Résumé
This study aimed at monitoring the biochemical reactions induced by an intense thermal treatment like sterilization of a liquid infant formula. The stake is the control of the nutritional quality of the product concerning undesirable newly formed compounds, most of them being Maillard reaction products. A fluorimetric method called FAST (Fluorescence of Advanced Maillard products and Soluble Tryptophan) was used for monitoring the accumulation of Maillard products along thermal treatment. UHT sterilization was achieved by ohmic heating in a lab scale reactor specially designed for this study. The reproducibility of the thermal treatment was characterized for the three phases of the sterilization: heating, holding and cooling. The extent of Maillard reaction was monitored under two types of conditions: (i) isothermal conditions at five holding temperatures (100, 110, 120, 130 and 140°C) and (ii) nonisothermal conditions at five heating rates (0.16 to 4.19 °C.s-1). A semi-empirical model was developed to predict product temperature history during a complete sterilization treatment with good adjustment. The extent of Maillard reaction was fitted with a kinetic model of pseudo-zero order and Arrhenius parameters were identified to model the temperature effect on the chemical reaction. The physical and the chemical models were coupled to predict the extent of Maillard reaction during ohmic treatment as a function of operating parameters (temperature and electrical conditions) and product parameters (electrical conductivity…); it was successfully adjusted to the experimental results.