Diffusion kinetics of sodium chloride in Grass carp muscle and its diffusion anisotropy

The diffusion properties of sodium chloride in Grass carp muscle were investigated. A diffusion model based on Fick’s second law and Newman expression was presented with the purpose of simulating the salt dynamic distribution in fish fillets. Experimental results indicated that the diffusion properties were greatly dependant on temperature, salt content and muscle orientation. The diffusion coefficients decreased with an increase in brining time but increased with increasing temperature. The diffusion coefficients Dx and Dy (normal and parallel to muscle fibers) calculated from the diffusion model ranged from 5.86 × 10−9 to 3.15 × 10−10 m2/s and from 6.53 × 10−9 to 4.72 × 10−10 m2/s. The differences in Dx and Dy values showed that there existed the anisotropic behavior of salt diffusion in muscle. Activation energy of sodium chloride transfer obtained from the modified Arrhenius model for Dx (30.54 kJ/mol) was higher than that for Dy (25.06 kJ/mol), which confirmed that sodium chloride diffusing normal to muscle fibers was more difficult than that parallel to muscle fibers.

► We developed a diffusion model to describe the NaCl distribution in fish fillets.
► Temperature, NaCl content and muscle orientation affect salt diffusion properties.
► NaCl diffusion coefficients parallel and normal to muscle fibers showed differences.
► Activation energy of NaCl transfer confirmed that there existed diffusion anisotropy.