Revealing the impact of different drying methods on the metabolites and bioactivities of Elsholtzia rugulosa based on untargeted metabolomics combined with chemometrics

Elsholtzia rugulosa Hemsl., a plant with a long history of use as a herbal tea, a honey source, and in folk medicine, is widely distributed in Southwest China. To investigate the effect of various drying approaches on the metabolites and biological activities of E. rugulosa, this study applied an untargeted metabolomics approach, utilizing ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) and gas chromatography-mass spectrometry (GC-MS), combined with chemometric analysis of the experimental data. The results indicated that vacuum freeze drying (VFD) yielded the highest contents of total phenols, total flavonoids, and total triterpenoids. In contrast, techniques-shade drying (SD) was more effective in preserving total proteins and soluble total sugar; while hot air drying (HAD) resulted in the most abundant volatile metabolites. Dattelic acid and epigallocatechin were identified as the most significantly differential metabolites in E. rugulosa across the three different drying methods. Additionally, comparative analysis of metabolic pathways identified flavonoid biosynthesis as the core differentially enriched pathway among various metabolites, underscoring its significance in the metabolic response to drying. Compared with SD and HAD, the VFD exhibited superior inhibitory activities against α-glucosidase, α-amylase, and lipase. The findings shed light on optimal processing for enhanced health properties of E. rugulosa. Furthermore, this study offers a systematic insight into the metabolic characteristics and variations in E. rugulosa under three different drying methods, providing a crucial scientific basis for future processing optimization and targeted exploration of bioactive constituents.