Coffee amino acid composition

To identify the amino acids in die protein, which are involved in radical formation, in a first experiment, we analyzed the amino acid composition in the coffee proteins before and after roasting of the coffee beans. The most drastic loss was observed for the amino acids lysine, arginine, cysteine emd histidine, the amounts of which are summarized in Table I. On the basis of these results, it was assumed that the degradation of one of diese amino acids is somehow involved in radical formation. 

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. 

Table 21.4. Amino acid composition of the acid hydrolysate of Colombia coffee beans prior to and after roasting...

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

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. 

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. 

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