Coffee aroma constituents identified

The major advantage of the seunpling technique developed, was that some trace chemicals could be trapped tind described for the first time as Black Truffle aroma constituents. In particular, some compounds, important flavor contributors, generally appearing in small concentrations, such as benzaldehyde, propanal, ethyl acetate, anisole or dimethyl disulfide - previously identified in Shiitake mushrooms (9) - could be characterized. This was also the case for three aromatic compounds, toluene, xylene and ethyl benzene, well known as raw vegetable constituents (1 ). In addition, two aliphatic esters, isopropyl and sec-butyl formates, and one cyclic sulfur compound (2-formyl thiophene) previously reported respectively in plums and apples (W) and in coffee and bread products (n) were identified. 

Table 4.2 The aroma constituents of roasted coffee identified before 1902...

In 1969, at the 4th ASIC symposium in Amsterdam, Merritt et al. (1970) asserted that the object of research on the composition of the constituents of coffee aroma is not the mere compilation of lists, but the relationship of the compounds to their precursors, in order to establish a mechanism for their formation, and ultimately for controlling the quality of the product. Merritt et al. (1970) tried to correlate the composition of green and roasted coffees and gave a list of some pyrolysis products of various amino acids, observing that proteins containing the same amino acids produce the same pyrolysates. After having identified 16 other constituents, the authors hoped that new techniques will lead to more direct correlations between the aroma and their precursors, providing a more secure basis to evaluate and control the quality of coffee. 

Identified in roasted-coffee aroma (steam-volatile constituents, then simultaneous distillation-extraction, preparative chromatography and analysis by GC/MS) by Silwar (1982). Silwar et al. (1987) gave a concentration of 0.10-0.15 ppm. 

As aroma carriers, the oils from roasted products have been analyzed in detail, specially for malt and chicory coffees. From the volatiles identified in the coffee aroma, numerous constituents are also found in these oils. However, a basic difference appears to be that the numerous sulfur-containing substances, e.g., 2-furfurylthiol, that are present in roasted beans appear in considerably lower amounts. 

More than 700 constituents have been identified in aroma extracts of roasted coffee. Heterocyclic aroma components represent the greatest amount of the steam volatile aroma complex (80 - 85 %) which amounts to 700 -900 ppm in medium roasted Arabica coffees. The concentration of individual components varies depending on coffee varieties and roasting conditions. Typical components are formed by thermal degradation of free and bound amino acid and chlorogenic acid precursors. Compared to other roasted foodstuffs, sulfur containing constituents and phenols are formed in high amounts and contribute to desirable coffee flavor or off-flavor. 

Procida et al. (1997) used dynamic headspace GC-MS to characterize the aroma volatiles of green arabica and robusta coffees (six varieties of each). They declared that robusta varieties have a higher content of methanol, acetone, pyridine, methylpyrazine and furfural, and that methyl formate, /cr/-butyl alcohol, and furfuryl alcohol are almost exclusively found in robustas. When looking at the figures, the conclusions are not as clear-cut. They identified 12 original constituents, mainly hydrocarbons and alcohols. 

Identified by Reichstein and Staudinger (1926b), Viani et al. (1965), and by Gianturco et al. (1966) in an aroma complex from roasted coffee. Cros et al. (1980) found it in headspace of brewed Columbian coffee. Silwar et al. (1987) gave concentrations of 0.25-0.30 ppm (simultaneous distillation-extraction of steam-volatile constituents, preparative GC). In headspace after a solid-phase microextraction of a brew, it was identified by Ramos et al. (1998). 

Sugar degradation products were determined as benzimidazole derivatives after reaction with o-phenylenediamine. More than 120 amino-acid specific Maillard products have been isolated and identified from the reaction of L-proline, hydixn roline, < teine and methionine with monosaccharides at 150° for 1-1.5 h, in connection with studies of thermally generated aromas. Proline derived components were important constituents of bread, malt and beer, and cysteine and methionine derived components were predominant in roasted coffee and meat flavours. The effects of temperature, pH, and the relative concentration of rhamnose and proline on the quantity of specific volatiles produced in the Maillard reaction of these substrates have been studied, and the data have been analysed 1 computer methodology. The glucosylated cyclopentenone (44) was one of the products of decomposition of the Amadori product 1-deoxy-l-piperidino-maltulose in warm water. ... 

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