Simple Summary
Marine fish are an important source of high-quality protein and beneficial fats in the human diet. In addition to fresh fish, canned fish is also widely consumed, but information on its nutritional value is limited. This study examined the protein, fat, and fatty acid composition of various commercially available canned fish species in brine. All samples contained relatively high amounts of protein, generally between 15 and 21 g per 100 g, while fat content varied from a few tenths to 15 g per 100 g, depending on the fish species. Canned marine fish proved to be a valuable source of the omega-3 polyunsaturated fatty acids, in particular eicosapentaenoic and docosahexaenoic acid, which are important for human health. As a result, consuming an average of 3 g of cod liver, 10 g of mackerel, 15 g of sardines, or 30 g of Atlantic and sockeye salmon is sufficient to ensure the recommended daily intake of these two acids. However, it would be necessary to consume 300–700 g of skipjack tuna. On the other hand, tuna remains a source of high-quality protein and other nutritionally valuable substances.
Keywords: protein, lipids, fat, EPA, DHA, dry matter
Abstract
Marine fish are a good dietary source of important macro- and micronutrients. In addition to fresh fish, fish with varying degrees of industrial processing—frozen, marinated, smoked, canned, etc.—is used extensively in the food market. This study comprehensively characterizes the protein content, fat content, and fatty acid composition of various commercially available canned marine fish species. All canned fish muscle and cod liver were in salted brine, to eliminate the influence of other ingredients. All samples obtained from muscle had a relatively high protein content, mostly between 15 and 21 g/100 g. The fat content was highly variable, ranging from a few tenths to 15 g/100 g. Of the fatty acids, PUFAs predominated in almost all samples. The fatty acid composition of canned fish was very similar to the fatty acid composition of fresh fish. The fact that the content of highly oxylabile PUFAs practically did not differ compared to fresh fish indicates that the preservation process does not lead to significant oxidative damage to this type of product. A significant benefit of eating marine fish is the intake of highly unsaturated fatty acids EPA and DHA of the omega-3 fatty acid series. Mainly mackerel and sardines are an excellent source of these two acids. Atlantic salmon and sockeye salmon are also very good sources. As a result, consuming an average of 3 g of cod liver, 10 g of mackerel, 15 g of sardines, or 30 g of Atlantic and sockeye salmon is sufficient to ensure the recommended daily intake of EPA and DHA.
1. Introduction
From a nutritional point of view, fish are primarily a source of high-quality protein, some minerals, and important micronutrients. Some fish (especially fatty fish—salmon, herring, sardines, anchovies, mackerel, etc.) are very good sources of polyunsaturated fatty acids (PUFAs), in particular eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). For fatty fish, the usable energy is mainly due to the fat content, while for other fish it is mainly due to the protein content [1,2,3,4,5].
The protein content of fish is usually in the range of 16–22 g/100 g. Muscle protein has a high nutritional value and is very easily digestible. Fish are also an important dietary source of some non-proteinogenic amino acids with high biological activity, e.g., carnitine or creatine [1,3,4,5,6,7,8,9,10].
The fat content in fish muscle is very variable, ranging from tenths of a gram to 25 g in 100 g of product. The content of saturated fatty acids (with predominant palmitic acid) ranges from 15 to 30% of the fat content. The presence of omega-3 PUFAs with a long chain and a higher number of double bonds, so-called HUFAs (highly unsaturated fatty acids), is significant. They are not synthesized in plants (except for genetically modified) and are found in significant quantities only in fish and seaweed. Freshwater fish contain lower levels of omega-3 HUFA. Of marine fish, only those that contain a larger amount of fat are a good source of EPA and DHA. They include, for example, Atlantic salmon (Salmo salar L.), Atlantic mackerel (Scomber scombrus L.), Atlantic herring (Clupea harengus L.), sardine (Sardina pilchardus Walb.), bluefin tuna (Thunnus thynnus L.) or swordfish (Xiphias gladius L.). To ensure the recommended daily intake of 250 mg EPA + DHA, 10–20 g of any of these fish is sufficient [1,3,4,5,6,7,9,11,12,13,14,15,16,17,18,19].
Canning and freezing technology are widely used in fish processing. In both cases, the technology must be conducted in such a way as to prevent, if possible, the loss of significant, chemically unstable nutrients. In the case of fish, these are mainly oxylabile HUFAs. In the case of fish products, the problem of oxidation can be solved by a suitable technological procedure or by the addition of effective natural antioxidants, e.g., rosemary extracts [3,9,12,16,20,21,22,23,24,25,26].
Even experts can find it difficult to follow the nomenclature of certain fish species. Identifying fish processed into various fish products then becomes a significant problem. A good example is the nomenclature of fish referred to by the English name tuna. This group includes four genera (Auxis, Euthynnus, Katsuwonus and Thunnus), all belonging to the Scombridae family, with a total of 13 species. These species differ significantly in composition; e.g., the fat content ranges from 0.5 to 16 g/100 g [27,28]. The aim of this study was therefore to comprehensively characterize macronutrient levels of various commercially available canned fish species that are currently produced worldwide and widely available on the European Union food market. This study is of major importance for public health, accurate dietary recommendations, food industry standards, and consumer awareness.
2. Materials and Methods
Samples of canned fish and fish products in brine (various producers and various batches; a total of 46 samples) were purchased for laboratory testing in 2024 in Czech Republic markets. All samples were at least 6 months prior to the best-before date at the time of analysis. In the cod liver (CL) samples, fish liver was processed; in other samples, the processed part was muscle tissue. Samples of canned fish in some vegetable oils or tomato sauce were not considered, because these ingredients could affect the fatty acid profile of the tested fish. Table 1 summarizes the basic characteristics of the analyzed samples.
Table 1.
List of samples of canned fish products from the Czech market.
