Appearance, Microstructure, and Bioactive Components of Bletilla striata Tuber as Affected by Different Drying Methods

Bletilla striata is widely used as healthy food and herbal medicine for its hemostasis, anti-ulcer, promoting wound healing, antibacterial, anti-inflammatory, and immune regulatory functions. Drying methods affect the quality of herbal medicine, including appearance and more importantly the content of active components, which play a decisive role in the medical and tonic functions. In this study, hot air drying (HD), infrared drying (ID), microwave drying (MD), vacuum drying (VD), and freeze drying (FD) were used to evaluate the effect of drying methods on the quality of B. striata tubers. Significant effects of drying methods on the appearance, color, microstructure, water activity, water content, and active component content of B. striata tubers were observed. FD-treated samples retained the majority of the appearance, color, and microstructure, while samples processed with other methods exhibiting various deformation and discoloration. In addition, a significant decline in water content and water activity was detected in FD-treated samples, yet, the content of active components, such as B. striata polysaccharides, total polyphenols, and militarine, was relatively high. After comprehensive comparison, freeze-drying is proposed to be the most suitable method for B. striata drying, which is also recommendable for other tuber drying.