Lipophilic extracts of ground roast Arabica coffees were authenticated by benchtop NMR.
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Small amounts of esterified 16-O-methylcafestol were found in Arabica coffees.
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The compound identity was confirmed by NMR and MS experiments.
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16-OMC remains a useful marker for non-Arabicas as these contain much higher amounts.
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6 out of 60 retail Arabicas contained significant amounts of non-Arabica species.
Abstract
High-field and low-field proton NMR spectroscopy were used to analyse lipophilic extracts from ground roast coffees. Using a sample preparation method that produced concentrated extracts, a small marker peak at 3.16 ppm was observed in 30 Arabica coffees of assured origin. This signal has previously been believed absent from Arabicas, and has been used as a marker for detecting adulteration with robusta. Via 2D 600 MHz NMR and LC-MS, 16-O-methylcafestol and 16-O-methylkahweol were detected for the first time in Arabica roast coffee and shown to be responsible for the marker peak. Using low-field NMR, robusta in Arabica could be detected at levels of the order of 1–2% w/w. A surveillance study of retail purchased “100% Arabica” coffees found that 6 out of 60 samples displayed the 3.16 ppm marker signal to a degree commensurate with adulteration at levels of 3–30% w/w.
