Study of mass transfer kinetics and effective diffusivity during osmotic dehydration of carrot cubes Bahadur Singh a, * , Ashok Kumar b , A.K. Gupta b a Department of Food Technology, Sant Longowal Institute of Engineering and Technology, Longowal 148 106 (Sangrur), India b Department of Processing and Food Engineering, Punjab Agricultural University, Ludhiana 141 004, India Received 9 February 2005; received in revised form 14 September 2005; accepted 17 January 2006 Available online 11 May 2006 Abstract The mass transfer kinetics during osmotic dehydration of carrot cubes in ternary solution of sucrose, NaCl salt and water were stu- died. The osmotic solution concentrations used were 50 °B + 5% salt (w/v), 50 °B + 10% salt (w/v) and 50 °B + 15% salt (w/v), osmotic solution temperature used were 35, 45 and 55°C, fruit to solution ratios 1:4, 1:5 and 1:6 and the process duration varied from 0 to 240 min. Among the models applied, Azuara model well represented the experimental data for water loss; whereas solute gain was well represented by the Magee model. Effective diffusivity of water as well as solute was estimated using the analytical solution of Fick’s law of diffusion and iterative technique, which was conducted by a simple computer program, was used to solve the equation with first six terms. For above conditions of osmotic dehydration, the effective diffusivity of water was found to be in the ranged between 1.594 · 10 9 and 2.078 · 10 9 m 2 /s and that of solute between 1.175 · 10 9 and 1.645 · 10 9 m 2 /s. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Osmotic dehydration; Effective diffusivity; Mass transfer kinetics; Carrots 1. Introduction Carrot (Daucus carota L.) is known for its nutrient con- tents viz. carotene and carotenoids besides appreciable amounts of vitamins B 1 ,B 2 ,B 6 and B 12 vitamins and min- erals. The various methods of extending shelf life are fer- menting, pickling, canning or cold storage freeze drying etc. (Mudahar, Toledo, Floros, & Jen, 1989). Out of these methods, freeze-drying produces the highest quality food products but it is the expensive method of preservation. So there is a need for simple and inexpensive alternate pro- cess, which are not only energy intensive and low capital investment but offer a way to make available this low cost, highly perishable and valuable crop available for the regions away from production zones and also during off season. The osmotic dehydration is one of these new meth- ods (Shi & Maguer, 2002). Osmotic dehydration is the process by which water is partially removed from the cellular materials when these are placed in a concentrated solution of soluble solute. Osmotic dehydration, which is effective even at ambient temperature and saves the color, flavor and texture of food from heat, is used as a pre-treatment to improve the nutri- tional, sensorial and functional properties of food. The influence of the main process variables, such as concentra- tion and composition of osmotic solution, temperature, immersion time, pre-treatments, agitation, nature of food and its geometry, solution to sample ratio, on the mass transfer mechanism and product quality have been studied extensively (Kaymak-Ertekin & Sultanoglu, 2000; Rastogi & Raghavarao, 1994). Numerous studies have been carried out to better under- stand the internal mass transfer occurring during osmotic dehydration of foods and modeled the mechanism of the process (Azuara, Cortes, Garcia, & Beristain, 1992; Kaymak-Ertekin & Sultanoglu, 2000; Magee, Murphy, & Hassaballah, 1983). A number of investigators used Fick’s 0260-8774/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2006.01.074 * Corresponding author. E-mail address: bshathan@yahoo.com (B. Singh). www.elsevier.com/locate/jfoodeng Journal of Food Engineering 79 (2007) 471–480