A New Way to Improve the Drying Kinetics and Final Quality of Peppermint

Abstract

Drying is the most common postharvest process to preserve medicinal and aromatic plants. Peppermint has a high worldwide commercial value. Newly harvested peppermint plants were dried by using four different drying air temperature profiles. They were constant 35°C, constant 55°C, incremental rises from 35°C to 55°C in four hours, and in eight hours. The samples were dried down to the final moisture content for 8 to 18.5 hours. The fastest drying was obtained with the use of the constant 55°C and the slowest drying was obtained with the use of the constant 35°C. The incremental rise of drying air temperature profile from 35°C to 55°C within 4 hours shortened the drying time by 46%. Page’s equation excellently represented all drying curves. Maximum color change and essential oil loss occurred with the drying at 55°C; however, incremental rise of drying air temperature over time reduced the extent of color change and essential oil loss. The highest essential oil change was -21.95% for the constant 55°C, the lowest essential oil change was -2.32% for the constant 35°C. The temperature of heated air affected the composition of peppermint essential oil. Drying at constant 55°C kept menthol content (43.31%) close to that (47.64%) of fresh peppermint but decreased menthone content (26.24%) and increased cineol content (8.18%). Considering the length of drying time and dried product quality values, the profile in which the drying air temperature rise within 4 hours was found to give the best results.

Key words:

• Drying technology
• Drying kinetics
• Essential oil
• Color analysis
• Peppermint