Orientador: Rosiane Lopes da Cunha / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-21T04:58:14Z (GMT). No. of bitstreams: 1 Moraes_MarisaCorreade_M.pdf: 1452448 bytes, checksum: cbfd0da3e6558c06281ba86e39f14050 (MD5) Previous issue date: 2012 / Resumo: O colágeno é um subproduto de matadouro sendo amplamente utilizado como ingrediente na indústria, depois de extraído e purificado. As propriedades tecnológicas do colágeno estão intimamente relacionadas com a distribuição da massa molecular de suas fibras, que varia de acordo com as características da matéria-prima e condições do processo de obtenção do material. Com o intuito de avaliar o efeito das variáveis de processo (tempo,temperatura e pH), o colágeno foi extraído da camada interna da pele bovina e submetido a hidrólise em diferentes condições de temperatura (50, 60 e 80°C) e pH (3, 5, 7 e 10) durante 6 horas. Os produtos obtidos foram avaliados quanto ao teor de proteína solúvel, carga superficial, distribuição de massa molecular, desnaturação protéica, capacidade gelificante e emulsificante. Os produtos mostraram teor de proteína solúvel entre 5 e 82% (m/m), sendo os maiores valores obtidos em tratamentos realizados em temperatura mais elevada e/ou condições mais ácidas. Produtos obtidos em condições extremas de pH (3 e 10) ou temperaturas acima ou similar à temperatura de desnaturação do colágeno (80 e 60°C, respectivamente) tiveram sua estrutura mais desnaturada. Em geral, os hidrolisados obtidos em pH ácido formaram géis mais firmes, exceto o produzido a 80°C. Já os hidrolisados obtidos nos outros valores de pH (5, 7 e 10) formaram géis com baixos valores de tensão de ruptura porém, quando tratados em temperatura acima da temperatura de desnaturação e maior tempo de processo, apresentaram uma melhora nas propriedades gelificantes. A capacidade de retenção de água (CRA) foi próxima de 100%, exceto para hidrolisados obtidos em pH igual a 7 e 10 e temperatura de 50°C. A capacidade emulsificante destes hidrolisados também foi avaliada em emulsões óleo/água (O/A). A estabilidade das emulsões aumentou com a redução do pH e com o aumento do tempo de hidrólise, porém somente a emulsão em pH 3 e 6 horas de hidrólise não apresentou separação de fases. As emulsões mais estáveis (pH 3) apresentaram gotas com baixa polidispersão e diâmetro médio entre 1,5 e 5 µm. Em valores de pH próximo ao pI do colágeno houve a formação de agregados que desestabilizaram as emulsões, o que acarretou elevados valores de diâmetro médio (entre 8 e 17 µm). As emulsões estáveis mostraram comportamento pseudoplástico, porém nas emulsões em que ocorreu a separação de fases, a fase inferior (aquosa) sempre apresentou comportamento Newtoniano, enquanto que a fase creme foi pseudoplástica. De maneira geral, o uso de temperaturas mais amenas e pH ácido, possibilita a produção de hidrolisados com boas propriedades mecânicas, no entanto, em temperatura mais elevada obtém-se um produto com alta solubilidade. Se o objetivo é a obtenção de um gel com alta capacidade de retenção de água o mais indica-se utilizar pH abaixo ou próximo do pI ou elevadas temperaturas. Para melhorar a capacidade emulsificante o uso em pH abaixo do pI é o mais indicado / Abstract: Collagen is a byproduct of the slaughterhouse that is widely used as an ingredient in industry, after being extracted and purified. The technological properties of collagen are closely related to the molecular weight distribution of the fibers, which varies with the characteristics of raw materials and process conditions used to obtain the material. In order to evaluate the effect of process variables (time, temperature and pH), collagen was extracted from the inner layer of bovine hide and subjected to hydrolysis under different conditions of temperature (50, 60 and 80°C) and pH (3, 5, 7 and 10) for 6 hours. The products were evaluated for soluble protein content, surface charge, molecular weight distribution, protein denaturation, gelling and emulsifying capacity. The products showed soluble protein content between 5 and 82% (w / w), in which the highest values were obtained in the treatments carried out at higher temperature and/or under more acidic conditions. Products obtained under extreme conditions of pH (3 and 