New approaches to monitor semi-volatile organic compounds released during coffee roasting using flow-through/active sampling and comprehensive two-dimensional gas chromatography

Abstract

A novel dynamic approach is described to profile volatile organic compound (VOC) and semi-VOC (SVOC) emission during coffee roasting aimed at analysing components present in the roasting plume, and to monitor their evolution during the process. Two sorbents - coconut shell charcoal (CSC) and styrene-divinylbenzene resin (XAD-2) - were evaluated while collecting substances in four sequential time intervals (0-3, 3-6, 6-9 and 9-12 min). Extracted VOCs (<200 Da) and SVOCs were analysed by gas chromatography (GC), and comprehensive two-dimensional gas chromatography (GC × GC) with flame ionisation (FID) and time-of-flight mass spectrometry (TOFMS) detection. Results showed CSC extraction presented poor recovery of VOCs and SVOCs released during roasting. However, XAD-2 was able to collect both groups, including SVOCs of >400 Da. GC × GC resolved many co-eluting compounds observed in 1D GC and allowed chemical group type cluster analysis, revealing that many non-polar VOCs are observed within the 0-3 min interval, and that the release of polar and higher molar mass SVOCs were mostly found within the 3-6 min interval. These group-type cluster analyses offer a broad spectrum chemical profile of the released substances. It may also reveal detailed insights into the roast process evolution over time.

Keywords: Caffeine; Coffee bean cracking; Fatty acids; GC × GC; Lipids; SVOC; Solid phase XAD-2 extraction; Sterols.