Bletilla striata (Thunb.) Reixchb.f., generally known as Baiji in China, belongs to Orchidaceae. Such plant is used as ornamental plant in Europe and North America, as well as East Asia (Masuhara & Katsuya, 1989; Wiart, 2012; Xu, Chen, Aci, Pan, Shangguan, Ma, et al., 2018; Yamamoto, Miura, Fuji, Nagata, Otani, Yagame, et al., 2017). As the tuber of B. striata has high edible and nutritional value, it was listed into healthy diet by the Health Ministry of PRC (the Health Ministry of PRC, 2002). In addition, the dried tuber of B. striata has been widely used as herbal medicine in East Asia for thousands of years(Chinese Pharmacopoeia Commission, 2015; Park, Woo, Choi, Lee, & Lee, 2014), showing a wide range of medicinal functions such as hemostasis (C. Zhang, Zeng, Liao, Fu, Luo, Yang, et al., 2017; Q. Zhang, Qi, Wang, Xiao, Zhuang, Gu, et al., 2019), anti-ulcer (Liao, Zeng, Hu, Maffucci, & Qu, 2018; C. Zhang, Gao, Gan, He, Chen, Liu, et al., 2019), promoting wound healing (C. Zhang, He, Chen, Shi, Qu, & Zhang, 2019; H. Zhou, Jin, Gu, Chen, & Xia, 2019), antibacterial (Guo, Binling, Chen, Jin, Jiang, Ding, et al., 2016; S. Jiang, Wan, Lou, Yi, Zhang, Zhou, et al., 2019), anti-inflammatory (Yue, Wang, Wang, Du, Shen, Tang, et al., 2016; D. Zhou, Chang, Liu, Chen, Yang, Hao, et al., 2020; Zu, Liu, Tian, Jin, Jiang, Li, et al., 2019) and immune regulation (Y. Wang, Han, Li, Cui, Ma, Qi, et al., 2019).
The chemical components of B. striata tuber play decisive roles of the medical and tonic functions. To date, more than 150 components have been isolated, including B. striata polysaccharides (BSP), bibenzyls, phenanthrenes, triterpenoids, steroids and saponins (Xirui He, Wang, Fang, Zhao, Huang, Guo, et al., 2016; Xu, Pan, & Chen, 2019). BSP accounts for 20–40% of the dry weight of B. striata tuber, often used as one of the quality evaluation indexes of B. striata (Y. Zhang, Sun, He, Wang, Wang, Yuan, et al., 2018). Polyphenols are another kind of important active ingredients of B. striata, including bibenzyls, phenanthrenes, militarine, etc (X. Wang & Lou, 2004; Y. Zhang, et al., 2018). The militarine content is high among them, and it can be detected by HPLC or UPLC as an indicator component of B. striata quality evaluation (Xun He, Wang, Li, Wang, & Zhou, 2009; A. Wang, Yan, Lan, Liao, Wang, & Li, 2014).
After harvesting, fresh B. striata tuber is always cut into pieces and dried for storing and using. Therefore, drying methods is the crucial factor affecting the quality of B. striata tuber, in addition to the planting and harvesting process. As an important part of herbal medicine processing, drying methods not only directly affects the appearance of the medicine, but also affects its components. In this study, B. striata tubers were treated by hot-air drying (HD), infrared drying (ID), microwave drying (MD), vacuum drying (VD) and freeze drying (FD). The effects of different drying methods on the appearance, microstructure and bioactive components of B. striata tuber were evaluated to provide a scientific basis for the production and processing of B. striata tuber.