant la complexité et la provenance : la β-lactoglobuline, une petite protéine très bien connu, provenant du lait de vache (système modèle); les protéines de plasma sanguin porcine, et le concentré protéique de soja (SPC). Le sang est généralement considéré comme un dechet de l'industrie de viande, le plasma est obtenu à partir de la centrifugation du sang et se compose principalement d'albumine sérique et de globulines (système simplifié à plusieurs éléments). Le concentré protéique de soja est un système complexe des protéines végétales composées de mélange divers de grosses glycoprotéines. Généralement le traitement de HP a affecté la structure et la fonctionnalité de protéine, mais les effets spécifiques de HP sur les protéines ont dépendu des caractéristiques du système en question. Les paramètres comme la concentration en protéine et le pH, ont exercé une influence importante sur la dénaturation des protéines et ainsi que la formation de gels. Un vrai gel a été formé seulement après application de 650 MPa et une concentr

This thesis examines a system consisting of two biopolymers, gelatine (a protein that forms a gel under certain conditions of temperature and concentration) and dextran (a non-gelling polysaccharide) in solution. At high temperatures the polymers are miscible but at low temperatures (less than ˜35°C) phase separation and gelation can occur. This thesis investigates this phenomenon using light scattering, microscopy and rheology. It is shown that very different structure are formed depending on the relative rates of phase separation and gelation. At high temperatures the gelation occurs slowly and confocal microscopy experiments have revealed that droplets of one phase in another result. At low temperatures the gelation occurs quickly and, for a sample in which the two polymers are present in similar quantities, an interconnected structure is produced. The evolution of these different structures is examined using several techniques, the main method being small angle light scattering, and analysed within the framework of several theories describing phase separation, the key one being the Cahn-Hilliard theory of spinodal decomposition. This theory was found to describe the early stages of phase separation well in spite of the effects of gelation, indicating the resilence of the underlying physical processes even in the presence of the molecular reorganisation that occurs in gelation. Effects of the gelation are seen at low temperatures (˜18°C), the principal effect it has is to alter the characteristic lengthscale produced in the sample - deeper quenches producing shorter lengthscales. In the later stages of phase separation the gelation has a more obvious effect, altering the mechanisms of the coarsening of the structure. In samples poor in gelatine coalescence of the droplets could occur, in others the gelation of the gelatine within the droplets prohibited coalescence over the period of observation. Rheology experiments also showed differences between samples quenched to different temperatures, the modulus of the sample depending to some extent on the concentration of gelatine in the continuous phase. The compositions of the phases produced were functions of temperature and the rates of phase separation and gelation.

This thesis presents investigations into supramolecular gels by Atomic Force Microscopy (AFM), rheometry and Small Angle Neutron Scattering (SANS) to study the assembly and disassembly processes of gels and their physical properties to develop a deeper understanding of the relationship between microscopic and macroscopic properties of gels. Supramolecular gels, which have a reversible nature and can be switched via external stimuli, and peptide gels of biological relevance were studied with the above-mentioned techniques.

Resorcinol-Formaldehyde (RF) xerogels are a type of porous material used in many applications, such as gas storage. These applications often require fine control of the material's porosity, and while it is known that the porosity of a xerogel can be changed through altering synthesis variables, it is not clear why these changes have such an impact. To understand this effect, the gelation process was studied using dynamic light scattering (DLS), with the xerogel products undergoing low temperature nitrogen adsorption measurements to determine textural properties. RF gels are composed of cross-linked clusters and DLS was used to study changes in how these clusters grow. It was found that cluster growth was a thermodynamically controlled process, and for a given catalyst, how the cluster size grows with time was independent of the catalyst concentration. However, the catalyst did kinetically control the number concentration of clusters initially formed, and in turn, the size to which they, therefore, had to grow to reach a critical volume fraction to form the gel, such that higher catalyst concentrations led to smaller clusters making up the gel. This resulted in smaller intercluster voids, hence, smaller pores. The catalysts used also demonstrated a range of different abilities to stabilise the colloidal suspension of clusters. This also affected cluster size, with less stabilising catalysts resulting in larger clusters. This knowledge led to the ability to further tailor the porosity by introducing a secondary catalyst, in various forms, into a separate gelling mixture. The different catalysts, with their varied abilities to stabilise the growing clusters, and the range of concentrations used, resulted in a variety of cluster sizes within the final gel, which changed the porosity of the xerogel products formed.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, May, 2020
Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages 195-201).