| Nr. | Description | Fish | Brand Name | Country of Origin | Place of Capture |
|---|---|---|---|---|---|
| T1, T2 * | Tuna in brine, chunks | Skipjack tuna, Katsuwonus pelamis L. | Giana | Spain | FAO 34, middle eastern Atlantic Ocean |
| T3, T4 * | Tuna in brine, chunks | Skipjack tuna, Katsuwonus pelamis L. | Sun&Sea | Spain | FAO 34, middle eastern Atlantic Ocean |
| T5, T6 * | Tuna in brine, chunks | Skipjack tuna, Katsuwonus pelamis L. | Blue Bay | Vietnam | FAO 71, central Pacific Ocean |
| T7, T8, T9 * | Tuna in brine, chunks | Skipjack tuna, Katsuwonus pelamis L. | Rio Mare | Mauritius | FAO 51, Indian Ocean |
| T10, T11 * | Tuna in brine, chunks | Skipjack tuna, Katsuwonus pelamis L. | Wellness Nekton | Vietnam | FAO 71, central Pacific Ocean |
| T12, T13 * | Tuna in brine, chunks | Skipjack tuna, Katsuwonus pelamis L. | Giana | Ecuador | FAO 77,87 middle western Pacific Ocean |
| CL1–CL4 * | Cod liver in its own oil | Atlantic cod, Gadus morhua L. | Giana | Iceland | FAO 27, northeastern Atlantic Ocean |
| S1–S5 * | Salmon in brine, chunks | Atlantic salmon, Salmo salar L. | Nekton | Poland | Norway, farm breeding |
| O1, O2 * | Salted salmon nerka from Alaska | Sockeye salmon, Oncorhynchus nerka Walb. | Marks & Spencer | USA | FAO 67, north Pacific Ocean |
| O3, O4 * | Salmon nerka in salted brine | Sockeye salmon, Oncorhynchus nerka Walb. | Marks & Spencer | Canada | FAO 67, north Pacific Ocean |
| M1, M2 * | Mackerel in brine | Atlantic mackerel, Scomber scombrus L. | Giana | Morocco | FAO 34, middle eastern Atlantic Ocean |
| M3, M4 * | Mackerel in brine | Atlantic mackerel, Scomber scombrus L. | Nekton | Morocco | FAO 34, middle eastern Atlantic Ocean |
| M5, M6 * | Mackerel in brine | Atlantic mackerel, Scomber scombrus L. | Nekton | Latvia | FAO 34, middle eastern Atlantic Ocean |
| P1–P4 * | Sardines in brine | European pilchard, Sardina pilchardus Walb. | Giana | Morocco | FAO 34, middle eastern Atlantic Ocean |
| P5, P6 * | Sardines in brine | European pilchard, Sardina pilchardus Walb. | Tesco | Morocco | FAO 34, middle eastern Atlantic Ocean |
| P7 | Sardines in brine | European pilchard, Sardina pilchardus Walb. | Gold-Plus | Morocco | FAO 34, middle eastern Atlantic Ocean |
| P8, P9 * | Sardines in brine | European pilchard, Sardina pilchardus Walb. | Hamé | Morocco | FAO 34, middle eastern Atlantic Ocean |
| P10–P12 * | Sardines in brine | European pilchard, Sardina pilchardus Walb. | Nekton Jardan | Morocco | FAO 34, middle eastern Atlantic Ocean |
| P13, P14 * | Sardines in brine | European pilchard, Sardina pilchardus Walb. | Giana | Morocco | FAO 34, middle eastern Atlantic Ocean |
* Different batches.
For each sample, three cans were opened, and the entire contents of the drained solid portion were homogenized using a flesh-suitable mixer, Grindomix GM200 (Retsch GmbH, Haan, Germany), and kept in the freezer at −55 °C until the analysis.
Dry matter was determined gravimetrically after drying approximately 1.5 g of homogenized samples at 105 °C in a laboratory drying oven, Binder E28 (Binder GmbH, Tuttlingen, Germany), to a constant weight according to ISO1442:2023 [29]. The Kjeldahl method was used to determine nitrogen by the KT200 Kjeltec system (FOSS, Hillerød, Denmark) according to AOAC method 920.105 [30]. The protein content was estimated by multiplying the determined nitrogen content by a nitrogen-to-protein conversion factor of 6.25 [31]. The fat content was determined gravimetrically after extraction according to ISO 659:2009 [32], adapted for the Soxtec 8000 apparatus (FOSS, Hillerød, Denmark). Fatty acids were first converted to fatty acid methyl esters according to EN ISO 12966-2:2011 [33] and then analyzed by gas–liquid chromatography using an SP-2560 fused silica capillary column (100 m × 0.25 mm i.d., 20 μm film thickness) (Supelco, Bellefonte, PA, USA) in an Agilent 6890 gas chromatograph (Agilent Technologies, Santa Clara, CA, USA) equipped with a flame ionization detector (FID) under the conditions described by Sabolová et al. [34]. The fatty acid quantification was carried out by the internal normalization method, and the results were expressed as relative percentages of all identified fatty acids.
For all of the above measurements, two parallel determinations were performed for each sample. In order to verify the reliability of the results, six parallel determinations of the previously mentioned methods were performed for a selected sample. The repeatability, expressed as relative standard deviation (RSD), did not exceed 5% for any of the methods. The statistical analysis comprised one-way analysis of variance (ANOVA) and cluster analysis, which was performed using STATISTICA v. 12.0 (StatSoft, Inc., Tulsa, OK, USA). Sheffe’s post hoc test was performed at the 5% significance level to identify differences among tested samples. Partial least squares discriminant analysis (PLS-DA) was performed on the free online platform MetaboAnalyst 6.0 (Xia Lab, McGill University, Montreal, QC, Canada). No normalization, transformation, or scaling was used prior to the analysis.
3. Results
3.1. Dry Matter, Protein, and Fat Content
A total of 46 canned fish samples commonly available on the Czech market were analyzed for dry matter, protein, and fat content. Table 2 summarizes the results of the proximate composition of the tested samples.
Table 2.
Proximate composition of the tested canned fish samples.
