Composition of Roasted Coffee

Protein is subjected to extensive changes when heated in the presence of carbohydrates. There is a shift of the amino acid composition of coffee protein acid hydrolysates before and after bean roasting (Table 21.4). The total amino acid content of the hydrolysate drops by about 30% because of considerable degradation. 

Arginine, aspartic acid, cystine, histidine, lysine, serine, threonine and methionine, being especially reactive amino acids, are somewhat decreased in roasted coffee, while the stable amino acids, particularly alanine, glutamic acid and leucine, are relatively increased. Free amino acids occur only in traces in roasted coffee. 

Amino acid Green coffee (%) Roasted coffee (%) 

Most of the carbohydrates present, such as cellulose and polysaccharides consisting of mannose, galactose and arabinose, are insoluble. During roasting a proportion of the polysaccharides are degraded into fragments which are soluble. Sucrose (cf. Table 21.2) present in raw coffee is decomposed in roasted coffee up to concentrations of 0.4—2.8%. Monosaccharides also hardly occur. 

The lipid fraction appears to be very stable and survives the roasting process with only minor changes. Its composition is given in Table 21.5. Linoleic acid is the predominant fatty acid, followed by palmitic acid. The raw coffee waxes, together with hydroxytiyptamide esters of various fatty acids (arachidic, behenic and ligno-ceric) originate from the fruit epicarp. These compounds are 0.06-0.1% of normally roasted coffee. The diterpenes present are cafestol (I, R = H), 16-0-methylcafestol (I, R = CH3), and kah- 

---

Mayer, F., Grosch, W. (2001) Aroma simulation on the basis of the odorant composition of roasted coffee headspace. Flavour Fragrance J. 16, 180-190... 

Table 21.3 provides information about the composition of roasted coffee. This varies greatly, depending on variety and extent of roasting. 

Table 21.3. Composition of roasted coffee (medium degree of roasting)...

Table 21.5. Lipid composition of roasted coffee beans (coffee oil)...

Smith (1963a) and Feldman et al. (1969) underlined the importance of non-volatile compounds to the flavor of coffee. The comparison between the composition of green and of roasted coffee showed an important decrease in the content of proteins, chlorogenic acid and sucrose on roasting. Fractionation and analysis of the aroma precursors in green coffee have also been studied by Russwurm (1970) who considers that the non-volatile constituents of green coffee that may be involved in flavor formation are carbohydrates, proteins, peptides and free amino acids, polyamines and tryptamines, lipids, phenolic acids, trigonelline and various non-volatile acids. 

Silwar R. and Lullmann C. (1993a) The aroma composition of the coffee beverage. Quantitative determination of steam-volatile aroma constituents. 15th Int. Colloq Chem. Coffee (Montpellier, 6-11.6.1993) (ASIC, 1993), 2,873-7. Silwar R. and Lullmann C. (1993b) Investigation of aroma formation in robusta coffee during roasting. Cafe, Cacao, The 37, 145-51. 

The composition of green coffee is dependent on variety, origin, processing and climate. A review of the differences between Arabica and Robusta coffee is provided in Table 21.2. The constituents will be covered in more detail in the section dealing with roasted coffee. 

The volatile fraction of roasted coffee has a very complex composition. Dilution analyses (cf. 5.2.2) have shown that of the 850 volatile cortqtounds identified until now, only the 40 listed in Table 21.7 contribute to the aroma. Indeed, 28 aroma substances in the concentrations present in a medium roasted Arabica coffee drink (Table 21.8) can largely approximate its aroma. The correspondence becomes even better by the addition of 4-methoxy-2-methylbutan-2-thiol (cf.5.3.2.5), which has a concentration of 0.022 pg/kg in the drink. 

For regular brewed coffee, 50 g of roasted coffee/1 (7.5g/150ml cup) is used for mocca, 100 g/1 and for Italian espresso, 150 g/1. Depending on the particle size and brewing procedure, 18-35% of the roasted coffee is solubilized. The dry matter content of coffee beverages is 1-3%. The composition is presented in Table 21.12. 

In conclusion, it can be seen that coffee is a highly variable beverage in terms of its chemical composition. It seems to be essential that studies of the physiological effects of coffee should include a description of the coffee used. In particular the species of coffee, the methods of bean separation, and roasting could be described. This would reduce the possibility of conflicting reports on coffee attributes, and it will allow us to discover how coffee can best be enjoyed. 

Rahn, W., Meyer, H. W., Koenig, W.A., Effect of steam treatment on the composition of phenolic components of green and roasted coffee, Z. Lebensm.-Unters. Forsch. 169, 346, 1979. (CA92 40077m)... 

Ara, V., Thaler, H., Studies of coffee and coffee-substitute. XVIII. Dependence of the quantity and composition of a high polymer galactomannan on the coffee species and the degree of roasting, Z. Lebensm.-Unters. Forsch., 161, 143, 1976. (CA85 92 372 d)... 

Mayer, F., Czerny, M., and Grosch, W. 1999. Influence of provenance and roast degree on the composition of potents odorants in Arabica coffees. Eur. Food Res. Technol. 209 242-250. 

Composition of Amino Acids in Green and Roasted Coffee (After Acid Hydrolysis),%... 

As in the case of wood, besides pyrolysate composition, smoke composition of other plant parts such as dry leaves has been the subject of different studies [34]. As plants may contain a variety of biopolymers and small molecules, some of them specific for a certain plant, smoke composition can be very diverse. This explains why certain particular types of smoke are related to specific plants and specific plant parts. As an example, the smoke associated with roasting coffee contains phenols and pyrazines generated from both biopolymers and small molecules. One such small molecule from coffee that generates by pyrolysis a variety of phenols is chlorogenic acid. 

In 1916 he began to study chemistry at the E.T.H. at Zurich and graduated in 1920. In 1922 he began a nine-year research project on the composition of the flavoring substances in roasted coffee. 

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... 

Measurements of this kind provide important information towards elucidating the kinetics of formation and release of coffee flavor compounds during roasting, and their dependence on process parameters. Ultimately, such data can be used to optimize roasting conditions with respect to aroma intensity and composition of the roasted coffee. 

Clifford M.N. (1975b), 4 pp., 73 ref. The composition of green and roasted coffee beans. 

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. 

---