Evaluation of drying kinetics, physical properties, bioactive compounds, antioxidant activity and microstructure of Acanthopanax sessiliflorus fruits dried by microwave-assisted hot air drying method

The A. sessiliflorus fruits have garnered attention among researchers for their medicinal and nutritional properties. However, traditional hot air drying (HAD) suffers from drawbacks, including extended drying time and loss of active substances. In this study, a microwave-assisted hot air drying (MAHD) method was implemented to dry A. sessiliflorus fruits. The material was initially dried by hot air to a certain moisture, followed by the microwave and hot air were used until the end. Drying was performed at different temperatures (55–75 °C) and powers (0.3–0.9 W/g), with freeze-drying (FD) as a control. The results showed that MAHD significantly reduced the drying time by 51–81% compared to HAD at 55 °C. Moreover, both FD and MAHD methods demonstrated high color retention and rehydration ratios. The active substance content including total anthocyanin content, total flavonoids content and total phenolic content was affected by microwave power and drying temperature. The samples of MAHD showed stronger antioxidant activity and active substance retention than those from HAD. The results of microstructure observation presented that the sample showed a distinct porous structure in the sample of MAHD.