Changes in the EPA and DHA content and lipids quality parameters of rainbow trout (Oncorhynchus mykiss, Walbaum) and carp (Cyprinus carpio, L.) at individual stages of hot smoking

The aim of this study was to evaluate qualitative changes in lipids of two most popular freshwater farmed fish (rainbow trout and carp) at particular stages of hot smoking process (brining, drying, smoking and heating). In order to characterize qualitative changes, the amount of peroxides (PV), secondary oxidation products (AsV) and the degree of hydrolysis of lipids (AV) was determined during the smoking process. The studies were carried out both in the fraction of lipids extracted using chloroform-based method (free lipids), as well as the fraction extracted by Bligh and Dyer method of the 1:1 chloroform: methanol ratio (bound lipids). Heat smoking results in loss of fat, especially at the last two stages of the process and the final contents of lipids were about 18% lower in the carp samples and about 10% lower in the trout samples. The dynamics of free lipid oxidation (Ch-lipids) was much smaller than the lipids extracted using B-D method, but the trend of lipid changes was similar. There was no significant difference in the anisidine value between two species, both for free lipids (Ch-lipids) and bound lipids (B-D-lipids), except for the last stage of smoking. No statistically significant differences between the studied species were found also in the case of lipid hydrolysis level, but after the smoking process an amount of free fatty acids increased. Subsequent stages of smoking process resulted in statistically significant losses of EPA and DHA in both fish species and in both types of lipids, i.e. B-D-lipids and Ch-lipids.