Secagem de pêra em secador a microondas

Abstract

The present work has as main objective the pear drying in three different dryers: convective, microwave and microwave-convective. It is also intended to evaluate the effect of the osmotic dehydration, as pré-treatment, in the quality of the dried product. Before they be dried or dehydrated the samples passed by a mechanical treatment, which consists of peeling, seeds removing and cutting the fruit, and a chemical treatment with its immersion in solution 1,5% of ascorbic acid for 15 minutes. The stage of osmotic dehydration was carried out by analying the influence of the osmotic agent concentration (sucrose to 25; 37,5 and 50%), of the temperature (30, 40 and 50ºC), of the sample geometry (cubes, toothpicks and slices) and of the use of agitation (0 and 120 rpm) in the kinetics of the process, through the loss of water and the sucrose incorporation by the fruit. The best kinetic condition obtained, through statistical analysis of the data, was to the sample in slices dehydrated at 40ºC, with 37,5% of sucrose and without agitation, being this condition used as pretreatment to the drying. The adjustment of the experimental data was accomplished by the empirical model of Azuara (1992). The drying stage was studied for the fresh and osmotically dehydrated fruit. In this stage, the best kinetic condition was stablished based on the analysis of the influence of the kind of drying used and the power of the microwave in the moisture content of the fruit. The speed and temperature of the air was maintained constant at 2 m/s and 50ºC, and the temperature inside the sample was measured during drying. The best kinetic condition obtained was for the microwave-convective drying at 0,3W/g of osmotically dehydrated samples. The adjustment of the experimental data was accomplished by the Lewis (1921) and Page difusion models (1949). The materials and products of the osmotic dehydration and drying were analyzed concerning their quality, being the main analyses, calcium, phosphorus, potassium, water activity, density, moisture content, total solids and shrink. The results obtained were compared in terms of the drying kinetics and quality of the product, for the equipments used through statistical treatment and with available data from the literature. The osmotic dehydration had beneficial effects on the properties analyzed, giving the best results to the main components detention and maintenance of the others analyzed properties. During the drying, the quality decreases with the increase in the inner sample temperature. The shrink data adjustment, presented by the volume decrease, was well represented by the Lozano et al. (1983) model, being linearly proportional to the moisture content variation.