Imaging and modeling of the microstructure of frozen foods during recrystallization and sublimation: A case study on plant-based products

Recrystallization and sublimation are the main physical phenomena responsible for the degradation of food quality of frozen products along the frozen cold chain. Both phenomena occur slowly at constant temperature over long periods of storage and more pronounced during temperature fluctuations often encountered in the cold chain. Recrystallization is characterised by ice crystal growth which leads to the damaging the tissue structures. Sublimation can be described as superficial ice migration from the products and forming frost causing weight loss and forming desiccated surface. These processes are strongly coupled to product microstructure, which is now recognised as a key parameter defining frozen food quality. Microstructure changes along frozen storage leads to the quality attributes degradation, including texture, sensory and nutritional losses. The ultimate consequences are a reduction of their storage life leading to consumer's rejection, thereby producing significant food losses. To reduce food losses, first a better understanding of the physical phenomena during frozen food storage is required. Plant based products pose a particular challenge with respect to freezing. The microstructure of these foods is composed of cells of different sizes and shapes, interconnected cell walls and intercellular air spaces, of again different sizes and shapes. During freezing, ice crystals will be formed and distributed over these compartments. In subsequent storage, they are resized and redistributed. There has been a lack of appropriate methods for imaging the changes in microstructure as well as for quantifying the ice redistribution process in the complex food matrix. This PhD aims to develop X-ray imaging and mathematical model to study the evolution of the microstructure of plant products along frozen cold chain under different storage conditions (constant and fluctuating temperature), with regard to recrystallisation and sublimation. New image processing will be developed to characterise the evolution of the ice crystal size distribution in the internal structure of plant products using X-ray microtomography. The 3D microscopic data achieved from imaging will be useful in developing mathematical models describing the recrystallisation and sublimation in the frozen food. The model will be based on a population balance equation that takes into account the ice crystal size distribution, as well as heat and mass transfer. Modeling of quality attribute changes of the frozen product is based on kinetic models affected by temperature. Combining both models will provide an opportunity for better understanding and prediction of quality losses of frozen foods during storage. From a technological point of view, the mathematical models could be used for better control of the cold chain.status: publishe