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[EN] Hot air drying is an energy intensive process and can affect bioactive components. A common method of food drying is in a fixed bed. The application of high-intensity ultrasound could constitute a way of improving traditional convective drying systems. Therefore, the main aim of this work was to assess the influence of high-intensity ultrasound on transfer phenomena during the convective drying in a high-void bed of non-porous materials, like thyme leaves. For this purpose, drying kinetics of thyme leaves were carried out at 1, 2 and 3 m s(-1) air velocity at different air temperatures (40, 50, 60, 70, and 80 +/- 1.2 degrees C), and different levels of acoustic power density (0, 6.2, 12.3, 18.5 kW m(-3)). To address the effect of US on the drying kinetics, a mathematical model was developed considering time varying boundary conditions for heat and mass transfer between the air and the product. Due to the physical characteristic of the material, the influence of the ultrasound power density applied on the internal resistance to the mass transfer was significantly lower than its influence of the external resistance; therefore process intensification is mainly linked to external resistance. Nevertheless, the influence of the application of ultrasound on transport phenomena was only observed at air temperatures and air velocities below 70 degrees C and 3 m s(-1) respectively. (C) 2013 Elsevier Ltd. All rights reserved.

[EN] Thyme leaves are an important source of essential oils with antioxidant activity; these compounds are located in trichomes on the leaf surface. The drying conditions affect not only the drying time but also the antioxidant activity. In the literature, a drying temperature of 70 ºC appears to be the best for drying thyme leaves according to their antioxidant capacity. Considering drying periods at different temperature also could be quality beneficial. From these considerations, the goal of this work was to establish a drying strategy with which to manage a drying temperature on the leaf surface which will enable the drying time to be shortened and improve the antioxidant capacity (AC) of the extract of dried thyme leaves. The drying strategy consisted of two consecutive drying periods in order to manage the drying temperature on the leaf surface. The first drying period was carried out at 80°C (Ta1) until the sample surface reached a temperature of 70 ºC, which then immediately being set to 70, 60, 50 and 40 °C (second drying period (Ta2)), at a different air velocity (v) (1 and 2 m s-1). Compared with constant drying conditions, two consecutive drying periods were found to improve the drying kinetics, the AC increased from 10.5% to 27.4 % while reducing the drying time by 14.5% to 39.2 %. The use of this drying strategy was found to be an interesting means of intensifying the convective drying of thyme leaves and its application should be considered when drying similar materials with bioactive compounds on the surface.

[EN] The drying kinetics of thyme was analyzed by considering different conditions: air temperature of between 40 C and 70 C, and air velocity of 1 m/s. A theoretical diffusion model and eight different empirical models were fitted to the experimental data. From the theoretical model application, the effective diffusivity per unit area of the thyme was estimated (between 3.68 10 5 and 2.12 10 4 s 1). The temperature dependence of the effective diffusivity was described by the Arrhenius relationship with activation energy of 49.42 kJ/mol. Eight different empirical models were fitted to the experimental data. Additionally, the dependence of the parameters of each model on the drying temperature was determined, obtaining equations that allow estimating the evolution of the moisture content at any temperature in the established range. Furthermore, artificial neural networks were developed and compared with the theoretical and empirical models using the percentage of the relative errors and the explained variance. The artificial neural networks were found to be more accurate predictors of moisture evolution with VAR 99.3% and ER 8.7%.

[EN] Food properties change during processing, altering the quality of the final product. Sometimes, the important causal relationships are not well known and thus process management is difficult. This is especially true when chemical changes can occur as in the case of the drying of bioactive materials. The aim of this work was to develop a management tool for the thyme drying process, assisted by power ultrasound, to allow the appropriate values of the operating conditions that maximize the antioxidant capacity (AC) of the dried thyme extracts to be determined. For this proposal, the thyme drying process was analyzed at different drying air temperatures (7) (40-80 degrees C), drying air velocities (v(a)) (1-3 m/s) and levels of power ultrasound (US) (0, 6.2, 12.3, 18.5 kW m(-3)). The essential oil was extracted by means of a supercritical fluid extraction method, and its AC was measured by FRAP. The drying velocity and the AC of the dried thyme extracts were both influenced by the magnitude of the air velocity and temperature, and also by power ultrasound. Artificial neural networks were developed to formulate and solve the optimization problem. The developed management tool allowed the optimal conditions of the process to be established, thereby maximizing the AC values in function of the raw materials, process characteristics and room air conditions. (C) 2013 Elsevier Ltd. All rights reserved.

