The Influence of Salting Procedures on the Characteristics of Heavy Salted Cod

Abstract: The production of heavy salted cod (bacalao) has changed from being a single-step process salting to a multistep procedure. The aim of this study was to gain a deeper understanding of water retention and yields of heavy salted cod as influenced by salting procedures. The effects of different pre-salting methods (injection and brining, brining only, and pickling) were compared to a single kench salting step. The products were evaluated at different stages of the process: after pre-salting, dry salting, storage and rehydration, with regard to changes in yields, chemical content and salt-induced changes in muscle proteins and microstructure. Injection was significantly different from other methods in increasing weight yields through brining, dry salting and rehydration. Salt concentrations of the brine did not influence the weight yields of dry-salted and rehydrated products. However, salt concentrations >20% had negative effects on the colour and commercial quality of the salted products. Addition of phosphates increased weight yield of salted but not of rehydrated products. Effects on quality varied between trials; both negative and positive effects were observed. Strong salting-out effects on proteins were seen due to high salt contents in the salted products regardless of the procedures applied. The effects of salting procedures on yields and quality of heavy salted cod products were related to the pathway of solubilisation, denaturation and aggregation of proteins in the muscle. Myosin was less aggregated when injection was applied during pre-salting. A greater degree of protein aggregation correlated with higher initial salt concentrations and dehydration during the first days of salting, which was obtained with brining, pickling and kench salting. In addition, these methods resulted in stronger enzymatic degradation of proteins, shown as an increase in lower molecular weight subunits. The connective tissue in the muscle was believed to play an important role in water retention of the muscle. Microstructural analysis of the dry-salted fillets showed that the intercellular spaces in injected and brined fillets were increased compared to only brining. However, the cross-sectional area of the fish fibres was similar in both groups. Based on this, the main reason for higher weight yields of injected products after salting and rehydration were believed to result from irreversible effects on the connective tissue in the muscle and better retention of myosin structure, thereby better water-holding. The drawback of the wet-salting methods (brining and injection) was that the yield of nitrogenous compounds was lower for injected and brine-salted fillets. However, the main changes were due to higher losses of non-protein nitrogen, which is more likely to influence the organoleptic properties of the products than the weight yields.