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The process of fish salting is based on patterns associated with the diffusion of salt in the fish tissue and the diffusion-osmotic transfer of water from the tissues of fish to the brine or in the opposite direction. Atlantic herring is an object of research. The character of the spatial-temporal distribution of salt within the product (herring) was established. As a method of experimental research was used a modern method of non-destructive testing, called photon correlation spectroscopy. The theoretical model of the process was obtained on the basis of the second Fick's law as a solution of a differential equation by the method of separation of variables. The qualitative nature of the mathematical model is interpreted as an exponential approach to the equilibrium value of salt concentration in the process of fish salting. Experimental dependences of the diffusion coefficient on the depth of salt penetration into the muscle tissue of fish were obtained. The mass transfer rate of salt in the first stage of the salting process is about 3·10-4 mm/s. The experimental value of the mass transfer rate is compared with the theoretical value of the proposed model. A satisfactory coincidence is obtained. The qualitative character of the advancement of the salt critical concentration (8.0%) in the form of a front has been established. This is consistent with the theory of P.B. Crean. The causes associated with the apparent increase in the diffusion coefficient at the second stage of the fish salting process are analyzed, which have been noted by many researchers. The expediency of using the effective diffusion coefficient in studies was expressed, which to a greater extent corresponds to the actual course of the process of mass transfer of salt and moisture. It is noted that the most recognized modern theoretical and empirical models of the process of salting fish are models that reflect an exponential approach to the equilibrium of substances involved in the process The acceptability of using the empirical model of salting fish Zugarramurdi and Lupine was confirmed as qualitatively corresponding to the theoretical model proposed in the article..

The relevance of herring brine salting at subzero temperatures, taking into account the positive dynamics of its catching, its reserves, a favorable cooling effect on the suppression of microorganizms activity, improvement of product quality and increasing of storage time are indicated in this paper. Changes in such a significant characteristics as the diffusion coefficient in the process of salting at subzero temperatures were studied. Method of photon correlation spectroscopy, based on the Rayleigh scattering of radiation from the substance was used for the study. The experimental diffusion coefficient dependences on the depth of penetration of the salt in brine, skin and meat of herring at temperatures ranging from -16 ° C to -6 ° C were obtained. They are of wave-like nature. The dependence of the diffusion coefficients on subzero temperature ranging from -18 ° C to 0 ° C, and having a harmonic form was also obtained in the work. The resulting temperature gradient is a source of perturbations, giving rise to thermoconvective waves. According to the theoretical research of Academician A.V. Lykov and chemical processes occurring at the border (skin) of phase separation using the basic equation of thermochemistry - Gibbs law, mechanism of thermoconvective waves influencing the diffusion coefficient is explained. A relation between the diffusion coefficients with the size of the diffusing particles, having hyperbolic character in the temperature range from -18 ° C to 0 ° C in the in brine, skin and meat of herring was determined . The possibility of acceleration of salting by means of mechanical impact on the object under study (in particular sound or ultrasound) was expressed. The destruction of the diffusing particles, representing the union of Na+ and Cl- with water molecules, increases the diffusion coefficient.

To the salting process of fish many studies are devoted, both in experimental and in theoretical terms. Study of features of fish salting in historical terms can be divided into 3 groups. One group of researchers believes that osmotic pressure has a major influence during the salting process. Another group attributed this process to the influence of molecular diffusion. The third group considers that during this process takes place both osmosis and diffusion. Determination of the main characteristics (salinity, diffusion coefficients, time of salting, etc.) is a very time-consuming task. This leads to the idea of searching for innovative research methods. Current state of science, in addition to theoretical solutions points to the possibility to determine the basic characteristics of salting and applying methods associated with the interaction of ultrasound and electromagnetic radiation with matter. In our studies, we have been producing laser beam scanning of salt solution and fish meat thickness. Scattered radiation is determined by the salt concentration, diffusion coefficients, the size of the diffusing particles. This method is called a photon correlation spectroscopy. It has been applied in our work. The dependence of the scattered light intensity on the concentration of sodium chloride solution (brine) has been investigated. According to diffusion coefficient a diffusion in solution to herring skin a conclusion was made that salt solution obtains fractal structure and its size was determined. Also we determined diffusion coefficients depending on the temperature in the layers. The layers are brine-leather, leather, and herring meat thickness. The process of diffusion-osmotic equilibrium revealed at temperatures of 10-12 ° C. Suggested the possibility of higher quality of fish salting at low temperatures. On the basis of the selfsimilar solution of the differential diffusion equation, a formula for calculating time salting fish was obtained

The process of co-extruding food masses is considered. The equations of motion in a circular cylindrical tube and two adjoining viscous-plastic fluids are obtained. The constant equation coefficients, depending on the process parameters and structural dimensions of coextrusion nozzle, are defined.