Comparison of volatile organic compounds and antioxidant activity in Dendrobii Officinalis Flos under different drying methods

Dendrobii Officinalis Flos (DOF) is the flower of Dendrobium officinale Kimura et Migo (Fam. Orchidaceae), distinguished by its uniquely shaped and elegantly pale blossoms. In recent years, this flower has attracted considerable attention in the food industry due to its pleasant flavor and rich nutritional profile. The present study investigated the effects of different drying methods-microwave drying (MD), vacuum drying (VD), hot-air drying (HAD), and vacuum freeze-drying (VFD)-on the appearance, volatile organic compounds (VOCs), and antioxidant capacity of DOF. Analysis via gas chromatography-ion mobility spectrometry (GC-IMS) identified a total of 52 VOCs across the five sample groups, including 16 alcohols, 18 aldehydes, 10 ketones, 4 esters, 1 carboxylic acid, 2 heterocyclic compounds, and 1 disulfide. The findings revealed that fresh flowers contained higher levels of VOCs such as 2-octanone and 3-methyl-1-butanol. VFD-treated flowers showed higher levels of key flavor markers (e.g., (E)-2-butenal, (E)-2-heptenal, (E)-2-pentenal), suggesting their potential as flavor enhancers. VD-treated samples retained more tea-like aromatics (e.g., (Z)-2-penten-1-ol), making them suitable for enhancing premium tea beverages. In contrast, MD and HAD resulted in noticeable color darkening and a significant loss of volatile constituents. The antioxidant activity was evaluated using two complementary assays: the 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation scavenging assay and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Fresh samples showed the strongest bioactivity, followed by VFD-treated ones. VFD was optimal for preserving morphology, flavor, and antioxidant capacity. This study provides a basis for optimizing DOF processing, with drying methods selected for specific applications.