Effect of Ultrasound-vacuum Pretreatment on Drying Kinetics and Physical Characteristics of Hot Green Pepper

Hot green pepper (Capsicum annuum) is a commonly used spice , that is highly spoilable due to  high moisture content. Therefore, drying is valuable in order to reduce volume, transportation cost and longer shelf life. For this purpose, using an ultrasound-vacuum bath and a water bath-vacuum (50 and 70 °C), under vacuum condition, until reaching 50% humidity were used as a pre-treatment. Then all samples were dried using microwave (360 w) until reaching 10% final moisture content. The diffusion coefficient of hot green pepper slices was calculated using the Fick diffusion model. Applying ultrasound-vacuum pretreatment caused a decrease of the drying time, and increased the diffusion coefficient and drying speed of the product in the microwave sample compared to other samples significantly (P<0.05). Ultrasonic pretreatment significantly reduced changes in the percentage of size change and browning index and increased the rehydration ratio of the sample significantly (P<0.05). In general, applying ultrasonic as a pre-treatment helps to dry green pepper in microwave conditions and increases the speed of drying in microwave and better maintaining the physical characteristics of the product. Finally, the use of ultrasonic can be a perspective to produce a product with better quality and appearance characteristics and more marketability.