The influence of vacuum application and vegetable structure on the osmotic dehydration

Abstract

Many studies have been conducted to better understand the mechanisms of mass transfer during the osmotic dehydration of food, and to evaluate the quality parameters of the osmodehydrated products and the mathematical modeling of the phenomena involved in this process. Osmotic dehydration is a pre-treatment that extends the shelf life of foods and aids in the development of products with aggregated value and differentiated characteristics. The use of vacuum during the first minutes of the osmotic dehydration (pulsed vacuum osmotic dehydration) enhances the transfer of moisture from product to the osmotic solution, and the transfer of solute to the food matrix. The material structure exercises great influence over the effect of osmodehydration on the characteristics of the final product and on the mass transfer kinetics. The present work was elaborated with the objective of studying the behavior of different vegetable slices (eggplant, carrot and beetroot) during osmotic processes, using different vacuum pressures and osmotic solutions. For all products, quality characteristics and dehydration kinetics, were evaluated, and mathematical model adjustments were conducted. The effect of the application of vacuum over optical, chemical, nutritional and structural parameters of foods was confirmed. The vegetable with greater porosity (eggplant and carrot) were more sensitive to vacuum. The mass transfer parameters (water loss, solid gain and consequent water activity reduction of the final product) were influenced by the type of agent employed as osmotic substance, as was the application of reduced pressure at the beginning of the process. The partial replacement of sodium chloride by other salts as osmotic agents was promising, with no significant changes in the characteristics of the osmodehydrated product, coupled with a decrease in the concentration of sodium chloride incorporated. According to the dehydration kinetics curves, the effective diffusivities of water and solutes were calculated by employing phenomenological mathematical models. In some conditions, a lack of adjustment of the above-mentioned models was observed. In conclusion, vacuum pulse osmotic dehydration affects the final characteristics of the product, and behavior during dehydration.