10) or temperatures above or similar to the collagen denaturation temperature (80 and 60°C, respectively) were more denatured. In general, the hydrolysates obtained at acidic pH formed firmer gels, except that produced at 80°C. The hydrolysates obtained in the other pH values (5, 7 and 10), in turn, formed gels with low values of strain at fractures but, when treated at temperatures above the denaturation during long time, they showed an improvement in those properties. The water holding capacity (WHC) was approximately 100%, except for hydrolysates obtained at pH 7 and 10 and temperature of 50°C. The emulsifying capacity of such hydrolysates, was also evaluated in oil/water (O/W) emulsions. The stability of the emulsion increases with decreasing pH and increasing hydrolysis time, but only at pH 3 and 6 hours of process the emulsion showed no phase separation. These emulsions showed low polydispersity and droplet size between 1.5 and 5 µm. At pH values near the pI of collagen the formation of aggregates that destabilized the emulsions occurred, which resulted in higher droplet size (between 8 and 17 mm). The stable emulsions showed shearthinning behavior, but in case of emulsions in which phase separation occurred, the lower phase (aqueous) always presented Newtonian behavior, while the cream phase was a shearthinning fluid. In general, lower temperatures and acid pH, allows the production of hydrolysates with good mechanical properties, however, at higher temperature gives a product with high solubility. If the goal is to obtain a gel with high water retention capacity, it is indicated using pH below or close to the pI or elevated temperatures. To improve the emulsifying capacity the use of pH below the pI is the most suitable / Mestrado / Engenharia de Alimentos / Mestre em Engenharia de Alimentos

Les produits laitiers d’aujourd’hui contiennent souvent des polysaccharides qui permettent de les texturer et de les stabiliser. La compréhension et le contrôle de ces mélanges sont essentiels pour la fabrication et le développement de nouveaux produits. Le carraghénane est un polysaccharide sulfaté provenant des algues. Il existe principalement trois types de carraghénanes : le λ-carraghénane, le κ-carraghénane (KC) et l’ τ-carraghénane (IC). Les deux derniers sont ceux utilisés pour notre étude. Le KC et l’IC présentent une transition pelote-hélice en dessous d’une température critique qui dépend du type et de la concentration de cations. Dans la conformation hélice, les chaînes peuvent s’agréger, puis gélifier. La caséine est la protéine majoritaire du lait. Dans le lait, elle est présente sous forme d’un complexe stabilisé par le phosphate de calcium colloïdal (CCP). Le caséinate de sodium (SC) est obtenu à partir de la caséine native en enlevant le CCP par acidification, puis par addition de soude. Dans l’eau, les particules de SC ont un rayon de 11nm et sont constituées d’environ 15 molécules de caséines. Les mêmes particules peuvent être formées par chélation du CCP par le triphosphate de sodium. Elles sont alors appelées submicelles de caséines. Le projet de cette thèse vise à approfondir les connaissances sur la nature des interactions dans les systèmes mixtes caséinates/carraghénane. Ce mélange est un modèle pour certains produits laitiers. Les principaux résultats de cette étude sont les suivants : Etude des mélanges de SC et de KC sous forme pelote. Nous avons établi un diagramme de phase à l’aide de la microscopie confocale à balayage laser (MCBL), de la spectroscopie UV et de la rhéologie. Deux domaines ont été définis : un domaine biphasique aux fortes concentrations de SC où la séparation de phase est ségrégative et un domaine monophasique aux faibles concentrations des deux composés. Dans les mélanges monophasiques ou biphasiques, nous avons observé des agrégats riches en protéines qui sont irréversibles. Ces agrégats contiennent très peu de carraghénane et ont un impact sur la viscosité du mélange. La teneur en protéine dans ces agrégats augmente linéairement avec l’augmentation de la concentration de KC mais est indépendante de la concentration de SC. Cette fraction est également influencée par le pH et la force ionique. Gélification des mélanges monophasiques de SC et de KC. Les