Browsing by Author "Cruz, Ana"
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- Convective drying of apples: kinetic study, evaluation of mass transfer properties and data analysis using artificial neural networksPublication . Guiné, Raquel; Cruz, Ana; Mendes, MateusIn the present work the effect of drying was evaluated on some chemical and physical properties of apples, and the functions were modelled using feed-forward artificial neural networks. The drying kinetics and the mass transfer properties were also studied. The results indicated that acidity and sugars were significantly reduced by drying. Regarding colour lightness decreases whereas redness and yellowness increased. As for texture, the dried samples were softer and less cohesive as compared to the fresh ones. Mass diffusivity increased with temperature, from 4.4x10-10 m2/s at 30 ºC to 1.4x10-9 m2/s at 60 ºC, and so did the mass transfer coefficient, increasing from 3.7x10-10 m/s at 30 ºC to 7.4x10-9 m/s at 60 ºC. As to the activation energy, it was found to be 34 kJ/mol. Neural network modelling showed that all properties can be correctly predicted by feed-forward neural networks. The analysis of the networks’ behaviours input layer weight values also show which properties are more affected by dehydration or more dependent on variety.
- Drying Kinetics and Product Quality for Convective Drying of Apples (cvs. Golden Delicious and Granny Smith).Publication . Cruz, Ana; Guiné, Raquel; Gonçalves, João CarlosOur work studied the convective drying of apples from two different cultivars, Golden Delicious and Granny Smith, in a range of temperatures from 30 to 60 ºC. Some chemical and physical properties were determined fresh and after drying: moisture, acidity and sugars contents, color and textural attributes, in order to evaluate the effect of drying and drying temperature on these properties. Furthermore the drying kinetics were studied in terms of thin layer models and also by means of the Fick’s equation of Diffusion, and some mass transfer properties were evaluated, such as effective moisture diffusivity and convective mass transfer coefficient. We concluded that drying decreased both acidity and sugar content for both apple cultivars. Color was significantly affected by drying, resulting in high values of the total color difference, between 19.43 and 25.04. Drying turned the products less hard and less cohesive. Furthermore, it was found that mass diffusivity increased with temperature following an Arrhenius type function, where Deo was 5.4621x10-4 and 1.8401x10-4 m2/s, and E was 35.3 kJ/mol and 32.8 kJ/mol, respectively for cultivars Golden and Granny Smith.
- Efeito da secagem sobre as propriedades de maçãs da variedade Golden.Publication . Cruz, Ana; Correia, Ana Cristina; Gonçalves, João C.; Guiné, RaquelA secagem de frutas é um método de preservação bem conhecido, principalmente porque a remoção de água e a baixa actividade da água reduzem o risco de desenvolvimento microbiano. Além disso, os frutos secados podem ser armazenados e transportados a um custo relativamente baixo. No entanto, a remoção de água usando altas temperaturas e longos tempos de secagem pode provocar reduções importantes no valor nutritivo e sensorial, prejudicando principalmente o sabor, a cor e os nutrientes dos produtos secos [1, 2]. A secagem de alimentos não só afecta o conteúdo em água do produto, como também altera outras propriedades físicas, químicas e biológicas, tais como a actividade enzimática, deterioração microbiana, textura, viscosidade, dureza, aroma, gosto e sabor dos alimentos [3]. Nesse sentido o presente trabalho teve por objectivo analisar as propriedades químicas das maças da variedade Golden Delicious que foram sujeitas a dois métodos de secagem, ambos por convecção de ar quente, em dois equipamentos distintos, estufa e secador, para as temperaturas de 30, 40, 50 e 60 ºC. As análises efectuadas envolveram a determinação da humidade, o teor em sólidos solúveis totais e a acidez titulável. A humidade foi determinada em balança de Halogénio (Mettler Toledo HG 53). A quantificação da acidez fez-se por titulação seguindo a norma NP-1421, e para a quantificação dos sólidos totais, que incluem os açúcares, usou-se leitura do ºBrix por refractometria (Refractómetro de bancada ATAGO - 3T). Para a preparação da amostra seguiu-se a NP-783. Foi ainda avaliada a cor com um colorímetro Minolta CR-400, nas coordenadas CIELAB. Dos resultados obtidos (Tabela 1), verificou-se que a secagem afectou ligeiramente a acidez e o teor de açúcares das maçãs. As amostras secadas no secador apresentam-se mais semelhantes entre si, independentemente da temperatura usada, e mostram que houve alguma degradação de açúcares, embora em pequena escala. No caso das maçãs secadas na estufa para a secagem a 60 ºC verifica-se uma menor razão entre os açúcares e a acidez, originando um produto potencialmente menos agradável ao paladar. Conclui-se, assim, que a secagem por convecção de ar quente pode ser usada para a obtenção de produtos na forma de fatias de maçã desidratada, escolhendo adequadamente as condições de secagem.
- Study and Analysis of a New Device for the Rehabilitation of the Tibiotarsal JointPublication . Cruz, Ana; Cunha, Beatriz; Pereira, Ana; Rodrigues, Maria; Seabra, Eurico Augusto; Silva, Luís; Colim, Ana; Viana, RuiIntroduction: Currently, there are several types of devices and techniques for the rehabilitation of the tibiotarsal joint. However, complete and effective rehabilitation still falls short of expectations, since the existing devices are not adaptable to the level of torque and the number of repetitions and sessions to be performed, as these depend on each patient and on the stage at which he is finds. Objetives: To improve a mechatronic device for the rehabilitation of the tibiotarsal joint, the Therapheet. Methods: This study presents a review of the tibiotarsal joint rehabilitation protocols, as well as the classification of devices used for this purpose. Thus, the purpose is to improve the Therapheet, developed at the Department of Mechanical Engineering of the University of Minho, obtaining a viable, functional and safe rehabilitation device, standing out from the rest on the market, since it allows the execution of the six rehabilitation exercises. Results: It was obtained a prototype of equipment for rehabilitation of the tibiotarsal joint was obtained, proposing changes for improvement according to the specificities and requirements for such a device, having been subjected to a series of preliminary tests to verify its functionality, performance and suitability. The equipment proved to be functional, in terms of executing the ankle rehabilitation movements, however, it still manifests some flaws in terms of the user's stability, sudden movements, and above all dysfunctions arising from excess mass that make up its structure and limitations pneumatic technology adopted. Conclusions: The control of the amplitude of the characteristic angles of the movements of the foot is still done manually, so it would be significant to implement an automated system that would allow the control of the range of amplitude, according to the patient's rehabilitation phase. One option would be the implementation of a new technology, such as the insertion of servomotors.