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Understanding the impact of industrial processes on the evolution of animal products: the example of smoked salmon

Scientists in the QuaPA Unit based near Clermont-Ferrand have developed a globalised approach at different study scales (ranging from the muscle to cells and macromolecules) in order to better understand the quality determinants of changes to animal products. This expertise, based on imaging techniques and initially acquired for meat products, can now be applied to aquacultural products such as smoked salmon.

Characterising the structure of a muscle at different scales using imaging techniques can improve the control of finished product quality.

Understanding the impact of industrial processes on the evolution of meat products

Industrial products result from a succession of technological steps which generally cause changes to the structure of foods. These changes, which occur at the molecular level, are likely to have repercussions on the texture, colour or even flavour of products. They may be desired, but are also sometimes uncontrolled.
Scientists in the Quality of Animal Products Research Unit (QuaPA) have developed an imaging approach applied at different scales: the tissue scale using magnetic resonance imaging, the cellular scale using optical microscopy, the ultrastructural scale using electron microscopy and the molecular scale using high-resolution microspectroscopy. These are coupled with conventional physicochemical measurements (pH, texture, salt content, water activity, etc.) so as to obtain a detailed characterisation of the structure of animal products during processing. This approach can also enable access to levers in order to optimise transformation processes, as well as aiding in the reformulation of products; for example, in the context of a strategy to reduce their salt content. Although this expertise was originally developed to study meat products, it is now being extended to aquacultural products.

The salting of smoked salmon

The preparation of smoked salmon involves a succession of steps such as salting, smoking and stiffening. The two main methods used for salting are dry salting or the injection of brine. Salting causes changes to ionic strength which at certain concentrations can denature structural proteins and also the proteolytic enzymes that degrade tissues. These molecular changes have repercussions on flesh structure and hence on the texture, water retention capacity and colour of the product.
Imaging techniques can supply precise knowledge of the structural organisation of salmon meat and notably the distribution of lipids. Different histological stains have enabled the identification of muscle cells, connective tissues and lipids at the tissue and cellular scales. Magnetic resonance imaging has made it possible to map lipids at the tissue scale, thus supplementing the data already acquired using cellular imaging techniques.
The salting method used for smoked salmon has a marked impact on muscle structure at different scales (histological, ultrastructural and macromolecular). Salting by injection favours the deposit of salt in muscle tissue when compared to dry salting alone. However, the injection of brine causes a marked heterogeneity of salt content within the fillets (higher in finer parts such as the belly). The distribution of salt followed the same profile as that of lipids, demonstrating the influence of the lipid network on the diffusion of salt in muscle tissue. Near infrared spectroscopy has been able to distinguish the samples obtained using different salting methods, including in finished products.
A clearer understanding of the mechanisms involved in the diffusion of salt within tissues will enable the optimisation of salting processes.

Scientific contact(s):

  • Thierry ASTRUC Quality of Animal Products Research Unit (UR0370, QuaPA), 63122 Saint Genés Champanelle
Associated Division(s):
Science for Food and Bioproduct Engineering
Associated Centre(s):