Salting and desalting of Fresh and frozen-thawed cod (Gadus morhua) fillets: A comparative study using 23Na NMR, 23Na MRI, low-field 1H NMR, and physicochemical analytical methods

Fresh and frozen-thawed cod raw materials were subjected to brining, dry salting, and rehydration. The effects of salting and desalting on iller water-related properties, salt content, and salt distribution were studied using 23 Na MBI, 25 Na NMR, and low-field (LF) 3 H NMR. The resulte were compared with the Volthard titration method for salt determination, fillet pH, water content, and water-holding capaclty. The relrydrated end preduct showed signiffcant difference only with respect to water-holding capacity (unfroren raw reaterail higher) when fresh and frozen-thawed raw materials were compared. Excellent carrelation was obrained between quantitative sait determinations using 23 Na NMR and Volhard titration. When using a typical salting method, it was shown that the salt uptake and salt distribution in the fillets were inhomogeneous. Protre relaxation times, obtained from LF 1 H NMR, were processed using either a 2-exponential model or the CONTIN algorithm. In several instances, a clear dependence on fillet pH, water-holding capacity, or salt content daring fish processing was observed. Our resalts indicate that NMR and MRI can be used as useful tools to evaloate and optimize fish processing unit operations and that rapid (LF) NMR methods have the potential for replacing traditional salt and water-related analytical methods.