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 (a w ) 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 J unior et al. The shrinkage effect was considered to estimate the water and solid diffusion. A lower a w of the osmotic solutions resulted in higher mass transfer parameters (WL and SG) and a lower a w 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 J unior et al. presented the best fit. The shrinkage resulted in lower water and solid diffusivity values. PRACTICAL APPLICATIONSBrazil 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.

Modeling mass transfer during osmotic dehydration of different vegetable structures under vacuum conditions

“…Although the effective diffusivity varies with the food material and the experimental conditions, which makes comparison difficult in terms of exact values, the D eff obtained according to Fick's model presented the analogous order of magnitude of food materials subjected to the OD (Bahmani et al, 2016;Junqueira et al, 2017c;Mendonça et al, 2017;Souraki et al, 2014). Table 2, Fick's model showed lower R 2 values (even 0.640) which indicates its low acuity in portraying the experimental data.…”

“…The Fito and Chiralt hydrodynamics model (Fito & Chiralt, 1997) considers an equilibrium approach (Equation 6): driving force between the product and the hypertonic solution is the strongest, and as the osmotic process extends, an osmotic pressure reduction occurs, due to mass transfer between the phases (Junqueira et al 2017c;Lombard et al, 2008;Ramya & Jain, 2017).…”

Shrinkage and rehydration characteristics of vacuum assisted microwave dried green bell pepper

“…Volume reduction brings significant shrinkage and subsequently low porosity due to which the final dried product bears poor rehydration ability (Aral & Beşe, ).The removal of water from plant cells causes shrinkage which changes its physical properties and affect the rehydration of dried product (Junqueira, Corréa, & Mendonça, ). Doymaz and Ismail () studied the rehydration of pretreated dried bell pepper samples at three different rehydration temperature (25, 50, and 75°C) and found that diffusion coefficient of bell peppers increased with increasing rehydration temperature.…”

“…Shrinkage and rehydration characteristics of any food material are significantly influenced by the drying methods (Doymaz & Ismail, ; Joardder et al, ; Junqueira, Corréa, & Mendonça, ). The osmotic properties of plants cell wall diminishes due to shrinkage during drying process.…”

“…Shrinkage and rehydration characteristics of any food material are significantly influenced by the drying methods (Doymaz & Ismail, 2013;Joardder et al, 2017;Junqueira, Corréa, & Mendonça, 2017).…”