Dual Mode Diffusion of NaCl in Japanese Radish under Cooking Conditions

Abstract

Sorption and diffusion of NaCl in Japanese radish have been studied. The sorption isotherm was obtained at 98 degrees C by the conventional method. The concentration profile by the 1-dimensional diffusion of NaCl in Japanese radish from the 3.0% solution was measured at 98 degrees C with the FRITRUC method involving a foodstuff rod in a thin rubber casing. Fick's diffusion coefficient, D, calculated therefrom showed a threefold variation with a maximum. This variation was quantitatively interpreted by applying a dual-mode sorption and diffusion theory under an assumption that the rate determining step of the diffusion is that in the cell wall. Two thermodynamic diffusion coefficients, D(T)(p) and D(T)(L), where p and L are the species of NaCl sorbed by partition and Langmuir modes, respectively, a parameter, alpha, derived from the local equilibrium relations between the p and L species, and S, the concentration of the Langmuir adsorption site in the cell wall of the radish, were estimated. D(T)(p) was found to be smaller than D(T)(L). As an explanation of the larger D(T)(L), we invoked the higher hydration state of the adsorption site of the L species, being ascribed to residual anionic pectin in the radish than the local environment of the p species. The sorption isotherm showed a convex upward deviation from the linear relation. By using the parameters for the local equilibrium and some assumed parameters, the isotherm was found to be explainable. We suggest possible applications of the present method and interpretation to the diffusion study on the cooking systems comprising varieties of seasoning components and foodstuffs.

Dual Mode Diffusion and Sorption of Sodium Chloride in Pre-Cooked Potato (Solanum tuberosum L.)

“…Table 1 shows the ranges observed. However, this has been found not to be the case for the three foodstuffs with the maximum showing variations of D at relatively low concentrations (Hashiba et al, 2007(Hashiba et al, , 2008(Hashiba et al, , 2009. See also the reported variations of D of NaCl with C t for L. dorsi and Emmental cheese (Guiheneuf, et al, 1997;Pajonk et al, 2003) shown in Table 1.…”

“…Thus, K and S in our former three reports should be read as K a and S a (Hashiba et al, 2007(Hashiba et al, , 2008(Hashiba et al, , 2009). In principle, r depends on C t .…”

“…Generally in cooked foodstuffs, the total weight of discrete liquid water droplets is considerable as compared with the weight of water in the swollen substrates. Also for NaCl sorption by the potato, the sorption isotherm is written in the form (Hashiba et al, 2007),…”

“…D can be the measure of the mobility of the diffusant only when D is constant over the concentration range of concern. During the last two decades, however, D values of NaCl that are explicitly concentration dependent, have been reported for pork meat (Guiheneuf, Gibbs, & Hall, 1997) and Emmental cheese (Pajonk, Saurel, & Andrieu, 2003) and recently for Japanese radish, solidified egg white and pork meat at 5-98°C by us (Hashiba et al, 2007(Hashiba et al, , 2008(Hashiba et al, , 2009). The dependences reported by us have a common character of each having skewed bell shape variation with a maximum at a C t value of NaCl slightly above 0.1 mol kg -1 .…”

“…Thus the original dual mode diffusion theory on nylon should be reexamined when applied to foodstuffs. Referring to the foregoing studies (Hashiba et al, 2007(Hashiba et al, , 2008(Hashiba et al, , 2009, we became aware of the fact that water imbibed in the foodstuffs is partitioned into one swelling the component macromolecular phase and the other one dispersed as liquid water. An extreme example is the radish containing about 95% water (Hashiba et al, 2007).…”