Kinetics of colour development in aqueous glucose systems at high temperatures

Non-enzymatic browning was studied in aqueous model systems containing glucose and aspartic acid, glutamic acid or asparagine at three different solid concentrations (15%, 30% and 45% by weight) which were heat treated for different times at four temperatures (85 degrees C, 90 degrees C, 95 degrees C and 100 degrees C). Some indicators were used to evaluate the extent of the Maillard reaction: spectrophotometric measurements at 280 and 420 nm (A(280) and A(420)), formation of 5-(hydroxymethyl)-2-furfural (HMF) and CIE, L*,a*, b* parameters. The pH and the formol index were also determined. The indicators A(280), A(420) and HMF formation showed that the kinetic constant values increased when increasing the heat-treatment temperature while the influence of solid concentration was not clear. After a short induction period, the data were well correlated to zero-order kinetics. With reference to colourless intermediate formation (A280 and HMF), aspartic acid turned out to be the most reactive amino acid while in brown pigment formation, it was asparagine. Glutamic acid was the least reactive amino acid for both processes. The activation energy was found to range from 110 to 180 kJ/mol for both, intermediate and brown pigment formation. (C) 2000 Elsevier Science Ltd. All rights reserved.