Moisture Diffusivity and Shrinkage of Fruit and Cladode of Opuntia ficus-indica during Infrared Drying

Drying behaviour of prickly pear cladodes and fruits was studied with an Infrared dryer. The volume shrinkage for Opuntia ficus-indica products is calculated and a linear relation was established to describe the experimental variation of shrinkage of the product versus its moisture content. Effective diffusion coefficient of moisture transfer was determined using the Fick law at three drying temperatures (40, 50, and 60°C). Shrinkage was also included into the diffusion model for the determination of the effective diffusion coefficient. The obtained results of the effective moisture diffusivity, for the cladode and the fruit, were evaluated in the range of 1.77 × 10？10–5.07 × 10？10？m2/s and 2.53 × 10？10–7.6 × 10？10？m2/s, respectively. The values of the activation energies for cladode and fruit were estimated to be 45.39 and 47.79？kJ/mol, respectively. However, these values of moisture diffusivity were estimated independently of the evolution of moisture content during drying process. Therefore, a correlation (full quadratic equation) for moisture diffusivity as a function of moisture content and temperature was developed. The parameters are obtained by a multilinear regression method. This equation was found satisfactory to describe the diffusivity evolution function of moisture content and temperature with correlation coefficients of 91.5 and 95%. 1. Introduction The Opuntia ficus-indica also named prickly pear is a xerophyte and a luscious plant. The consumption of prickly pear remains artisanal and the culture of the fruit and the cladode in view of industrial transformation remains insufficient. Recently, in some countries the prickly pear tree is cultivated for food industrial, medical, and cosmetic purposes [1]. Therefore, the use of dried fruits and cladodes increased with the increasing of their derivatives products, which urge the necessity of developing an efficient and effective method for the dehydrating of prickly pear fruits and cladodes. Infrared (IR) radiation drying has been investigated as a potential method for obtaining high quality dried foodstuffs, including fruits, vegetables, and grains [2–6]. Infrared heating offers many advantages over conventional drying under similar drying conditions. These may include a reduced drying time, high energy efficiency, high quality finished products, uniform temperature in the product while drying, and a reduced necessity for air flow across the product [7]. Infrared drying has been recognized as a potential method for obtaining high quality dried foodstuffs. IR radiation energy is transferred