Modelling of Soy Sauce Desalting by Electrodialysis

In this work, the main features of electrodialytic (ED) desalting of microfiltered samples of a traditional soy sauce under constant electric current in the range of 1.25 to 6.5 A were quite well reconstructed using a mathematical model based on the Nernst–Planck equation. Amino nitrogen migration was characterised by a small effective transport number ( t AN = 0.070 ± 0.01), resulting in an average loss in amino nitrogen of about 30% whatever the electric current tested. The sodium chloride transport number ( t B = 0.969 ± 0.05) and diffusion rate ( L B ≈ 0), as well as the effective membrane surface area, essentially coincided with those previously established when dealing with concentrated model brines. On the contrary, there was a significant diversity in the water transport number ( t W = 8.3 ± 0.1) and diffusion rate [ L W = (6.9 ± 0.2) × 10 −5 mol m −2 s −1 bar −1 ], as well as in the anion- and cation-exchange membrane resistances ( R a = R c ≈ 0.04 Ω). The experimental procedure and mathematical model described in this work may be recommended not only to optimise the ED desalination of soy sauce but also to generate a first-cut design for ED desalting of other natural seasonings.