Microwave, air and combined microwave-air drying of grape leaves (vitis vinifera l.) and the determination of some quality parameters

Abstract

Grape leaves (Vitis vinifera L.) weighing 50 g (+/- 0.08) with a moisture of 4.08 kg((moisture)) kg((dry matter))(-1) (75.35% wb) were dried using three different drying methods: microwave, air and combined microwave- air. Drying continued until the leaf moisture decreased to 0.14 (+/- 0.01) kg((moisture)) kg((dry matter))(-1) (9.07% (+/- 0.20) wb). Drying periods lasted 5-11, 30-70 and 1.5-6 min for microwave, air and combined microwave-air drying, respectively, depending on the drying level. In this study, measured values of moisture were compared with values of predicted obtained from several thin-layer equations; the Alibas Model was found to have the best fit. The optimum drying period, color and ascorbic acid content were obtained by using the combined microwave-air drying method with the optimum combination of 500 W of microwave power at a temperature of 75 degrees C.