The presence of valuable bioactive compounds in European eel (Anguilla anguilla) skin was studied. For it, proximate and lipid class compositions and analysis of the fatty acid (FA) profile (individual FAs; FA groups, i.e., saturated, monounsaturated, and polyunsaturated; FA ratios, i.e., polyunsaturated/saturated, ω3/ω6) were determined and compared to the composition of the eel muscle. As a result, higher (p<0.05) levels of proteins (271.6 g·kg-1), lipids (38.0 g·kg-1), ash (27.7 g·kg-1) and ω6 FAs were observed in the skin tissue. Contrary, the muscle tissue showed higher (p<0.05) moisture, ω3 FA and ω3/ω6 values. Regarding lipid classes, a higher (p<0.05) proportion of phospholipids (111.1 g·kg-1 lipids), sterols (104.7 g·kg-1 lipids), α-tocopherol (274.0 mg·kg-1 lipids), and free fatty acids (43.6 g·kg-1 lipids) was observed in the skin tissue. No differences (p>0.05) between both tissues could be detected for triacylglycerol and FA group (saturated, monounsaturated, and polyunsaturated) values, as well as for the polyunsaturated/saturated ratio. It is concluded that eel skin, a by-product resulting from commercial processing, can be considered a valuable source to provide the food and pharmaceutical industries with useful value-added constituents such as proteins, lipids, ω3 FAs, phospholipids, and α-tocopherol.

The combined effects of the thermal processing (i.e., sterilisation treatment) and the prior frozen storage time (3 or 6 months at –18 ºC) on the quality loss in canned Atlantic horse mackerel (Trachurus trachurus) were determined. Thus, the sterilisation step led to a remarkable (p<0.05) formation in canned fish muscle of fluorescent compounds, free fatty acids (FFAs) and trimethylamine and to an increase of the L* and b* colour parameters; meantime, a decrease (p<0.05) of the total ω3 FA/total ω6 FA ratio and the a* colour value were detected. The prior frozen storage period led to an increased (p<0.05) lipid oxidation (peroxide, thiobarbituric acid reactive substance and fluorescent compound formation) and hydrolysis (FFA formation) development and to increased L* and b* colour values in the corresponding canned samples; additionally, a lower (p<0.05) polyene index and phospholipid content were observed in canned fish previously subjected to frozen storage. In most indices, physico-chemical changes related to quality loss were found higher if the previous storage period was increased. According to the marked effects of the sterilisation step and the prior frozen storage period, optimisation of such processing conditions is recommended to maximise the quality of canned horse mackerel.

Among cephalopod discards, ink has revealed several beneficial properties regarding human health, environmental preservation and food preservation. In this study, different concentrations of an aqueous extract of cuttlefish (Sepia spp.) ink (CI) were added, respectively, to the packing medium employed during golden seabream (Sparus aurata) canning. Quality parameters of the resulting canned fish were determined and compared to the counterpart control and raw samples. As a result, an important effect of the CI concentration added to the packing medium was proved. The presence in the packing medium of a relatively low CI concentration led to lower (p<0.05) lipid oxidation development (fluorescent compound formation), lower (p<0.05) changes of colour parameters (L* and a* values) and lower (p<0.05) trimethylamine values in canned fish. Additionally, the two lowest CI concentrations tested led to higher average values of C22:6ω3 and ω3/ω6 ratios. Remarkably, higher average values of free fatty acids, polyene index and C20:5ω3 were detected in all kinds of CI-treated fish when compared to control canned samples. In agreement with environmental sustainability and circular economy requirements, the study provides a first approach to a novel and beneficial use of the present marine discard for the quality enhancement of canned fish.