Identification of markers of sensory quality in ground coffee: an untargeted metabolomics approach.

INTRODUCTION: In the last years, consumers increased the demand for high-quality and healthy beverages, including coffee. To date, among the techniques potentially available to determine the overall quality of coffee beverages, metabolomics is emerging as a valuable tool. OBJECTIVE: In this study, 47 ground coffee samples were selected during the 2018 Edition of the "International coffee tasting" (ICT) in order to provide discrimination based on both chemical and sensory profiles. In particular, 20 samples received a gold medal ("high quality" group), while lower sensory scores characterized 27 samples (without medal). METHODS: Untargeted metabolomics based on ultra-high pressure liquid chromatography coupled with quadrupole-time-of-flight (UHPLC-QTOF) and head space-gas chromatography coupled with mass spectrometry platforms followed by multivariate statistical approaches (i.e., both supervised and unsupervised) were used to provide new insight into the searching of potential markers of sensory quality. RESULTS: Several compounds were identified, including polyphenols, alkaloids, diazines, and Maillard reaction products. Also, the headspace/GC-MS highlighted the most important volatile compounds. Polyphenols were scarcely correlated to the sensory parameters, whilst the OPLS-DA models built using typical coffee metabolites and volatile/Maillard compounds possessed prediction values > 0.7. The "high quality" group showed specific metabolomic signatures, thus corroborating the results from the sensory analysis. Overall, methyl pentanoate (ROC value = 0.78), 2-furfurylthiol (ROC value = 0.75), and L-Homoserine (ROC value = 0.74) established the higher number of significant (p < 0.05) correlations with the sensory parameters. CONCLUSION: Although ad-hoc studies are advisable to further confirm the proposed markers, this study demonstrates the suitability of untargeted metabolomics for evaluating coffee quality and the potential correlations with the sensory attributes.

Quantification of caffeine, trigonelline and nicotinic acid in espresso coffee: the influence of espresso machines and coffee cultivars.

Caffeine, trigonelline and nicotinic acid are important bioactive constituents of coffee. In this work, the combination of different water temperatures and pressures in the settings of the espresso coffee (EC) machine was evaluated, to assess how these factors influence how effectively caffeine, trigonelline and nicotinic acid are extracted from both Arabica and Robusta samples. The proposed analytical method, based on a high performance liquid chromatography (HPLC) system coupled to a variable wavelength detector (VWD), showed good linearity (R²> 0.9985) and good recoveries (71-92%); after validation for three monitored compounds, the method was used to analyze 20 commercial samples. The combination of a temperature of 92 °C and pressure at 7 or 9 bar seems to be the ideal setting for the most efficient extraction of these compounds and consequently for their intake; the compound extracted in the greatest quantity was caffeine, which was in the range of 116.87-199.68 mg in a 25 ml cup of coffee.

Optimization of espresso machine parameters through the analysis of coffee odorants by HS-SPME-GC/MS.

The aroma profile and the final quality of espresso coffee (EC) are influenced by such technical conditions as the EC machine extraction temperature and the pressure used. The effect of these two parameters on EC quality were studied in combination by headspace solid phase micro extraction-gas chromatography-mass spectrometry (SPME-GC-MS) and sensory profile. Moreover, 10 key odorants at the best EC machine settings were examined to compare the two coffee cultivars (Arabica and Robusta) and two EC machines [Aurelia Competizione (A) and Leva Arduino (B)]. The data obtained provides important information about espresso making technique, suggesting that the usual espresso machine temperature and pressure settings (i.e. 92°C and 9bar) are very close to those needed to obtain the best quality espresso. This confirms the traditional wisdom of coffee making, which judges 25ml, the typical volume of a certified Italian EC, to be ideal for very strong aroma intensity.