The mechanism of mass transfer in the process of fish salting

Abstract

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..