caséines n’influencent pas la température critique de gélification, mais augmentent la température critique de fonte ainsi que le module du gel. Nous avons montré que le système forme un gel mixte. Ce gel mixte contient deux types de liaisons : des liaisons entre SC-KC et des liaisons entre KC-KC purs. La compétition entre ces deux types d’interactions dépend de la force ionique et de la nature du sel. Etude comparative des SC et des submicelles de caséines. On n’observe aucune différence entre les deux systèmes, à part la diminution de la température critique de gélification due au triphosphate de sodium. Etude comparative de KC et d’IC en présence de SC. La séparation de phase ségrégative des mélanges d’IC est déplacée vers les hautes concentrations de SC. Le pourcentage d’agrégats dans le mélange est négligeable. On observe également la présence d’un gel mixte, mais de module plus faible. En conclusion, cette thèse a permis de mieux comprendre le comportement complexe des carraghénanes dans les suspensions de caséines, ce qui devrait permettre le développement plus rationnel de certains produits laitiers. / The carrageenan is a sulphated polysaccharide extracted from red algae. In a acqueous solution carrageenan change its conformation when we cool from a coil to a helix, this coil-helix transition is thermoreversible. In generally, Helical carrageenan aggregates and can form a gel. Rheology shows that carrageenan forms gel during cooling at a critical gelation temperature Tc and that upon heating, the gel melts at a critical melting temperature Th. These critical temperatures depend on the nature and the concentration of kations that are present in the solution, but not on the carrageenan concentration. The shear modulus depends both on nature and concentration of salt and on the carrageenan concentration. Casein is the major milk protein component and consist of 4 kinds of casein molecules: alpha s1, alpha s2, beta and kappa casein. In milk, the caseins form a large complex with a size of about 200nm. This complex is stabilized by colloidal calcium phosphate. SC (sodium caséinate) can be prepare by precipitation of casein micelles at pH 4, washing the precipitate to remove the colloidal calcium phosphate and returning to pH 7 by adding NaOH. The SC is present in water in the form of small particles with a radius of about 11 nm that contain approximately 15 casein molecules. The objective of this work is to study the structure and mechanical properties of SC/carrageenan (kappa carrageenan (KC) and iota carrageenan (IC)) mixtures and to better understand the nature of the interaction between them. mixtures of KC and SC show a segregative phase separation at high concentrations of either. Cluster containing mostly SC and little KC are formed by association between KC and SC. With time, the clusters flocculate and precipitate, but they can be redisperse in solution by heating and shaking. The fraction of protein in the clusters depends on the pH, the ionic strength and the KC concentration, but very little on the protein concentration. During cooling, SC associates with helical KC and forms a mixed network. These mixed gels have two types of crosslinks: links between protein free KC chain sections and links involving of proteins. The break up of these two types of bonds can be seen during the melting process depending on the relative amounts of SC and KC. The gel strength depends on the KC and SC concentration and also the type and the concentration of salt. Mixtures of τ-carrageenan (IC) and sodium caseinate (SC) were investigated and the results are compared with a similar study of mixture of κ-carrageenan (KC) and SC. Segregative phase separation was observed at high biopolymer concentrations and the binodal was determined. At low IC concentrations SC formed aggregates involving a very small amount of IC that were characterized with light scattering. The influence of adding SC on the gelation of IC during cooling and the shear modulus of the gels, was studied in the presence of NaCl or KCl. The main conclusion of this work is that SC binds to both IC and KC, in the coil conformation as well as in the helix conformation, but that its effect on the rheology is much weaker for IC than for KC.

