Evaluating How Different Drying Techniques Change the Structure and Physicochemical and Flavor Properties of Gastrodia elata

We evaluated the drying characteristics and structure, as well as the physicochemical and flavor properties, of G. elata treated by hot-air drying (HAD), vacuum drying (VD), freeze drying (FD), microwave drying (MD), and microwave vacuum drying (MVD). We found that MD and MVD showed the shortest drying times, while FD and MVD were able to better retain the active ingredients and color of the samples. However, the different drying methods did not change the internal structure of G. elata, and its main components did not fundamentally change. In addition, E-nose and HS-SPME-GC-MS effectively differentiated the volatile components, and 36 compounds were detected by HS-SPME-GC-MS. Of these samples, alcohols and aldehydes were the main substances identified. In particular, MVD samples possessed the most species of organic volatiles, but the FD method effectively eliminated pungent odors from the G. elata. Overall, MVD shows the most obvious advantages, improving drying rate while maintaining the original shape, color, and active components in G. elata. Ultimately, MVD is the preferred method to obtain high-quality dried G. elata, and our drying-method characterizations can be used to investigate similar structural and chemical changes to similar herbs in the future.

Effects of Steam and Water Blanching on Drying Characteristics, Water Distribution, Microstructure, and Bioactive Components of Gastrodia Elata

In the current work, the effects of steam and boiling water blanching on the drying characteristics, water distribution, microstructure, and contents of bioactive substances of Gastrodia elata (G. elata) were explored. Results showed that the degree of steaming and blanching was related to the core temperature of G. elata. The steaming and blanching pretreatment increased the drying time of the samples by more than 50%. The low-field nuclear magnetic resonance (LF-NMR) of treated samples showed that the relaxation time corresponded to water molecule states (bound, immobilized, and free) and G. elata became shorter, which indicated a reduction in free moisture and increased resistance of water diffusion in the solid structure during drying. Hydrolysis of polysaccharides and gelatinization of starch granules was observed in the microstructure of treated samples, which was consistent with changes in water status and drying rates. Steaming and blanching increased gastrodin and crude polysaccharide contents and decreased p-hydroxybenzyl alcohol content. These findings will contribute to a better understanding of the effect of steaming and blanching on the drying behavior and quality attributes of G. elata.