Carlos Alberto Márquez

VOLUME AND AREA SHRINKAGE OF WHOLE SOUR CHERRY FRUITS (PRUNUS CERASUS) DURING DEHYDRATION

ABSTRACT Whole sour cherry fruits were dehydrated in heated air at temperatures of 50, 55, 60, 65, 70 and 75°C, air velocities of 0.1, 1, 2, 3, 5 m/s, and air relative humidities of 5 and 50%. Volume changes were evaluated by picnometric techniques and with geometric measurements by micrometer and superficial area from geometric measurements. It was observed that, volume and area changes do not depend on dehydration operating variables. A linear relationship was found between the dimensionless volume change and the moisture content of the partially dehydrated fruits. The area depended on moisture according to a third degree polynomial.

Desorption isotherms for sweet and sour cherry

For sorptional data to be useful in simulation and design purposes, they must be represented by equations valid in a range similar than the used in the industrial practice. In this regard sorptional models accounting for the influence of temperature on equilibrium values or desorption isotherms are most valuable. In this work, water desorption isotherms were experimentally determined, by the gravimetric method, for fresh sweet and sour cherries (Xdb ¼ 3:54 and 3.39 respectively). According to the ANOVA test, no significant differences among experimental values of both fruits were found. Seven models were tested to mathematically represent the moisture content as a function of water activity (in the range of 0.11–0.85) and temperature (20, 40 and 60 C), for further use in process simulation. Those more accurate were the three-parameter GAB, the Iglesias & Chirife and the Ratti models. Any of the three models should be used to predict sorptional equilibrium values in the range tested, but the Ratti equation had the best statistical error. 2003 Elsevier Ltd. All rights reserved.

Equilibrium Sorption Isotherms and Isosteric Heat of Rose Hip Fruits (Rosa Eglanteria)

For sorptional data to be useful in simulation and design purposes, they must be represented by equations valid in the conditions usually found in industrial practice. In this regard sorptional models that include the influence of temperature on desorption and sorption equilibrium values are most valuable. In this article, water desorption and sorption isotherms of rose hip fruits (Rosa Eglanteria) were experimentally determined by the gravimetric method, and from these the isosteric heat of sorption was calculated. According to the ANOVA test carried out for this fruits, no significant differences were found between experimental desorption and adsorption isotherms. Seven models were tested to mathematically represent the moisture content as a function of water activity (aw) in the aw range of 0.11 to 0.85 and temperatures of 20, 40, and 60°C, for further use in process simulation. The five-parameter GAB model was most accurate, with an MRE of −2,9 % and R2 = 0.989. The values obtained for the isosteric heat of sorption were fitted with a previous published equation, with an MRE% = −0.05. The isosteric heat of sorption derived from the GAB five parameters equation, for the corresponding monolayer moisture content, only differed by 1.25% with the calculated in this paper.

Cambios de volumen, área superficial y factor de forma de Heywood durante la deshidratación de cerezas (Prunus avium)

En este trabajo, se evaluaron experimentalmente los cambios de volumen, area superficial y factores de forma durante la deshidratacion de cerezas enteras. En base a los resultados obtenidos, se propusieron modelos muy simples para la evaluacion matematica de dichos cambios para su uso en simulacion de lechos profundos de particulas. Los cambios de volumen se pudieron representar con una ecuacion lineal y los de area superficial con un polinomio de tercer orden, en ambos casos como una funcion de la humedad adimensional del producto. Con respecto a la evaluacion de los factores de forma, se encontro que las particulas, cuanto mas se deshidratan, mas tienden a la forma esferica, lo cual es un hecho auspicioso, ya que no solo el producto posee un aspecto visual agradable, sino que se habilita la utilizacion de la forma esferica para los efectos de adoptar una dimension caracteristica para la evaluacion de cineticas de deshidratacion en monocapa y/o en lechos de particulas.

Application of transfer functions to the thermal processing of particulate foods enclosed in liquid medium

Abstract The application of transfer functions in foods for heat and mass transfer problems with variable boundary conditions has been the subject of several studies over the last decade. In this work, the heat processing of products immersed in a low-viscosity medium (where convection is the main heat transfer mechanism), is analyzed. The thermal histories are related to kinetic parameters to evaluate the target value of different processing conditions to inactive quality-degrading enzymes.

Calculation of the Effective Diffusion Coefficients in Drying of Chemical and Mechanical Pretreated Rosehip Fruits (Rosa eglanteria L.) with Selected Mass Transfer Models

Abstract The aim of this work was to select models of mass transfer to estimate effective mass diffusion coefficients during the dehydration of Rosa eglanteria fruits with air at 70°C. Fruits were pretreated chemically and mechanically (dipping it in NaOH and ethyl oleate solutions and cutting or perforating the fruit cuticle). Selected models were those of Becker and Fick’s second law, considering fruit shrinkage during drying. Both models satisfactorily predict the fruit drying, and the different pretreatments, to total or partially remove this waxen cuticle, noticeably improved water diffusion, reducing the time of processing from 28% (NaOH) to 52% (oleate and mechanical pretreatments). Mechanical pretreatments were the more effective, because oleate presents quality problems.

Application of Transfer Functions to the Thermal Processing of Sweet and Sour Cherries Preserves: Influence of Particle and Container Sizes

The conditions of thermal processing of fruit preserves packed in transparent glass containers have great importance from the point of view of the final product appearance. Process simulation can allow to predict the quality of the product and its possible degradation. This work applied the transfer function method to simulate the pasteurisation of whole sweet and sour cherries canned in glass containers, with a 25 °Brix sucrose solution as covering liquid, and the predicted results were experimentally tested. The influence of fruit and container diameters on the treatment times was analysed. Kinetic models for enzyme degradation were coupled to the prediction model as examples of the possibilities of optimising the whole pasteurisation process. The accuracy (average error in predicted temperatures: 2.1%) of the simulation method was satisfactory for practical purposes, its use resulted simple and fast, and it allowed adjusting of pasteurisation times, even during the process.

Propiedades de lechos fijos durante la deshidratación convectiva de cerezas, guindas y rosa mosqueta: cambios de volumen y porosidad

En este trabajo, se determinaron experimentalmente y modelaron los cambios de volumen y porosidad de lecho fijo durante la deshidratacion de cerezas, guindas y frutos de la rosa mosqueta. Se utilizaron un equipo de secado experimental y frutas frescas. La altura de lecho variaba entre 0,04 y 0,12 m, la temperatura del aire entre 50 y 70 oC, su velocidad entre 1 y 4 m/s, y su humedad relativa fue de 5 y 50%. Al inicio y durante la deshidratacion se media la altura del lecho como promedio de 8 escalas graduadas colocadas simetricamente en la camara de secado y el peso de las muestras correspondientes. Con los valores obtenidos se calculaba el volumen de lecho y su porosidad en funcion del contenido de agua de la muestra. Mediante regresion, se obtuvieron correlaciones para estimar el volumen y la porosidad de lecho. Los errores porcentuales obtenidos fueron: para cambios en el volumen de lecho, entre -16,4 y 23,3 para cerezas y guindas, y entre -4,9 y 4,4 para frutos de la rosa mosqueta; y para los cambios de porosidad, entre -15,2 y 21,1 para cerezas y guindas, y entre -2,6 y 6,1 para frutos de la rosa mosqueta.