Fully automatic quantitation of eight different metabolites in coffee using 1H‐NMR spectroscopy and the PULCON methodology

Abstract

AbstractBackgroundCoffee contains a plethora of constituents with some of them being especially important either due to their physiological effects or as quality markers. As quantitative proton nuclear magnetic resonance spectroscopy (1H‐NMR) has been established as a fast and reliable analytical tool its application was evaluated for the simultaneous quantitation of lactic acid, acetic acid, formic acid, caffeine, caffeoylquinic acid (CQA) isomers, N‐methylpyridinium, trigonelline, and 5‐hydroxymethylfurfural (HMF) in aqueous extracts of roasted Coffea arabica samples.ResultsSimultaneous quantitative determination was achieved by an automated analysis based on the PULCON methodology (pulse length‐based concentration determination). The method was validated regarding linearity, accuracy, precision, limit of detection (LOD), and limit of quantitation (LOQ). Recovery rates were between 76% (CQA) and 116% (HMF), and precision was between 1.7% (caffeine) and 10.3% (HMF). The LOD varied between 0.06 g/kg (HMF) and 1.35 g/kg (caffeine and CQA), with the LOQ being between 0.22 g/kg (HMF) and 4.87 g/kg (CQA). To verify the results of the 1H‐NMR method, caffeine, trigonelline, HMF, 3‐CQA, 4‐CQA, and 5‐CQA were additionally quantitated by HPLC‐DAD and the results were compared. The described 1H‐NMR method was additionally applied to coffee samples that contained different coffee defects. Results showed only slight changes in the concentrations of the analytes by adding defective beans to defect‐free coffee.DiscussionThe developed 1H‐NMR approach was proven to be fast (30 min), reliable, and precise. Thus, it is well suited to analyze several coffee constituents of interest in a large number of samples in, for example, quality control.