Coffee character impact compounds

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. 

The volatiles of roasted coffee include the aliphatic compounds with different carbonyl compounds, and sulfur containing compounds, and alicyclic compounds containing ketones and aromatic benzenoid compounds. Among the character impact compounds, the (2-furyl)-methanethiol and kahwefuran (2-methyl-3-oxa-8-thiobiocyclo-[3.3.0] octa-l,4-diene) are present in relatively high amounts. The burnt coffee-like character is mostly associated with 2-ethylfuran, IV-ethyl formylpyr-role, thiobutyrolactone, and 2-acetyl-3-methylthiopen [35,37]. 

Furfurylthiol is the primary character impact compound for the aroma of roasted Arabica coffee (45). It has a threshold of 5 ppt and smells like freshly brewed coffee at concentrations between 0.01 and 0.5 ppb (46). At higher concentrations it exhibits a stale coffee, sulfury note. Other potent odorants in roasted coffee include 5-methylfurfurylthiol (0.05 ppb threshold), which smells meaty at 0.5-1 ppb, and changes character to a sulfury mercaptan note at higher levels (46). Furfuryl methyl disulfide has a sweet mocha coffee aroma (15). A key aromatic that markedly contributes to coffee aroma is 3-mercapto-3-methylbutyl formate. The pure compound has a blackcurrant-like, catty note, however, in the context of brewed coffee, it contributes roast coffee likeness (47,48). 

The aroma is changed when a brew is prepared from ground coffee. Caramel-like, buttery and phenolic notes become more intense. AEDA shows that this change in the aroma profile is caused by a shift in the concentrations [102]. As detailed in Table 6.52, the polar odorants are preferentially extracted by hot water leading to yields higher than 80% for S-compounds nos. 1 and 4, furanones nos. 13 and 14, vanillin (no. 20) and pentanedione (no. 28). On the other hand, the yield of the character impact odorant of ground coffee, 2-furfurylthiol, is with 19% relatively low. 

Mayer, F., Czerny, M., Grosch, W. (2000) Sensory study on the character impact aroma compounds of coffee beverage. Eur. Food Res. Technol. 211. 272-276... 

Organic sulphur compounds usually play a considerable role in the sensory characteristics of food and beverages, as they are frequently contributors to the character of impact-scents. Examples of these products include truffle (Diaz et al., 2003 Aprea et al., 2007), garlic and onion (Yan et al., 1993 Bocchini et al., 2001), cooked meat (Hinrichsen and Pedersen, 1995 Andres et al., 2002 Carrapiso et al., 2002), coffee (Shimoda and Shibamoto, 1990 Semmelroch and Grosch, 1996), fruit juices (Winter et al., 1976 Boelens and van Gement, 1993 Hinterholzer... 

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