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 was performed in samples of arabica and robusta coffees, before and after roasting at either different temperatures (160–240°C) or different periods of time exposures, in order to study their thermal degradation. A reverse-phase HPLC/Diode-array detector method was used. The results were compared with a model dry system roast of the compounds under study, individually 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 showed diversified behavior of the compounds when in their native form or in an artificial mixture, eliciting the chemical environmental influence. Rate constants for the chemical reactions at 240°C were determined.