Effects of various drying methods on chemical constituents, in vitro biological activities and metabolites of Dendrobium chrysotoxum Lindl. stems

Dendrobium chrysotoxum stems (DCS) are valuable in the traditional Chinese medicine and in functional foods catagory. Their bioactive composition is critically influenced by the post-harvest drying methods. Here, we evaluated the effect of five drying methods (shade drying (SD), oven drying (OD), vacuum freeze-drying (FD), microwave drying (MD), and infrared drying (ID)), on the bioactivity of the compounds in the DCS. OD-treated stems exhibited elevated total flavonoid contents (TFC) and total phenolic content, along with strong antioxidant activities. Although ID and MD yielded higher polysaccharides and alkaloids contents, they caused a marked deterioration in appearance. In contrast, FD better preserved the stem color and yielded higher erianin contents and anti-inflammatory activities than the thermal drying methods. Under OD, zeatin biosynthesis was specifically differentially regulated, as compared to the other methods. Additionally, L -homoserine, (7 S , 8 S )-DiHODE, and L -pipecolate showed positive correlations with erianin and TFC in the OD group. Based on a comprehensive evaluation, this study offers scientific and technical support for selecting appropriate drying methods to achieve desirable appearance and product quality of DCS.