Characterization, differentiation, and adulteration detection of peppermint essential oil: An NMR approach

Peppermint essential oil (PEO) is a valuable natural product widely used in food, cosmetics, and therapeutics. However, its quality and authenticity are frequently compromised by adulteration and compositional variability. This study explored the application of Nuclear Magnetic Resonance (NMR) technique for the characterization and differentiation of PEO, as well as for the identification of adulterants in commercial PEO samples. Comprehensive analyses of 1D and 2D NMR spectra allowed for the identification of characteristic ¹H NMR signals associated with the key components of PEO, and significant compositional variations between PEOs from different geographical origins were revealed. To facilitate differentiation, a straightforward indicator ratio method was developed to distinguish between PEOs from the United States and India, the two primary production regions. A total of 50 commercial PEO samples were evaluated using NMR in combination with chemometric tools, uncovering a high adulteration rate (42 %). Adulterants, including synthetic chemicals, de-mentholized cornmint oil, and lower-cost oils, were identified. This work demonstrates the potential of NMR as a useful tool for quality assessment and authenticity testing of essential oils. The methodology presented may also be extended to other essential oils to ensure product integrity.