Salting and Desalting of Fresh and Frozen-thawed Cod (Gadus morhua) Fillets: A Comparative Study Using ~(23)Na NMR, ~(23)Na MRI, Low-field ~1H NMR, and Physicochemical Analytical Methods

摘要

Fresh and frozen-thawed cod raw materials were subjected to brining, dry salting, and rehydration. The effects of salting and desalting on fillet water-related properties, salt content, and salt distribution were studied using ~(23)Na MRI, ~(23)Na NMR, and low-field (LF) ~1H NMR. The results were compared with the Volhard titration method for saft determination, fillet pH, water content, and water-holding capacity. The rehydrated end product showed significant difference only with respect to water-holding capacity (unfrozen raw material higher) when fresh and frozen-thawed raw materials were compared. Excellent correlation was obtained between quantitative salt determinations using ~(23)Na NMR and Volhard titration. When using a typical salting method, it was shown that the salt uptake and salt distribution hi the fillets were inhomogeneous. Proton relaxation times, obtained from LF ~1H 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 during fish processing was observed. Our results indicate that NMR and MRI can be used as useful tools to evaluate and optimize fish processing unit operations and that rapid (LF) NMR methods have the potential for replacing traditional salt and water-related analytical methods.