| Sample | Sample | ||||||
|---|---|---|---|---|---|---|---|
| No. | DM | Protein | Fat | No. | DM | Protein | Fat |
| (g/100 g) | (g/100 g) | (g/100 g) | (g/100 g) | (g/100 g) | (g/100 g) | ||
| T1 | 18.9 ± 1.1 | 16.9 ± 0.8 | 0.5 ± 0.1 | S1 | 37.0 ± 1.4 | 17.0 ± 1.2 | 12.4 ± 0.7 |
| T2 | 18.9 ± 0.8 | 17.6 ± 1.4 | 0.8 ± 0.2 | S2 | 38.8 ± 2.8 | 18.9 ± 1.0 | 12.6 ± 0.7 |
| T3 | 17.8 ± 0.7 | 15.5 ± 0.6 | 0.8 ± 0.1 | S3 | 39.5 ± 2.7 | 19.5 ± 1.0 | 12.5 ± 1.1 |
| T4 | 19.6 ± 0.7 | 18.1 ± 1.1 | 0.6 ± 0.1 | S4 | 38.7 ± 2.1 | 15.7 ± 0.7 | 11.5 ± 0.8 |
| T5 | 20.7 ± 1.1 | 18.5 ± 0.9 | 0.6 ± 0.2 | S5 | 40.6 ± 3.4 | 17.9 ± 0.8 | 12.0 ± 0.6 |
| T6 | 19.9 ± 0.9 | 18.9 ± 0.9 | 0.7 ± 0.3 | O1 | 29.8 ± 1.9 | 20.4 ± 0.9 | 4.3 ± 0.4 |
| T7 | 20.8 ± 1.1 | 18.4 ± 0.6 | 0.5 ± 0.1 | O2 | 28.5 ± 1.2 | 21.5 ± 0.8 | 3.9 ± 0.3 |
| T8 | 20.1 ± 0.7 | 18.9 ± 1.1 | 0.6 ± 0.2 | O3 | 24.6 ± 1.3 | 20.9 ± 1.0 | 3.2 ± 0.2 |
| T9 | 19.9 ± 1.0 | 18.2 ± 1.0 | 0.9 ± 0.1 | O4 | 26.3 ± 1.6 | 22.2 ± 0.9 | 2.8 ± 0.4 |
| T10 | 22.0 ± 1.2 | 21.3 ± 1.0 | 0.4 ± 0.2 | SP1 | 30.5 ± 1.2 | 14.7 ± 1.2 | 11.8 ± 0.8 |
| T11 | 21.6 ± 1.0 | 20.6 ± 0.9 | 0.5 ± 0.1 | SP2 | 29.9 ± 1.5 | 16.9 ± 1.0 | 10.6 ± 0.7 |
| T12 | 21.5 ± 0.7 | 20.5 ± 0.5 | 0.6 ± 0.1 | SP3 | 27.1 ± 1.6 | 18.7 ± 0.9 | 8.7 ± 0.8 |
| T13 | 20.9 ± 1.0 | 19.8 ± 0.9 | 0.7 ± 0.3 | SP4 | 28.6 ± 1.8 | 19.5 ± 1.0 | 7.9 ± 0.6 |
| CL1 | 71.8 ± 3.2 | 7.2 ± 0.4 | 56.9 ± 3.4 | SP5 | 29.2 ± 1.2 | 20.0 ± 0.8 | 7.3 ± 0.5 |
| CL2 | 72.6 ± 3.8 | 6.8 ± 0.5 | 60.3 ± 2.2 | SP6 | 28.9 ± 1.7 | 19.7 ± 1.1 | 7.6 ± 1.0 |
| CL3 | 70.3 ± 3.5 | 6.8 ± 0.5 | 58.3 ± 3.0 | SP7 | 32.2 ± 1.6 | 20.5 ± 0.6 | 8.6 ± 0.9 |
| CL4 | 69.8 ± 4.5 | 8.3 ± 0.7 | 55.9 ± 3.8 | SP8 | 32.1 ± 1.3 | 20.5 ± 0.9 | 10.4 ± 0.8 |
| M1 | 30.7 ± 1.9 | 19.5 ± 0.8 | 10.3 ± 0.9 | SP9 | 31.6 ± 1.4 | 20.8 ± 1.1 | 9.6 ± 0.5 |
| M2 | 34.1 ± 2.4 | 20.3 ± 0.9 | 12.5 ± 0.7 | SP10 | 32.1 ± 1.2 | 21.9 ± 1.1 | 10.0 ± 0.7 |
| M3 | 32.9 ± 2.0 | 18.2 ± 1.1 | 11.9 ± 1.0 | SP11 | 30.1 ± 1.3 | 19.7 ± 0.8 | 8.9 ± 0.4 |
| M4 | 31.9 ± 2.1 | 19.1 ± 0.7 | 11.6 ± 0.7 | SP12 | 31.0 ± 1.2 | 19.6 ± 0.9 | 10.1 ± 1.0 |
| M5 | 36.2 ± 2.0 | 18.9 ± 1.2 | 16.2 ± 1.3 | SP13 | 30.6 ± 1.3 | 21.8 ± 1.6 | 8.4 ± 0.6 |
| M6 | 35.7 ± 1.5 | 19.5 ± 0.8 | 14.8 ± 0.5 | SP14 | 30.9 ± 0.7 | 20.1 ± 0.7 | 9.4 ± 0.7 |
Legend: DM = dry matter content; Protein = crude protein content; Fat = fat content; Sample groups: T = tuna (skipjack); CL = cod liver; M = mackerel; S = salmon; O = salmon nerka; SP = sardine samples.
Significant differences (p = 0.05) for all three parameters (dry matter, total fat, and crude protein contents) were found for all sample groups (T = tuna; CL = cod liver; M = mackerel; S = salmon; O = salmon nerka; SP = sardine). Within the individual groups, significant differences were not found for any parameter. The biggest differences can logically be observed in cod liver samples, where the processed part of the fish (liver) is different from the other samples, where the fish muscle is processed.
The protein content in fish samples (excluding cod liver) ranged between 15 and 22 g/100 g of sample. While the variability in protein content was relatively small in muscle fish samples, the variability in fat content was very high. Skipjack tuna had a very low amount of fat; all samples were found to contain less than 1 g/100 g. In the monitored samples of canned sockeye salmon, a fat content in the range of 2.8–4.3 g/100 g of the sample was found. A moderately high fat content was found in samples of mackerel, salmon (slightly above 10 g/100 g in both cases), and sardines (around 10 g/100 g on average).
3.2. Fatty Acid Composition
Fatty acid composition of the samples is summarized in Table 3 and Table 4.
Table 3.
Composition of selected fatty acids in canned fish products (as % of total fatty acids).
