Sulfur compounds coffee flavors

As these examples indicate, the characteristic flavor of a food, fruit, etc., usually derives from a complex mixture of components. In a few cases, one unique sulfur compound is a character-impact compound, a material recognized as having the same organoleptic character as the material itself. Although some 670 compounds, of which more than 100 are sulfur-containing, have been identified in roast coffee, one material, furfurylmercaptan (2-furylmethanethiol) is considered to be a character-impact compound.43,44 The threshold level for detection of 2-furylmethanethiol in water is 0.005 ppb, and at levels of 0.01-0.5 ppb, it has the very characteristic aroma of freshly roasted coffee. However, as in many other cases, there is a concentration effect. At levels from 1-10 ppb the aroma is that of staled coffee with a sulfury note .43 Hence, 2-furylmethanethiol has a two headed property - at low concentrations it is a character impact compound and at higher levels it is an off-flavor component. 

Sulfur containing compounds play an important role in the flavor spectrum of roasted coffee. They amount 5 to 15 ppm and are influenced by variety, roasting level and storage conditions. More than 100 sulfur compounds were characterized in roasted coffee (2 4). ... 

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. 

The extremely elusive nature of the chemical basis of Cheddar-like flavors supports the hypothesis that an unstable aroma compound is involved in the flavor of Cheddar cheese, and this view deserves thorough investigation. The circumstantial evidence in favor of the existence of a Cheddar-like aroma also includes considerations relating to the sensitivity of Cheddar flavor to heat and oxygen, and the fact that the redox of cheese is quite low. Additionally, sulfury or sulfide-like defects as well as brothy flavor-like defects are often encountered in Cheddar cheeses of various compositions and origin. These flavors could reflect either production of excessive amounts of certain sulfur compounds or the absence of certain essential compounds that are initially required to allow formation of a Cheddar compound. While attempts to date have not resulted in the isolation of such a compound, this could reflect the very unstable nature of the proposed compound. Other similar circumstances appear to occur in freshly roasted coffee and nuts where transient... 

Since Reichstein and Staudinger, we have been aware that furan compounds containing one or more sulfur atoms play an essential role in the aroma of roasted coffee. A review of the sulfur volatile constituents of coffee, showing the importance for coffee flavor of furans substituted on the 3-position by a sulfur atom, has been published by Flament and Chevallier (1988). As can be seen in the values given for the furfuryl sulfur compounds, the concentrations are higher in robustas than in arabicas when there is no methyl substituent on the ring. When there is a 5-methyl the concentrations are lower overall but higher in the arabicas than in the robustas (compare for example 1.128 and 1.129). 

Soeltoft M. (1988) Flavor active sulfur compounds in beer. Brygmesteren 45, 18-20. (Chem. Abstr. 109, 147858). Spadone J.C. and Liardon R. (1988) Identification of specific volatile components in Rio coffee beans. 12th Int. 

C,H OS, Mr 114.16. Liquid with an unpleasant, sulfur-like odor, coffee-like odor at high dilution (O.l-I ppb) bp. I60 C,D. 1.132. F. is long known as one of the important aroma constitutents of coffee flavor, but also contributes to the aroma of meat flavor The olfactory threshold is 5 ppt. F. is formed by the Maillard reaction and is thus considered as a secondary flavor compound. For production, see Ut.. Use in meat and coffee flavors. 

For years researchers have investigated the sulfur compounds present in various foods. Cooked foods typically contain numerous sulfur compounds, especially heterocyclic compounds like thiazoles, thiophenes, thiazolines, etc. In 1986, Sha-hidi et al. (7) reported that 144 sulfur compounds had been identified in beef. Other heated food systems like bread, potato products, nuts, popcorn, and coffee also contain many sulfur compounds. Aliphatic thiols have been found in fruits, vegetables, dairy products etc., as well as in heated foods. No discussion of the occurrence of sulfur compounds in foods would be complete without mention of their major role in the various allium species. Indeed, more than half of the volatile compounds reported in garlic, onion, leek, and chive contain sulfur (2). Comprehensive reviews of the literature concerning the role of thiazoles, thiophenes, and thiols in food flavor through 1975 can be found in Maga s series of review articles (3-5). 

Our interest in the analysis of nonvolatiles, thus, may involve taste substances or substances that indirectly influence taste or aroma. As mentioned earlier, in the first case, we are interested in the analysis of substances that impart sweetness, tartness, bitterness, saltiness, or unmami sensations. The analysis of these substances is reasonably well defined. In the latter case, the analyses employed are less well defined and are unique to the components one wishes to analyze. For example, we may wish to measure substances (e.g., melanoidins) that interact with sulfur aroma compounds (in coffee). There are no standardized methods for the analysis of melanoidins in foods and thus, the protocols have to be developed. In this chapter, we will only briefly discuss the established methods for the analysis of taste substances. Due to the specificity of methods for the analysis of nonvolatiles that may indirectly influence flavor perception, we will only refer the reader to the literature [93-100]. 

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