Inspired by their role in the extraordinary mechanical properties of aquatic mussel threads, reversible metal ion cross-links have been utilized to engineer the toughness, stress relaxation, and healing ability of polymer hydrogel networks. Such transient network hydrogels are easily made by reversibly cross-linking a growing variety of polymers modified with ligands capable of binding metal ions in dynamic coordination complexes, and researchers by now have developed a range of orthogonal strategies to tune the viscoelastic properties of these metal ion cross-linked hydrogels. However, several critical challenges have slowed the further development of these materials. Like any two-component cross-linked network, metal ion cross-linked hydrogels are limited by a reliance on strict stoichiometric balance between the metal and ligand to achieve full network connectivity, or percolation, and robust mechanical properties.
Additionally, the application space for any hydrogel is ultimately limited by their tendency to either dehydrate or freeze, whereupon the unique material properties that motivated their initial use are lost. Finally, it remains challenging to predict the mechanical properties of metal ion cross-linked hydrogels a priori. This thesis reports new strategies to expand the conditions that allow gelation to occur, create viable materials with a defined application, and predict the mechanical properties of metal ion cross-linked hydrogels. Specifically, we demonstrate that metal ion cross-linked hydrogels avoid traditional stoichiometric limits on gelation through self-regulating hydroxide competition. Additionally, we show that metal ion crosslinked hydrogels can assemble in the presence of large quantities of competitor ligand, further expanding the range of conditions resulting in gelation.
Building on these discoveries, we provide a practical demonstration of metal ion cross-linked hydrogels by assembling a broad spectrum vibration damping material, while additionally suppressing dehydration and freezing of the gel. Finally, we develop a computational framework to predict the plateau moduli of metal ion cross-linked hydrogels, a measure of their connectivity and stiffness, as a function of an arbitrary combination of metal ions, ligands, and polymer architecture. The progress made in this thesis should advance the engineering of metal ion cross-linked hydrogels by demonstrating their robust assembly through expanded gelation conditions, their ease of design through our computational model, and their potential application in a broader range of environments due to suppressed dehydration and freezing.
More broadly, this thesis pushes forward the development of metal ion cross-linked hydrogels for applications in 3D printing and bioinspired manufacturing and presents a general hypothesis of how to expand gelation conditions in all transient networks outside of metal ion cross-linked hydrogels.
