Analysis of amino acids and carbohydrates in green coffee
The analysis of carbohydrates and amino acids in green coffee is of the utmost importance since these two classes of compounds are precursors of the Maillard reaction during which the colour and aroma are formed. During the course of the Maillard reaction potentially harmful substances like acrylamide or 5-hydroxymethyl-furfural accrue as well. The carbohydrates were analysed by anion-exchange chromatography with pulsed amperometric detection and the amino acids by reversed phase chromatography after derivatization with 6-amino-quinolyl-N-hydroxysuccinimidyl carbamate and fluorescence detection. Both methods had to be optimized to obtain a sufficient resolution of the analytes for identification and quantification. Sucrose is the dominant carbohydrate in green coffee with a concentration of up to 90 mg/g (mean = 73 mg/g) in arabica beans and significantly lower amounts in robusta beans (45 mg/g). Alanine is the amino acid with the highest concentration (mean = 1200 µg/g) followed by asparagine (mean = 680 µg/g) in robusta and 800 µg/g and 360 µg/g in arabica respectively. In general, the concentration of amino acids is higher in robusta than in arabica.