The impact of microwave heating of infant formula model on neo-formed contaminant formation, nutrient degradation and spore destruction

Heat treatment of milk results in the development of a large range of Maillard products, especially in infant formulas due to their high content in Maillard reaction substrates. The Maillard reaction should be minimized because some of those products, called neo-formed contaminants (NFC), are currently suspected of promoting deleterious health effects. The objective of this work was to study the impact of microwave heating on the formation of Maillard compounds, degradation of nutrients and destruction of spores of an infant formula model. An infant formula model based on pure-whey proteins was used as experimental model. A spore suspension of Geobacillus stearothermophilus was prepared and inoculated in the formulated milk before microwave treatment. The treatment was performed on a laboratory device running at 2450 MHz and equipped with a magnetron (power range 0-1860W) and the temperature was controlled by three optical fibers. Heating kinetics were established at several microwave specific powers (5, 7, 10, 12 W/mL). The impact of the treatment on NFC formation was evaluated by 3 indicators: the FAST index (indicator of global advancement of Maillard reaction), carboxymethyllysine (CML) and furosine. All these NFC indicators seemed to follow an exponential model as a function of time. The thermal sensitive nutrient vitamin C was chosen as indicator of the nutritional quality. Like in conventional heating, an exponential model was observed for spore inactivation and vitamin C degradation. Furthermore, laws similar to those used for conventional heating could be used to express heat resistance regarding germ viability, vitamin C concentration and Maillard products. As a result, D and z-values relative to specific microwave powers were determined for each indicator. Finally, it was found that the best way to minimize NFC formation and nutrient degradation was to use high specific power for a short time, similar to what is obtained with the UHT process for conventional heating.