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.
Highlights
Coffee is a major tropical agricultural crop, and one of the most widely traded global commodities (International Coffee Organization., 2017b)
In a recent paper (Defernez et al, 2017), we reported the use of lowfield (60 MHz) 1H NMR spectroscopy to screen lipophilic extracts from ground roast coffees for the undeclared presence of robusta in products labelled “100% Arabica”
The presence of the 3.16 ppm marker peak was confirmed in every sample, irrespective of genetic background and provenance. In view of these results, we propose that 16-OMC and 16-OMK is likely to be present at low levels in most if not all Arabica coffee beans, but in many previous studies had not been detected (Bonnlander et al, 2007; de Roos et al, 1997; Defernez et al, 2017; Kamm et al, 2002; Kurzrock & Speer, 2001; Pacetti et al, 2012; Speer & Kölling-Speer, 2006; Speer & Mischnick, 1989)
Summary
Coffee is a major tropical agricultural crop, and one of the most widely traded global commodities (International Coffee Organization., 2017b). (Arabica coffee) and C. canephora Pierre ex A. Generally more difficult to grow than robusta, Arabica represents around 60% of global production. Due to the superior organoleptic properties of the roasted beans, Arabica coffees command a higher price than robusta. The opportunity for fraudulent economic gain by substituting Arabica with robusta beans is obvious (Toci, Farah, Pezza, & Pezza, 2016). The identity of intact beans can be verified by inspection (International Coffee Organization, 2017b; Mendonca, Franca, & Oliveira, 2009), but for ground roast products some form of chemical assay becomes necessary
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