| Sample No. | C14:0 | C16:0 | C18:1 | C18:2 | C18:3 | C20:5 | C22:6 | C20:4 |
|---|---|---|---|---|---|---|---|---|
| T1 | 14.3 ± 0.2 | 18.4 ± 0.3 | 12.8 ± 0.1 | 1.4 ± 0.1 | 0.4 ± 0.1 | 3.1 ± 0.1 | 11.7 ± 0.3 | 2.3 ± 0.1 |
| T2 | 11.5 ± 0.1 | 23.6 ± 0.2 | 12.5 ± 0.1 | 1.1 ± 0.1 | 2.3 ± 0.1 | 2.0 ± 0.1 | 9.9 ± 0.2 | 1.2 ± 0.1 |
| T3 | 18.4 ± 0.2 | 19.3 ± 0.3 | 11.4 ± 0.1 | 1.5 ± 0.1 | 0.9 ± 0.1 | 3.6 ± 0.1 | 6.3 ± 0.2 | 2.8 ± 0.1 |
| T4 | 16.8 ± 0.1 | 16.8 ± 0.3 | 12.4 ± 0.2 | 1.3 ± 0.1 | 1.2 ± 0.1 | 3.8 ± 0.1 | 10.3 ± 0.3 | 2.5 ± 0.1 |
| T5 | 18.3 ± 0.2 | 21.4 ± 0.3 | 11.8 ± 0.1 | 1.1 ± 0.1 | 0.3 ± 0.1 | 2.8 ± 0.1 | 12.8 ± 0.3 | 1.3 ± 0.1 |
| T6 | 11.4 ± 0.1 | 21.7 ± 0.4 | 15.1 ± 0.1 | 1.9 ± 0.1 | 3.3 ± 0.1 | 2.5 ± 0.1 | 9.3 ± 0.3 | 1.6 ± 0.1 |
| T7 | 17.7 ± 0.3 | 23.2 ± 0.4 | 12.0 ± 0.1 | 0.7 ± 0.1 | 0.2 ± 0.1 | 2.3 ± 0.1 | 9.0 ± 0.3 | 2.3 ± 0.1 |
| T8 | 8.7 ± 0.1 | 21.3 ± 0.3 | 14.8 ± 0.2 | 0.8 ± 0.1 | 0.5 ± 0.1 | 2.9 ± 0.1 | 9.9 ± 0.2 | 1.5 ± 0.1 |
| T9 | 11.0 ± 0.1 | 28.9 ± 0.3 | 10.9 ± 0.1 | 1.0 ± 0.1 | 1.8 ± 0.1 | 2.1 ± 0.1 | 8.7 ± 02 | 0.7 ± 0.1 |
| T10 | 22.4 ± 0.3 | 15.6 ± 0.2 | 14.0 ± 0.3 | 0.7 ± 0.1 | 2.5 ± 0.1 | 2.6 ± 0.1 | 7.3 ± 0.1 | 2.1 ± 0.1 |
| T11 | 12.3 ± 0.1 | 24.3 ± 0.3 | 13.3 ± 0.1 | 0.9 ± 0.1 | 0.9 ± 0.1 | 2.3 ± 0.1 | 9.0 ± 0.2 | 0.4 ± 0.1 |
| T12 | 21.0 ± 0.2 | 16.7 ± 0.2 | 14.9 ± 0.2 | 0.7 ± 0.1 | 0.6 ± 0.1 | 2.2 ± 0.1 | 9.2 ± 0.2 | 0.3 ± 0.1 |
| T13 | 17.2 ± 0.1 | 22.6 ± 0.2 | 12.3 ± 0.2 | 1.2 ± 0.1 | 1.2 ± 0.1 | 2.5 ± 0.1 | 8.9 ± 0.2 | 2.2 ± 0.1 |
| CL1 | 5.6 ± 0.1 | 12.6 ± 0.1 | 17.4 ± 0.3 | 1.6 ± 0.1 | 9.3 ± 0.1 | 9.0 ± 0.2 | 10.5 ± 0.3 | 7.5 ± 0.1 |
| CL2 | 6.0 ± 0.1 | 10.8 ± 0.1 | 15.9 ± 0.1 | 1.4 ± 0.1 | 8.8 ± 0.1 | 10.1 ± 0.2 | 9.8 ± 0.2 | 8.9 ± 0.1 |
| CL3 | 4.6 ± 0.1 | 10.1 ± 0.1 | 19.6 ± 0.2 | 1.6 ± 0.1 | 13.6 ± 0.2 | 7.6 ± 0.1 | 10.3 ± 0.2 | 8.3 ± 0.1 |
| CL4 | 5.0 ± 0.1 | 9.8 ± 0.1 | 21.3 ± 0.2 | 1.1 ± 0.1 | 11.2 ± 0.2 | 7.1 ± 0.1 | 9.5 ± 0.2 | 9.8 ± 0.2 |
| M1 | 8.3 ± 0.2 | 18.2 ± 0.3 | 7.4 ± 0.1 | 2.5 ± 0.1 | 1.0 ± 0.1 | 13.0 ± 0.2 | 16.7 ± 0.3 | 3.1 ± 0.1 |
| M2 | 6.8 ± 0.1 | 16.4 ± 0.1 | 8.6 ± 0.1 | 2.2 ± 0.1 | 1.3 ± 0.1 | 11.3 ± 0.2 | 18.1 ± 0.3 | 3.9 ± 0.1 |
| M3 | 7.6 ± 0.1 | 17.1 ± 0.1 | 6.8 ± 0.1 | 2.1 ± 0.1 | 0.8 ± 0.1 | 11.2 ± 0.2 | 21.9 ± 0.4 | 3.1 ± 0.1 |
| M4 | 7.5 ± 0.1 | 18.6 ± 0.3 | 7.9 ± 0.1 | 2.0 ± 0.1 | 1.1 ± 0.1 | 11.8 ± 0.2 | 17.5 ± 0.3 | 3.4 ± 0.1 |
| M5 | 7.7 ± 0.1 | 15.5 ± 0.2 | 9.5 ± 0.2 | 2.9 ± 0.1 | 1.9 ± 0.1 | 10.0 ± 0.2 | 16.8 ± 0.3 | 4.3 ± 0.1 |
| M6 | 8.0 ± 0.2 | 18.2 ± 0.3 | 10.1 ± 0.2 | 2.2 ± 0.1 | 1.6 ± 0.1 | 9.6 ± 0.1 | 17.3 ± 0.1 | 3.1 ± 0.1 |
| S1 | 3.5 ± 0.1 | 9.1 ± 0.1 | 39.2 ± 0.3 | 14.9 ± 0.2 | 3.6 ± 0.1 | 2.7 ± 0.1 | 3.4 ± 0.1 | 1.7 ± 0.1 |
| S2 | 7.2 ± 0.1 | 11.6 ± 0.2 | 36.5 ± 0.4 | 13.1 ± 0.2 | 4.2 ± 0.1 | 1.9 ± 0.1 | 5.6 ± 0.1 | 1.9 ± 0.1 |
