Development and characterization of edible and biodegradable nano-laminate coatings as vehicle of incorporation of functional and antimicrobial agents from Aloe vera, for extending shelf life of Lycopersicum esculentum Mill. (tomato)

Doctoral Dissertation for PhD degree in Chemical and Biological Engineering.During the last decades, there has been an increasing demand for fresh fruits and vegetables forcing the food industry to develop new and better methods for maintaining food quality and extending shelf life. Great losses (from 20% to 80%) in the quality of fresh fruits have been reported; such losses occur from harvesting to final consumption. In this context, edible coatings offer a beneficial impact on the produce quality (e.g. acting as a selective gas barrier and presenting an antimicrobial effect) and also to the environment, by means of reducing food waste. Currently, the utilization of nanotechnology represents a good tool to overcome problems regarding the application of edible coatings, such as high water vapour permeability and poor mechanical properties in comparison with synthetic materials. Some advantages when these coatings are at nanoscale are: higher stability at the substrate surface, facility of preparation and lower concentration of materials are required. Also, these systems can provide additional protection for the produce, and can incorporate antimicrobial, antifungal and antioxidant substances into their structure. Based in these ideas, the main purpose of this thesis was the development and characterization of nano-laminate coatings using bioactive components of Aloe vera for extending the shelf life of tomato fruit (Lycopersicum esculentum Mill.). Tomato was utilized here as model, being of course possible to apply these systems to other fruits. Aloe vera fractions (gel and liquid) evidenced both antifungal and antioxidant activities, representing a good alternative to extend the shelf life of tomato fruit. Therefore, polyelectrolyte solutions based on alginate and chitosan and their optimal concentrations were selected to build nano-laminate coatings; also, the effect of surfactant and plasticizer concentrations was determined. The best formulations were selected based on their wettability on tomato fruit surface. On the other hand, nano-laminate coatings with carvacrol (directly applied or encapsulated into zein) also showed (in vitro) their potential to be a good candidate to improve the shelf-life of foodstuffs due to the improved barrier properties and antifungal activity. Nano-laminate films functionalized with bioactive fractions of A. vera (gel and liquid fraction) have shown good barrier properties and evidenced in vitro antifungal activity. The system based on alginate/chitosan functionalized with A. vera liquid fraction was selected in order to evaluate its effectiveness in vivo. Tomatoes coated with this system exhibited a lower weight loss and microbial contamination was delayed (mainly in terms of yeasts and molds), together with a reduction in the gas transfer rate and ethylene production during cold (11 °C and 90% relative humidity, RH) and room temperature (20 °C and 85% RH) storage of tomato fruits. It should be noted that nano-laminate coating technology is transferable to other fruit models (both climacteric and non-climacteric), being an attractive postharvest tool for extending the quality and shelf life of fruits and vegetables.Durante as últimas décadas, verificou-se uma crescente procura de frutas e vegetais frescos, o que obrigou a indústria alimentar a desenvolver novos e melhores métodos para manter a qualidade dos alimentos e prolongar a sua de vida de prateleira. Elevadas perdas (de 20% a 80%) na qualidade de frutos frescos foram reportadas; tais perdas ocorrem desde a colheita até o seu consumo final. Neste contexto, os revestimentos comestíveis oferecem um impacto benéfico sobre a qualidade do produto (por exemplo, atuando como uma barreira seletiva a gases e apresentando efeito antimicrobiano) e também para o meio ambiente, através da redução do desperdício de alimentos. Atualmente, o uso da nanotecnologia representa uma boa ferramenta para superar os problemas relacionados com a aplicação de revestimentos comestíveis, tais como a elevada permeabilidade ao vapor de água e fracas propriedades mecânicas em comparação com materiais sintéticos. Algumas vantagens quando estes revestimentos são à escala manométrica são: maior estabilidade na superfície do substrato, facilidade de preparação e menor concentração de materiais necessários. Adicionalmente, estes sistemas podem oferecer uma proteção adicional para o produto, e podem incorporar substâncias antimicrobianas, antifúngicas e antioxidantes na sua estrutura. Com base nestas ideias, o principal propósito desta tese foi o desenvolvimento e caracterização de revestimentos nano-laminados utilizando componentes bioativos de Aloe vera para prolongar a vida de prateleira do fruto de tomate (Lycopersicum esculentum Mill.). O tomate foi utilizado como modelo, sendo, naturalmente, possível aplicar estes sistemas a outros frutos. Ambas as frações de Aloe vera (gel e líquido) evidenciaram atividades antifúngicas e antioxidantes, o que representa uma boa alternativa para prolongar a vida de prateleira do fruto de tomate. Deste modo, soluções de polieletrólitos baseadas em alginato e quitosano e as suas concentrações ótimas foram selecionadas para construir revestimentos nano-laminados; além disso, determinou-se o efeito das concentrações de surfactante e plasticizante. As melhores formulações foram selecionadas com base na sua capacidade molhante da superfície do fruto de tomate. Por outro lado, os revestimentos nano-laminados com carvacrol (aplicado diretamente ou encapsulado em zeína) também demonstraram (in vitro) o seu potencial para serem bons candidatos para melhorar a vida de prateleira dos produtos alimentares devido às propriedades de barreira melhoradas e à atividade antifúngica. Os filmes nano-laminados funcionalizados com frações bioativas de A. vera (frações gel e líquida) demonstraram boas propriedades de barreira e evidenciaram atividade antifúngica in vitro. Selecionou-se o sistema baseado em alginato/quitosano funcionalizado com fração líquida de A. vera com a finalidade de avaliar a sua eficácia in vivo. Tomates revestidos com este sistema registaram a menor perda de peso e a contaminação microbiana foi retardada (principalmente em termos de leveduras e bolores), juntamente com uma redução da taxa de transferência de gás e produção de etileno durante armazenamento sob refrigeração (11 °C e 90% de humidade relativa, HR) e a temperatura ambiente (20 °C e 85% HR) de frutos de tomate. Finalmente, é importante referir que a tecnologia de revestimentos nano-laminados é transferível para outros frutos (climatéricos e não climatéricos), sendo uma ferramenta de pós-colheira atrativa para prolongar a qualidade e vida de prateleira de frutos e vegetais

