NMR approach for differentiation and adulterant detection of peppermint essential oils

Authors: ZHAO, JIANPING - University Of Mississippi; Wang, Mei; LEE, JOSEPH - University Of Mississippi; ALI, ZULFIQAR - University Of Mississippi; KHAN, IKHLAS - University Of Mississippi

Submitted to: Journal of Pharmaceutical and Biomedical Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2025
Publication Date: 5/1/2025
Citation: Zhao, J., Wang, M., Lee, J., Ali, Z., Khan, I. 2025. NMR approach for differentiation and adulterant detection of peppermint essential oils. Journal of Pharmaceutical and Biomedical Analysis. 263,2025:116941. https://doi.org/10.1016/j.jpba.2025.116941.
DOI: https://doi.org/10.1016/j.jpba.2025.116941

Interpretive Summary: Peppermint essential oil (PEO) is a versatile and aromatic essential oil derived from leaves of the peppermint plant, scientifically known as Mentha x piperita. Renowned for its refreshing minty aroma and numerous potential benefits, PEO holds a significant position in traditional herbal medicine, contemporary wellness practices, and even the culinary industry. Despite its widespread use and economic importance, PEO is frequently subjected to adulteration. While ISO standards for PEO are in place, identifying complex adulteration practices remains challenging. Nuclear Magnetic Resonance (NMR) spectroscopy has emerged as a powerful technique for distinguishing and uncovering adulterants in PEO. This research employed NMR to explore the variation of chemical composition and component distributions across various categories of oil samples: US PEO, India PEO, blended PEO, and de-mentholized cornmint oil (DCO). Additionally, fifty commercially labeled PEO samples from the market were examined. Through a combination of NMR and chemometric analysis, outlier samples were identified and subjected to further investigation for potential adulteration, leading to the discovery and characterization of various adulterants. Out of the 50 PEO commercial samples, 21 were found to be adulterated. This study illustrated the indispensable role of NMR spectroscopy as a tool for distinguishing between different PEO varieties and identifying adulterants. As a result, it contributes to bolstering quality assurance and ensuring authenticity within the essential oil industry.

Technical Abstract: Peppermint essential oil (PEO), obtained from steam distillation of the fresh aerial parts of peppermint plant (Mentha x piperita L.), is a versatile and popular natural product with many benefits for health and wellness. Not only has it been widely used in foods, beverages, soaps, and cosmetics, but it has also been used to address health conditions such as the common cold, sinus infections, headaches, and neurological issues. However, due to high demand and limited supply, it is often subject to adulteration by unscrupulous sellers in an attempt to increase profits. The adulteration of PEO is a serious issue that can compromise the quality, purity, and efficacy of the oil. Most importantly, adulteration may also pose safety risks for the consumer. Therefore, it is important to detect and prevent adulteration of PEO by using reliable and efficient methods that can identify the presence of adulterants in the oil. In this study, nuclear magnetic resonance spectroscopy (NMR) was applied to explore the variation of chemical composition and the distribution of component contents in oil samples belonging to different categories, i.e. US PEO, India PEO, blend PEO, and de-mentholised cornmint oil (DCO). Additionally, fifty commercial PEO-labelled samples obtained from the marketplace were evaluated. Outlier samples were detected and further explored for possible adulteration based on NMR and chemometric analysis resulting in the detection and identification of various adulterants, including the synthetic chemicals triethyl citrate, bis(2-ethylhexyl) azelate, bis(2-ethylhexyl) adipate, and diethyl phthalate, as well as DCO and vegetable oils. Among the 50 commercial PEO samples, 21 were found to be adulterated. This study demonstrated that NMR can be a useful and effective tool in differentiating PEOs, detecting PEO adulterations, and identifying adulterants.