| S3 | 5.6 ± 0.1 | 8.8 ± 0.1 | 31.6 ± 0.4 | 15.4 ± 0.1 | 5.6 ± 0.1 | 2.9 ± 0.1 | 5.1 ± 0.1 | 0.9 ± 0.1 |
| S4 | 9.0 ± 0.2 | 12.9 ± 0.2 | 33.3 ± 0.4 | 12.4 ± 0.2 | 5.8 ± 0.1 | 2.3 ± 0.1 | 5.0 ± 0.1 | 1.0 ± 0.1 |
| S5 | 8.2 ± 0.1 | 11.9 ± 0.3 | 31.2 ± 0.3 | 14.6 ± 0.3 | 5.0 ± 0.1 | 2.8 ± 0.1 | 4.4 ± 0.1 | 1.5 ± 0.1 |
| O1 | 7.6 ± 0.1 | 19.7 ± 0.3 | 11.9 ± 0.2 | 2.2 ± 0.1 | 5.6 ± 0.1 | 7.1 ± 0.1 | 19.7 ± 0.3 | 4.3 ± 0.1 |
| O2 | 7.2 ± 0.1 | 18.8 ± 0.2 | 12.9 ± 0.1 | 2.0 ± 0.1 | 4.1 ± 0.1 | 7.8 ± 0.2 | 21.5 ± 0.4 | 4.0 ± 0.1 |
| O3 | 5.3 ± 0.1 | 20.5 ± 0.3 | 13.2 ± 0.1 | 2.5 ± 0.1 | 3.8 ± 0.1 | 8.0 ± 02 | 20.5 ± 0.4 | 2.5 ± 0.1 |
| O4 | 6.4 ± 0.1 | 18.5 ± 0.2 | 11.8 ± 0.1 | 2.3 ± 0.1 | 3.2 ± 0.1 | 7.2 ± 0.1 | 18.9 ± 0.3 | 3.1 ± 0.1 |
| SP1 | 8.7 ± 0.1 | 19.1 ± 0.2 | 10.7 ± 0.1 | 3.5 ± 0.1 | 1.7 ± 0.1 | 20.1 ± 0.3 | 4.5 ± 0.1 | 1.4 ± 0.1 |
| SP2 | 8.2 ± 0.1 | 18.9 ± 0.3 | 10.3 ± 0.2 | 3.1 ± 0.1 | 1.3 ± 0.1 | 19.3 ± 0.2 | 6.9 ± 0.1 | 1.0 ± 0.1 |
| SP3 | 12.3 ± 0.3 | 23.6 ± 0.3 | 9.4 ± 0.1 | 3.0 ± 0.1 | 1.2 ± 0.1 | 15.7 ± 0.2 | 3.9 ± 0.1 | 1.4 ± 0.1 |
| SP4 | 8.1 ± 0.1 | 19.8 ± 0.2 | 10.1 ± 0.2 | 2.8 ± 0.1 | 1.0 ± 0.1 | 16.8 ± 0.2 | 7.8 ± 0.1 | 0.9 ± 0.1 |
| SP5 | 6.3 ± 0.1 | 17.6 ± 0.3 | 5.5 ± 0.1 | 3.7 ± 0.1 | 0.6 ± 0.1 | 25.4 ± 0.3 | 7.9 ± 0.2 | 1.3 ± 0.1 |
| SP6 | 8.6 ± 0.2 | 17.9 ± 0.3 | 9.2 ± 0.1 | 2.5 ± 0.1 | 0.9 ± 0.1 | 18.6 ± 0.2 | 9.7 ± 0.1 | 1.1 ± 0.1 |
| SP7 | 7.1 ± 0.1 | 19.9 ± 0.3 | 8.4 ± 0.2 | 1.6 ± 0.1 | 0.5 ± 0.1 | 15.5 ± 0.2 | 13.0 ± 0.3 | 1.6 ± 0.1 |
| SP8 | 9.4 ± 0.2 | 19.6 ± 0.3 | 5.0 ± 0.1 | 2.7 ± 0.1 | 0.6 ± 0.1 | 20.4 ± 0.3 | 8.6 ± 0.2 | 0.7 ± 0.1 |
| SP9 | 8.0 ± 0.2 | 18.8 ± 0.2 | 8.5 ± 0.2 | 2.0 ± 0.1 | 0.9 ± 0.1 | 18.6 ± 0.2 | 9.1 ± 0.2 | 1.2 ± 0.1 |
| SP10 | 8.8 ± 0.1 | 20.8 ± 0.2 | 9.6 ± 0.2 | 3.2 ± 0.1 | 0.6 ± 0.1 | 19.7 ± 0.3 | 6.3 ± 0.1 | 0.2 ± 0.1 |
| SP11 | 7.6 ± 0.1 | 19.5 ± 0.3 | 10.3 ± 0.3 | 2.6 ± 0.1 | 1.1 ± 0.1 | 17.9 ± 0.2 | 7.8 ± 0.1 | 0.9 ± 0.1 |
| SP12 | 9.1 ± 0.1 | 18.9 ± 0.2 | 9.1 ± 0.2 | 2.8 ± 0.1 | 0.8 ± 0.1 | 18.2 ± 0.3 | 8.3 ± 0.1 | 0.5 ± 0.1 |
| SP13 | 10.2 ± 0.3 | 20.9 ± 0.3 | 5.2 ± 0.1 | 2.9 ± 0.1 | 0.7 ± 0.1 | 21.1 ± 0.3 | 8.1 ± 0.2 | 0.7 ± 0.1 |
| SP14 | 7.9 ± 0.1 | 18.9 ± 0.3 | 9.6 ± 0.1 | 2.5 ± 0.1 | 1.1 ± 0.1 | 18.9 ± 0.2 | 8.9 ± 0.1 | 0.6 ± 0.1 |
Values are expressed as mean ± standard deviation (SD); fatty acid: C14:0 = myristic acid; C16:0 = palmitic acid; C18:1 = oleic acid; C18:2 = linoleic acid; C18:3 = α-linolenic acid; C20:5 = eicosapentaenoic acid (EPA); C22:6 = docosahexaenoic acid (DHA); C20:4 = arachidonic acid; Sample groups: T = tuna (skipjack); CL = cod liver; M = mackerel; S = salmon; O = salmon nerka; SP = sardine samples.
Table 4.
Composition of fatty acids in fish products (as % of total fatty acids and in mg/100 g of sample).
