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Kulwinder Kaur & A K Singh
material, osmotic solution to fruit ratio, physico-chemical properties of food materials and operating pressure. However, the specific effect of the osmotic solution is of great importance when choosing the solution. Several solutes, alone or in combination have been employed in hypertonic solutions for osmotic dehydration (Tortoe, 2010). Sugar and salt solutions proved to be best choices based on effectiveness, convenience and flavor. Further, the potential for improving food quality through modeling is tremendous but limited by the lack of quantitative data and predictive models. Engineers require quantitative models to design and optimize processes. Therefore, modeling using empirical models namely Azuara, Fick’s second law, page, power law and generalized exponential, provide a useful tools for understanding the osmotic dehydration process of beetroot. The purpose of the present work was to study mass transfer parameters during the osmotic dehydration of beetroot and examine the predictive capacity of Azuara, Fick’s second law, Page, Power law and Generalized exponential equations to the experimental data. Theory Azuara et al. (1992) modeled the rate of water loss (WL) and solute gain (SG) as function of time by using a mass balance on water movement inside the food, obtaining equations with two fitting parameters. In the model formulation, the following relation for WL is established:
(1) where WL∞ is the corresponding value at infinite time (i.e., at equilibrium) and S1 is the constant related to the outward water diffusion rate in the food. Equation (1) can be expressed in linear form as:
(2) The water loss at equilibrium (WL∞) and the constant S1 were estimated from the slope and intercept of the plot (t ⁄ ) vs. t using the eqn (2). Thus, the equations for SG can be written as:
(3)
(4) Where, SG∞ is the corresponding value at infinite time (i.e. at equilibrium) and S 0 is the constant related to the incoming solute diffusion rate in the food. Similarly to WL ∞ and S1, SG∞ and S0 parameters are obtained from the straight line (t ⁄
) vs. t using equation 4. Considering the beetroot slices as slab geometry with initially uniform water or solutes content, the solution for Fick’s
equation for constant process conditions is (Crank, 1975): (5)