Changes in macro- and microelements in freshwater fish during food processing

Fish meat is a valuable dietary component owing its exceptionally high nutritional value, as it contains high quality protein, fat (including n-3 acids) and a variety of vitamins and minerals. The aim of this study was to determine the content of ash and minerals (macro- and microelements) in three freshwater fish species, and quantitative changes in smoked and marinated products. The research material originated from three species, i.e. common carp (Cyprinus carpio), rainbow trout (Oncorhynchus mykkis) and northern pike (Esox lucius). The following parameters were determined in samples of raw as well as processed fish meat: ash (using the gravimetric method, according to PN-ISO 936:2000) and the minerals Na, K, Ca, Mg, P, Fe, Zn, Mn, Cu (using inductively coupled plasma optical emission spectrometry ICP-OES). The statistical analysis of the results did not show significant differences in the ash content in meat of the three fish species. The ash content in processed fish meat differed significantly from that in raw fish, thus indicating changes in concentrations of the minerals. The differences depended on the applied processing technology. As for the mineral content, the examined fish species achieved high nutritional quality, with the highest content of magnesium, iron and zinc in common carp, potassium and phosphorus in rainbow trout and calcium in pike. The levels of the minerals in processed fish meat differed significantly from those in the raw material, especially in carp products (higher amounts of almost all the determined elements). Smoking as well as marinating resulted in a considerable increase in the sodium contet, and the highest values were obtained for marinated rainbow trout. Monitoring the content of macro- and microelements in fish meat is important for the consumer.