Nutritional quality changes in salted-dried mackerel (Scomber scombrus) and cod (Gadus morhua) during processing and storage

Salting and drying is one of the most important methods of processing fish and is predicted to continue to be nutritionally and economically important in the foreseeable future. This study investigated the effect of different methods of salting on the quality of fish during processing and one months storage using mackerel (Scomber scombrus) and cod (Gadus morhus). The four methods of salting used were 15% brine, saturated brine, pickle and dry salting. Thiamine and riboflavin assays were investigated and developed to increase reliability to flesh foods of this type. The results indicated that the use of non-specific protease for two hours before autoclaving gave maximum extraction for the riboflavin assay. The enzyme phosphatase gave maximum extraction of thiamine, and the optimum potassium ferricyanide concentration for thiochrome formation was established. Changes in quality of the fish and its products were monitored by determination of moisture content, total volatile basic nitrogen, peroxide value, pH, fluorescence of rancidity, free fatty acid, and fatty acid changes. These were correlated to changes in nutritional value. There were no significant changes in prox imate composition both in mackerel and cod during processing and storage. However, considerable changes in available lysine, thiamine and riboflavin occurred during salting, drying and one months storage. In mackerel, losses of between 16 and 59% of available lysine, 26 and 49% of thiamine and 16 and 35% of riboflavin were incurred. The pickle salting method resulted in the lowest losses of all three of these nutrients whilst the greatest losses were incurred using 15% brine method. The effect "of quality of raw material on the quality of end product of salted-dried mackerel has been investigated. The results for available lysine, thiamine, and riboflavin show that better quality raw material fish produced a better nutritional quality of end product (salted-dried fish). The development of lipid oxidation in cod correlated with decreases in available lysine, the greatest reactions occuring in the samples with the highest salt content (samples salted with dry salting). The overall losses of available lysine during processing and storage were between 26 and 33%. The losses in thiamine were between 31 and 41%, with the pickle salting method minimises losses of thiamine, whereas little changes occurred in riboflavin (13%).