Collard leaves (Brassica oleracea L. var. acephala) with an initial moisture content of 6.65 on percentage dry basis (%db) were dried by three different drying methods: microwave, air, and vacuum. Samples of fresh leaves, 25 g each, were dried until their moisture was down to 0.1 on a dry basis. The following drying levels were used in each of the drying processes: 350, 500, 650, 750, 850, and 1000 W for microwave drying; 50, 75, 100, 125, 150, and 175°C for air drying; and 0.4, 50, and 100 mmHg at 50 and 75°C for vacuum drying, respectively. Drying times ranged between 2.5 to 7.5 min, 8 to 210 min, and 35 to 195 min for microwave, air, and vacuum drying, respectively. The data obtained compared well with a thin-layer drying model. Microwave drying at 750 W provided optimal results with respect to drying time, color, and ascorbic acid content (vitamin C).

Chard leaves (Beta vulgaris L. var. cicla), which weighs 25 g with a moisture of 9.35 (db), were dried using three different drying methods, microwave, convective, and combined microwave-convective. Drying continued until leaf moisture fell down to 0.1 (db). Drying periods lasted 5–9.5, 22–195, and 1.5–7.5 min for microwave, convective, and combined microwave-convective drying, respectively, depending on the drying level. In this study, measured values were compared with predicted values obtained from Page's semi-empirical equation. Optimum drying period, color, and energy consumption were obtained for combined microwave and convective drying. The optimum combination level was 500 W microwave applications at 75°C.