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Research analyses the effects of pre-salting methods on salt and water distribution of heavily salted cod

17 June 2015

Equal distribution of salt and water in salted cod is important for food safety during storage and for quality of the final product. Uneven amounts of salt across the fish muscle may result in bacterial, yeast and mould spoilage in fish. The Journal Food Chemistry reports a recent study by Danish and Icelandic researchers who investigated the effect of different salting methods on salt and water distribution in dry salted cod. Using fresh Atlantic cod (3 days old) Gudjonsdottir et al. either i. injected the fish with salt solution (18.4%) followed by 2-day immersion in brine (12.4%), ii. injected the fish with salt and phosphates solution (12.3% and 2.7% respectively) followed by 2-day immersion in salt brine (12.4%), iii. immersed the fish in salt brine (12.4%) for 2 days without prior salt injection or iv. stacked the alternating layers of fish and salt and left in a closed container for 2 days (pickled). To compare various physicochemical properties of salted fish the researchers used such analytical techniques as Nuclear Magnetic Resonance (NMR) spectroscopy and Magnetic Resonance Imaging (MRI). 

The highest water content was observed in fish injected with salt and phosphate prior to brining (59.7 ± 0.3 %) and the lowest in pickled fillets (57.1 ± 1.8 %). Pickled fish also had the lowest salt content (20.7%) compared to the highest in fish injected with salt prior to brining (21.6 ± 0.4 %). Brined and pickled fillets had higher water holding capacity than injection treated fish, but lost more water during the salting process. Water distribution was dependent on protein denaturation, its structure, muscle cells and fibers distribution across the fillet of fish. The data suggest that protein denaturation during dry salting (pickling) may minimize the differences in water distribution. Also, the more protein is denatured the more strongly the water is bound within the fish fillet. Overall there were differences in water distribution between different salting methods. Salt distribution was the least homogenous in brined fillet and the most in pickled fish. However ‘none of the pre-salting treatments in this study lead to a fully homogeneous water and salt distribution’ say authors of the study, and there is a need for further optimization of the salting technique used for cod fillets.

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