Evaluation of drying methods with respect to drying parameters, some nutritional and colour characteristics of peppermint (Mentha x piperita L.)

Peppermint leaves (Mentha x piperita L.) were dried by using sun, oven (50 C) and microwave oven (700W) drying methods. Page, Modified page, Midilli and 1(00k models adequately described the oven, sun and microwave oven drying behaviours of peppermint leaves. The drying process was explicated through the diffusional model in order to obtain effective diffusivity values, which were determined as 3.10 x 10-12, 2.68 x 10-12 and 4.09 x 10-1 for the sun, oven and microwave oven drying process, respectively. Fresh and dried herbs had high amounts of K, Ca, P. Mg, Fe and Al minerals. Microwave oven drying method leaded to the lowest increase in Ag, Al, B, Na, Mn, Mg and Zn values than the other drying methods. Microwave oven drying shortened the drying time, revealed the highest phenolic content and optimum colour values. (C) 2010 Elsevier Ltd. All rights reserved.