Lipid composition and contaminants in farmed and wild salmon

Levels of omega-3 (n-3) and omega-6 (n-6) fatty acids and lipid-adjusted concentrations of polychlorinated biphenyls (PCBs), dioxins, toxaphene, and dieldrin were determined in 459 farmed Atlantic salmon, 135 wild Pacific salmon, and 144 supermarket farmed Atlantic salmon fillets purchased in 16 cities in North America and Europe. These were the same fish previously used for measurement of organohalogen contaminants. Farmed salmon had greater levels of total lipid (average 16.6%) than wild salmon (average 6.4%). The n-3 to n-6 ratio was about 10 in wild salmon and 3-4 in farmed salmon. The supermarket samples were similar to the farmed salmon from the same region. Lipid-adjusted contaminant levels were significantly higher in farmed Atlantic salmon than those in wild Pacific salmon (F = 7.27, P = 0.0089 for toxaphene; F = 15.39, P = 0.0002 for dioxin; F > or = 21.31, P < 0.0001 for dieldrin and PCBs, with df = (1.64) for all). Levels of total lipid were in the range of 30-40% in the fish oil/fish meal that is fed to farmed salmon. Salmon, especially farmed salmon, are a good source of healthy n-3 fatty acids, but they also contain high concentrations of organochlorine compounds such as PCBs, dioxins, and chlorinated pesticides. The presence of these contaminants may reduce the net health benefits derived from the consumption of farmed salmon, despite the presence of the high level of n-3 fatty acids in these fish.     

Flesh quality of market-size farmed and wild British Columbia salmon

This study compared the flesh quality of farmed and wild sources of British Columbia (BC) salmon with respect to concentrations of polychlorinated biphenyl compounds, polychlorinated dibenzodioxins/dibenzofurans and their associated toxic equivalents, total mercury (THg), methylmercury (MeHg), and selected fatty acids of known importance for human health viz., omega-3 (n-3) highly unsaturated fatty acids (n-3 HUFAs) and (n-6) fatty acids. Skinned fillets from known sources of farmed Atlantic, coho, and chinook salmon (n = 110) and wild coho, chinook, chum, sockeye, and pink salmon (n = 91) were examined. Atlantic salmon contained higher PCB concentrations (means, 28-38 ng/g) than farmed coho or chinook salmon, and levels in these latter species were similar to those in wild counterparts (means, 2.8-13.7 ng/g). PCB levels in Atlantic salmon flesh were, nevertheless, 53-71-fold less than the level of concern for human consumption of fish, i.e., 2000 ng/g as established by Health Canada and the U.S. Food and Drug Administration (US-FDA). Similarly, THg and MeHg levels in all samples were well below the Health Canada guideline (0.5 microg/g) and the US-FDA action level (1.0 microg/g). On average, THg in farmed salmon (0.021 microg/g) was similar to or lower than wild salmon (0.013-0.077 microg/g). Atlantic salmon were a richer source (mean, 2.34 g/100 g fillet) of n-3 HUFAs than the other farmed and wild sources of salmon examined (means, 0.39-1.17 g/100 g). The present findings support the recommended weekly consumption guidelines for oily fish species (includes all BC salmon sources) for cardio-protective benefits as made by the American Heart Association and the UK Food Standards Agency.     

Global assessment of polybrominated diphenyl ethers in farmed and wild salmon

We have shown recently that levels of persistent, bioaccumulative contaminants (polychlorinated biphenyls, dioxins, and several chlorinated pesticides) are significantly higher in farmed than in wild salmon and that European farm-raised salmon have significantly greater toxic contaminant loads than those raised in North and South America. In this paper, we extend these results to polybrominated diphenyl ethers (PBDEs) and show that farm-raised salmon have higher levels of these compounds than wild salmon. We also show that farm-raised salmon from Europe have higher PBDE levels than those raised in North America and that both European and North American farm-raised salmon have higher PBDE levels than those farm-raised in Chile. Among the species of wild salmon, chinook had significantly elevated PBDE levels relative to the other wild species. These elevated PBDE levels may be related to chinook's feeding behavior and trophic level. Among all of the wild species we studied, chinook tend to feed higher in the food web throughout their adult life and grow to be larger individuals.     