by Seth Allen Cazzell.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering

L’encapsulation d’huile par gélification inverse consiste à ajouter, goutte-à-goutte, une émulsion de chlorure de calcium/huile dans un bain d’alginate. Lesions Ca2+ migrent ensuite à travers l’émulsion vers l’extérieur du bain et réticulent les macromoléculesd’alginate (gélification inverse). Des capsules millimétriques (3- 7 mm) avec une morphologie coeurcouronne sont ainsi formées. La production de capsules de taille inférieure à 1 mm par gélification inverse n’a cependant jamais été démontrée. L’intérêt des microcapsules repose sur un vaste champ d’applications pour lesquelles la capsule ne doit pas ou peu interférer avec la texture ou l’apparence du produit final. L’objectif de la thèse repose ainsi sur le développement de procédés de gélification inverse en visant une réduction de la taille des capsules. De plus, la compréhension du mécanisme de gélification inverse à partir des émulsions huile-dans-eau (H/E) et eau-dans-huile (E/H) a aussi été étudié. Une méthode de dispersion a ainsi été proposée afin de réduire la taille des capsules, qui consiste à former des gouttelettes par dispersion de l’émulsion dans un bain d’alginate sous agitation. Après réticulation de l’alginate pour former la membrane, des microcapsules de tailles comprises entre 370 et 600 μm ont été obtenues. La méthode de dispersion a ensuite été adaptée à un procédé millifluidique afin de contrôler la polydispersité en taille de microcapsules. Des capsules monodisperses en taille avec des diamètres de 140 μm jusqu’à 1. 4 mm ont ainsi été produites par millifluidique
Encapsulation of oil by inverse gelation consists of dropwise addition of a calcium chloride/oil emulsion into an alginate bath. Calcium ions inside the emulsion migrate towards the bath cross-linking the alginate molecules (inverse gelation). Millimetric capsules (3-7 mm) with a core-shell structure are formed. However, the production of capsules with sizes lower than 1 mm by inverse gelation was never demonstrated. The interest of microcapsules is based on a vast range of applications for which the capsule does not have to or little interfere with the texture or the appearance of the end product. The objective of this thesis is therefore to develop an inverse gelation process that yields capsules at reduced sizes. In this frame, the comprehension of the inverse gelation mechanisms from oil-in-water (O/W) and water-in-oil (W/O) emulsions was also studied. In order to reduce the capsules size, a dispersion method was proposed. A dispersion method was therefore proposed to reduce the size of capsules, which consists in the formation of droplets by dispersion of the emulsion in a bath of alginate under stirring. After cross-linking of alginate to form the membrane, microcapsules of sizes between 370 and 600 μm were obtained. To control the wide size distribution of the microcapsules, the dispersion method was adapted for the millifluidic method. Monodispersed capsules with desired mean particle size were produced. The mean size of the particles (within 140 μm to 1. 4 mm) was controlled by variation in the flow rates of the dispersed and continuous phases in the millifluidic circuit

Gelation due to the Maillard reaction took place when solutions containing a low level of bovine serum albumin were heated in the presence of carbonyl compounds. The Maillard reaction caused a change in colour, a decrease in the pH and induced gelation. These changes were dependent on the type and concentration of sugars or protein and on the heating conditions used. Reducing sugar and Maillard reaction products (e.g. glyoxal) affected these changes, yet their order of reactivity for browning and gelation were not necessarily the same. Loss of available lysine and arginine plus changes in the thio amino acids showed that these were implicated in the reaction. The gelation kinetics (gelation time and development of storage modulus) were followed in real time using a Bohlin CS Rheometer at a temperature of 90 °C. These studies showed that the gels did not form at a specific pH, the pH being lower for samples where the more reactive carbonyl compounds were used. Measurement of the charge on the protein after the Maillard reaction showed an increased negative charge, hence causing a lowering in the protein's isoelectric point. This had the effect of changing the critical protein concentration necessary for gelation at any pH above the isoelectric point. This reasoning would also explain the low syneresis seen in the Maillard gels. Hydrodynamic studies on dilute solution showed that the protein molecules heated in the presence of xylose associated in an orderly manner despite having a low pH. The aggregates could be described as "stiff and rod like". The linkages holding *the aggregates together were mostly attributed to additional non-disulfide linkages resulting from the Maillard reaction. Similar types of crosslinks were formed in the Maillard gels heated at 90°C and were thought to have enhanced the gel strength. Extrusion of soya grits with reducing sugars did not form a retort-stable product. However, microwave heating of the extruded product was successful in producing a product that survived a typical canning process. This suggests that formation of crosslinks may be controlled to produce novel food products.