Master of Science / Department of Physics / Christopher M. Sorensen / We investigated the effect of shear on the structure and aggregation kinetics of unstable colloids using small angle light scattering. We used an aqueous suspension of 20 nm polystyrene latex microspheres and MgCl2 to induce aggregation. The sample was only sheared once for approximately 33 seconds at different times, typically 1 min., 5 min., or 15 min., after the onset of aggregation. The average shear rate was in the range of 0.13 - 3.56 s-1, which was in a laminar regime. The unsheared sample gelled after ca. 45 min. When the sample was sheared soon after the onset of aggregation, the aggregation followed DLCA kinetics to yield = 1.80 ± 0.04 aggregates unaffected by the shear. The gel time also remained the same as the unsheared gel. Shearing at later stages of aggregation shortened the gel time and enhanced the scattered light intensity significantly indicating rapid growth. Then, depending on the shear rate, there were three different behaviors. At high shear rates, the aggregate structure was inhomogeneous after the shear was stopped with a crossover in slope in the scattered light intensity vs. q, to imply hybrid superaggregates with two different fractal dimensions. At intermediate shear rates far from the gel point, there was a similar crossover after the shear was stopped; however, the fractal dimension regained 1.80 ± 0.04 at the gel point. At low shear rates, the aggregation rate was increased, but the aggregate structure was uniform, and the fractal dimension remained 1.75 ± 0.05.

Doctor of Philosophy / Department of Physics / Christopher M. Sorensen / We investigated the effect of shear on the structure and aggregation kinetics of unstable colloids using small angle light scattering. We used an aqueous suspension of 20 nm polystyrene latex microspheres and MgCl[subscript]2 to induce aggregation. The sample was only sheared once for approximately 33 sec at different times, typically 1 min, 5 min, or 15 min, after the onset of aggregation. The average shear rate was in the range of 0.13 - 3.56 sec[superscript]−1 , which was in a laminar regime. The unsheared sample gelled after ca. 45 min. When the sample was sheared soon after the onset of aggregation, the aggregation followed the diffusion limited cluster cluster aggregation (DLCA) kinetics to yield D[subscript f] = 1.80 [plus or minus] 0.04 aggregates unaffected by the shear. The gel time also remained the same as the unsheared gel. Shearing at later stages of aggregation shortened the gel time and enhanced the scattered light intensity significantly indicating rapid growth. Then, depending on the shear rate, there were three different behaviors. At high shear rates, the aggregate structure was inhomogeneous after the shear was stopped with a crossover in slope in the scattered light intensity versus q, to imply hybrid superaggregates with two different fractal dimensions. At intermediate shear rates far from the gel point, there was a similar crossover after the shear was stopped; however, the fractal dimension regained 1.80 [plus or minus] 0.04 at the gel point. At low shear rates, the aggregation rate was increased, but the aggregate structure was uniform, and the fractal dimension remained 1.75 [plus or minus] 0.05.

Doctor of Philosophy / Department of Physics / Christopher M. Sorensen / We demonstrated that an aerosol can gel. This gelation was then used for a one-step method to produce an ultralow density porous carbon or silica material. This material was named an aerosol gel because it was made via gelation of particles in the aerosol phase. The carbon and silica aerosol gels had high specific surface area (200 – 350 sq m/g for carbon and 300 – 500 sq m/g for silica) and an extremely low density (2.5 – 6.0 mg/cm[superscript3]), properties similar to conventional aerogels. Key aspects to form a gel from an aerosol are large volume fraction, ca. 10[superscript-4] or greater, and small primary particle size, 50 nm or smaller, so that the gel time is fast compared to other characteristic times. Next we report the results of a study of the cluster morphology and kinetics of a dense aggregating aerosol system using the small angle light scattering technique. The soot particles started as individual monomers, ca. 38 nm radius, grew to bigger clusters with time and finally stopped evolving after spanning a network across the whole system volume. This spanning is aerosol gelation. The gelled system showed a hybrid morphology with a lower fractal dimension at length scales of a micron or smaller and a higher fractal dimension at length scales greater than a micron. The study of the kinetics of the aggregating system showed that when the system gelled, the aggregation kernel homogeneity attained a value 0.4 or higher. The magnitude of the aggregation kernel showed an increase with increasing volume fraction. We also used image analysis technique to study the cluster morphology. From the digitized pictures of soot clusters the cluster morphology was determined by two different methods: structure factor and perimeter analysis. We find a hybrid, superaggregate morphology characterized by a fractal dimension of D[subscript f] nearly equal to 1.8 between the monomer size, ca. 50 nm, and 1 micron and D[subscript f] nearly equal to 2.6 at larger length scales up to [similar to] 10 micron. The superaggregate morphology is a consequence of late stage aggregation in a cluster dense regime near a gel point.

