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Low Field (LF) Nuclear Magnetic Resonance (NMR) spectrometers have been used for routine inline quality control in the processed meat industry for many years.   Recent advancements have made the technology more accessible for other applications.

This proof-of-concept study (open access) demonstrates the potential of LF NMR for rapid oil authentication in an industrial setting. Their approach was based on solvent-free oil analysis using a single scan ¹H NMR measurement on a LF 80 MHz NMR instrument. The analysis identified the allylic signals at δ 2.0 ppm as a potential diagnostic region, effective in detecting adulteration in the oil samples. They limited the integration to this one spectral region in order to make data analysis rapid and easy to use in a food factory.

The authors demonstrated successful detection of adulteration in two types of vegetable oils rich in polyunsaturated fatty acids (PUFA), rapeseed and sunflower oil, at levels ranging from 5 % to 25 %. Specifically, the study found that adulteration in rapeseed oil could be detected at levels as low as 5 % when adulterated with soybean oil, 10 % when adulterated with sesame and cottonseed oils, and 25 % for corn oil and safflower oil. In the case of sunflower oil, cottonseed oil can be identified at 5 % adulteration, while corn, sesame, and safflower oils can be detected at 25 % adulteration.

The authors consider that the approach is fast, user-friendly, and ecological.  LF NMR could be a valuable tool for identifying adulteration in edible oils, with applications in various industries. This method would benefit from further research to validate the allylic region as a diagnostic region of oil adulteration.

Photo by Fulvio Ciccolo on Unsplash

This study (open access) used Nuclear Magnetic Resonance (NMR) ratios of key signals to differentiate the origin of Peppermint Essential Oil (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.  Signals were assigned for 12 key components.  Significant compositional variations between PEOs from different geographical origins were revealed.

The US and India are the two primary production regions for PEO.  The model was built from authentic PEO samples of US origin (18),  India origin (15), twenty-seven blended PEO (US/India) samples and five de-mentholized cornmint (Mentha arvensis) oils.  All reference samples were collected by the National Center for Natural Products Research (NCNPR), University of Mississippi.

To facilitate differentiation, a straightforward indicator ratio method was developed to distinguish between PEOs from the United States and India.

A total of 50 commercial PEO samples were evaluated using the indicator model.  These included forty-three samples claiming to be pure PEO and seven claiming to be premium or therapeutic grade PEO.  They were purchased from various domestic and international suppliers of the US market

Results indicated a high adulteration rate (42 %). Adulterants, including synthetic chemicals, de-mentholized cornmint oil, and lower-cost oils, were identified.

The authors conclude that NMR is 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.

For an explanation of the principles of NMR see FAN's introductory guide.

Photo by Anna Hliamshyna 💙💛 on Unsplash

This application note from Canadian testing company Purity-IQ builds upon published methods to describe the use of proton NMR in authenticity testing of herbs and spices.  Proton NMR, with non-targeted metabolomic profiling, can be used for botanical species authentication but also to detect product anomalies.  It is particularly useful for detecting dyes, as both natural and synthetic dyes tend to contain spectrally-distinctive aromatic ring structures.  In this application, the principle was demonstrated by the clear differentiation of paprika spiked with Sudan dyes, turmeric spiked with metanil yellow, and beet/grape extracts spiked with black rice extract.

Image from the application note.