Influence of Some Drying Techniques on Drying Characteristics and Quality of Mint Leaves

The method of conservation by drying is very important methods used with medicinal and aromatic plants such as peppermint. There are many changes in color and active substances, which affects the quality of the product. Three drying methods were used for drying mint leaves, oven drying (40, 50, 60 and 70 o C), microwave drying (180, 360, 540, 720 and 900 Watts) and solar drying with three levels of load (0.5, 1.25 and 5kg/m 2 ). The drying characteristics and quality aspects of the dried mint leaves were studied. The lowest drying time to achieve the equilibrium moisture content ( 0.35 ,0.38 g. w./g. d. m) was 5 minutes by microwave drier at use powers 900 and 720 Watt with loading 0.5 kg/m 2 , while the highest time took for drying mint was 20 hours to achieve equilibrium moisture content (0.72 g. w./g. d. m ) at 40 o C. Meanwhile, the solar dryer required 8 hr to achieve the final moisture content (0.68 g. w./g. d. m) at both 1.25 and 0.5 kg/m 2 loading. The results showed that drying of the mint leaves at temperature 50 o C with loading 1.25 kg/m 2 was the best treatment to getting the highest amount of essential oil. Midili - kucuk, model adequately described the oven and solar drying behaviors and logarithmic model adequately described the microwave drying behaviors. In conclusion, Solar drying with its low cost and oven drying (at 50 o C and load level 1.25 kg/m 2 ) could be a potent drying method of mint leaves since it maintains much of its essential oil. Whereas, and based on the result of this study, microwave drying is not advisable to obtain aromatic oils of medicinal and aromatic plants.