Instrumental analysis and sensory studies on the role of melanoidins in the aroma staling of coffee brew
The objective of this study was to investigate the chemical mechanisms which might be involved in the rapid aroma staling during warm-keeping of freshly brewed coffee beverages. Melanoidins isolated from coffee brew were added to a model solution containing 25 aroma compounds mimicking the aroma of a coffee brew. Sensory analyses revealed that the intensity of the roasty-sulfury aroma was reduced when melanoidins were present. Comparative aroma dilution analysis on the headspace of aqueous solutionscontaining the total volatile fraction isolated from coffee brew, alone, or in combination with melanoidins visualized that losses of the odourous thiols (2-furfurylthiol, 3-methyl-2-butenthiol, 3-mercapto-3-methylbutyl formate, 2-methyl-3-furanthiol, and methane thiol) are responsible for the aroma change. Stable isotope dilution assays confirmed that these thiols are rapidly degraded with increasing time during warm-keeping of coffee brews in a thermos flask. Quantitative model studies and labelling experiments with (2H2)-2-furfurylthiol, followed by 2H-NMR and LC/MS detection gave strong evidence that these thiols are covalently bound to pyrazinium ions which are key intermediates in roasting-induced melanoidin genesis. Results suggest that the thiol-binding activity of pyrazinium derivatives in melanoidins undoubtedly contribute to the decrease of the sulfury-roasty odour quality shortly after preparation of the coffee brew.
| Main Authors: | , , , , |
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| Format: | biblioteca |
| Published: |
Trieste (Italia) ASIC
2001
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| Subjects: | COFFEA, CAFE, TECNICAS ANALITICAS, SABOR, BEBIDAS, COMPOSICION QUIMICA, TECNICAS DE TRAZADORES, CROMATOGRAFIA, ESPECTROMETRIA DE MASAS, ESPECTROMETRIA, IMAGENES, ANALISIS ORGANOLEPTICO, TIOLES, COMPUESTO VOLATIL, |
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