Modelagem e simulação do processo de secagem convectiva de fatias de kiwi pré-tratadas osmoticamente utilizando geometria de parede infinita.

Abstract

The present work aimed to evaluate the influence of osmotic dehydration process variables, using different temperatures (40, 50 and 60 ° C) and different types of sucrose in solutions (40, 50 and 60 ° Brix) and convective drying of kiwi slices cv. Hayward (40, 50 and 60 ° C) in the chemical, physical and chemical characteristics of the final product. In addition to evaluating the suitability of empirical and diffusive mathematical models to obtain a description of the process of applying wall geometry, the use of infinity and boundary conditions of first and third types. The mathematical models of Lewis, Wang and Singh, Henderson and Pabis, Page, Peleg and Silva, and others were fitted to the experimental data used by the LAB Fit adjustment software. For an analytical solution of the diffusion equation, the software "Adsorption desorption prescription 2.2" and Adsorption-desorption convection 2.5" were used, making it possible to determine the number of Biot, effective diffusivity and convective mass transfer coefficient. How dehydrated kiwi slices were evaluated in relation to the theoretical parameters of production, water activity, carbohydrates, lipids, maximum amounts of water, pH, acidity, ascorbic acid, reducing and total sugars, proportion, carotenoids, chlorophyll and color. An instrumental analysis of the texture of the colors was carried out in relation to the parameters of firmness, chewability and cohesiveness. The increase in temperature and the concentration of sucrose in the osmotic dehydration process provide greater water loss and strength gain, however during drying, if sucrose causes greater resistance to mass transfer in the product. The page model has greater specifications in the description of the drying process for dehydrated kiwi slices, including the Silva model and also shows good adjustments in the experimental data. The diffusive models are capable of describing the hydrated osmodia slicing process, a contour condition of the third type more efficient when compared to the contour condition of the first type. The increase in temperature in the drying process provides an increase in the effective diffusivity of the kiwi and the higher drying rates, with respect to physical-chemical methods, reductions in water content, water activity, pH, ratio, proteins, acid were observed ascorbic, chlorophyll and carotenoids, luminosity, a * and b * and the increase in the content of ash, lipids, complete soluble solids, reducing and total sugars. The firmness, cohesiveness and chewability parameters were provided directly at the drying temperature and the sucrose concentration of the osmotic agent.