16-O-methylcafestol is present in ground roast Arabica coffees: Implications for authenticity testing

• Published in: Food chemistry 2018-05, Vol.248, p.52-60
• Main Authors: Gunning, Yvonne, Defernez, Marianne, Watson, Andrew D., Beadman, Niles, Colquhoun, Ian J., Le Gall, Gwénaëlle, Philo, Mark, Garwood, Hollie, Williamson, David, Davis, Aaron P., Kemsley, E. Kate
• Format: Article
• Language: English
• Subjects: Adulteration; Arabica; Authentication; Coffee; Low-field; NMR; Robusta; Species; Spectroscopy
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2017.12.034

•Lipophilic extracts of ground roast Arabica coffees were authenticated by benchtop NMR.•Small amounts of esterified 16-O-methylcafestol were found in Arabica coffees.•The compound identity was confirmed by NMR and MS experiments.•16-OMC remains a useful marker for non-Arabicas as these contain much higher amounts.•6 out of 60 retail Arabicas contained significant amounts of non-Arabica species. 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.