Kinetics of colour development in aqueous fructose systems at high temperatures

Abstract

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−1), 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 (A280 and A420) and CIE (Commission Internationale de l'Eclairage) parameters L* (lightness), a* (redness), b* (yellowness) and ΔE* (colour difference, which is expressed as [(Δa*)2 + (Δb*)2 + (ΔL*)2]1/2). The pH and the formol index were also determined. The indicator for colourless intermediate formation, A280, showed that the kinetic constant values increased with increasing heat treatment temperature, while the influence 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, A420 and ΔE*, 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−1, the data were best correlated with combined kinetics. © 2000 Society of Chemical Industry