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Doctoral Thesis
DOI
https://doi.org/10.11606/T.3.2016.tde-07062016-151129
Document
Author
Full name
Arlet Patricia Franco Peñata
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2015
Supervisor
Committee
Gut, Jorge Andrey Wilhelms (President)
Augusto, Pedro Esteves Duarte
Laurindo, João Borges
Tadini, Carmen Cecilia
Velloso Junior, Walter Ferreira
Title in Portuguese
Estudo das propriedades dielétricas de água de coco verde e sucos de frutas cítricas relevantes para o aquecimento por micro-ondas.
Keywords in Portuguese
Água
Aquecimento dielétrico
Coco
Micro-ondas
Propriedades dielétricas
Suco de laranja
Abstract in Portuguese
O aquecimento por micro-ondas (MO) é uma tecnologia emergente para o processamento térmico contínuo de alimentos líquidos. A taxa d aquecimento e a profundidade de penetração das MO dependem das propriedades dielétricas (PD) do alimento (permissividade elétrica relativa e fator de perda dielétrica ). As PD de água de coco verde e de sucos de frutas cítricas (laranja, limão e tangerina) foram estudadas empregando a técnica de cabo coaxial. As medições foram realizadas em 101 frequências na faixa de 500 MHz até 3000 MHz e em temperaturas entre 0 °C e 90 °C, o que permitiu estudar o efeito da frequência e da temperatura. A profundidade de penetração foi calculada com uma expressão derivada das equações de Maxwell para eletromagnetismo. O trabalho experimental começou com as PD de: água de coco verde simulada, água destilada, solução de açúcares e sais da água de coco verde e água de coco verde natural. Resultados foram comparados para avaliar a contribuição de cada componente (água, açúcares e sais). PD de sucos de diferentes variedades de laranjas, tangerinas e limões, assim como misturas de sucos de duas variedades de laranja, foram também avaliadas. A condutividade elétrica das amostras foi medida nas diferentes temperaturas e o seu efeito sobre o fator de perda foi analisado. Os resultados foram comparados nas frequências comerciais de 915 MHz e 2450 MHz. O comportamento dielétrico das amostras estudadas foi caracterizado por dois mecanismos principais: a condução iônica de sais dissolvidos e a rotação dipolar da molécula de água, os quais têm predominância variável dependendo da frequência e da temperatura. A permissividade elétrica relativa de todas as amostras decresceu com o incremento da temperatura e da frequência, enquanto que o comportamento do fator de perda com a temperatura e frequência foi determinado pela composição. Os sais apresentaram maior efeito que os açúcares sobre as PD da água de coco verde. A profundidade de penetração foi maior na frequência de 915 MHz, associada com o aumento no comprimento de onda. Correlações polinomiais foram ajustadas nas frequências comerciais para representar a dependência com a temperatura.
Title in English
Study of dielectric properties of green coconut water and citrus fruits juices relevants to microwave heating.
Keywords in English
Dielectric properties. Microwaves. Green coconut water. Orange juice. Dielectric heating.
Abstract in English
Microwave (MW) heating is an emergent technology for thermal processing of liquid food products. Heating rate and MW penetration depth depending on dielectric properties (DP) of food material (relative electrical permittivity () and dielectric loss factor ()). DP for green coconut water (GCW) and citrus fruits juices (orange, tangerine and lemon) were studied by open-ended coaxial line probe technique. The measurements were carried out for frequencies between 500 MHz and 3000 MHz at 101 points in this range and temperatures from 0 °C to 90 °C, which allowed studying temperature and frequency effect. The power penetration depth was calculated using an expression derived from the Maxwell equations for electromagnetism. Experimental work started with DP measurement for: simulated (GCW), distilled water, sugars and salts solutions of (GCW) and natural (GCW). Results were compared in order to evaluate the each component contribution (water, sugars and salts). DP for juices from different orange, tangerine and lemon varieties as well as mixtures of orange juice from two varieties, were also evaluated. Electrical conductivity was measured and its effect on dielectric loss factor was analyzed. Obtained results were compared at commercial frequencies of 915 MHz and 2450 MHz. Dielectric behavior of studied samples was characterized by two main mechanisms: ionic conduction of dissolved salts and dipole rotation of water molecules, which presented variable predominance, depending on frequency and temperature. Relative electrical permittivity decreased with increase on both temperature and frequency for all tested samples, whereas dielectric loss factor behavior with temperature and frequency was determined by composition. Salts showed higher effect than sugars on dielectric properties of GCW. Penetration depth was higher at 915 MHz, associated to increasing wave length. Polynomial correlations for DP were adjusted at commercial frequencies in order to illustrate the temperature dependence.
 
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Publishing Date
2016-07-29
 
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  • FRANCO, A.P., et al. Efecto de la composición sobre las propiedades dieléctricas de solución simulada de agua de coco verde. In 9 Congreso Iberoamericano de Ingeniería de Alimentos, Valencia, 2014. Libro de Actas 9-CIBIA.Valencia : Universitat Politècnica de València, 2014. Disponible en Internet: http://ocs.editorial.upv.es/index.php/CIBIA/CIBIA9.
  • FRANCO, A.P., GUT, J.A.W., e TADINI, C.C. Effect of temperature on the dielectric properties of simulated green coconut water from 500 to 3000 MHz. In EFFOST Annual Meeting, Bologna, 2013. 2013 EFFoST Annual Meeting Abstracts., 2013. Resumo.
  • FRANCO, A.P., TADINI, C.C., and GUT, J.A.W. Dielectric properties of simulated green coconut water from 500 to 3,000 MHz at temperatures between 10 and 80 ºC. In AIChE Annual Meeting, San Francisco, 2013. AIChE 2013 Annual Meeting Conference Proceedings., 2013. Available from: http://www3.aiche.org/proceedings/Session.aspx?SessionID=24585.
  • FRANCO, A.P., TADINI, C.C., e GUT, J.A.W. Effect of composition and temperature on the dielectric properties of simulated green coconut water for field frequencies between 0.5 and 3.0 GHz. In 10º Simpósio Latino Americano de Ciência dos Alimentos, Campinas, 2013. 10º SLACA.Campinas : Unicamp, 2013. Resumo.
  • FRANCO, A.P., TADINI, C.C., e GUT, J.A.W. Estudo das propriedades dielétricas do suco de laranja relevantes para o processamento contínuo por micro-ondas. In XXIV Congresso Brasileiro de Ciência e Tecnologia de Alimentos, Aracaju, 2014. Anais do XXIV CBCTA.Aracaju : UFS, 2014. Resumo.
  • FRANCO, A. P.; TADINI, C. C.; GUT, J. A. W. Predicting the dielectric behavior of orange and other citrus fruit juices at 915 and 2450 MHz. International Journal of Food Properties, v. 20, n. 2, p. 1468-1488, 2017. DOI: https://doi.org/10.1080/10942912.2017.1347674
  • FRANCO, A. P.; YAMAMOTO, L. Y.; TADINI, C. C.; GUT, J. A. W. Dielectric properties of green coconut water relevant to microwave processing: Effect of temperature and field frequency. Journal of Food Engineering, v. 155, p. 69-78, 2015. DOI: http://dx.doi.org/10.1016/j.jfoodeng.2015.01.011
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