Coffee has attracted significant research interest owing to its complex volatile composition and aroma, which imparts a pleasant sensorial experience that remains challenging to analyse and interpret. Majority of the analytical challenges are associated with coffee’s matrix complexity, hence state-of-the-art instrumental techniques are particularly important for the understanding of niche volatile compounds in coffee. In this study, thin-film solid-phase microextraction (TF-SPME) coupled with comprehensive apolar-polar gas chromatography (GCxGC) and a quadrupole time-of-flight mass spectrometer (QTOF/MS) was utilised to fingerprint eight specialty coffees, with the purpose of enriching and resolving trace organosulfur compounds (OSCs) in these samples. A total of 50 OSCs were detected in this manner, of which 2-methyltetrahydrothiophen-3-one (2-MTHT) was of particular interest due to its stereoisomerism, which was hypothesized to result in structure-odour activity. After confirming the differences in odour properties between the 2-MTHT enantiomers (chiral GC-olfactometry) and elucidating their absolute structures (nuclear magnetic resonance, NMR), (<i>R</i>)-2-MTHT was deduced to be the enantiomer possessing a lower odour threshold. The enantiomeric ratios of 2-MTHT in coffee matrices were also elucidated using heartcutting apolar-chiral GC-GC coupled to a MS and flame photoionisation detector (FPD) on solid phase extraction (SPE)-purified coffee. Further sensory analyses also indicate that 2-MTHT may be a potential driver of coffee quality, with (<i>R</i>)-2-MTHT possibly having a greater sensory impact in-matrix. In conclusion, niche solutions for sample preparation, separation, and detection are critical for understanding the contribution of trace and impactful odorants to coffee aroma.

Multidimensional gas chromatography approach to elicit the odour-structure activity of chiral 2-methyltetrahydrothiophen-3-one in coffee

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