The effect of cold plasma pretreatment on drying efficiency of beetroot by intermittent microwave-hot air (IMHA) hybrid dryer method: Assessing drying kinetic, physical properties, and microstructure of the product
Amir Kamkari, Saeed Dadashi, Maryam Khakbaz Heshmati, Jalal Dehghannya, Yousef Ramezan
Abstract
This study examined the effects of cold plasma (CP) pretreatment with durations of 1, 3, and 5 minutes on drying kinetics, microstructure, and physical properties, including shrinkage, rehydration ratio (RR), and bulk density of beetroot dried samples using intermittent microwave-hot air (IMHA) drying at 40 °C and pulse ratios (PR) of 1 and 2. While increasing PR decreased drying rate (DR) and effective moisture diffusivity ( Deff ), increasing microwave power from 180 to 600 W increased both, reducing drying time and specific energy consumption (SEC). Extended CP-pretreatment doubled DR, 66% increased Deff , and 24% reduced SEC. Both increasing CP-pretreatment time and microwave power had similar effects on shrinkage, RR, and bulk density, but CP-pretreatment was more prominent; reducing shrinkage by 18%, bulk density by 23%, and increasing RR by approximately 36% in 5-minutes. X-ray imaging showed that 600 W of microwave power increased porosity by 87%, while 5-minute CP-pretreatment increased it by 27%. As the optimum condition, CP-pretreatment for 5 minutes, continuous microwave application, and 600 W of MW power produced the best kinetics and physical properties. Overall, the results demonstrated that the appropriate CP-pretreatment duration could produce high-quality dried samples. • An intermittent microwave-hot air (IMHA) drying process was designed to dry beetroot. • Cold Plasma (CP) pretreatment reduced drying time significantly. • X-ray imaging showed 27 and 87% porosity increase by 5-min CP-pretreatment and 600 W MW, respectively. • The combination of CP-pretreatment and IMHA reduced structural damage significantly.