HPLC/diode-array applied to the thermal degradation of trigonelline, nicotinic acid and caffeine in coffee

A simultaneous determination of trigonelline, nicotinic acid and caffeine w as performed in samples of arabica and robusta coffees, before and after ro asting at either different temperatures (160-240 degrees C) or different pe riods of time exposures, in order to study their thermal degradation. A rev erse-phase HPLC/Diode-array detector method was used. The results were comp ared with a model dry system roast of the compounds under study, individual ly and in mixture. The loss of trigonelline was strongly dependent upon the degree of roast and was associated with the formation of nicotinic acid. A slight decrease in caffeine was verified in both species. This study showe d diversified behavior of the compounds when in their native form or in an artificial mixture, eliciting the chemical environmental influence. Rate co nstants for the chemical reactions at 240 degrees C were determined. (C) 20 00 Elsevier Science Ltd. All rights reserved.