Non-enzymatic browning was studied in aqueous model systems containing fructose and aspartic acid, glutamic acid or asparagine at three different soluble solid concentrations (150, 300 and 450 g kg À1 ), which were heat treated for different times at four temperatures (85, 90, 95 and 100 °C). Various indicators were used to evaluate the extent of the Maillard reaction: spectrophotometric measurements at 280 and 420 nm (A 280 and A 420 ) and CIE (Commission Internationale de l'Eclairage) parameters L* (lightness), a* (redness), b* (yellowness) and DE* (colour difference, which is expressed as [(Da*) 2 (Db*) 2 (DL*) 2 ] 1/2 ). The pH and the formol index were also determined. The indicator for colourless intermediate formation, A 280 , showed that the kinetic constant values increased with increasing heat treatment temperature, while the in¯uence of soluble solid concentration was not clear. After a short induction period the data were well described by assuming zero-order kinetics. Glutamic acid turned out to be the most reactive amino acid, while asparagine was the least reactive. With reference to brown pigment formation, A 420 and DE*, glutamic acid was the least reactive amino acid. In all the experiments assayed, except for glutamic solutions with fructose concentrations of 150 and 300 g kg À1 , the data were best correlated with combined kinetics.