Roast effects on coffee amino acid enantiomers

The effects of roast on the amino acid enantiomers (d- and l-) of two green coffee samples (arabica and robusta) were determined, by gas chromatography, on a Chirasil l-Val column. The free amino acids were present in low amounts in both green samples and destroyed to a very high degree with roast. After hydrolysis, the amino acids behaved according to their thermal stabilities: some amino acids remained unchanged whilst the more thermally sensitive were slightly reduced. Generally, the mean free amino acid racemisation value was higher than that calculated after hydrolysis, and was also higher for the robusta sample. In both cases, an increase in the racemisation value with temperature was observed, with aspartic acid being the most sensitive amino acid. The results suggested that the robusta coffee matrix is more affected by roast than the arabica. The amount of d-amino acids ingested per coffee cup does not seem to constitute a serious food safety problem.