[EN] The antioxidant properties of medicinal plants have been at the center of research for their use as preservatives or nutraceuticals by the food industry; additionally, to obtain quality products at a minimum cost and maximum yield, through optimal operating parameters, is a challenge for the food industry. The aims of this work was to effect operating conditions drying process on antioxidant capacity of the thyme and optimize the drying process creating a process management system to formulate and solve an optimization problem. The thyme drying process was analyzed under different drying air temperatures (T) (40-80 degrees C) and drying air velocity (V) (1-2 m/s). The essential oil was extracted by applying a super-critical fluid extraction method (35 degrees C, 35 x 10(3) kPa). To formulate and solve the optimization problem, artificial neural networks were developed. The optimum value of the optimization problem depend of the constraints established, shorting the drying time to research the final moisture content fixed. (C) 2013 Elsevier B.V. All rights reserved.

El secado por aire caliente es el método de conservación más utilizado en la transformación de productos agroalimentarios. Debido al alto contenido agua que contiene los productos de origen natural, el proceso de secado permite, eliminar parte del agua contenida (responsable en mayor parte de su perecibilidad) y poder alargar su vida útil para su posterior utilización. El secado por aire caliente, es también unas de las actividades industriales que generan mayor consumo energético y, por ende, un impacto ambiental considerable, al mismo tiempo que influye sobre importantes parámetros de calidad nutricional y organoléptica. Persiguiendo el objetivo de reducción del impacto medioambiental de los procesos y mejorar el efecto sobre los parámetros de calidad de los productos deshidratados, tanto la utilización de pre-tratamientos como de fuentes adicionales de energía constituyen alternativas interesantes para aumentar la velocidad del proceso sin incrementar la carga medioambiental del mismo. En este sentido, la introducción de nuevas tecnologías podría conducir a una reducción del tiempo de procesamiento o una mejora de las condiciones de operación. Algunas de las principales tecnologías aplicadas son las microondas, la radiofrecuencia, la radiación infrarroja, ultrasonidos de potencia y secado intermitente. La aplicación de ultrasonidos de alta intensidad en los procesos de secado se ha demostrado que puede acelerar la transferencia de masa en el proceso de secado, acortando el tiempo de caliento al que se ven sometidos los productos deshidratados. El secado intermitente es tecnología de secado que se fundamenta en la implementación y combinación de condiciones variables, tales como el suministro de calor y la velocidad del aire de secado. El objetivo es obtener una alta eficiencia energética sin someter al producto más allá de su admisible límite de temperatura y límite de tiempo para la eliminación de la humedad, lo que permite preservar la calidad del producto, al

El objetivo de este trabajo ha sido desarrollar una metodología para la obtención de películas de gliadinas mediante su procesado en caliente. Para ello, previamente se ha obtenido una resina de gliadinas plastificada con glicerol, a partir de la cual es posible obtener películas transparentes y homogéneas de bajo espesor. La temperatura de procesado tiene un gran efecto en las propiedades de las películas desarrolladas. De forma que el termoprocesado de gliadinas produce el entrecruzamiento de la red proteica mejorando su resistencia al agua y sus propiedades mecánicas. Sin embargo, las películas disminuyen en luminosidad y desarrollan un color amarillo parduzco. Temperaturas de procesado de 130 ºC permiten obtener películas resistentes al agua, de elevada transparencia, y con propiedades mecánicas mejoradas, además de una mayor resistencia a la permeación de vapor de agua en comparación con las películas obtenidas por la técnica de "casting", sin comprometer su apariencia. También se ha comprobado que el procesado a temperaturas superiores a 130 ºC no implica un incremento en la resistencia mecánica ni a la permeación de vapor de agua, ni un aumento en la resistencia al hinchamiento en agua de las películas, pero sí una alteración de su apariencia en cuanto a desarrollo de pardeamiento.

Para optimizar la aplicación de la tecnología de secado intermitente al secado convectivo de patata se desarrolló una herramienta de optimización del proceso, definida como la búsqueda de los tiempos de duración de cada periodo de calentamiento y reposo que minimizaran la ganancia entálpica del producto. Para poder cuantificar la ganancia entálpica se modelizó el proceso de secado. El problema de optimización y la identificación de los parámetros se resolvió con el desarrollo de algoritmos computacionales COMSOL Multiphysics 3.4 y Matlab R2007b. En la identificación de parámetros del modelo se empleó información experimental de la experiencias de secado continuo e intermitente que se realizaron en cilindros de patata a diferentes temperaturas de calentamiento (40, 50, y 60ºC) y diferentes velocidades (1 y 2 m s-1). A partir de los resultados se puede resaltar que en el secado intermitente el tiempo de calentamiento es menor que en el secado continuo. La aplicación de la herramienta de optimización desarrollada permitiría optimizar las condiciones de operación minimizando el tiempo de calentamiento y, por lo tanto, el consumo energético, y mejorando la calidad del producto final al disminuir su impacto térmico.