Development of rancidity in salmonoid steaks during retail display. A comparison of practical storage life of wild salmon and farmed rainbow trout

The quality of wild salmon and farmed rainbow trout from aquaculture, both packed in transparent vacuum-skin packaging, was followed during storage for 6 months in an illuminated freezer cabinet (product temperature -17 degrees C, half of the packs protected against light, and half of the packs fully exposed to light), combining (a) colour determination of the carotenoid-pigment flesh by tristimulus colorimetry, (b) determination of thiobarbituric-acid-reactive substances (TBA value), (c) carotenoid analysis and, at the end of the storage experiment, (d) sensory evaluation. Rancidity developed faster in steaks of wild salmon (TBA increased during 6 months of storage from 2.8 mumols malonaldehyde/kg flesh to 12.5 mumols/kg for light-protected packages, and to 17.6 mumols/kg for packages exposed to fluorescent light) as compared to steaks of farmed rainbow trout (TBA increased from 1.2 to 5.8 mumols/kg, independent of light exposure), a finding also confirmed by sensory evaluation. In both products, the carotenoid pigment was identified as astaxanthin; salmon steaks, the product more susceptible to developing rancidity, had the lower astaxanthin content (rainbow trout 9.1 mg/kg flesh, salmon 4.9 mg/kg, prior to storage). While the astaxanthin content remained virtually constant in salmon steaks during storage, the content decreased significantly in steaks of rainbow trout, an observation which suggests the role of astaxanthin as a sacrificial protector against radical processes.     

Risk characterisation from the presence of environmental contaminants and antibiotic residues in wild and farmed salmon from different FAO zones

Salmon consumption is increasing year by year. Salmon aquaculture is the fastest growing food production system in the world, and often uses feed mixed with antibiotics or other drugs. Feed can be also contaminated by environmental contaminants like persistent organic pollutants and organophosphorus pesticides that usually accumulate in fatty tissue, or emerging contaminants such as perfluoroalkyl substances (PFASs), that instead bioaccumulate in protein tissues. Therefore, there is the need to investigate the presence of antibiotics and environmental contaminants, with multi-class and multi-residue liquid chromatography-high resolution mass spectrometry and gas chromatography tandem mass spectrometry methods to monitor a broad spectrum of residues comparing between wild and farmed salmons. The presence of residues was encountered at a concentration range of 0.35–51.52 ng g^?1 for antibiotics only in farmed salmon, 0.19–34.51 ng g^?1 for PFASs and 0.26–9.01 ng g^?1 for (polybrominated diphenyl ethers) PBDEs, and 0.19–5.91 ng g^?1 for organochlorine pesticides with higher frequencies and concentrations in farmed fish. Finally, the risk deriving from salmon intake is low, being of minor concern only for PBDE 99 and perfluorooctanoic acid.     

PCBs, PCDD/Fs, and organochlorine pesticides in farmed Atlantic salmon from Maine, eastern Canada, and Norway, and wild salmon from Alaska

Farmed Atlantic salmon (Salmo salar) from Maine and eastern Canada, wild Alaskan Chinook salmon (Oncorhynchus tshawytscha), and organically farmed Norwegian salmon samples were analyzed for the presence of polychlorinated biphenyls (PCBs), dioxin-like PCBs, polychlorinated dibenzo-p-dioxins (PCDDs), dibenzo-p-furans (PCDFs), and chlorinated pesticides. PCDD and PCDF congeners were not detected in > 80% of the samples analyzed. Total PCB concentrations (7.2-29.5 ng/g, wet weight, ww) in the farmed salmon were significantly higher than those in the wild Alaskan Chinook samples (3.9-8.1 ng/g, ww). Concentrations of PCBs, WHO PCB TEQs, and chlorinated pesticides varied significantly by region. PCB and WHO PCB TEQ concentrations in farmed salmon from eastern Canada were lower than those reported in samples collected two years earlier, possibly reflecting recent industry efforts to lower contaminant concentrations in feed. Organically farmed Norwegian salmon had the highest concentrations of PCBs (mean: 27 ng/g, ww) and WHO PCB TEQs (2.85 pg/g,ww); their TEQ values are in the higher range of those reported in farmed salmon from around the world. Removal of skin from salmon fillets resulted in highly variable reductions of lipids and contaminants, and in some skin-off samples, contaminant levels were higher, suggesting that skin removal does not protect the consumer from health risks associated with consumption of farmed salmon.     

