Origin assessment of green coffee (Coffea arabica) by multi-element stable isotope analysis of caffeine

The delta(13)C(VPDB), delta(2)H(VSMOW) and delta(18)O(VSMOW) values of caffeine isolated from Arabica green coffee beans of different geographical origin have been determined by isotope ratio mass spectrometry (IRMS) using elemental analysis (EA) in the "combustion" (C) and "pyrolysis" (P) modes (EA-C/P-IRMS). In total, 45 coffee samples (20 from Central and South America, 16 from Africa, six from Indonesia, and three from Jamaica and Hawaii) were analysed, as well as three reference samples of synthetic caffeine. Validation was performed by excluding isotope discrimination in the course of sample preparation and determining linear dynamic ranges for EA-P-IRMS measurements. The values for caffeine from green coffee ranged from -25.1 to - 29.9 per thousand, -109 to -198 per thousand, and +2.0 to -12.0 per thousand for delta(13)C(VPDB), delta(2)H(VSMOW), and delta(18)O(VSMOW), respectively. Data evaluation by linear discrimination analysis (LDA) and by classification and regression tree (CART) analysis revealed the delta(18)O(VSMOW) values to be highly significant. Use of LDA on the delta(2)H(VSMOW) and delta(18)O(VSMOW) data from coffee of African and Central/South American provenance led to error rates of 5.7% and 7.7% for adaption and cross validation, respectively.