Influence of Microwave Power on Drying Kinetic, Chemical Composition and Antioxidant Capacity of Peppermint Leaves

Influence of microwave power on dehydration kinetics as well as quantity, chemical composition and antioxidant potential of peppermint essential oil was evaluated. The leaves were dried using microwave powers of 200, 400 and 800 W. and the essential oils extracted by hydro-distillation. The antioxidant potential of the essential oils was quantified by DPPH radical-scavenging activity method. The obtained results showed that increasing microwave power caused significant decrement (p <= 0.01) in drying duration. Drying over the considered microwave powers reduced essential oil yield significantly (p <= 0.01). In total, 36 compounds were identified in the essential oils belonging mainly to oxygenated monoterpenes. The main constituents namely menthol, menthone and menthyl acetate showed significant variation (p <= 0.01 or p <= 0.05) with the drying process. Antioxidant assaying indicated significant effect (p <= 0.05) on radical scavenging activity of the essential oil by drying and essential oil concentration. Compared to the fresh samples (with an IC50 of 103 mu g/ml), the leaves dried at microwave power levels of 200, 400 and 800 W resulted in significant lower antioxidant activities with IC50 values of 201, 291 and 615 mu g/ml, respectively.