Low-field 1H NMR spectroscopy for distinguishing between arabica and robusta ground roast coffees

• A new screening method for identifying the species in ground roast coffees using low-field NMR spectroscopy.
• A calibration-free statistical approach to detecting adulteration of arabica with robusta coffee.
• A study of time-varying spectral changes in the 16-OMC component of lipophilic extracts following sample preparation.

This work reports a new screening protocol for addressing issues of coffee authenticity using low-field (60 MHz) bench-top 1H NMR spectroscopy. Using a simple chloroform-based extraction, useful spectra were obtained from the lipophilic fraction of ground roast coffees. It was found that 16-O-methylcafestol (16-OMC, a recognized marker compound for robusta beans) gives rise to an isolated peak in the 60 MHz spectrum, which can be used as an indicator of the presence of robusta beans in the sample. A total of 81 extracts from authenticated coffees and mixtures were analysed, from which the detection limit of robusta in arabica was estimated to be between 10% and 20% w/w. Using the established protocol, a surveillance exercise was conducted of 27 retail samples of ground roast coffees which were labelled as “100% arabica”. None were found to contain undeclared robusta content above the estimated detection limit.

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