Evaluation of the Shrinkage Effect on the Modeling Kinetics of Osmotic Dehydration of Sweet Potato (Ipomoea batatas (L.))

Abstract

The kinetics of water loss (WL), solid gain (SG) and water activity (aw) of the osmotic dehydration of sweet potato (Ipomoea batatas (L.)) slices were investigated. Three osmotic solutions, sucrose, sorbitol and fructose, were used with two different water activities, 0.900 and 0.940. The diffusivities of both water and solute were evaluated by using Crank's analytical solution to Fick's second law and according to the models of Azuara and Barbosa Júnior et al. The shrinkage effect was considered to estimate the water and solid diffusion. A lower aw of the osmotic solutions resulted in higher mass transfer parameters (WL and SG) and a lower aw of the product. Sorbitol promoted higher WL and sorbitol and fructose, higher SG. The shrinkage was directly proportional to moisture reduction. Among the tested mathematical models, the Barbosa Júnior et al. presented the best fit. The shrinkage resulted in lower water and solid diffusivity values. Practical Applications Brazil is the largest producer of sweet potatoes (Ipomoea batatas (L.)) in Latin America. This root is considered as the fifth most important crop in developing countries. Like most vegetables, its shelf life is short and its storage is difficult. Therefore, improved techniques for conservation are welcome. Osmotic dehydration is a pretreatment process that provides partial water removal from a food product, with low energy consumption. In the literature, there are few studies on osmotic dehydration with nonionic agents and considering the shrinkage that occurs during the process in sweet potatoes. This study investigates the effects of different osmotic agents and water activities of osmotic solutions on the drying kinetics and effective diffusivities. The mathematical models provide information about the processes. Three different empirical models were employed and one approach investigates the shrinkage that occurs during the process.