Aggregation and gelation in colloidal suspensions are studied by computer simulation using the diffusion-limited cluster aggregation (DLCA) model. By studying the structure of the aggregating system in detail using computational methods analogous to scattering experiments, direct comparison is made with recent scattering experiments on fast colloidal aggregation. The simple DLCA model is shown to reproduce many features observed in experiments, including the appearance of an intense scattering peak at small angle or large length-scale, which is shown to correspond with a density modulation in the aggregating system at the inner-cluster length scale. The calculated scattering function is examined in detail by studying the structure of individual aggregates, the arrangement of aggregates in the system, and the effect of aggregate size-position correlations. The scaling properties of the scattering function are examined and simulation results compared to experiments. More direct investigation of scaling in the system is carried out by comparing the time evolution of various length scales. The DLCA model is extended to allow thermal restructuring of aggregates. In this 'reversible' model the typical morphology of the system varies from a near-fluid-like state with no long-lived large aggregates, through a system of near-compact clusters, to a near-space-filling gel made from locally compact filaments which are ramified at longer length scales. The irreversible DLCA model is thus the strong-bonding limit of this more general model of particle aggregation.

Bis(3-pyridyl)ureas with ethylene, propylene, butylene, phenylene and napthy- lene spacer groups were synthesised by the reaction of 3-isocyanato-pyridine, pre- pared in situ from nicotinoyl azide, with the appropriate diamine. Each ligand was crystallised and their structures were solved using X-ray crystallography. The urea groups of the napthylene-spaced ligand adopt a bifurcated hydrogen-bonding mode, thereby forming an α-tape whereas in the the propylene-, butylene- and phenylene- spaced ligands, every other bifurcated interaction is replaced with a NH···Ourea and a NH···Npyridyl , caused by the presence of a single competing intramolecular CH···Ourea set-up by the electron-withdrawing pyridyl nitrogen. With the ethylene-spaced urea, the bifurcated hydrogen-bonding motif is absent. These differences in the intermolec- ular bonding may be only be due to the packing requirements of the spacer group: as these interactions become stronger, either by greater van der Waals attraction in a longer oliomethylene chain or the greater π-π stacking interactions of the napthy- lene ring, adjacent urea groups become closer and bind preferentially to form the bifurcated interaction. The bis(3-pyridyl)ureas were subsequently tested for their ability to form gels, and in some cases, crystallised in the presence of selected silver(I) salts. Compound 2.1 formed five pseudo-polymorphs of a Borromean-type structure upon slow crys- tallisation in various solvent mixtures with silver(I) nitrate. Within each struc- ture, there are layers made up of paired Borromean weaves and the mechanism by which these layers stack, though unclear, must ultimately be driven by the inter- actions of the solvent molecules incorporated into the structures. When the coun- teranion in the crystallisation was replaced by either acetate, tetrafluoroborate or hexafluorophosphate, several coordination polymers were synthesised but the Bor- romean structure was not reproduced. A similar dependency on counteranion was observed with N,N''-pentylene-1,5-diylbis(N'-pyridin-3-ylurea) which was similarly crystallised with silver(I) nitrate, acetate and tetrafluoroborate. In the presence of the latter, a quintuple helix formed. Several bis(3-pyridylureas) with ethylene, pyridine, methylenebisphenylene and cyclohexylene spacer groups were shown to form gels and crystals in the presence of silver(I) nitrate. Two macrocyclic structures were grown from gel states which may be further indication as to how the same molecules aggregate in the gel fibres with silver(I) nitrate promoting aggregation of the molecules along one direction.

