Drying of ultrasound pre-treatment Poulk leaves (Stachys schtschegleevii Sosn.) and survey of its physical and chemical properties

Using the ultrasound waves has been studied as a new pre-treatment for food drying in recent years. The aim of the present research is survey of the ultrasound pre-treatment effects (59 kHz, 10 min) on some physical and chemical properties of dried Poulk leaves (Stachys schtschegleevii Sosn.) using by hot dry at 40, 50 and 60°C with air velocity of 1 m/s. The results of this research showed that the lowest drying time, total phenol, antioxidant capacity and the maximum drying kinetics, reabsorption of water, and diffusion coefficient (2.42×10-10 to 4.52×10-10m2/s) was observed in the ultrasound pretreatment samples, additionally the activation energy in untreated samples was less compared to ultrasound samples. The fitted mathematical models of rate drying with the experimental data showed the model Page can satisfactory describe the rate drying curve of Poulk leaves by hot air with high correlation coefficient (R2=0.998), the minimum root mean square error (RMSE=0.02109), and chisquare (χ2=0.00058).