Dual mode diffusion and sorption of sodium chloride in pork meats under cooking conditions

This study aims to obtain insight into mechanisms of NaCl diffusion in pork meats under cooking conditions: the loins at 5 (raw), 63 (pre-cooked) and 98 °C (pre-cooked), the mince at 98 °C (pre-cooked), and the filet at 98 °C (pre-cooked). It has been generally presumed that NaCl in any of pork meats diffuses with a constant Fick's diffusion coefficient, D, through liquid water channel imbibed in them. However in the present study, we experimentally obtained skewed bell shape variations of D in all of the above meats with respective maxima at certain low NaCl concentrations. These variations were interpreted in terms of a dual mode sorption and diffusion theory, which had been successfully applied to NaCl diffusion behaviors in Japanese radish and solidified egg white. This interpretation gives a thermodynamic diffusion coefficient, DT(p) for the partition species of NaCl and another one, DT(L) for the Langmuir type sorption species, both in the water swollen substrates in the meats. It was found that DT(p) values are sizably smaller than corresponding DT(L) values. This difference was ascribed to the lower water content in the p region than that in the L region. With the two DTs and additional equilibrium parameters, the theory explained the remarkable decrease of D value with C at 21 °C found by Guiheneuf et al. and nearly constant D values in the higher C range at 5 °C reported by other researchers. Experimentally obtained sorption isotherms of NaCl, which were slightly convex upward in the low C range, were satisfactorily reproduced with the parameters and the fractions of water swollen substrates in the whole meats.