Characterization and potential applications of chemical composition and biological activities in combined essential oils of Mentha haplocalyx and Schizonepeta tenuifolia

Mentha haplocalyx and Schizonepeta tenuifolia constitute a classic herbal pair with dual medicinal and food applications, traditionally combined to dispel wind-heat and clear toxic heat. However, the physicochemical transformations and synergistic mechanisms underlying their volatile co-extraction remain insufficiently understood. This study systematically characterized the volatile profiles, olfactory traits, antioxidant capacities, and antibacterial activities of essential oils obtained from single herbs (M. haplocalyx, EOmh; S. tenuifolia, EOst) and their co-distilled combination (EOcc). Gas chromatography-mass spectrometry (GC-MS) coupled with an electronic nose revealed 19, 18, and 22 volatile compounds in EOmh, EOst, and EOcc, respectively. It identified 11 core shared constituents and 8 newly emerging chemical entities unique to EOcc. In vitro bioassays demonstrated that EOcc exhibited superior antibacterial potency against Escherichia coli and Methicillin-Resistant Staphylococcus Aureus (MRSA) compared to single-herb oils, while the activity against Staphylococcus aureus followed the hierarchy of EOmh > EOcc > EOst. Furthermore, EOcc displayed pronounced ABTS radical neutralization and significantly enhanced DPPH radical-scavenging activity relative to EOst. Overall, herb–herb co-distillation structurally reshapes the volatile landscape and amplifies specific bioactivities, providing a mechanistic foundation for the rational utilization of this herbal pair in functional foods and phytotherapeutics.