El continuo af'an por reducir la cantidad de act'¿nidos minoritarios (MA) procedentes del combustible quemado en los reactores de agua ligera (Light Water Reactor, LWR) y de esa forma reducir la radiotoxicidad, ha llevado a desarrollar nuevos conceptos de combustible nuclear. El nuevo combustible por empaquetamiento de esferas (Sphere-Pac, SP) ofrece la oportunidad de reintroducir los MA en una matriz y quemarlos en un reactor r'apido de neutrones, donde se facilitan ciclos mu'ltiples por transmutaci'on de elemen- tos. Este combustible se puede utilizar tambi'en en un sistema subcr'¿tico r'apido de neutrones, es decir, un sistema nuclear accionado por un acelera- dor de part'¿culas (Accelerator Driven System, ADS), donde la subcriticidad (seguridad de parada del reactor) permite utilizar combustibles con mayor contenido de MA que en un reactor normal, reduciendo eficazmente en un solo paso la radiotoxicidad. El combustible SP se produce a partir de una soluci'on base (formada por metales y elementos qu'¿micos) mediante un proceso de gelificaci'on in- terna. Este proceso garantiza una buena homogeneidad del producto final y un riesgo de contaminaci'on mucho menor si se compara con la fabricaci'on cl'asica de pellets (combustible comprimido), puesto que se evita el uso de prensas y amoladoras. La gelificaci'on interna es una reacci'on qu'¿mica acu- osa que se produce al calentar la soluci'on hasta 80 ± 5¿ C. Cuando se realiza el proceso por calentamiento electromagn'etico, se observan algunas venta- jas con respecto al calentamiento tradicional por conducci'on (contacto de la muestra con aceite de silicio precalentado): se evita la etapa de reciclado del aceite y de los disolventes org'anicos necesarios para eliminar el aceite de la superficie de las part'¿culas producidas. En la unidad de gelificaci'on in- terna por microondas (Microwave Internal Gelation, MIG), las microondas representan una alternativa mucho m'as simple y segura: el calentamiento volum'etrico sin contacto facilita la producci'on a distancia del combustible en celdas calientes y adem'as reduce los residuos de l'¿quido contaminado. Esta tesis se enmarca dentro del proyecto Platform for Innovative Nu- clear FuEls (PINE), que tiene como objetivo fundamental la producci'on de combustible SP por MIG. En el sistema MIG, el tiempo de calentamiento es muy corto (del orden de decenas de milisegundos), por lo que se deben optimizar los par'ametros que contribuyen al calentamiento por microondas y es necesario conocer en profundidad la interacci'on entre las microondas y las muestras. En la primera parte de este trabajo se investiga un modelo t'ermico basado en diferencias finitas en el dominio del tiempo (FDTD), el cual es capaz de determinar, en cada instante durante el proceso de calentamiento, el comportamiento t'ermico de un punto definido dentro del material que se calienta. Adem'as se presenta una descripci'on detallada de los par'ametros m'as relevantes del modelo, incluyendo las condiciones de contorno (entre ellas la convecci'on). Por otra parte, se implementa anal'¿ticamente y se valida con diferentes t'ecnicas: una basada en teor'¿a de la f'¿sica, otra basada en la herramienta de ecuaciones diferenciales parciales (PDEtools) y la u'ltima basada en ejemplos encontrados en la literatura. En segundo lugar, se investigan los posibles disen¿os de cavidades de microondas para su aplicaci'on en MIG. Tanto las cavidades (selecci'on de los modos, frecuencia de resonancia, factores de calidad, etc.) como su posterior caracterizaci'on, se detallan con el objetivo de especificar el acoplamiento de energ'¿a. Los mecanismos de transferencia de energ'¿a de las cavidades se explican utilizando el m'etodo de perturbaci'on, con el que adem'as se analizan las p'erdidas de la cavidad cuando se coloca una muestra diel'ectrica en su interior. Con el modelo de transferencia de energ'¿a desar- rollado, se obtiene la tasa de generaci'on de calor por microondas, que se aplica al modelo t'ermico FDTD mencionado anteriormente. Los resultados anal'¿ticos demuestran la viabilidad de producir esferas gelificadas por MIG. Seguidamente se introducen los principales par'ametros relacionados con el calentamiento de un material por microondas, es decir, las propiedades diel'ectricas. Se desarrolla un nuevo procedimiento que permite medir estas propiedades en gotas que caen libremente a trav'es de una cavidad de mi- croondas. Se presenta el montaje experimental, cuya viabilidad se prueba a trav'es de diferentes experimentos. Las propiedades diel'ectricas medidas se incluyen en los modelos (perturbacional y t'ermico) con la intenci'on de determinar la potencia absorbida por la sustancia (en forma de gotas) y la temperatura que alcanza. En la u'ltima parte se presenta la implementaci'on del sistema MIG apli- cada al proyecto PINE, fundamental para la pr'actica de calentamiento (basado en frecuencias altas) dentro del laboratorio. Las propiedades de cada dispositivo se evaluan para realizar un estudio de potencia antes del ensamblaje del sistema MIG. De esa forma se evitan fallos al poner el sis- tema en funcionamiento. Adem'as se aportan las t'ecnicas experimentales y los resultados. La producci'on con 'exito de esferas gelificadas demuestra, sin duda, el uso favorable de las microondas en la producci'on de combustible SP por gelificaci'on interna.
