Kinetic studies for microwave-assisted drying of Oraby date slices

Abstract

This study was conducted to evaluate the effects of microwave (MW) output power on the drying kinetics and quality of ascorbic acid pretreated and untreated Oraby date slices (2, 4 and 6 mm in thickness and 24 ± 2 mm in diameter) at the end of khalal stage. The initial moisture content was 1.7397 d.b. The drying experiments were carried out using three levels of MW output power 160, 320 and 480 W. The obtained experimental data were fitted with three empirical models. The effect of MW power on drying time and drying rate were determined. Effect of drying on sugars, total phenols, tannins contents and color measurements were studied. Because of occurrence of some charring (burning) when MW drying of 4- and 6-mm slices goes beyond moisture content of 0.3678 kg[H2O].kg-1dry matter, thereafter MW drying was stopped, then drying was completed using a conventional oven at 60°C to avoid sample discoloration or burning. MW drying of 2 mm slices was completed without showing such burning. The Midilli et al. model was the best fit for the data of MW drying as well as the following convention oven drying. All sensory attributes for the dried Oraby date slices were acceptable by the panelists, however, the 2 mm slices received the highest panelists’ scores. MW shortened the time needed for drying.