High resolution two-dimensional electrophoresis as a tool to differentiate wild from farmed cod (Gadus morhua) and to assess the protein composition of klipfish

Tris and CHAPS–urea extracts from wild and farmed cod muscle and from rehydrated cod klipfish fillets were analyzed by one (1DE) and two-dimensional electrophoresis (2DE). 2DE maps of tris extracts from farmed cod differed from the wild in a series of spots of Mw 35 and 45 kDa. The CHAPS–urea extracts from farmed cod had a several spots of Mw between 100 and 45 kDa, which were hardly detectable in wild cod and very prominent in klipfish. Klipfish was clearly different from the other samples: the myosin heavy chain was hardly detectable in these samples, and the tris extracts contained fewer, and the CHAPS–urea more spots than the corresponding extracts from the raw muscles. Further identification of these potentially diagnostic spots will make it easier the differentiation of farmed from wild cod and the evaluation of klipfish processing on the protein content of the product.     

Development of a PCR test to differentiate between Staphylococcus aureus and Staphylococcus intermedius

The presence of Staphylococcus intermedius in food remains unclear because routine laboratory analysis does not discriminate between S. intermedius and Staphylococcus aureus, a major cause of food poisoning. Both species share many phenotypic characteristics, including coagulase and thermonuclease production. In both species, some strains can produce enterotoxin and therefore can be the cause of food poisoning outbreaks. Although the ID32 Staph System (bioMérieux, SA, Marcy l'Etoile, France), based on a miniaturized phenotypic characterization, gives satisfactory results for discriminating between these two species, some rapid molecular PCR-based methods have been developed to identify S. aureus specifically, but they do not identify S. intermedius. Here, we developed a rapid, accurate, and discriminative multiplex PCR method that targets species-specific sequences in the nuc gene, which encodes thermonuclease in the two species. The test includes an internal positive control that targets a highly conserved region of 16S ribosomal RNA gene (rDNA). A total of 116 strains were used to validate our test. The test gave no signal on the following Staphylococcus species: S. epidermidis, S. chromogenes, S. hyicus, S. warneri, S. xylosus, S. lentus, and S. sciuri. It allowed a 100% successful discrimination between S. aureus (44 strains tested) and S. intermedius (57 strains) isolated from different origins.     

Differences in muscle cellularity and flesh quality between wild and farmed Coilia nasus (Engraulidae)

BACKGROUND: Populations of Coilia nasus, an anadromous fish, have declined dramatically in the Yangtze River estuary and its associated lakes owing to excessive fishing and changes in aquatic ecology. Recently, the success of artificial breeding programmes and advanced methods of propagation have allowed great increases in production of this species. Thus, to gain a better understanding of the flesh quality of C. nasus, muscle cellularity and quality parameters of the flesh were studied in wild and farmed specimens. RESULTS: Muscle cellularity was different between wild and farmed fish. Muscle fibre density was significantly higher in farmed specimens, while muscle fibre diameter was higher in wild specimens. Farmed fish had higher moisture, hydroxyproline and collagen contents and a lower fat content compared with wild fish. No significant differences in textural parameters were found between the two groups. Saturated (SFA), polyunsaturated (PUFA) and total n‐6 fatty acid contents were significantly higher in farmed fish, but monounsaturated fatty acid (MUPA) content was higher in wild fish. CONCLUSION: The variation in the studied parameters determined significant differences in the flesh quality of wild and farmed C. nasus. Depending on muscle cellularity and fatty acid composition, farmed fish could be more suitable for human consumption than wild fish. Copyright © 2011 Society of Chemical Industry     

First processing steps and the quality of wild and farmed fish

First processing steps of fish are species-dependent and have common practices for wild and for farmed fish. Fish farming does, however, have certain advantages over traditional fisheries in that the processor can influence postmortem biochemistry and various quality parameters. This review summarizes information about the primary processing of fish based on the influence of catching, slaughtering, bleeding, gutting, washing, and filleting. Recommendations are given for the correct primary processing of fish.     