In this project we aim to produce a thermally triggered PLGA particulate gel, which is injectable and biocompatible. This will act as a scaffold for soft tissue repair. Three coating polymers were tested: Pluronics (PEG-PPG-PEG), poly(PPGMA-co-PEGMA) and poly(PNIPAm-DMA+). These were first tested as a dilute solution for clouding behaviour and then added to PLGA nanoparticles dispersions and tested rheologically for gel behaviour. These three polymers were chosen for their amphiphilic nature which may allow for surface attachment and decreasing miscibility with temperature. The PLGA copolymer in this work contained 75% lactic acid and 25% glycolic acid, and was made into a nanoparticle dispersion by interfacial deposition. The Pluronic L62 showed a promising cloud point temperature (Tclpt) of 37 °C, but did not show gel behaviour with the PLGA dispersions. It conferred thermally triggered aggregation, which may be useful as a drug delivery system. The poly(PPGMA-PEGMA) was synthesised using a free radical polymerisation feed method. These copolymers showed promising Tclpt values (20-37 °C) but only showed increased viscosity when heated at high concentration and when mixed with a PLGA dispersion. The structure-property relationships for these copolymers were analysed. Poly(NIPAM-DMA+) showed gelation at low concentrations without the particles, when the particle dispersion was added the gel maintained its strength up to 300% strain. This is unlike most particulate gels which tend to be brittle. Using cell culture the biocompatibility of these gels was tested. After 72 hours the cells appeared healthy and to be proliferating.

Le travail de thèse présenté dans ce manuscrit a pour objectif de mettre en place un nouveau procédé d’élaboration de membranes à base de chitosane pour le traitement d’effluents acides contenants des ions métallique. Soluble en milieu aqueux acide, le chitosane présente la propriété de gélifier lorsque le pH devient basique, ce qui permet d’envisager l’élaboration de membrane sans solvant organique contrairement aux polymères synthétiques classiques. Par ailleurs, ce travail de thèse s’est intéressé à un procédé original de gélification par voie enzymatique, dans lequel la gélification in-situ de la solution de chitosane permet une structuration contrôlée de la membrane contrairement aux procédés classiques qui donnent lieu à un front de gélification. Une étude des cinétiques de gélification en fonction des paramètres d’élaboration (température et concentration en urée) a mis en évidence que seule la température est significativement influente sur le temps de gélification dès lors que la concentration en urée n’est pas limitante. Un modèle a été mis en place pour décrire la gélification enzymatique du chitosane afin de comprendre les mécanismes des cinétiques réactionnelles et de transferts lors de la formation du gel. Des membranes de chitosane ont ainsi été élaborées par le procédé par voie enzymatique, la porosité de ces membranes ayant été générée avec un agent porogène (PEG 6000) et une réaction d’acétylation du chitosane ayant permis d’obtenir des membranes insolubles en milieu acide. Les membranes obtenues ont été caractérisées en termes de morphologie et de propriétés fonctionnelles (filtration, sorption du Cu(II) comme élément métallique modèle). / The Ph-D work presented in this manuscript aims to develop a new process for elaborate chitosan membranes for treatment of acidic media containing metal ions. Soluble In acidic aqueous media, gelation occurs when the pH becomes basic, allowing elaboration of membrane without the use of organic solvents unlike classical synthetic polymers. Moreover, this Ph-D work has focused on an original process enzymatic gelation which the in-situ gelation of chitosan solution allows a controlled structuration of the membrane unlike conventional processes which leads to a front gelling.A study of gelation time as a function of the elaboration parameters (temperature and urea concentration) highlighted that only the temperature is a main parameter on gelation time since the urea concentration is not limiting. A model was developed to describe the chitosan enzymatic gelation in order to understand mechanisms of reaction kinetics and transfers during the gel formation.Chitosan membranes have been prepared by enzymatic process, the porosity of such membranes have been generated with a blowing agent (PEG 6000) and an acetylation of chitosan having yielded insoluble membranes in acid medium. The resulting membranes were characterized by their morphology and functional properties (filtration, sorption of Cu (II) as model metal element).

