Mechanistic modelling of heat and mass transfer in processing of solid and semi-solid foods

The heating of solid and semi-solid foods is a complex process that comprises coupled heat and mass transfer in a continuously changing porous medium. The irreversible changes in the composition, microstructure and other physical food properties during the heating process affect directly or indirectly the food quality such as texture, taste or appearance.

In order to optimize existing heating processes and develop sustainable, healthy and high-quality food products, a quantitative knowledge about the mechanisms that lead to the physical and chemical changes is required. The aim of my PhD project was to develop a mechanistic model of heat and mass transfer and couple it with kinetic models to predict the quality changes of solid and semi-solid foods during thermal processing.

Based on the conservation of mass and energy, we developed a mechanistic model of heat and mass transfer for the roasting of chicken breast meat from first principles, thoroughly considering the physical phenomena as well as natural variations in the chicken breast size and shape. A detailed description of the heat and mass transfer during the roasting process should include the dynamic changes of the chicken meat microstructure and physical properties.

Therefore, we established semi-empirical correlations that describe the structural properties (i.e. storage modulus) and thermophysical properties (i.e. specific heat capacity and thermal conductivity) of chicken breast meat as function of the temperature and moisture content. This enabled us to predict precisely the temperature and moisture content profiles inside the chicken breast meat during the roasting process, which also agreed well with experimental data.

In order to predict the quality changes of chicken breast meat during roasting, we established kinetic models for the texture and color changes as function of the temperature and heating time by modifying the general rate law, taking the non-zero equilibrium of food quality attributes into account. Coupling the mechanistic model of heat and mass transfer with the kinetic models then enabled us to study the influence of the local temperature and moisture content changes on the spatial texture and color development.

Accordingly, the direct influence of the process parameters on the spatial quality changes was obtained. This model of combined transport phenomena and quality kinetics provides a quantitative understanding of the phenomena that lead to the quality changes of chicken breast meat during the roasting process.

It can be used as a knowledge-based decision tool to optimize the heating process with the aim of the highest possible food quality for the consumer.