Development of selective chemosensors for the on-line monitoring of coffee roasting by SOMMSA and COTA technology

Gas chromatography combined with a sniffing device (GC/O) or a chemosensor array (GC/SOMMSA) was used to develop a fast and objective method for monitoring flavor generation during roasting of coffee beans. The responses of the human nose and those of the chemosensors to single roast coffee volatiles were compared. Human odor perception and artificial volatile detection revealed 2-furfurylalcohol as an indicator volatile in the coffee headspace. This compound was selectively detected with high sensitivity by the chemosensors and was found to quantitatively correlate with 2-furfurylthiol, a character impact odorant of coffee. The chemosensors used in these experiments were then used to monitor the coffee roasting process on-line. To overcome problems occurring with the on-line use of chemosensors, such as contamination and overloading of the sensing metal oxides, we developed the Cyclic Operating-Temperature Alteration (COTA)-technology. This new technique, which involves switching each chemosensor between a measuring and a desorption mode, proved to be a powerful tool for monitoring flavor formation during coffee roasting on-line.