We studied the quality and taste of commercially available fish sauces. The manufacture of fish sauces from fishery products and salts require long-term aging, because self-digestion of proteins in fishery products is a limited step in their production. The salt content was higher than in other types of fish sauce for preventing in increase in microbes, and significant increases in total amino acids and glutamic acid were observed in this type of fish sauce. The addition of salt and koji in the production of fishery sauce reduced the aging period. This type of fish sauce, therefore, did not require a great deal of salt, and the sweet fragrance of koji was characteristic. The differences in fish as material as well as manufacturing procedures affected the content of amino acid and organic acid, and the levels of lactic acid and glutamic acid caused differences in taste. When we used it for soup, the quality of the taste affected mildness and preference, suggesting a need for suitable addition quantity that we could put together quality.
We have developed a new technique of electrodialysis with a bipolar membrane and ion-exchange membranes. The technique has a separating zone with acidic pH steps between compartments. The electrodialyzer was composed of six compartments, which were divided by an anion-exchange membrane, a bipolar membrane, and three cation-exchange membranes. The solutions including sodium chloride were circulated by chemical pumps through the compartments and reservoirs at constant flow rate. When a voltage was applied to the electrodialyzer, hydrogen ions were electrically generated by the bipolar membrane, and partially moved to cathode-side compartments through cation-exchange membranes. The hydrogen concentration in each compartment was almost equal to the concentration of coexisting anions, and formed acidic-pH steps in the electrodialyzer. All the experimental data were simulated by a mathematical model which considered ionic flux in the membrane based on the Nernst-Planck’s equation, ion-exchange equilibrium between solution and membrane, electroneutrality in the solution, hydrogen production rate, and material balances of ionic species. The model well explained the experimental results of formation of pH steps in the electrodialyzer.
We prepared novel cation-exchange membranes （CEMs） from synthesized PVA-based block copolymers with various contents of cation-exchange groups, CmSSS. The CEMs were cross-linked physically by annealing them, and cross-linked chemically with 0.01 vol.％ of a glutaraldehyde （GA） solution. The water content of the CEMs increased with increasing ion-exchange capacity of the CEMs. The membrane resistance of the CEM with CmSSS=13 mol.％ was 0.81Ωcm2 and only one third of a commercial CEM, Neosepta® CMX although the dynamic state transport number of the PVA-based CEM was 0.93, which is about 5 ％ lower than that of 0.98 for CMX.