Phytochemical Profiling and Antioxidant Potential of Phlomoides rotata Essential Oils: Insights into Bioactive Constituents

The antioxidant properties and characteristic metabolites of Phlomoides rotata (P. rotata) essential oils (EOs) remain largely unexplored. To address this gap, we combined metabolomic profiling with in vitro antioxidant assays to systematically characterize EOs from P. rotata. Cryoprecipitation of EOs yielded two fractions: crystals (Crs) and crystal-free EOs (CEs). GC-MS identified 125 components (84.41-94.86%), including 94 novel reports in P. rotata. Dominant constituents were long-chain fatty acids (LCFAs, 42.33-75.73%) and their esters (3.44-15.21%), notably palmitic acid (14.49-63.13%), myristic acid, linoleic acid, oleic acid, and methyl palmitate. Eleven norisoprenoids, including trans-β-damascenone, were discovered—a fivefold increase from previously reported diversity—with their biosynthetic pathways elucidated. Eleven chemical markers were established, encompassing geraniol, linalool, trans-β-damascenone, hexahydrofarnesyl acetone, palmitic acid, α-terpineol, myristic acid, phytol, linoleic acid, oleic acid, and methyl palmitate. Palmitic acid, myristic acid, methyl palmitate, and hexahydrofarnesyl acetone showed negligible or pro-oxidative activity. Linoleic acid, oleic acid, trans-β-damascenone, and phytol exhibited concentration-dependent antioxidant effects. Phytol demonstrated exceptional potency, surpassing quercetin in cellular antioxidant activity at 80 μmol/L. CEs exhibited significantly stronger antioxidant capacity in both DPPH and ABTS assays compared to EOs and Crs. Palmitic acid depletion in CEs was identified as a critical factor driving enhanced antioxidant performance. This study not only establishes P. rotata EOs as a rich source of phytol-based antioxidants but also deciphers the dual roles of LCFAs, providing a foundation for developing natural antioxidants.