In the continuous aim to reduce the amount of minor actinides (MA) from the spent fuel of Light Water Reactors (LWR) and therefore reduce its radiotoxicity (radioactive toxicity), new nuclear fuel concepts have been developed. Sphere-Pac (SP) fuel gives the opportunity to reintroduce the MA in a fuel matrix and to burn them in a fast reactor, which facilitates a multi-cycle because of its breeding feature, or in a subcritical fast system, i.e. an Accelerator Driven System (ADS) where its sub-criticality allows higher MA contents than a normal fast reactor reducing efficiently the radiotoxicity in one step. SP fuel is produced from the base solution (already containing all the elements) by internal gelation, which guarantees a good material homo- geneity and a lower contamination risk compared to the classical pellet fabrication, avoiding presses and grinding machines. The internal gelation is an aqueous chemical reaction occurring when the solution is heated up to 80 ± 5¿C. When performing the internal gelation process with electro- magnetic heating, some advantages appear with respect to the traditionally heating through conduction by contact of the sample with hot silicon oil: the recycling step of the oil and the organic solvents necessary to clean the particles from oil are avoided. In the Microwave Internal Gelation (MIG) unit, the microwaves represent a much simpler and safer alternative: the contactless volumetric heating facilitates the remote production of the fuel in hot cells and furthermore reduces the contaminated liquid waste. The fuel related project called Platform for Innovative Nuclear FuEls (PINE), in which this thesis is embedded, aims for the production of SP- fuel by MIG. In the MIG system, the heating time is very short (in the order of tens of milliseconds), therefore the microwave heating parameters have to be optimized and a good knowledge of the interaction between the microwaves and the samples must be achieved. In the first part of this dissertation a finite difference time domain (FDTD) thermal model capable to determine over each instant about the thermal behaviour of a definite point inside a material during heat process- ing is investigated. A detailed overview of the most relevant parameters on the model including the boundary conditions (e.g. convection) is pre- sented. Furthermore, the model is analytically implemented and validated with different techniques: a theoretical based physically validation, a par- tial differential equations (PDEtools) based validation and a validation with examples from the literature. Secondly, possible microwave cavity designs for MIG are researched. The cavities (selection of modes, resonant frequency, Q-factor, etc.) and its subsequent characterization for the coupling of energy are explained. Furthermore, the power transfer mechanisms of the cavities are explained using the perturbation method to analyse the losses when a dielectric sam- ple is placed inside a cavity. The developed power transfer model delivers the microwave heat generation rate which is applied to the FDTD thermal model mentioned in the previous paragraph. The analytical results provide a positive impression about the feasibility of producing gelated spheres by MIG. Next, the main parameters dealing with the heating of a material by microwaves are introduced. A new procedure that enables the measure- ment of dielectric properties of aqueous droplets freely falling through a microwave cavity is developed. The experimental setup is presented and several experiments prove its feasibility. The measured dielectric properties are afterwards included in the perturbation and thermal models with the main intention of determining the absorbed power by the material in form of drops and the reached temperature. In the last part the MIG system for the laboratory practice of the high frequency heating applied to the PINE project is implemented. Each device is characterized for a power study precedent to the MIG system assembly, avoiding then failures when putting the system into operation. In addition, the experimental techniques and the results are reported. Successful pro- duction of gelated spheres shows the favourable usage of microwave for the production of SP-fuel by internal gelation.
