Specific energy consumption and quality of Citrus hystrix leaves treated using convective and microwave vacuum methods

This study compared the effects of three drying techniques on Citrus hystrix leaves: convective hot air drying (CAD), microwave vacuum drying (MVD), and convective hot air pre-drying followed by microwave vacuum finishing drying (CPD-MVFD). As a control, freeze-drying (FD) was employed. As a result, the modified Page model best described the drying kinetics of C. hystrix leaves. Furthermore, CPD-MVFD significantly lowered the specific energy consumption by 51.6%. Meanwhile, MVD, at density of 12 W/g, retained the greatest antioxidant capacity, TPC content, and volatile compounds. In physical terms, CPD-MVFD and MVD performed best in retaining the color characteristics of C. hystrix leaves under all circumstances. Finally, all samples were microbiologically stable. In conclusion, it is suggested that MVD with a power density of 12 W/g be used for drying C. hystrix leaves, due to its low specific energy consumption, strong antioxidant and TPC capacity, and good recovery of volatile organic compounds. Practical applications: Citrus hystrix, also known as kaffir lime, is a popular medicinal plant that is high in essential oils and possesses potent antibacterial, anticancer, anti-inflammatory, and antioxidant properties. However, the essential oils of C. hystrix are prone to degradation during post-harvesting activities such as drying. Drying is an important procedure because the drying temperature may impact the retention of essential oils. Furthermore, drying is reported to consume the most energy compared with other post-harvesting procedures such as extraction. The investigation of microwave-vacuum drying demonstrated the considerable potential of this method to retain essential oils while consuming very little energy throughout the drying process. Further investigation and application of this drying procedure in the food industry might increase the quality of essential oils obtained from C. hystrix or other medicinal plants.