| Sample No. | Σ SFA (%) |
Σ SFA (mg/100 g) | Σ MUFA (%) |
Σ MUFA (mg/100 g) | Σ PUFA (%) |
Σ PUFA (mg/100 g) |
|---|---|---|---|---|---|---|
| T1 | 42.3 ± 0.4 | 190 | 20.6 ± 0.4 | 93 | 36.2 ± 0.4 | 163 |
| T2 | 47.6 ± 0.4 | 343 | 18.8 ± 0.2 | 135 | 33.0 ± 0.3 | 238 |
| T3 | 51.1 ± 0.5 | 368 | 17.8 ± 0.3 | 128 | 30.4 ± 0.3 | 219 |
| T4 | 46.1 ± 0.4 | 332 | 18.9 ± 0.3 | 136 | 34.1 ± 0.3 | 246 |
| T5 | 51.3 ± 0.5 | 277 | 17.8 ± 0.2 | 96 | 30.6 ± 0.3 | 165 |
| T6 | 44.6 ± 0.4 | 281 | 23.9 ± 0.3 | 151 | 30.9 ± 0.3 | 195 |
| T7 | 55.2 ± 0.5 | 248 | 17.9 ± 0.2 | 81 | 26.4 ± 0.2 | 119 |
| T8 | 40.0 ± 0.4 | 216 | 25.9 ± 0.3 | 140 | 33.3 ± 0.3 | 180 |
| T9 | 53.2 ± 0.5 | 431 | 16.9 ± 0.2 | 137 | 29.7 ± 0.3 | 241 |
| T10 | 51.3 ± 0.5 | 185 | 22.2 ± 0.2 | 80 | 26.1 ± 0.2 | 94 |
| T11 | 48.8 ± 0.4 | 220 | 20.6 ± 0.2 | 93 | 30.2 ± 0.3 | 136 |
| T12 | 50.3 ± 0.5 | 272 | 22.6 ± 0.3 | 122 | 26.9 ± 0.3 | 145 |
| T13 | 52.8 ± 0.5 | 333 | 18.9 ± 0.2 | 119 | 27.6 ± 0.3 | 174 |
| CL1 | 21.3 ± 0.3 | 10,900 | 34.0 ± 0.4 | 17,400 | 44.4 ± 0.3 | 22,700 |
| CL2 | 19.2 ± 0.3 | 10,400 | 27.5 ± 0.3 | 14,900 | 52.9 ± 0.4 | 28,700 |
| CL3 | 17.7 ± 0.3 | 9290 | 35.6 ± 0.3 | 18,700 | 46.4 ± 0.4 | 24,300 |
| CL4 | 20.5 ± 0.3 | 10,300 | 29.8 ± 0.3 | 15,000 | 49.5 ± 0.4 | 24,900 |
| M1 | 35.0 ± 0.4 | 3250 | 18.7 ± 0.2 | 1730 | 46.0 ± 0.4 | 4260 |
| M2 | 32.6 ± 0.3 | 3670 | 17.3 ± 0.2 | 1950 | 49.7 ± 0.5 | 5590 |
| M3 | 34.5 ± 0.3 | 3700 | 17.8 ± 0.1 | 1910 | 47.6 ± 0.4 | 5100 |
| M4 | 33.1 ± 0.3 | 3460 | 18.8 ± 0.3 | 1960 | 47.5 ± 0.4 | 4960 |
| M5 | 28.6 ± 0.3 | 4170 | 23.0 ± 0.2 | 3350 | 48.3 ± 0.4 | 7040 |
| M6 | 29.8 ± 0.3 | 3970 | 23.8 ± 0.3 | 3170 | 46.0 ± 0.4 | 6130 |
| S1 | 15.3 ± 0.2 | 1710 | 52.7 ± 0.5 | 5880 | 31.7 ± 0.3 | 3540 |
| S2 | 21.5 ± 0.2 | 2440 | 48.6 ± 0.5 | 5510 | 28.9 ± 0.3 | 3280 |
| S3 | 19.4 ± 0.2 | 2180 | 41.5 ± 0.3 | 4670 | 38.8 ± 0.3 | 4370 |
| S4 | 27.2 ± 0.3 | 2820 | 41.5 ± 0.4 | 4300 | 31.0 ± 0.3 | 3210 |
| S5 | 25.3 ± 0.3 | 2730 | 39.8 ± 0.4 | 4300 | 33.9 ± 0.3 | 3660 |
| O1 | 32.6 ± 0.3 | 1260 | 22.2 ± 0.1 | 859 | 45.1 ± 0.4 | 1750 |
| O2 | 30.9 ± 0.3 | 1090 | 23.1 ± 0.2 | 811 | 44.9 ± 0.3 | 1580 |
| O3 | 30.6 ± 0.3 | 881 | 24.6 ± 0.2 | 708 | 44.2 ± 0.3 | 1270 |
| O4 | 29.8 ± 0.3 | 751 | 21.2 ± 0.3 | 534 | 48.2 ± 0.5 | 1220 |
| SP1 | 32.2 ± 0.3 | 3420 | 26.2 ± 0.3 | 2780 | 40.9 ± 0.4 | 4340 |
| SP2 | 30.8 ± 0.3 | 2940 | 23.8 ± 0.2 | 2270 | 45.0 ± 0.4 | 4290 |
| SP3 | 41.5 ± 0.3 | 3250 | 25.9 ± 0.3 | 2030 | 32.1 ± 0.3 | 2510 |
| SP4 | 33.8 ± 0.3 | 2400 | 24.6 ± 0.3 | 1750 | 41.1 ± 0.3 | 2920 |
| SP5 | 28.9 ± 0.3 | 1900 | 22.6 ± 0.3 | 1490 | 48.2 ± 0.4 | 3170 |
| SP6 | 30.1 ± 0.3 | 2060 | 19.5 ± 0.3 | 1330 | 49.8 ± 0.4 | 3410 |
| SP7 | 33.6 ± 0.3 | 2600 | 25.0 ± 0.3 | 1940 | 41.0 ± 0.4 | 3170 |
| SP8 | 33.9 ± 0.3 | 3170 | 20.5 ± 0.3 | 1920 | 45.1 ± 0.5 | 4220 |
| SP9 | 30.9 ± 0.3 | 2670 | 19.9 ± 0.2 | 1720 | 48.6 ± 0.4 | 4200 |
| SP10 | 35.0 ± 0.4 | 3150 | 25.7 ± 0.3 | 2310 | 38.6 ± 0.3 | 3470 |
| SP11 | 33.5 ± 0.3 | 2680 | 20.6 ± 0.2 | 1650 | 45.3 ± 0.3 | 3630 |
| SP12 | 33.3 ± 0.3 | 3030 | 16.9 ± 0.2 | 1540 | 49.1 ± 0.4 | 4460 |
| SP13 | 36.6 ± 0.4 | 2770 | 20.8 ± 0.3 | 1570 | 42.2 ± 0.4 | 3190 |
| SP14 | 31.8 ± 0.3 | 2690 | 20.9 ± 0.3 | 1770 | 47.0 ± 0.4 | 3980 |
Values are expressed as mean ± standard deviation (SD); fatty acid: SFA = saturated fatty acids; MUFA = monounsaturated fatty acids; PUFA = polyunsaturated fatty acids; Sample groups: T = tuna (skipjack); CL = cod liver; M = mackerel; S = salmon; O = salmon nerka; SP = sardine samples.
The contents of fatty acids in canned fish samples are expressed in Table 3 as the relative % of fatty acid from the total content of all fatty acids. Only selected fatty acids with a known physiological effect and oleic acid are displayed in the results [1,3,5,7,9,11,12,13,15,16,17,18,19,23,35,36]. The total contents of saturated acids (SFAs), monounsaturated acids (MUFAs), and PUFAs are also given (Table 4). The diversity of fatty acid profiles can be clearly demonstrated based on the PLS-DA results (Figure 1a,b).
Figure 1.
(a) PLS-DA score plot representing sample separation based on their fatty acid profile; sample groups: T = tuna (skipjack); CL = cod liver; M = mackerel; S = salmon; O = salmon nerka; SP = sardine samples. (b) PLS-DA loading plot complementary to the score plot (Figure 1a); fatty acid: C14:0 = myristic acid; C16:0 = palmitic acid; C18:1 = oleic acid; C18:2 = linoleic acid; C18:3 = α-linolenic acid; C20:5 = eicosapentaenoic acid (EPA); C22:6 = docosahexaenoic acid (DHA); C20:4 = arachidonic acid.
