Characteristic Metabolites and Antioxidant Activities of Essential Oils from Phlomoides rotata (Benth. ex Hook. f.) Mathiesen

Abstract

Limited research has been conducted on the metabolites present in the essential oils (Es) of Phlomoides rotata (Benth. ex Hook. f.) Mathiesen (PR, syn. Lamiophlomis rotata (Benth.) Kudô), and their potential pharmacological activities, such as antioxidant and anticancer properties, are often overlooked. We conducted a metabolomics-based screening to identify the characteristic metabolites (CMs) present in the Es extracted from PR. Furthermore, we evaluated their in vitro antioxidant activities (AOAs). The Es obtained through hydro-distillation are characterized by a light yellow color and a fresh, elegant fragrance. Cryoprecipitation was used to separate the crystals (Cs) from the Es, resulting in the extraction of crystal-free essential oils (CFs). A total of 107 components belonging to 8 categories were identified and quantified in the Es, Cs, and CFs using GC-MS and GC-FID techniques. Among these components, 76 were reported for the first time in the Es of PR. The major compounds identified include long-chain fatty acids (LCFAs) and their esters, such as palmitic acid (PA), myristic acid (MA), linoleic acid (LA), oleic acid (OA), and methyl palmitate. Additionally, seven C13-norisoprenoids, with trans-β-damascenone being particularly notable for its flavor, were also identified. A sum of nine CMs were identified in the Es, including PA, MA, LA, OA, methyl palmitate, hexahydrofarnesyl acetone, phytol, trans-β-damascenone, and hexanal. The main metabolic pathway in the Es is the biosynthesis of FAs and terpenoids revealed by MetaboAnalyst 6.0 and KEGG analyses. Furthermore, the in vitro AOAs of the Es, Cs, CFs, and four selected CMs (PA, MA, LA, and OA) were evaluated. Generally, PA and MA exhibited pro-oxidant activities (POAs) or weak AOAs. LA and OA demonstrated POAs or weak AOAs at lower concentrations, but at higher concentrations, they displayed medium to strong AOAs. Importantly, the CFs exhibited stronger AOAs compared to the corresponding Es, which may be attributed to their different PA content. Overall, this study provides valuable insights into the potential utilization of Es from PR.