Citron melon peel flours: drying kinetics and physicochemical evaluation

Abstract

In the utilization of citron melon (Citrullus lanatus var. citroides), it is necessary to deal with a large amount of residues constituted by the peels. These materials commonly discarded can be fully utilized, since they are a source of nutrients. The peels contain not only fibers, but also proteins, sugars and minerals, which, after drying, are concentrated to values that make them interesting for various uses, including for the enrichment of flours or combinations to prepare bakery products. Therefore, the drying of the peels, besides enabling the conservation and storage at room temperature, expands the forms of use and the possibilities of entering the production chain. This study aimed to characterize physico-chemically and determine drying kinetics, effective diffusivity, activation energy and thermodynamic properties of citron melon peels at different drying temperatures. The peels were dried in an oven with forced air circulation, in a thin layer, at temperatures of 60, 70, 80 and 90 °C. With the data collected in the drying, the drying kinetic curves were constructed and eleven mathematical models were fitted to the experimental data. The dried material was crushed in a knife mill and characterized for physicochemical parameters. Midilli model resulted in the best fits, followed by Page and Approximation of Diffusion models. Effective diffusivity increased with drying temperature; activation energy was obtained from the Arrhenius equation and was equal to 8.18 kJ/mol. Enthalpy and entropy were reduced with increased temperature, while Gibbs free energy increased.