Vol. 69, Nr. 6, 2004—JOURNAL OF FOOD SCIENCE E259 Published on Web 7/9/2004 © 2004 Institute of Food Technologists Further reproduction without permission is prohibited E: Food Engineering & Physical Properties JFS E: Food Engineering and Physical Properties Increased Mass Transfer during Osmotic Dehydration of -Irradiated Potatoes N.K. RASTOGI AND K.S.M.S. RAGHAVARAO ABSTRACT: -irradiation pretreatment was tested to accelerate the osmotic dehydration of potato. Applied irra- diation in the range of 3.0 to 12.0 kGy resulted in decrease in hardness of the potato sample, as indicated by texture profile analysis. The effective diffusion coefficients (D) of water and solute determined using a Fickian diffusion model increased exponentially with doses of -irradiation (G) according to an equation of the form D = A exp(–B/G), where A and B are constants. The microstructures of irradiated potato samples resulted in swelling and aggregation of starch granules as well as breaking up of cell wall structure, leading to channeling effect, facilitating transport of water from the tissue and solute into it. Keywords: -irradiation, osmotic dehydration, mass transfer, microstructure, textural analysis, potato Introduction  -irradiation is used to inhibit the sprouting of vegetables, extend shelf-life of fresh produce, control pathogenic organisms and in- sect and microbial disinfestations, and sterilize foods (Masefield and Dietz 1983; Thayer 1990). After many experiments, Food and Agriculture Organization/Intl. Atomic Energy Agency/World Health Organization (FAO/IAEA/WHO 1991a, 1991b, 1992, 1994, 1995) announced that dosages of irradiation not more than 10 kGY on average would not result in problems of toxicity and nutrition loss, while ensuring microbial safety of food. On the basis of the exten- sive scientific evidence, the same joint committee in 1997 conclud- ed that food irradiated to any dose appropriate to achieve the in- tended technological objective is both safe to consume and nutritionally adequate (FAO/IAEA/WHO 1997). -irradiation pretreatment has been reported to change and damage the interior tissue structure, thereby increasing the perme- ability of plant cells, resulting in improved mass transfer during air drying (Wang and Chao 2002). The effect of -irradiation on drying characteristic and quality (appearance, vitamin C content, rehydra- tion ratio) of dehydrated apple and potato was studied by Wang and Chao (2003a, 2003b). The rate of mass transfer during osmotic dehydration is gener- ally low; therefore, acceleration of mass transfer would be advanta- geous. A number of techniques have also been tried to improve mass transfer rate. These techniques include subjecting the food material to ultra high hydrostatic pressure (Rastogi and Niranjan 1998) or high-intensity electrical field pulses (Rastogi and others 1999) before osmotic dehydration or applying ultrasound (Simal and others 1998) or partial vacuum (Rastogi and Raghavarao 1996) or centrifugal force (Azuara and others 1996) during osmotic treat- ment (Rastogi and others 2002, 2004). Osmotic dehydration is widely used for the partial removal of water from plant tissues by immersion in a hypertonic (osmotic) solution. The driving force for the diffusion of water from the tissue into the solution is provided by the higher osmotic pressure of the hypertonic solution. The diffusion of water is accompanied by the simultaneous counter diffusion of solutes from the osmotic solution into the tissue. Because the membrane responsible for osmotic transport is not perfectly selective, other solutes present in the cells can also be leached into the osmotic solution. The rate of diffusion of water in any material made up of such tissues depends on fac- tors such as temperature and concentration of the osmotic solu- tion, the size and geometry of the material, the solution-to-material mass ratio and the level of agitation of the solution. A number of publications have described the influence of these variables on mass transfer rates during osmotic dehydration (Torreggiani 1993; Raoult-Wack 1994; Rastogi and others 2002, 2004). It is worth not- ing that these variables can be manipulated only over a limited range, outside of which they adversely affect quality even though mass transfer rates may be enhanced. Hence, there is a need to identify methods that increase mass transfer rates without affecting quality significantly. The mechanism of mass transfer during os- motic water removal from cellular biological materials was present- ed by Rastogi and others (2000). The objective of the present work was to study the effect of - irradiation pretreatment on mass transfer rates during osmotic dehydration of potatoes. Materials and Methods Raw material preparation Fresh potatoes (Solanum tuberosum) were purchased locally in large quantities and stored at low temperature to have uniformity of raw material. The potatoes were cut into circular pieces of 3.5-cm dia and 0.5-cm height. The average moisture content of the pota- to was found to be 86.5% (on a wet weight basis), as determined by vacuum drying at 70 °C for 24 h (AOAC 1990). Commercial food grade sucrose was used for the preparation of osmotic solutions. -irradiation treatment -irradiation treatment was carried out at Central Food Techno- logical Research Inst., Mysore using CO-60 -cell (Model:  Cham- ber 5000, BARC, Mumbai, India) with a power source of 12000 Ci. MS 20030448 Submitted 8/11/03, Revised 10/27/03, Accepted 3/28/04. Au- thors are with the Dept. of Food Engineering, Central Food Technological Research Inst., Mysore 570 013, India. Direct inquiries to author Rastogi (E- mail: nkrastogi@cftri.com).