Cabanes Sempere, M. (2013). Innovative production of nuclear fuel by microwave internal gelation [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31641
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Thesis (Ph. D.)--Chemical and Biomolecular Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Dr. Victor Breedveld; Committee Member: Dr. Clifford Henderson; Committee Member: Dr. David Rosen; Committee Member: Dr. Peter Ludovice; Committee Member: Dr. Sai Kumar.

This thesis presents the designs and results of experimental investigations into gelation and melting point behaviour for polymer gel electrolytes. The study used one of the most prominent types of materials in the commercial world—polyvinylidene fluoride-based (PVDF) gel electrolytes—focussing on the effects of gelation temperature and gel composition on the properties of its solid electrolytes. While PVDF was used as the polymer matrix, propylene carbonates (PC) and diethyl carbonate (DEC) were used as solvents. Lithium tetrafluoroborate (LiBF4) and lithium bisoxalatoborate (LiBOB) were used as the electrolyte salts. Gelation from molten PVDF solutions was studied isothermally, using 30% PVDF/PC unsalted and 30% PVDF/PC/ LiBF4 salted gels to investigate the effect of salt addition on gelation behaviour. Crystallisation behaviour and subsequent melting was also investigated. Varying the gel composition involved changing polymer concentration, solvent nature and salt concentration. The measured properties included gel structure and morphology, melting point and ionic conductivity. The techniques of DMTA, DSC, WAXS, dielectric spectroscopy and optical microscopy were used to investigate gelation behaviour and gelation properties. It was found that gelation time is significantly increased at higher temperatures, and that the addition of salt reduces gelation time at any given temperature whilst extending the gelation process to higher temperatures. Gelation occurs without crystallisation at high temperatures, whereas it is induced by crystallisation at low temperatures. The sharp cut-off for crystallisation gives two distinct temperature windows, within which gelation occurs via different mechanisms. The addition of salt has found to raise the gel melting point by about 25C for 1M LiBF4, and hence to enhance its thermal stability, which is attributed to the salt affecting the Flory interaction parameter. Salt also reduces crystal size and gel pore size, and this is attributed to the nucleating effect of the salt molecules. The incorporation of up to 40% DEC in the solvent increases the gel melting point by 5 to 10 C, and is accompanied by a negligible reduction in ionic conductivity, which shows a possible route for further enhancing the properties of the electrolytes.

We report a result of the research on the effect of hydroxyapatite nanoparticles (nHAP) on the process-es of enzymatic gelation in milk. There has been made a research on the nHAP effect on duration of the ge-lation and its modulus of elasticity. There has been revealed the existence of the process’s bifurcation point, from which it can develop by two different scenarios. There is shown the nHAP’s behavior to involve serum proteins into the process of gelation. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35416

Low molecular weight gelators (LMWGs) are small molecules that are capable of entrapping solvents to form a gel in organic solvents or aqueous solution. These compounds rely solely on noncovalent forces to form the fibrous networks necessary to entrap a variety of solvents. The organogels and hydrogels thus formed could have applications in a variety of fields from environmental to biological to medicinal. Carbohydrates are ideal starting materials to synthesize LMWGs, because of their natural abundance, dense chirality, and biocompatibility. D-Glucose is the most common monosaccharide and D-glucosamine is isolated from natural sources, such as crab shells. Several series of compounds were synthesized using compounds 1-3 as the starting materials. These include esters, carbamates, amides, and ureas. The structure and gelation relationship was analyzed to obtain guidelines for designing new LMWGs. Compound 1 is a simple derivative of D-glucose and its terminal alkynyl esters and saturated carbamates are effective gelators. Compound 2 is a simple derivative of D-glucosamine and its amide and urea derivatives are also effective gelators. Compound 3 is formed from the deoxygenation of D-glucose. 1OOHOOCH3OHOPh2OOHOOCH3NH2OPh3OOHOOHOPh The design, synthesis and gelation properties of several classes of sugar based low molecular organo/hydrogelators will be discussed in this thesis in chapters 2, 3, and 4. After obtaining highly effective organo/hydrogelators, potential applications of these novel molecular systems can be explored. Some preliminary study on using one of the gelator in enzyme assay has shown that it is possible to utilize the hydrogels to immobilize enzymes. However, future research can explore further on the applications of these gelators.