It is interesting to monitor the distribution of MUFAs in the individual genera of the monitored fish. Oleic acid (C18:1, ∆9 cis) is the major acid in all cases. From wild fish, mackerel and sardine samples contain between 30 and 50% of the total MUFA content, sockeye salmon about 55%, and skipjack tuna about 66%. For farm-raised salmon, it is 74–80%. Of the other MUFAs, the most common are palmitoleic acid (C16:1, ∆9 cis) and the positional isomers of eicosenoic (C20:1) and docosenoic (C22:1) acid. They accounted for 20–70% of the total MUFA content.
The basic member of the group of omega-6 PUFAs is linoleic acid (C18:2, ∆9,12 cis, cis). The content of linoleic acid in wild fish is usually up to 3% of fatty acids; significantly more is contained in the fat content of the muscle of farm-raised salmon (12–15%), which is in good agreement with literary sources [1,15,18]. Biological activity is shown by arachidonic acid (C20:4, ∆5,8,11,14 all cis) from the group of omega-6 PUFAs. In most samples, its content was very low (up to 2%); the content was higher in mackerel and sockeye salmon samples (3–5%). In canned cod liver, 7.5–9.8% of arachidonic acid was found, which is the highest value of all fish tissue samples.
The basic member of the omega-3 PUFAs is α-linolenic acid (C18:3, ∆9,12,15 cis, cis, cis). The content of α-linolenic acid in wild fish is usually up to 2% of fatty acids; the content is higher in sockeye salmon samples (3.2–5.6%). More α-linolenic acid is also contained in the fat content of farmed salmon muscle (3.6–5.8%).
Cod liver had a very high fat content (55–60%), containing a small amount of saturated acids (around 20%) and, conversely, a large amount of PUFAs (44–53%), of which a significant proportion was α-linolenic acid (8.8–13.6%) and EPA and DHA (16.6–19.9%) (Table 3 and Table 4).
3.3. EPA and DHA Content
Undoubtedly, the most important source of EPA and DHA from the diet is marine fish from the cold sea with a higher fat content in the muscle tissue. Canned fish is also a very good source (see Table 3). Table 5 shows the amount of the product (canned fish) in which 250 mg of EPA and DHA are present.
Table 5.
Nutritional evaluation of canned fish in terms of content and intake of EPA and DHA.
| Sample | Sample | ||||
|---|---|---|---|---|---|
| No. | Σ EPA, DHA | Amount of Sample for 250 mg of EPA + DHA | No. | Σ EPA, DHA | Amount of Sample for 250 mg of EPA + DHA |
| (mg/100 g of Sample) | (g) | (mg/100 g of Sample) | (g) | ||
| T1 | 66.6 | 375 | S1 | 680.8 | 36.7 |
| T2 | 85.7 | 292 | S2 | 850.5 | 29.4 |
| T3 | 71.3 | 351 | S3 | 900.0 | 27.8 |
| T4 | 76.1 | 328 | S4 | 755.6 | 33.1 |
| T5 | 84.2 | 297 | S5 | 777.6 | 32.2 |
| T6 | 74.3 | 336 | O1 | 1037 | 24.1 |
| T7 | 50.9 | 492 | O2 | 1028 | 24.3 |
| T8 | 69.1 | 362 | O3 | 820.8 | 30.5 |
| T9 | 87.5 | 286 | O4 | 657.7 | 38.0 |
| T10 | 35.6 | 702 | SP1 | 2613 | 9.6 |
| T11 | 50.9 | 492 | SP2 | 2500 | 10.0 |
| T12 | 61.6 | 406 | SP3 | 1535 | 16.3 |
| T13 | 71.8 | 348 | SP4 | 1749 | 14.3 |
| CL1 | 9986 | 2.5 | SP5 | 2188 | 11.4 |
| CL2 | 10,800 | 2.3 | SP6 | 1936 | 12.9 |
| CL3 | 9392 | 2.7 | SP7 | 2206 | 11.3 |
| CL4 | 8352 | 3.0 | SP8 | 2714 | 9.2 |
| M1 | 2753 | 9.1 | SP9 | 2393 | 10.4 |
| M2 | 3308 | 7.6 | SP10 | 2340 | 10.7 |
| M3 | 3545 | 7.1 | SP11 | 2059 | 12.1 |
| M4 | 3058 | 8.2 | SP12 | 2409 | 10.4 |
| M5 | 3907 | 6.4 | SP13 | 2208 | 11.3 |
| M6 | 3583 | 7.0 | SP14 | 2352 | 10.6 |
Sample groups: T = tuna (skipjack); CL = cod liver; M = mackerel; S = salmon; O = salmon nerka; SP = sardine samples.
From the results in Table 5, it can be seen that (excluding cod liver) the richest source of EPA and DHA is mackerel (less than 10 g of product is enough to receive 250 mg of EPA & DHA) and sardines (10–12 g of product). A very good source of EPA and DHA is also canned farm-raised Atlantic salmon and sockeye salmon (required intake of around 30 g per day). However, it can also be seen that in order to receive 250 mg of EPA and DHA, it would be necessary to consume 300–700 g of tuna. On the other hand, tuna remains a source of high-quality protein and other nutritionally valuable substances.
4. Discussion
As all samples were in brine, only a minimal amount of the other ingredients was added during their preservation. This, together with careful preservation, is the main reason why the data obtained, within the range of variability, are consistent with the data on fresh fish from databases and scientific articles [1,3,4,5,6,7,11,12,13,14,15,18,19,20,21,22,23,24,28].
In terms of the crude protein content, EFSA (2017) [2] reports a PRI value (Population Reference Intake) of 0.83 g/kg body weight/day for protein intake in an adult. At a weight of 70 kg, this corresponds approximately to the necessary intake of 58 g of proteins. Results in Table 2 show that one regular can of fish (usual weight 100–125 g) will supply a relatively significant proportion of the daily protein requirement. The obtained values of the fat content are also in very good agreement with published data. From a nutritional point of view, the amount of fat in the skipjack tuna sample can be considered completely insignificant. Fish of the genus Oncorhynchus—O. tshawytscha (Chinook salmon), O. mykiss (rainbow trout), O. gorbuscha (pink salmon), O. nerka (sockeye salmon), O. kisutch (coho salmon), and O. keta (chum salmon)—usually contain a small amount of fat, up to 5 g/100 g [1,4,5,6,7,11,12,13,15,18,19,20,28]. EFSA [2] recommends 20–35% of the total energy intake as an adequate fat intake. EFSA recommends an energy intake of 9.3 MJ/day for men and 7.5 MJ/day for women in middle age (40–49 years old) with moderate physical activity [2]. After conversion (useable energy from fat 37 kJ/g) [2], this recommendation corresponds to a fat intake of 50–88 g for men and 41–71 g for women. The results show that even the intake of medium-fatty fish, which included the case of sockeye salmon samples, is not the cause of a significant increase in fat intake in the diet.
