Drying methods for Rheum tanguticum: a comprehensive study of quality traits and metabolite dynamics

Rheum tanguticum (R. tanguticum) originates from high-altitude regions such as Qinghai and Gansu in China. It serves as both a precious traditional medicinal botanical drug and a potential functional food, and its extensive pharmacological activities have stimulated global demand. However, existing research predominantly focuses on optimizing individual drying techniques or single bioactive metabolites, failing to integrate multi-omics technologies to elucidate the chemical and physical alterations induced by drying. To this end, we evaluated five drying methods by integrating an approach that links physical indicators with chemical composition, revealing that, for the preservation of physical indicators, especially color and rehydration properties, vacuum freeze drying (LD) is optimal; for the retention of the key pharmaceutical metabolite free anthraquinones, microwave drying (WB) is the most effective. Whereas in the comprehensive evaluation of multi-dimensional quality, SG is optimal. Metabolomic analysis confirmed that LD and YG were most effective in preserving key metabolites. Flavonoids, phenolic acids, and amino acids collectively form the core metabolites of differential metabolites in dried R. tanguticum, primarily enriched in pathways such as purine metabolism. Collectively, this work systematically elucidates the impact of drying on R. tanguticum's metabolite profile and physicochemical traits, offering both a theoretical basis for its precision processing and a transferable framework for optimizing drying techniques in related medicinal edible plants.