Made available in DSpace on 2015-04-17T14:49:25Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 4903475 bytes, checksum: de295b0d0669974bfd97c402fd3bbeee (MD5) Previous issue date: 2013-05-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Edible oils are important sources of energy, fat soluble vitamins and essential fatty acids. However, their unsaturated fatty acids nature makes them highly susceptible to oxidative processes, making necessary the use of antioxidant additives. Synthetic antioxidants are widely employed by the industry, although there are several restrictions due to their adverse effects on human health. For this reason, this study investigated the antioxidant potential of 24 plant extracts: saffron (Crocus sativus L), rosemary (Rosmarinus officinalis), boldo (Peumus boldus Molina), white tea (Camellia sinensis (L.) Kutntze), mate tea (Ilex paraguariensis St. Hilaire), black tea (Camellia sinensis (L.) Kutntze), green tea (Camellia sinensis (L.) Kutntze), chamomile (Matricaria recutita L.), cinnamom (Cinnamomum zeylanicum), carqueja (Baccharis trimera (Less.) DC), lemon balm (Cymbopogom citratus), coriander (Coriandrum sativum L.), clove (Syzygium aromaticum), fennel (Foeniculum vulgare (Mill.) Gaertn), marjoram (Origanum majorana L.), basil (Ocimum basilicum), oregano (Origanum vulgare L. ssp Virens), senna (Cassia angustifólia), barbatimão (Stryphnodendron barbatimam Mart.), chapéu-de-couro (Echinodorus grandiflorus Mitch.), juca (Caesalpinia ferrea Mart. Ex Tul.), guarana (Paullinia cupana Kunth), pau d arco (Tabebuia serratifolia (Vahl) Nich.) and cat s claw (Uncaria tomentosa), by determining total phenolic content and antioxidant activity measured through the DPPH and FRAP assays. Thermogravimetric Analysis (TG), with both dynamic and isothermal (110 °C) analysis methods, was used to evaluate the thermal stability of the 24 plant extracts, as well as commercial antioxidants. Corn, soybean and sunflower oils, composed of unsaturated fatty acids, are widely used in Brazilian cuisine. Thus, antioxidant action of the extracts (rosemary, chamomile, coriander, fennel and senna) was also investigated by controlling the oxidative stability of edible vegetable oils when added to these, through the accelerated Rancimat methods, PetroOXY, PDSC and oven test. Clove extract showed the highest antioxidant capacity by FRAP assay and the best CFT. Extracts of juca and barbatimao, both from the Amazon Region, showed high TFC (133.63 ± 1.94 and 147.37 ± 1.99 mg GAE/g extract), confirming the excellent antioxidant capacity determined by the foregoing methods. The thermogravimetric profile of the extracts of cat's claw, saffron, rosemary, white tea and cinnamon stood out due to its good thermal resistance, indicating that may be used as antioxidant additives in formulations requiring heating. The rosemary extract applied to edible oils exhibited greater protective effect than other extracts tested, including the synthetic antioxidant BHT and TBHQ, when evaluated by the PDSC and PetroOXY methods. When the assessment was based on the Rancimat technique, its effect was similar to the one of BHT. Clove extract, although it is an excellent antioxidant, showed no thermal stability, with a mass loss of 81.4% in the first event (28.1 to 266.7 °C), due to the degradation of its main chemical constituent, eugenol. / Óleos comestíveis são fontes importantes de energia, vitaminas lipossolúveis e de ácidos graxos essenciais. Entretanto, a natureza insaturada dos seus ácidos graxos os torna altamente suscetíveis a processos oxidativos, tornando necessário o uso de aditivos antioxidantes. As indústrias de oleaginosas utilizam os de natureza sintética, todavia existem várias restrições quanto ao uso destas substâncias, devido aos efeitos nocivos atribuídos à saúde humana. Por estas razões, este trabalho investigou o potencial antioxidante de 24 extratos vegetais: açafrão (Crocus sativus L), alecrim (Rosmarinus officinalis), boldo-do-Chile (Peumus boldus Molina), chá branco (Camellia sinensis (L.) Kutntze), chá mate (Ilex paraguariensis St. Hilaire), chá preto (Camellia sinensis (L.) Kutntze), chá verde (Camellia sinensis (L.) Kutntze), camomila (Matricaria recutita L.), canela (Cinnamomum zeylanicum), carqueja (Baccharis trimera (Less.) DC), erva-cidreira (Cymbopogom citratus), coentro (Coriandrum sativum L.), cravo-da-Índia (Syzygium aromaticum), erva-doce (Foeniculum vulgare (Mill.) Gaertn), manjerona (Origanum majorana L.), manjericão (Ocimum basilicum), orégano (Origanum vulgare L. ssp Virens), sene (Cassia angustifólia), barbatimão (Stryphnodendron barbatimam Mart.), chapéu-de-couro (Echinodorus grandiflorus Mitch.), jucá (Caesalpinia ferrea Mart. Ex