Tissue-Specific Metabolite Profiling and Antioxidant Potential of Eclipta prostrata Following Different Drying Treatments

Eclipta prostrata is a medicinal plant widely used in traditional medicine because of its antioxidant and therapeutic properties; however, comprehensive information on the effects of drying methods on tissue-specific phytochemical composition remains limited. This study evaluated the influence of freeze drying (FD), shade drying (SD), and oven drying (OD) on the antioxidant activity, phenolic and flavonoid contents, elemental composition, and metabolomic profiles of flowers, leaves, roots, and stems of E. prostrata. Antioxidant activity was determined using DPPH, ABTS, and FRAP assays; elemental composition was analyzed by ICP-OES; and untargeted metabolomic profiling was performed using LC-QTOF-MS in both positive and negative ionization modes. Freeze-dried samples consistently exhibited the highest antioxidant capacity and retained the greatest total phenolic and flavonoid contents, particularly in flowers, whereas oven drying generally resulted in the greatest reduction in antioxidant activity, especially in roots. ICP-OES analysis demonstrated tissue-dependent differences in mineral composition, with calcium, potassium, magnesium, sodium, iron, zinc, and manganese being the predominant essential elements retained after drying. Untargeted metabolomics revealed tissue-specific metabolic responses to drying, with root tissues exhibiting the greatest metabolomic variation, whereas flowers and stems remained comparatively stable. Multivariate analyses indicated that drying primarily altered the relative abundance of metabolite classes rather than the overall metabolome. The major metabolites detected belonged to flavonoids, coumestans, phenolic acids, lipid-derived metabolites, amino acid derivatives, oxylipins, and triterpenoid/saponin-related compounds, which are associated with the medicinal properties of E. prostrata. These findings demonstrate that both plant tissue and drying method significantly influence the retention of bioactive compounds and provide valuable information for optimizing post-harvest processing to preserve the phytochemical quality and therapeutic potential of E. prostrata.