Studies on Salting and Drying Fish. II. Dynamic Aspects of the Salting of Fish

Abstract

SUMMARY—The diffusion coefficient for the penetration of salt into swordfish muscle was not constant but depended upon the salt concentration in the muscle and upon the temperature; the coefficient‐salt concentration curve for 25°C had a minimum value at a salt concentration of approximately 1.5 moles/liter and was always lower in fish muscle than in aqueous salt solutions of the same salt concentration as the muscle. Other parameters which also served to characterize the migration of salt in fish muscle were determined as follows: the equivalent conductance of salted fish muscle was found to be an inverse linear function of the square root of the salt concentration in the muscle and to be always lower in muscle than in aqueous solutions of the same concentration as the muscle; the sodium and chloride ion transference numbers, found to be approximately of the same magnitude in muscle and in water, exhibited the same qualitative variation with salt concentration and with temperature in both media.As in aqueous solution, the diffusion coefficient and the equivalent conductance of salt in fish muscle were found to increase with increasing temperature. It was found that experimental values of the diffusion coefficient at a given temperature agreed reasonably well with values predicted by the equation is the diffusion coefficient in the muscle at infinite dilution and γ is the “mean molar activity coefficient” of salt, also in the muscle, at concentration c. The activation energies for salt diffusion in fish muscle and in water at infinite dilution were both found to be of the order of 4700 calories per gram‐mole, a value within the region of hydrogen‐bonding energies.