The PLS analysis showed a significant difference through samples according to the fish species (Figure 1a,b). Salmon samples (S) were distinctly separated due to their higher proportion of oleic and linoleic acids resulting from farm feeding. Cod liver samples (CL) were also clearly separated by the higher proportion of linolenic and arachidonic acids as a result of metabolic processes different from those in muscle tissue. The fatty acid composition of the other samples was more similar, and therefore they were only partially separated. The determining fatty acids were DHA (predominant in mackerel and sockeye salmon samples) and EPA (in sardine samples). Tuna samples also contained these HUFAs; however, they were separated mainly due to the higher content of saturated acids (myristic and palmitic).
The evaluation of fatty acid composition (see Table 3 and Table 4) shows a significant share (71–88%) of the total content of saturated acids are atherogenic [17] myristic (C14:0) and palmitic (C16:0) acids. Skipjack tuna samples had a high proportion (around 50%) of saturated fatty acids. From a nutritional point of view, this fact is uninteresting, because the fat content here is extremely low (see Table 2). Mackerel, sockeye salmon, and sardines usually contain slightly more than 30% saturated acids, which is very acceptable from a nutritional point of view. A smaller amount of saturated acids (15–27%) is contained in the fat of farm-raised salmon. This is a consequence of the continuous development of fish farming in recent decades, which has led to fundamental changes in the composition of fish feed [1,11,15,18]. The linoleic acid content in wild fish is usually in the order of a few percent of fatty acids, while in salmon it reaches up to 15%. It is well known that linoleic acid is present in large quantities in most vegetable oils. Therefore, its intake from fish is completely marginal from a nutritional point of view. α-linolenic acid, which is relatively significant in the fatty acid profile of sockeye salmon and salmon samples (Table 3), is a precursor to the formation of biologically active EPA and DHA. Nutritional guidelines for the intake of fatty acids are given either in mass units or in % of the energy received—even in this case, however, the data must be converted to mass units. For the intake of α-linolenic acid, the nutritional guideline is 0.5% of the energy intake (EFSA, 2017 [2]). With an energy intake of 9300 kJ and 7500 kJ (see above), the required intake of α-linolenic acid is 1.26 g and 1.0 g. To assess the contribution of a given fat to fulfilling the nutritional guideline, the fatty acid content must also be converted to a weight unit. In this case, the fact is used that in common food lipids, fatty acids represent approximately 90% of the weight of the fat fraction [3,37,38]. The stated 5.6% α-linolenic acid in sockeye salmon represents 217 mg of α-linolenic acid in 100 g of product, 5.8% in salmon, and then 652 mg/100 g. Therefore, our results show that these two types of fish can contribute relatively significantly to the intake of insufficient α-linolenic acid. In the liver, dietary α-linolenic acid is metabolized by Δ5 and Δ6 desaturase enzymes to form EPA and DHA. The physiological importance of these acids is absolutely fundamental, as they are direct precursors of tissue hormones, eicosanoids, and docosanoids. Another significant benefit of EPA and DHA intake is the highly positive effect on the solubility of blood lipids [2,3,9,17,35,36,39], and it may lower metabolic dysfunction-associated steatotic liver disease [40]. The mutual ratio of EPA/DHA is very different in different fish species, but it has not yet been proven that it affects the formation of eicosanoids in any way [3,9,15,17,23,35,36,39]. For this reason, the sum of both acids is usually used in nutritional assessment. EFSA (2017) [2] issued a recommendation for an EPA and DHA intake of 250 mg per day for an adult. This amount should be covered by intake from diet and supplements, with intake from a normal diet being preferred. High content of EPA + DHA was found in cod liver, mackerel, and sardines; medium levels in sockeye salmon and farmed salmon; and lower content in the very popular canned fish, skipjack tuna. Fatty acids, as well as other lipophilic components, accumulate in the body. For that reason, it is, of course, possible to consume the necessary amount of the product in longer time intervals. PUFAs are known to be highly oxylabile. The high content of PUFAs in samples of canned fish is proof that the canning technology is conducted very carefully, and during the technological processing, oxygen is practically completely removed from the canned food, and the extent of oxidation is negligible [12,20,21,22,23,24,25,26,41,42].
5. Conclusions
The study demonstrated that the composition of the macronutrients in commercially available canned marine fish differs significantly by species. Protein content in assessed muscle samples was mostly between 15 and 22 g/100 g (with the exception of cod liver ≈ 7.3 g/100 g), with a typical value for canned muscle tissue of 18–20 g/100 g. Protein variability was relatively low, whereas fat content showed considerable variation (approximately 0.5–15 g/100 g). The lowest fat content was found in skipjack tuna (<1 g/100 g); sockeye salmon exhibited low fat content (2.8–4.3 g/100 g); sardines had moderate fat (~9–10 g/100 g); and mackerel and farmed Atlantic salmon had higher fat (10–15 g/100 g). The proportion of PUFAs was mostly 40–50% of total fatty acids; a lower proportion was observed in salmon and skipjack tuna. Probably the most significant nutritional benefit of consuming marine fish is the intake of long-chain n-3 HUFAs (EPA and DHA). With the exception of skipjack tuna, all the monitored products were good sources of these acids. Considering a typical reference serving size of 85 g for canned fish, this portion corresponds to an intake of approximately 250 mg EPA and DHA for two days (canned Atlantic and sockeye salmon), five days (sardines), and nine days (mackerel). These results support including canned marine fish in the diet as a source of high-quality protein and n-3 HUFAs, while species choice substantially affects the energy and lipid composition of a portion.
Author Contributions
Conceptualization, J.P. and M.D.; methodology, L.K., M.D., J.P. and P.K.; validation, D.C., V.I., M.R. and P.K.; formal analysis, D.C. and P.K.; investigation, V.I., M.R. and M.P.; data curation, D.C., L.K. and J.P.; writing—original draft preparation, D.C., J.P. and M.D.; writing—review and editing, M.P., L.K. and P.K.; supervision, J.P. and M.D.; funding acquisition, L.K. and M.D. All authors have read and agreed to the published version of the manuscript.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
The data analyzed during the current study are available from the corresponding author upon reasonable request.
Conflicts of Interest
The authors declare no conflicts of interest.
Funding Statement
This work was supported by the METROFOOD-CZ research infrastructure project (Ministry of Education, Youth and Sports of the Czech Republic (MEYS), grant number LM2023064), including access to its facilities, and by the specific university research project no. A1_FPBT_2025_004.
Footnotes
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data analyzed during the current study are available from the corresponding author upon reasonable request.