Modeling mass transfer during osmodehydration of apple cubes with sucrose or apple juice concentrate solutions: Equilibrium estimation, diffusion model, and state observer-based approach

This article investigates the modeling aspects of mass transfer during osmodehydration of apple cubes. The obtained experimental data were fitted to three mathematical models: Azuara's equilibrium mass-transfer model (AM), Fick's second law (FSL), and a Luenberger observer (LO). Two scenarios were considered for the mathematical modeling of mass transfer between the osmotic solution and the apple cubes. First, constant apple volume during the osmodehydration process was assumed. Then we included volume shrinkage in the dehydrated product as part of the model. The effect of the osmotic agent in the apple dehydration was also addressed by considering two different osmotic solutions, apple juice concentrate, and sucrose solutions, with different concentrations (40, 50, and 60 degrees Brix). The equilibrium parameters estimated with the AM model were similar to the parameters determined experimentally (p > .05). The LO model accurately describes the solute mass transfer dynamics during the osmodehydration process (R-2 > .950). The overall findings indicate that considering the volume shrinkage as part of the model strongly influences the parameter estimation. When considering volume shrinkage in the FSL model, the estimated diffusivity parameters ranged from 1.26 to 5.05 x 10(-10) m(2)/s for water and 0.68-19.35 x 10(-10) m(2)/s for solutes, respectively. Not considering product shrinkage in the diffusivity model leads to overestimating both water diffusivity (29.9-76.8%) and solute diffusivity (25.3-52.8%). Practical Applications Osmotic dehydration (OD) refers to a mass transfer process where solutes are transported from a hypertonic solution to a food material, while water moves from the food material towards the solution. OD improves the appearance and taste of dehydrated foods, helps inhibit the growth of dangerous microorganisms, and decreases enzymatic browning in some foods. Sucrose solutions are frequently used as osmotic solutions for food treatment in OD. An alternative to sucrose is to treat food with fruit juice concentrates. Fruit juice concentrates have low water activity and can provide bioactive compounds that enrich the dehydrated product. Understanding the effect of different factors on mass transfer during osmotic dehydration is thus critical for the efficient design, optimization, scaling-up, and operation of OD food treatment processes. Furthermore, the proper selection of osmodehydration conditions allows us to obtain high-quality food products with specific composition, textural/sensory properties, and microbiological characteristics. Therefore, osmotic dehydration is a food processing alternative that allows us to obtain high-quality food products with good nutritional attributes.