Thermodynamic approach of meat freezing process

• The usefulness of Thermal Imaging as a freezing control technique has been proved.
• The thermodynamic model explains accurately the phenomena that occurred during pork freezing.
• The thermodynamic model provides a new insight of the phenomena that occurred during freezing.
• The real structural impact caused by ice crystal formation is shown.

Frozen storage is a method widely implemented in meat industry in order to maintain the nutritional value and sensorial characteristics of meat products. The aim of this research was to implement and validate the use of the infrared technique as a non-destructive control tool to monitor the physicochemical phenomena that occurred during the freezing stage. This enables to evaluate the final impact of this operation in a complex system such as meat. To do this, the evolution of the freezing process in pork loin (Longissimus dorsi) was followed by a thermographic camera Optris PI® 160 thermal imager (Optris GmbH, Berlin, Germany), whose spectral infrared range of wavelength is comprised between 7.5 and 13 μm. The results obtained have demonstrated the existence of a chemical potential gradient which caused an internal flux of water. In turn, as a result of nucleation phenomena and the influence of the surface tension existent, a new water chemical potential gradient appeared, leading to the displacement of water molecules towards the ice agglomerates. This provoked the progressive dehydration of the tissue areas immediately close to the ice crystals. Micrographs obtained in different positions of the meat tissue confirm this theory.Industrial relevanceCurrently, there is a significant gap in the knowledge of the complex phenomena that occurred during food freezing. This research develops a thermodynamic model which provides an accurate explanation and a new insight of the main mechanisms involved in the meat freezing process. Moreover, this model enables to leave a proof of the real structural impact that occurred in the muscular tissues, as a consequence of the generation of ice crystals and agglomerates. In order to carry out this research, the thermal imaging (TI) technique has been used. This is an innovative and emergent technology whose popularity and use at the food industry has experienced a significant growth in recent years. The results obtained represent a starting point for the future development of on-line cold chain monitoring systems in the food industry. The aim is no other than to provide the necessary basis to meet current demands for food quality and safety.