COMPARISON OF DRYING CHARACTERISTICS AND QUALITY OF PEPPERMINT LEAVES USING DIFFERENT DRYING METHODS

摘要

In this study, we investigated the effects of hot air, infrared and combined hot airinfrared drying methods on the drying time, energy consumption, color, rehydration and oil content of peppermint leaves. Three different air temperatures (30, 40 and 50C) and air velocities (0.5, 1 and 1.5 m/s) were used in the hot air drying. Infrared drying process was implemented using three levels of radiation intensity (1500, 3000 and 4500 W/m2), three distances between emitter and sample (10, 15 and 20 cm) and three air velocities (0.5, 1 and 1.5 m/s). The results showed that the optimum drying period and energy consumption were obtained when infrared- and hot air-drying were applied simultaneously. The results also showed that combined drying resulted in dried leaves of superior quality when compared to the leaves dried separately by either hot air alone or infrared, exhibiting lower total color change, greater rehydration ratio and higher extraction oil yield.