Overdamped van Hove function of atomic liquids

Using the generalized Langevin equation formalism and the process of contraction of the description we derive a general memory function equation for the thermal fluctuations of the local density of a simple atomic liquid. From the analysis of the long-time limit of this equation, a striking equivalence is suggested between the long-time dynamics of the atomic liquid and the dynamics of the corresponding \emph{Brownian} liquid. This dynamic equivalence is confirmed here by comparing molecular and Brownian dynamics simulations of the self-intermediate scattering function and the long-time self-diffusion coefficient for the hard-sphere liquid.Comment: 4 Figures, 23 page

Radiative two-pion decay of the tau lepton

We consider the bremsstrahlung and model-dependent contributions to the radiative decay $\tau^- \to \pi^-\pi^0\nu_{\tau}\gamma$ in the context of a meson dominance model. We focus on several observables related to this decay, including the branching ratio and the photon and di-pion spectra. Particular attention is paid to the sensitivity of different observables upon the effects of model-dependent contributions and of the magnetic dipole moment of the $\rho^-(770)$ vector meson. Important numerical differences are found with respect to results obtained in the framework of chiral perturbation theory.Comment: 14 pages, 8 figures, submitted for publicatio

Validation of the 3-under-2 principle of cell wall growth in Gram-positive bacteria by simulation of a simple coarse-grained model

The aim of this work is to propose a first coarse-grained model of Bacillus subtilis cell wall, handling explicitly the existence of multiple layers of peptidoglycans. In this first work, we aim at the validation of the recently proposed "three under two" principle.Comment: Revised introduction, results unchange

Final-state, Open-loop Control of the Heat equation in Tensorial Domains (full version)

In this paper, a quadratic optimal control problem will be considered for the heat equation in tensorial domains with homogeneous Dirichlet boundary conditions, in which the control function (depending only on time) constitutes a source term. These problems involve choosing a control function (with or without "peak-value" constraints) to approximately steer the solution of the heat equation to a desired function at the end of a prescribed (finite) time-interval. To compute approximations to the desired optimal control functions, semi-discrete, spectral (with eigenfunctions) Galerkin approximations to the corresponding heat equation and the corresponding (approximating) control problems are tackled. Two simple, illustrative examples are presented in the final section.Comment: 32 pages, 11 figures, submitte

Comportamiento Biológico de Implantes Tendinosos Autógenos Intraarticulares. Interfase con los distintos medios receptores

En el presente trabajo se ha efectuado un estudio experimental de la respuesta biológica de implantes intraarticulares de tendones autógenos insertados en canales óseos. Se ha seguido, mediante microscopía óptica y electrónica, la revascularización de los implantes, los cambios tendinosos intrínsecos y, fundamentalmente, la interfase establecida entre la estructura tendinosa y los distintos medios del lecho receptor. En las zonas bañadas por líquido sinovial se produce "sinovialización", con presencia de sinoviocitos A (aspecto macrofágico) y B (aspecto fibroblástico). En las zonas que delimitan con cartílago aparece una hendidura, cuya superficie tendinosa es también sinovializada. En la interfase hueso-tendón se pueden diferenciar zonas de aposición lateral y termino-terminales. Las primeras muestran fenómenos de remodelación (presencia de abundantes osteoblastos y osteoclastos) y dispositivos arciformes de las fibras colágenas que "anclan" el tendón a trabéculas óseas. En las zonas término-terminales se establece continuidad entre la colágena del tendón y del hueso. En las regiones en que el tendón se relaciona con el tejido adiposo de la médula ósea, se produce también continuidad entre fibras colágenas pertenecientes a ambos componentes.The authors presented an experimental work in rabbits. They rewiewed the revascularization an morfology ("Sinovialization" and "Ligamentation") of tendon autograft used to replace the anterior cruciate ligament (18 rabbits studied) by histological techniques