Tul.), guaraná (Paullinia cupana Kunth), pau d arco (Tabebuia serratifolia (Vahl) Nich.) e unha de gato (Uncaria tomentosa), através da determinação do conteúdo de fenólicos totais (CFT) (método Folin-Ciocateau) e da capacidade antioxidante aplicando os ensaios DPPH e FRAP. A análise Termogravimétrica (TG), pelos métodos dinâmicos e isotérmicos (110 °C) foi utilizada para avaliar a estabilidade térmica dos extratos vegetais e antioxidantes comerciais. Os óleos de milho, soja e girassol, constituídos de ácidos graxos insaturados, são muito utilizados na culinária brasileira. Assim, a ação antioxidante dos extratos (alecrim, camomila, coentro, erva-doce e sene) também foi investigada através do controle da estabilidade oxidativa de óleos vegetais comestíveis quando adicionados a estes, por meio dos métodos acelerados Rancimat, PetroOXY, PDSC e teste de estufa. O extrato de cravo exibiu o maior CFT e a melhor capacidade antioxidante pelo ensaio FRAP. Os extratos de jucá e barbatimão, oriundos da Região Amazônica, apresentaram altos CFT (133,63 ± 1,94 e 147,37 ± 1,99 mg EAG/g de extrato) confirmando a excelente capacidade antioxidante pelos métodos empregados. O perfil termogravimétrico mostrou que os extratos unha-de-gato, açafrão, alecrim, chá branco e canela destacaram-se por apresentar boa resistência térmica, indicando que podem ser utilizados como aditivos antioxidantes em formulações que necessitem de aquecimento. O extrato de alecrim aditivado nos óleos vegetais exibiu um efeito protetor superior aos demais extratos antioxidantes testados, inclusive aos sintéticos BHT e TBHQ quando avaliados pelos métodos PDSC e PetroOXY e efeito semelhante ao do BHT pela técnica Rancimat. O extrato de cravo, embora seja um excelente antioxidante, não apresentou estabilidade térmica, com perda de massa de 81,4% na primeira etapa (28,1 a 266,7 ºC), relativa à degradação do constituinte químico principal, o eugenol.

L'idée centrale de cette thèse est de comprendre la notion d'accélération dans les algorithmes d'approximation stochastique. Plus précisément, nous tentons de répondre à la question suivante : Comment l'accélération apparaît-elle naturellement dans les algorithmes d'approximation stochastique ? Nous adoptons une approche de systèmes dynamiques et proposons de nouvelles méthodes accélérées pour l'apprentissage par différence temporelle (TD) avec approximation de fonction linéaire : Polyak TD(0) et Nesterov TD(0). Contrairement aux travaux antérieurs, nos méthodes ne reposent pas sur une conception des méthodes de TD comme des méthodes de descente de gradient. Nous étudions l'interaction entre l'accélération, la stabilité et la convergence des méthodes accélérées proposées en temps continu. Pour établir la convergence du système dynamique sous-jacent, nous analysons les modèles en temps continu des méthodes d'approximation stochastique accélérées proposées en dérivant la loi de conservation dans un système de coordonnées dilaté. Nous montrons que le système dynamique sous-jacent des algorithmes proposés converge à un rythme accéléré. Ce cadre nous fournit également des recommandations pour le choix des paramètres d'amortissement afin d'obtenir ce comportement convergent. Enfin, nous discrétisons ces ODE convergentes en utilisant deux schémas de discrétisation différents, Euler explicite et Euler symplectique, et nous analysons leurs performances sur de petites tâches de prédiction linéaire. / The central idea of this thesis is to understand the notion of acceleration in stochastic approximation algorithms. Specifically, we attempt to answer the question: How does acceleration naturally show up in SA algorithms? We adopt a dynamical systems approach and propose new accelerated methods for temporal difference (TD) learning with linear function approximation: Polyak TD(0) and Nesterov TD(0). In contrast to earlier works, our methods do not rely on viewing TD methods as gradient descent methods. We study the interplay between acceleration, stability, and convergence of the proposed accelerated methods in continuous time. To establish the convergence of the underlying dynamical system, we analyze continuous-time models of the proposed accelerated stochastic approximation methods by deriving the conservation law in a dilated coordinate system. We show that the underlying dynamical system of our proposed algorithms converges at an accelerated rate. This framework also provides us recommendations for the choice of the damping parameters to obtain this convergent behavior. Finally, we discretize these convergent ODEs using two different discretization schemes, explicit Euler, and symplectic Euler, and analyze their performance on small, linear prediction tasks.