Evidence of different flavour formation dynamics by roasting coffee from different origins: On-line analysis with PTR-ToF-MS

Coffees from different origins were roasted to different roast degrees and along varying time temperature roasting profiles. The formation of volatile organic compounds (VOCs) during roasting was analyzed on-line by proton-transfer-reaction time-of-flight mass-spectrometry (PTR-ToF-MS). Coffee samples were Coffea arabica from Colombia, Guatemala (Antigua La Ceiba), Ethiopia (Yirga Cheffe, Djimmah) and Coffea canephora var. robusta from Indonesia (Malangsari). The roasting profiles ranged from high temperature short time (HTST) to low temperature long time (LTLT) roasting, and from medium to dark roast degree. The release dynamics of the on-line monitored VOCs differed for the different coffees and showed a strong modulation with the time–temperature roasting profile. While for Guatemalan coffee the formation of VOCs started relatively early in the roasting process, the VOC formation started much later in the case of Yirga Cheffe and Malangsari. Off-line analysis of the coffee brew augmented the measurements. These included headspace solid phase micro extraction gas chromatography mass spectrometry (HS SPME GC/MS), content of total solids, chlorogenic acids, caffeine, total polyphenols (Folin Ciocalteu), organic acids (ion chromatography), titratable acidity and pH. Some general trends, irrespective of the coffee origin, were observed, such as an increase in pH when going from an HTST to an LTLT profile or from a medium to dark roast degree. Furthermore, a decrease of total headspace intensity was observed from an HTST to an LTLT roasting profile. In general, the changes of the time temperature roasting profiles and/or the roast degree influenced the intensity of the respective coffee constituents as well as their relative composition differently for different coffee origins.