Innovative Nondestructive Measurements of Water Activity and the Content of Salts in Low-Salt Hake Minces

Impedance spectroscopy (IS), low-field proton nuclear magnetic resonance (LF ¹H NMR), chloride titration, ion chromatography, and an ion selective electrode were used to investigate the physicochemical parameters and measure sodium and potassium contents in low-salt brines and fish. Salt solutions (0–3 w/w, %) and model products of minced hake with added NaCl (0.5–3.0 w/w, %), or a mixture of NaCl and KCl (50/50 w/w, %), were analyzed. Good correlation was observed between the sodium content determined by using the ion selective electrode method and ion chromatography (R² = 0.97). In both salt solutions and fish minces, the impedance spectroscopy measurements could detect the difference in salt contents in mince with salt contents down to 0.5%. The NMR transversal relaxation time T₂ measurements clearly distinguished samples with 0, 0.5, and 1.0–3.0% salt, based on principal component analysis (PCA). Therefore, LF ¹H NMR seems to be a suitable technique for studies of low-salt products.