The purpose of this research was to relate lactose reactivity and age gelation of UHT processed concentrated milk. Skim milk was pasteurized, diafiltered batchwise to reduce lactose concentration to less than 0.05%, and UF concentrated to 3X (one-third volume reduction). Lactose and sucrose were then each added at 3% or 6% w/v to part of the concentrate. The five samples, control ( < 0.05% lactose), 3% w/v lactose, 6% w/v lactose, 3% w/v sucrose, and 6% w/v sucrose, were UHT processed at 140°C for 4 s using the indirect heating method. Samples were collected aseptically in presterilized plastic containers and stored at 4°C, 20°C, and 35°C for periodic analysis. All samples stored at 4°C and 20°C gelled after 21 weeks of storage. The viscosity changed slightly during the first 19 weeks of storage but increased suddenly (> 100 cPs) just before gelation. Samples stored at 35°C did not gel but showed sedimentation. Samples stored at 4°C or 20°C underwent little browning; but samples containing 3% and 6% lactose, stored at 35°C, browned considerably. The SOS-PAGE patterns of gelled samples showed new bands because of proteolysis whereas samples stored at 35°C showed bands due to proteolysis and protein crosslinking and a streaking pattern. Electron micrographs of gelled samples showed various casein particles connected together by hairy appendages protruding from the surface of casein particles, to form a continuous three-dimensional network. In non-gelled samples, the micelles were not joined into a continuous network and few hairy appendages protruded from their surfaces. Hairy appendages were not a result of Maillard reaction occurring during storage. Maillard reaction neither provided protection against nor promoted age gelation. Proteolysis was not the only cause for gelation. Protein modifications prevented gelation in samples stored at 35°C. Age gelation was probably a two-step process involving dissociation of proteins from the casein micelles that reformed onto the micelle surface as hairy appendages. Aggregation of the protein particles occurred through these appendages rather than through the original micelle surface.

No description available.

This dissertation aims to both deepen and broaden our understanding of copolymers with pendent benzophenone (BP) in relation to both established applications and novel directions in materials science. Photo-reaction of these BP copolymers is explored in attempts to achieve three distinct goals: (1) robust and efficiently photo-crosslinkable solid polymer films, (2) photo-reacted polymer blends with disordered bicontinuous nanostructures, and (3) photo-patterned hydrogel materials with environmental UV stability. We begin by investigating the fundamental gelation behavior of solid polymer films, finding BP copolymers to be particularly effective crosslinkable materials. Gelation efficiency can be tuned according to comonomer chemistry, as BP hydrogen abstraction on the main polymer chain increases chain scission, reducing crosslinking efficiency. This knowledge is then applied in Chapter 3, wherein we discuss two potential methods for preparing nanostructured polymer blends from these copolymers, namely spinodal decomposition of a photo-crosslinked polymer blend and solution-state photografting to create interfacially active species. While each technique shows promise, the ultimate goal of a disordered bicontinuous morphology will require further tuning of materials systems and protocols. Finally, chemical deactivation of BP photo-crosslinker in copolymers for use as photo-patternable and environmentally stable hydrogel materials is investigated. Reduction of BP by sodium borohydride proves a feasible route toward deactivating residual photo-crosslinker in patterned hydrogel films. These results confirm the utility of copolymers with pendent benzophenone photo-crosslinkers as useful tools for complex material systems.