Effects of solar drying operation equipped with a finned and double-pass heat collector on energy utilization, essential oil extraction and bio-active compounds of peppermint (Mentha Piperita L.)

Three methods of shade (MI), open sun (MII) and new designed of solar (MIII) drying were used for peppermint dehydration. The air velocity (u) and temperature (T-d ) of MI, MII and MIII were 0.5, 0.5, and 1.5 m/s and 32, 36, and 48 degrees C, respectively. The energy utilization efficiency, T-d /u ratio and drying rate of MIII reached 85%, 48 degrees C.s.m(-1) and 12.5 g(H2O)/min, respectively, which were higher than those in MI and MII. The inhibition power of dried peppermints against 6-log colony forming unit/ml of Staphylococcus aureus (Sa) were also evaluated. While the chlorophyll and essential oil extraction efficiency of MIII-product were 30% and 60% respectively higher than those in MII-product, its total phenolic contents and antioxidants activities were 25% and 26% more than those in MI-product. The essential oil of MIII-product had significantly (p < 0.05) higher inhibiting compounds (mainly Menthone) against pathogenic gram-positive Sa compared with those in MI and MII-products.