Otto Vitzthum

Steam volatile aroma constituents of roasted coffee: Neutral fraction

ZusammenfassungDie flüchtigen Verbindungen des Röstkaffeearomas wurden durch Wasserdampfdestillation isoliert und in basische und neutrale Fraktionen aufgetrennt. Die Neutralfraktion wurde an einer 200 m x 0,31 mm I.D. UCON HB 5100 Glascapillarsäule analysiert, die mit einem Massenspektrometer gekoppelt war. 120 Verbindungen konnten identifiziert werden, darunter 26 für das Kaffeearoma neue Substanzen. Die Strukturen der neu identifizierten Verbindungen wurden anhand ihrer Massenspektren und ihrer gaschromatographischen Retentionsdaten gesichert. Hierbei handelte es sich um 15 Furane, 6 Pyrrole, 3 Thiophene und 2 Ketone, darunter einige Methylvinylfurane, Dimethyivinylfurane und Alkenylfurane, die bisher noch nicht in gerösteten Lebensmitteln nachgewiesen werden konnten.Die Massenspektren der neu identifizierten Substanzen sind tabellarisch wiedergegeben. Die Fragmentierungen von N-Acetyl-2-methylpyrrol, N-Furfuryl-2-methylpyrrol, 2-Vinyl-3-methylfuran und 2-Vinyl-3,5-dimethylfuran werden diskutiert. Mögliche Bildungswege für Furane, Pyrrole und Thiophene werden aufgezeigt.SummaryThe volatile components of roasted coffee, isolated by normal-pressure steam distillation, were separated into basic and neutral fractions. The neutral fraction was analysed on a UCON HB 5100 glass capillary column (200 m x 0.31 mm W.) coupled to a low-resolution mass spectrometer. One hundred and twenty compounds were identified, of which twenty-six had not been previously reported in coffee aroma. Identification of the structures of the newly identified compounds was accomplished by comparison of their mass spectra with reference spectra. GLC retention times were used to confirm identifications. The new compounds identified for the first time in roasted coffee include 15 furans, 6 pyrroles, 3 thiophenes, and 2 ketones. Of the 15 furans eight methylvinylfurans, dimethyl-vinylfurans and alkenylfurans, which had not been previously found in roasted foodstuffs, should be specially mentioned.Mass-spectral data of the newly identified substances are tabulated. Fragmentation patterns of N-acetyl-2-methylpyrrole, N-furfuryl-2-methylpyrrole, 2-vinyl-3-methylfuran and 2-vinyl-3,5-dimethylfuran are discussed. Comments are made with respect to possible formation patterns and precursors in green coffee beans.

AROMA ANALYSIS OF COFFEE, TEA AND COCOA BY HEADSPACE TECHNIQUES

The greatest part of the numerous volatile components from coffee, tea and cocoa has been analysed in the past after pre-concentration by known procedures as extraction or steam distillation. Thus compounds with wide boiling range are isolated, which normally were identified by GC/MS combination. Though the human nose, a specific multicomponent trace detector can perceive and recognize yet the characteristic food aroma from the surrounding atmosphere of a product only little attention up to now has been paid to the investigation of the headspace aroma of coffee, tea and cocoa. This is due to the fact that there were no detectors selective and sensitive enough to analyse completely the ultra traces in gas samples directly.