Generating Maillard reaction products in a model system of d-glucose and l-serine by continuous high-intensity ultrasonic processing

• A continuous ultrasonic processing system was set up and applied to Maillard reaction.
• Ultrasound significantly decreased activation energy required for Maillard reaction.
• A different flavour profile was generated by ultrasonic Maillard reaction.

In this paper, a continuous ultrasonic processing system was established and firstly applied to a Maillard reaction (MR) model system of d-glucose and l-serine. Furthermore, the effects of high-intensity ultrasound assisted MR were compared with those of thermally induced MR through kinetic modelling. The ultrasonic MR had higher depletion rates of reactants as well as higher generation rates of intermediate and final MR products (MRPs) at relatively low processing temperatures (55 and 60 °C). However, both rates were lower for ultrasonic MR than thermal MR when the temperature was raised to 70 and 75 °C. Moreover, the ultrasonic MR had significantly lower activation energy compared with thermal MR. Lastly, three pyrazines, two amines and five O-containing flavour compounds were only produced in ultrasonic MR, not in thermal MR. The difference in flavour generation was attributed to the extremely high, albeit momentary, temperature and pressure condition produced by high-intensity ultrasound.Industrial relevanceUltrasound-assisted processing, a novel technology for non-thermal processing, has been utilized as an alternative to conventional thermal processing. High, albeit momentary, temperature and pressure that are generated by high-intensity ultrasound during processing provide a favourable environment for a number of chemical reactions. Moreover, strong shear stress, turbulence and agitation are among the unique characteristics generated by high-intensity ultrasound, which help to keep excellent mixing during food processing. In our study, a continuous ultrasonic processing system was established so as to achieve a good temperature control as well as to minimize the loss of volatile products during processing, which are major concerns to any liquid-based processing with ultrasound. Furthermore, a Maillard reaction (MR) model system of d-glucose and l-serine under the continuous ultrasonic processing were studied and compared to the most common batch processing of thermal MR through kinetic investigation at the same processing temperature and time conditions. The kinetic models that focused on reactants, intermediates, and final MR products (i.e. melanoidins and flavour compounds), and the kinetic parameters obtained for the MR system may enable controlling the reaction at industrial scale. The different flavour profile that was generated in ultrasonic MR points to new approaches to the food flavour industry to produce more alternatives and varieties.