Lipid distribution and composition of commercially farmed atlantic salmon (salmosalar)

Skin, red and white muscle, belly flap, dorsal fat depot, backbone, head, visceral tissue and liver of commercially farmed Atlantic salmon (Salmo salar) were analysed for total lipid content, lipid classes and fatty acid composition. The fat is deposited in a number of tissues and organs with the highest level in the dorsal fat depot (38.4% of wet weight), red muscle (27.2%) and belly flap (28.1%). The fat content in white muscle is 9.6% of wet weight. The lipid class distribution is nearly uniform throughout the fish body. The belly flap contains the highest amount of triacylglycerols (98.8% of total lipid) and white muscle and visceral tissue have the lowest levels, 93.3% and 93.1%, respectively. The variation in total saturates, monoenes, polyenes, n-6 and n-3 fatty acids was much less between tissues than the variation in total lipid content. In the edible part, the belly flap (16.7%) contained significantly lower levels of n-3 fatty acids than red (18.4%) and white muscle (19.7%) mainly due to lower level of 22: 6n-3 and 20: 5n-3 fatty acids.     

Collagen characteristics of farmed Atlantic salmon with firm and soft fillet texture

The possible role of collagen in texture variations among Atlantic salmon (Salmo salar L.) grown under commercial conditions at a Norwegian farm was studied. The texture was determined instrumentally as the breaking strength, and collagen and its salt (SSC), acid (ASC), pepsin (PSC) and insoluble (IF) fractions were analysed in order to determine the collagen aggregation degree. The collagen solubility and its overall amino acid (AA) composition showed no correlation to the breaking strength, but a positive correlation was observed between the breaking strength and glycine (r = 0.74) and alanine (r = 0.87) contents of the PSC fraction. Salmon with high breaking strength had higher T_peak (temperature of transition) and ΔH (enthalpy of transition), and the collagen seemed to have triple helix structures mainly stabilized by covalent associations as compared to salmon with low breaking strength. The glycosylation degree was also positively correlated to the breaking strength (r = 0.88, p ? 0.05). It is concluded that firmness of salmon muscle was not related to the total amount of collagen in the muscle, but rather higher collagen stability.     

Granularity and its importance for traceability in a farmed salmon supply chain

Identifying the optimal granularity level of traceable units is necessary when implementing traceability of food. This study examines granularity in a farmed salmon supply chain through the qualitative methods interview, observation, and document analysis. The results show that fish feed and farmed salmon can have fine or coarse granularity of the batches. Fine granularity will give large numbers and smaller batch sizes. Coarse granularity will give fewer numbers and bigger batch sizes. The granularity correlates to different levels depending on the application of information within a company and between companies in supply chains.     

Non-invasive and non-destructive percutaneous analysis of farmed salmon flesh by near infra-red spectroscopy

Near infra-red (NIR) reflectance spectroscopy (700–1100 nm wavelength range) has been applied to the percutaneous measurement of oil and moisture in farmed salmon carcasses. Spectra were recorded through the skin and scales by means of a fibre-optic probe. Six selected sites were used on the dorsal and ventral surfaces of each fish side; 294 sample sites were utilized. Reference chemical values for oil and moisture were determined on these sites after excision. Calibrations were developed and evaluated separately for dorsal and ventral sites. The best dorsal calibration produced a standard error of prediction (SEP) for oil and moisture of 2.0 and 1.45%, respectively; corresponding figures for the best ventral calibration were 2.4 and 1.9%, respectively.     

