Carrot Kinetics Modeling (Daucus Carota) by Osmodehydro freezing

Abstract

Carrot is a high nutritional value product due to the content of carotenoids, which are precursors of vitamin A and possess antioxidant properties. As the other orchard vegetables it is known for its high water content being consequently a highly perishable food. The partial elimination of water represents an advantage of diminishing the microbial deterioration, simultaneously reducing packing, storaging and transport costs. Moreover, a more efficient use of energy encourages the application of dehydration processes that require a lower energy intake such as pre-treatment of the vegetables with osmotic dehydration followed by freezing, which shortens the length of this last stage (osmodehydrofreezing).
Osmotic dehydration (OD) is a technique of partial food dehydration that consists of the immersion of food in solute concentrated solutions with high osmotic pressure and low water activity. The employment of osmotic dehydration in
the food industry as a pre-treatment improves the product quality in terms of colour, flavour and texture with a minimum energetic requirement, as it is performed at low temperatures. The conditions of osmotic dehydration were: 40% m/m sucrose concentration, 5% m/m salt concentration, 40°C temperature, mass ratio solution to product of 4, cubes of 1 cm of edge and 120-130 rpm of stirring.
Later on, the thermal history of the process of freezing of carrots pre-treated with OD in a range of temperatures from 18°C to -30°C was studied. A pilot scale tray freezing tunnel was used. The temperature in function of time was registered by placing a Cu-Co thermocouple in the center of the cubes (thermal center). The energy transfer coefficient is 23 W/(m2°C) and the temperature reached by the air is -35°C.
The modeling of osmotic dehydration was carried out with the Crank phenomenological model that consists in the solution of the second Fick´s law that describes the diffusional mechanism and an empirical model, Azuara's, which
doesn't require values of the variables in the equilibrium but can predict them, although it presents the disadvantage of limiting the validity range to the experimental one. The estimated effective water diffusivity in the osmotic dehydration process in the previously mentioned conditions was 1,57 10-9 m2/s. The freezing times were estimated very satisfactorily by applying the equation of Salvadori-Mascheroni. The error regarding the experimental time was less than 10%,
such as the authors which worked with other products inform.