Quality, energy requirement and costs of drying tarragon (Artemisia dracunculus L)

Abstract

Tarragon ( Artemisia dracunculus L.) is a favorite herbal and medicinal plant. Drying is necessary to achieve longer shelf life with high quality, preserving the original flavor. Essential oil content and color are the most important parameters that define the quality of herbal and medicinal plants. Hot air batch drying is the most common drying method for these plants but affects the essential oil content and color. The drying conditions affect essential oil content and color as well as the energy consumption and costs. Process engineers and farmers need to know how they have to dry to obtain the best quality. The objective of this work is to investigate the conditions for optimal drying in terms of quality, energy consumption and costs.Adsorption and desorption experiments were done to find the equilibrium moisture content and water exchange between the material and surrounding air during drying and storage at temperatures of 25ºC to 70ºC and relative humidities of 5% to 90%. Drying of tarragon leaves and chopped plants was investigated separately and the best model was selected from the drying equations in literature. The effect of drying temperature and relative humidity on the essential oil content and color change was studied. Experiments were done at temperatures of 40ºC to 90ºC and the optimal conditions were. Long‑term effects of the drying conditions were also investigated during the storage time. Material dried at 45, 60 and 90ºC was stored and the essential oil content and color of the material was measured after 15, 30, 60 and 120 days of storage. Drying at 45ºC was found as the best condition based on the changes of essential oil and color during drying and storage.Optimization of drying of tarragon was studied based on the results of the sorption isotherms, drying equations and the changes of essential oil content and color during drying and storage. Models were made for the drying process, energy consumption and cost calculation. The current conditions in The Netherlands andIranwere applied for various drying scenarios. The simulation model was run at selected ranges of temperature, humidity ratio, air speed and bed heights, with and without recirculation of the drying air. Considering the quality of dried material and costs, a temperature of 50ºC was found as the optimal temperature for drying tarragon. The costs per kg dried product was about three times higher for The Netherlands compared toIran. The recirculation is less important inIranbecause the ambient air has a higher drying potential and energy prices are lower