Estudio experimental de la Microangiografía del Tronco Ciático de la rata en situaciones de normalidad: compresión y descompresión

Se hace un estudio en 20 ratas sometidas a compresión del nervio ciático según variante de la técnica de WEISL y OSBORNE, y compresión-descompresión a tiempos variables y se estudia la microcirculación del mismo en estas situaciones, comparativamente con el nervio normal. Entre los cambios del patrón vascular en la compresión nerviosa, resalta la intensa vascularización de las zonas inmediatamente proximales y distales al a compresión, contrastando con la escasez de vasos en el área selectivamente comprimida. Después de la descompresión se apreció una recuperación paulatina del patrón vascular, sin que se llegase a alcanzar una cuantificación de vasos similar a la de las zonas adyacentes.A study in 20 rats with nerve sciatic compression (WEISL and OSBORNE method), and compression descompresión in diferent time s wa s made. The authors studied the sciatic nerve microcirculation in this situations in front of the normal nerve. They saw an intensive vascularization immediately after and before the place of the compression, and a vessels scarcity in the compression area. After the descompresion it saw a normal and slowly recuperation of the vascular role, but never so many vessels as in the proximal zones

Características Histológicas del Menisco de la rodilla durante el Desarrollo Intrauterino de la rata

Con el objetivo de profundizar en el conocimiento del desarrollo embriológico del esbozo meniscal de la rodilla, los autores realizan un estudio en embriones de rata de 16 y 20 días de gestación. Se comprueba como este esbozo meniscal, que en su inicio esta formado por una masa de células mesenquinales, adopta una configuración triangular al corte frontal, situada entre las dos superficies articulares. Posteriormente su vértice experimenta diferenciación cartilaginosa (futuro menisco), mientras que la región periférica sigue siendo altamente vascular y se continúa con tejido conjuntivo fibroso (zona parameniscal).An study in embryos of rat betwen 16-20 days of pregnancy was made to show the meniscus development. The meniscus sketch in the first time was made by mesenchyme cells, later takes a triangular configution. An at past his vertex became to be a cartilage (future meniscus), while the peripheral placer is highly vascular and is followed by a fibrous connective tissue (parameniscal zone)

Estudio histológico de la respuesta reparativa tras extirpación del menisco y parcial del Paramenisco: estudio experimental

Los autores efectúan un estudio en la rat a utilizando un modelo experimental de meniscectomía completa y extirpación parcial del paramenisco, comprobándose como se origina un proceso de regeneración que conduce a la formación de una nueva estructura, de aspecto meniscal, de menor tamaño que el primitivo menisco y formado por tejido fibroso con focos condroides.An experimental study was made in the rat with total meniscus extirpation. This study show a regeneration process that take us to a new structure formation like meniscus, with fibrous tissue formation with condroid points

Regeneración del Tronco Nervioso Periférico: estudio experimental

Los autores realizan un estudio en 24 ratas sometidas a axonectomía parcial subepineural o axonectomía y vaciamiento troncular, con objeto de valorar el comportamiento de los distintos elementos celulares del nervio durante la regeneración nerviosa. Durante el tiempo del experimento las células perineurales se conservan alrededor de un espacio virtual, lo que se interpreta como que intervienen como aislante, aún en condiciones de ausencia de fibras nerviosas, impidiendo la entrada de estructuras vasculares neoformadas y la cicatrización intraperineural. Por todo ello se postula que el papel de "guía" para el crecimiento de los axones regenerativos, atribuido fundamentalmente a las células de SCHWANN, debe ser revisado, en el sentido de dar un mayor protagonismo a las células perineurales.A study of 24 rats with partial subepineural axonectomy or axonectomy with trunckular casting was made in order to value the role of the diferent cellular elements of the nerve during his regeneration. In the experiment the perineural cells persist around a virtual space. This mean that the cells works like an insulate, also in absence of nerve fibres, impeding the neoformed vessels entrance and the perineural cicatrizacion. The role of the SCHWANN cells is cuestioned in front of the perineural cells importance