Soybeans contain around 40% of high quality protein and 20 % of oil. Soy protein has long been used as ingredients for its emulsification and texturizing properties in a variety of foods, soymilk and tofu being the most popular. Soymilk is essentially a water extract of soybeans and there are many variations on the basic soymilk processing steps. Tofu, or bean curd, is made by coagulating soy milk, and then pressing the resulting curds into blocks. This thesis was mainly devoted to thermal denaturation and coagulation of soy proteins and targeted several selected important factors as they relate to the functional properties. The effects of different chemical coagulants as well as proteases on yield and quality of tofu from soybeans were studied. Eight tested chemical coagulants were able to coagulate the soymilk and the results showed that the concentration of soymilk and type of coagulant had a great influence on the properties of the tofu gel. The results also confirmed that the use of a suitable concentration of the quick-acting coagulants is more critical than that of the slow-acting coagulants in tofu making. In general, the extent of soymilk gelation is not determined by a single characteristic but rather results from a combination of factors. The gelation ability of various most common commercially available proteases to coagulate non-defatted soymilk was surveyed and the thermal stabilities of selected protease systems were compared. The difference in the temperature where the enzyme shows its highest activity seemed to be the most significant indicator when choosing a suitable enzyme for a certain industrial application. The three most effective and versatile soymilk coagulants were identified. The presence of small amounts of ficin in the system increased the protein recovery when calcium chloride was used as a coagulant. The most commonly used techniques of analysis of degree of hydrolysis (TNBS, OPA and pH-stat) of soy protein were compared. It was concluded that the pH-stat technique was useful for evaluating the progress of an enzyme-catalyzed protein hydrolysis process on an industrial scale while the OPA method seemed to be the most suitable method to be used for determining DH during the proteolysis of soymilk in laboratory conditions. The roles of soybean proteins, protein fractions and subunits to differences in gelling properties of different soybean varieties were examined. The variability and the interrelationship between soybean seed traits were established and the seed characteristics related to soymilk yield and tofu quality were identified. The results suggested that it is useful to predict the quality of tofu from a combination of characteristics of the soybean seed. It was concluded that large differences exist in soybean seed characteristics and their contributions towards the properties of the final product and implications were made towards the relative importance of individual soybean seed traits to the functional and textural properties of soy products. The SDS gel capillary electrophoresis was applied to characterize soybean storage proteins. The lab-on-a-chip technology was compared with capillary electrophoresis and these two methods were used to quantify the relative amount of 7S and 11S fractions in various soybean cultivars. It was concluded that both lab-on-a-chip instrument and a traditional CGE were adequate for analysis of soy-based products. Both systems were able to reliably quantify the relative amount of protein fractions in samples and thus demonstrate their different genetic origin. The great advantage of the lab-on-a-chip technology is its time-efficiency while the traditional CGE is a preferred instrument for method development. The usefulness of the chemometrical analysis of electrophoretic profiles as a method for objective evaluation, data reduction and interpretation was shown. The possibility of improvement of the protein extraction from soybeans in order to provide a basis for the optimization of soymilk production was studied. The enzyme-assisted extraction using the hydrolytic enzyme treatment to disrupt the soybean cell wall components was expected to improve the protein extraction yield. The results confirmed that the right selection of operational variables led to an increased yield of soymilk as well as its protein concentration. It was also shown that the addition of selected enzyme preparations into the soymilk process design resulted in an increased extraction yield of proteins from seeds into soymilk. The protein quality did not deteriorate during the enzyme-assisted extraction process and a small amount of microbial transglutaminase added together with a coagulant produced tofu with a significantly increased yield while maintaing satisfactory textural properties.