Lipid and fatty acid compositions differentiate between wild and cultured Japanese eel (Anguilla japonica)

The lipid profile and fatty acid composition of muscle, liver, and plasma lipoprotein were examined in wild and cultured Japanese eel (Anguilla japonica). Although, the muscle lipid levels of wild eels (11.6%) were less than those of cultured eels (13.1%), both eels were classified as typical fatty fish. Compared with the liver lipid composition of cultured eels, triacylglycerol (TG) level of the liver decreased in wild eels, whilst phosphatidylcholine and phosphatidylethanolamine levels of the liver increased in wild eels, reflecting the difference of liver lipid levels in both eels. Wild eels contained more cholesteryl ester (CE) and less TG, phospholipid, and free cholesterol in their plasma than cultured eels. The ratio of TG to CE decreased, whilst that of CE to total cholesterol increased in the plasma of wild eels. Different fatty acid compositions were found between wild and cultured eels. Compared with the fatty acid compositions of cultured eels, wild eels contained high percentages of 18:2, 18:3, and 20:4 and low percentages of 22:6, 20:1, and 20:5 in their muscle, liver, and plasma lipoprotein. The lipid profile and fatty acid composition seemed to be useful criteria for distinguishing between wild and cultured eels.     

Identification of organically farmed Atlantic salmon by analysis of stable isotopes and fatty acids

Using isotope ratio mass spectrometry (IRMS), the ratios of carbon (δ ¹³C) and nitrogen (δ ¹⁵N) stable isotopes were investigated in raw fillets of differently grown Atlantic salmon (Salmo salar) in order to develop a method for the identification of organically farmed salmon. IRMS allowed to distinguish organically farmed salmon (OS) from wild salmon (WS), with δ ¹⁵N-values being higher in OS, but not from conventionally farmed salmon (CS). The gas chromatographic analysis of fatty acids differentiated WS from CS by stearic acid as well as WS from CS and OS by either linoleic acid or α-linolenic acid, but not OS from CS. The combined data were subjected to analysis using an artificial neural network (ANN). The ANN yielded several combinations of input data that allowed to assign all 100 samples from Ireland and Norway correctly to the three different classes. Although the complete assignment could already be achieved using fatty acid data only, it appeared to be more robust with a combination of fatty acid and IRMS data, i.e. with two independent analytical methods. This is also favourable with respect to a possible manipulation using suitable feed components. A good differentiation was established even without an ANN by the δ ¹⁵N-value and the content of linoleic acid. The general applicability in the context of consumer protection should be checked with further samples, particularly regarding the variability of feed composition and possible changes in smoked salmon.     

Role of dietary patterns for dioxin and PCB exposure

Dietary patterns were related to intake and blood concentrations of polychlorinated dibenzo‐p‐dioxins and dibenzofurans (PCDD/PCDFs), dioxin‐like polychlorinated biphenyls (dl‐PCBs) and selected non‐dioxin‐like‐PCBs (ndl‐PCBs). Intake calculations were based on an extensive food frequency questionnaire and a congener‐specific database on concentrations in Norwegian foods. The study (2003) applied a two‐step inclusion strategy recruiting representative (n=73) and high consumers (n=111) of seafood and game. Estimated median intakes of sum PCDD/PCDFs and dl‐PCBs of the representative and high consumers were 0.78 and 1.25 pg toxic equivalents (TEQ)/kg bw/day, respectively. Estimated median intakes of ndl‐PCBs (sum chlorinated biphenyl (CB)‐28, 52, 101, 138, 153, 180) were 4.26 and 6.40 ng/kg bw/day. The median blood concentrations of PCDD/PCDFs/dl‐PCBs were 28.7 and 35.1 pg TEQ/g lipid, and ndl‐PCBs (sum of CB‐101, 138, 153 and 180) 252 and 299 ng/g lipid. The Spearman correlations between dietary intake and serum concentration were r=0.34 (p=0.017) for dl‐compounds and r=0.37 (p<0.001) for ndl‐PCBs. Oily fish was the major source of dl‐compounds and ndl‐PCBs in high and representative consumers. Four dietary patterns were identified by principal component analysis. Two were related to high intakes, one dominated by oily fish ((Ω‐3)), the other by fish liver and seagull eggs (“northern coastal”). Only the latter was closely associated with high blood concentrations of dioxins and PCBs.