Formation kinetics of hydroxymethylfurfural, lactulose and furosine in milk heated under isothermal and non-isothermal conditions

A detailed kinetic study of hydroxymethylfurfural. lactulose and furosine formation was performed upon heating milk at temperatures between 90 degreesC and 140 degreesC. In case of prolonged heating. formation kinetics could be described by a fractional conversion model. Considering only the first phase of the model, kinetics could be simplified to a pseudo-zero order model. A first assessment of kinetic parameters was made by isothermal experiments. Data were analysed using both a 2-step linear and a 1-step non-linear regression method. Only for furosine. did the global 1-step regression approach seem to give better results than the individual 2-step regression approach. Next, the estimated parameters k(ref) and E-a were reevaluated under non-isothermal conditions by subjecting milk to a time variable temperature profile. Given the complexity of Maillard reaction, it seemed better to estimate kinetic parameters under non-isothermal conditions When using a simplified model. Formation of hydroxymethylfurfural, lactulose and furosine was characterized by an E-a value of 90.2 kJ/mol (k(110 degreesC) 1.2 mu mol/l, min), 99.1 kJ/mol = 51,5 mg/l, min) and 88.7 kJ/mol (k(110 degreesC) = 16.3 mg/100 g protein, min) respectively. Additionally, 90% joint confidence regions were constructed in order to obtain an accurate representation of the statistical confidence associated with the simultaneously estimated parameters.