Effects of temperature and pH on the kinetics of caramelisation,protein cross-linking and Maillard reactions in aqueous model systems

Solutions of either glucose, bovine serum albumin (BSA), casein, glucose–BSA or glucose–casein were heated at 60 to 100 °C at pH 8.0 and pH 9.7, and the kinetics of the reaction markers (disappearance of the glucose and amino groups, development of UV absorbance and browning, and protein reticulation) were monitored. All the markers were enhanced at increasing temperatures, and, except for the disappearance of the free amino group and protein polymerisation, at alkaline pH levels. The loss of the amino group occurred in parallel with increase in polymerisation. The two proteins reacted in line with their amino content and solubility. The activation energy (E_a) of the amino group loss in the protein–glucose mixture was around 100 kJ per mol and that in the protein heated alone was higher. The E_a associated with the disappearance of glucose was around 90 kJ per mol. The E_a of UV absorbance and browning processes, which showed parallel time courses, were found to range from 90 to 150 kJ per mol.