APPLICATION OF LASER IONIZATION MASS-SPECTROMETRY FOR ONLINE MONITORING OF VOLATILES THE HEADSPACE OF FOOD-PRODUCTS - ROASTING AND BREWING OF COFFEE

Resonance-enhanced multi-photon ionization time-of-flight mass spectro metry (REMPI/TOFMS) has been applied to the detection of volatiles in the headspace of brewed coffee and in the coffee roasting process-gas. A frequency quadrupled Nd:YAG laser (266 nm) was used for REMPI ioniz ation (REMPI@266nm) of the volatiles in an effusive molecular beam ins ide the ion source of a linear TOF mass spectrometer. A special sampli ng system provided a time correlated sampling. Under these circumstanc es REMPI@266nm is highly selective for ionization of phenolic compound s. Several phenolic compounds, such as the flavour-active 4-vinylguaia col, can be detected in the headspace of coffee brew as well as in the roast off-gas with the application of this approach. Moreover, the ni trogen heterocyclic compounds, indole and caffeine, were detected in b oth cases. During the roasting process the relative changes in concent ration of some volatile components of coffee have been recorded by EMP I@266nm with a time resolution of 1 Hz. The different volatiles exhibi t characteristic concentration profiles as a function of the roast tim e. These results demonstrate the applicability of REMPI-TOFMS for on-l ine monitoring of coffee processing technologies. Such an on-line moni toring technique is of particular interest for process-control purpose s, e.g. quality-protection or feedback process control, For example, m onitoring of off-gases from the coffee roast process or monitoring of certain unit operations during the instant-coffee manufacturing could be promising industrial applications.