Novel Microwave-Assisted Drying Technique for Thai Medicinal Herbs Utilizing an Asymmetrical Double-Feed Microwave/Vacuum System
Abstract
This study explored the drying efficiency of various medicinal herbs – Fa Talai Jone, Gotu Kola, Pueraria Krua, Turmeric, Plai and Black Galingale – employing different methods, such as a low-power microwave system with asymmetric biphasic waves coupled with a vacuum at power settings of 800 W and 1,600 W, and traditional hot-air oven and freeze-drying techniques. The investigation assessed the effect of different drying approaches on herb quality for batches of 1,000 g and 2,000 g, noting the temperatures used: 80 oC for hot air and 60 oC for microwaves at 1,600 W. Findings demonstrated that microwave drying, especially when integrated with a vacuum system, outperformed hot-air oven drying in terms of efficiency, achieving faster moisture reduction without compromising herb volume or moisture content. In contrast, hot air-drying exposed herbs to greater temperatures, resulting in significant colour changes and texture degradation, whereas freeze-drying preserved the herbs’ original volume, colour and texture intact. The study further examined how vacuum pressure and microwave energy contributed to moisture elimination, underscoring microwave technology’s ability to rapidly reduce moisture content and efficiently generate heat. Additionally, post-drying analyses of microbial, yeast and mould levels varied across the drying methods, indicating that microwave and vacuum drying technologies could significantly enhance the preservation and drying power of medicinal herbs, making them preferable for processing in the pharmaceutical and herbal industries.