In this study, the effect of infrared (IR) and hot air dryers on the drying properties of saffron petals was investigated. Drying of saffron petals was done under three level temperature 40, 50, and 60 C and distance from IR lamps 10, 14, and 20 cm and the main physical and thermal properties were measured. The highest value effective moisture diffusion (D eff ) was evaluated for IR-dried samples at 60 C and 10 cm with 5.57 Â 10 À7 m 2 /s. The lowest value of color changes is related to the sample dried at 40 C at a distance of 20 cm with a color change of 11.99 in the IR dryer. Increasing the drying temperature reduced the drying time and energy consumption and increased the drying rate and D eff . Also, the results showed that Midilli model was selected as the best model for drying saffron petals with an IR and hot air dryer. Practical ApplicationsDue to the importance and sensitivity of saffron petals to the application of heat in the drying process, it is necessary to dry this product like other medicinal plants scientifically. Theoretical research, with the help of mathematical modeling and numerical simulation, provides a powerful and fast tool for analyzing the process of mass and heat transfer under natural drying conditions. Careful study of the drying kinetics of the product, evaluation of parameters affecting the physical quality properties, and the concomitant and reciprocal effects of these parameters is necessary. It can be used in the drying industry of medicinal plants.

BACKGROUND Echinacea is a perennial and herbaceous herb containing the most active phenolic compounds and valuable antimicrobial and antioxidant content, such as chicoric acid, which increases the body immune function. The root of this plant is mainly used in pharmaceutical fields to treat inflammation, kidney infections and colds. In the present study, we investigated the drying of echinacea root in an infrared dryer with airborne ultrasonic pretreatment aiming to determine shrinkage, color changes, extraction, total phenolic content, flavonoid content and radical inhibition of 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH). The experiments were performed in an infrared dryer at three temperature levels of 40, 45 and 50 °C, with ultrasonic pretreatment at frequencies of 2000, 3000 and 4000 Hz and a time duration of 20, 40 and 60 min in three replications. RESULTS Shrinkage and color changes of the samples varied in the range 27.2–6.3% and 39.82–39.64%, respectively. According to all of the evaluated physical and chemical factors, the optimal conditions for echinacea root processing were a drying temperature of 40 °C, a frequency of 3000 Hz and an ultrasound duration of 60 min, in which case shrinkage was 3.35% and color changes were 38.25%. Total phenolic content was 27.41 mg g−1, flavonoid content was 39.36 mg g−1 and DPPH radical inhibition was 34.87%. CONCLUSION Therefore, the use of airborne ultrasound pretreatment demonstrates increased chemical properties compared to the optimal state when drying the echinacea root with an infrared dryer by 54/21–81/64%. Hence, ultrasound pretreatment preserves the quality and quantity of active ingredients in the therapeutic root of Echinacea. © 2021 Society of Chemical Industry.