Determination of the 2H/1H and 15N/14N Ratios of Alkylpyrazines from Coffee Beans (Coffea arabica L. and Coffea canephora var. robusta) by Isotope Ratio Mass Spectrometry

Abstract

The delta15N(AIR) and delta2H(VSMOW) data for several alkylpyrazines formed during the roasting process of coffee are reported. Samples of commercially available roasted (n = 9) as well as self-roasted (n = 8) coffee beans (Coffea arabica L. and Coffea canephora var. robusta) of different origins were investigated. By use of extracts prepared by simultaneous distillation extraction (SDE) and subsequently fractionated by liquid chromatography on silica gel, on-line capillary gas chromatography-isotope ratio mass spectrometry was employed in the combustion (C) and pyrolysis (P) modes (HRGC-C/P-IRMS) to determine the delta15N(AIR) and delta2H(VSMOW) values, respectively. In addition to the constituents of coffee beans, data for commercial synthetic alkylpyrazines and substances declared to be "natural" were determined. The delta15N(AIR) data for coffee alkylpyrazines under study-2-ethyl-5-methylpyrazine (1) and 2-ethyl-6-methylpyrazine (2) (measured as sum 1/2), 2-ethyl-3-methylpyrazine (3), 2-methylpyrazine (4), 2,5-dimethylpyrazine (5) and 2,6-dimethylpyrazine (6) (measured as sum 5/6), and 2,3-dimethylpyrazine (7), as well as 2,3,5-trimethylpyrazine (8)-varied in the range from +8.3 to -10.2 per thousand, thus revealing their biogeneration from amino acids (delta15N(AIR) ranging from +8 per thousand to -10 per thousand). The delta2H(VSMOW) values were determined in the range from -5 per thousand to -127 per thousand. Owing to the analytical differentiation observed between coffee alkylpyrazines and synthetic/"natural" samples of 3, 4, and 7, authenticity assessment of coffee-flavored products seems to be promising, provided that extended data will be available in the future. In the literature, there were no IRMS data available for the alkylpyrazines (1-8) under study.