Prediction of Drying Characteristics of Pomegranate Arils
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Prediction of Drying Characteristics of Pomegranate Arils İbrahim Doymaz
Received: 13 June 2011 / Accepted: 3 October 2011 / Published online: 20 October 2011 # Springer Science+Business Media, LLC 2011
Abstract The thin-layer drying characteristics of pomegranate arils were investigated at the temperature of 55, 65 and 75°C, and the thin-layer drying models were used to fit the drying data. The increase in drying air temperature resulted in a decrease in drying time. Five different thinlayer drying models were used to predict the drying characteristics. The Midilli et al. model showed a better fit to experimental drying data as compared to other models. Effective moisture diffusivities were calculated based on the diffusion equation for a spherical shape using Fick’s second law, and varied from 9.373×10−11 to 3.429× 10−10 m2/s over the temperature range. Moisture diffusivity values increased as air temperature was increased. The dependence of moisture diffusivity on temperature was described by an Arrhenius-type equation. The activation energies of control and pre-treated samples were determined to be 49.7 and 40.1 kJ/mol, respectively. Keywords Activation energy . Effective moisture diffusivity . Pre-treatment solution . Pomegranate arils . Thin-layer drying
Introduction Pomegranate (Punica granatum L.) belongs to the Punicaceae family and is one of the oldest known edible fruits. It is also known as Chinese apple or Apple of Carthage (Hindi, Anar) and has been cultivated extensively in İ. Doymaz (*) Department of Chemical Engineering, Yildiz Technical University, 34210, Esenler, Istanbul, Turkey e-mail: [email protected]
Mediterranean countries (Turkey, Tunisia, Isreal, Egypt, Spain and Morocco), Iran, Afghanistan, India and USA, China, Japan and Russia (Singh and Singh 2004). The fruits have many varied uses. Pomegranate fruit is consumed directly as fresh seeds but can also be used for making juice, jelly, grenadine or as flavouring and colouring agents (Miguel et al. 2010). In India, the arils are dried in the sun for 10 to 15 days and then sold as a spice, named “anardana”. Pomegranates also have pharmaceutical and medicinal uses (Weusthuis 2009). Drying is the most widely employed method for preserving food materials, which is based on reduction of the water activity values through moisture removal to achieve physicochemical and microbiological stability (Gorjian et al. 2011). Dried products have almost unlimited shelf life in proper packages and substantially lower transportation, handling and storage costs compared to foodstuffs produced with other preservation methods (Ertekin and Yaldiz 2010). Traditionally, fruit and vegetables are dried in open sunlight. However, sun drying is weather dependent, affecting the homogeneity and quality of the final product. Moreover, the products are prone to microbial and other contaminations. To overcome these problems, the use of industrial type dryers (solar or convective dryers) should be used (Kingsly et al. 2007; Falade and Solademi 2010). Drying of fruit and
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