Mercury comparisons between farmed and wild Atlantic salmon (Salmo salar L.) and Atlantic cod (Gadus morhua L.)

Wild and farmed Atlantic salmon ( Salmo salar L.) and Atlantic cod ( Gadus morhua L.) were collected to assess changes in mercury with size in wild vs. farmed fish. Mercury concentrations were compared with Health Canada and United States Environmental Protection Agency consumption guidelines. Lipid dilution of mercury was examined by comparing lipid-extracted (LE) and non-lipid-extracted (NLE) flesh samples in both farmed and wild fish. Mercury concentrations in the flesh and liver of farmed salmon were significantly lower than concentrations in wild salmon of similar fork length ( P <0.001), possibly due to growth dilution in rapidly growing farmed fish. Mercury concentrations were higher in LE tissue compared with NLE ( P <0.05), suggesting lipid dilution of mercury in farmed fish with a high lipid content. Farmed cod, which do not grow more rapidly than wild cod, did not have significantly different flesh and liver concentrations compared with wild cod of similar fork length ( P >0.05). Between species of farmed fish, cod had significantly higher mercury concentrations than salmon ( P <0.05), but neither farmed nor wild salmon mercury concentrations exceeded federal consumption guidelines. These results suggest that rapid growth rates and a high lipid content may play important roles in regulating concentrations of contaminants such as mercury.     

Effect of Temperature on Quality-Related Changes in Cod (Gadus morhua) During Short- and Long-Term Frozen Storage

Cod (Gadus morhua) was stored at eight temperatures (?10 to ?80°C) for 1 to 18 months, after which quality indicators were measured—including drip loss, water holding capacity, low field NMR spin-spin relaxation, color, amount of thiobarbituric acid reactive substances, and sarcoplasmic reticulum Ca2+-ATPase and lysosomal Cathepsin D activities. Results from samples stored up to 12 months showed no significant differences between ?30°C and lower temperatures. The NMR measurements, however, indicated some changes in the water distribution of samples stored at ?30°C for 12 or more months compared to storage at ?40°C or lower.     

Quality Changes During Salt-Curing of Cod (Gadus morhua) at Different Temperatures

ABSTRACT

The main aim of this study was to assess the quality changes and their causes during cod salt-curing for up to 76 days at different temperatures and a relative humidity below 80%. Salt-curing made the fish more yellow (L*a*b* scale), a color change that is more easily detected in sensory analysis against a cream color scale. Intense proteolytic breakdown took place at 12 and 18°C, leading to a greater proteolysis degree and a higher pH. A red surface discoloration of the flesh was apparent after 76 days at 18°C due to the high number of red-halophilic bacteria. These bacteria were also responsible for the highest intensity of “off”-odors and mucus obtained under these conditions. Cod salt-curing should be done below 12°C to reduce the spoilage activity of halophilic bacteria and is best done at chill temperature (close to 6°C) to obtain a good quality product.     

Muscle Quality and Proteolytic Enzymes of Farmed Atlantic Cod (Gadus morhua) During Storage: Effects of Pre-Slaughter Handling and Increased Storage Temperature

ABSTRACT

In the present experiment, the characteristics of minimally handled, directly slaughtered farmed Atlantic cod were compared to cod subjected to 2 h preslaughter handling stress. The results strongly indicate that increasing the storage temperature from 0 to 5°C had a larger negative impact on the quality characteristics than the handling stress applied. Further, there may be interaction effects between handling, storage temperature, and storage time.     

Evaluation of Electrical Stunning of Atlantic Cod (Gadus morhua) and Turbot (Psetta maxima) in Seawater

The aim of this study was to assess electrical stunning of Atlantic cod and turbot in seawater to develop a protocol for the process of stunning and killing. An induced general epileptiform insult (unconscious) had a duration of 40 ± 27 s (n =14) in cod (2.6 ± 0.5 kg) and 34 ± 18 s (n = 19) in turbot (520 ± 65 g). Seven cod and 3 turbot displayed a physical reaction, and 11 turbot registered an electroencephalogram (EEG) response to pain stimuli administered 30 s post-stun. The heart rate was 32 ± 6 beats/min in cod and 25 ± 7 beats/min in turbot prior to stunning. Post-stunning, the electrocardiogram (ECG) revealed fibrillation and reduced activity post-stun. EEG, ECG recordings, and behavioral observations indicate that when a bipolar square wave current was applied with a frequency of 133 Hz and 43% duty cycle side to side (turbot) and at 170 Hz and 33% duty cycle (cod) head to tail, both species were stunned in seawater at current densities of 3.2 A/dm² and 2.5 A/dm², respectively. For turbot, a 5 s exposure to electricity followed by chilling in ice water for 15 min is sufficient to prevent recovery. For cod, a killing method needs to be established.     

Quality and Shelf Life of Liver of Farmed Cod (Gadus morhua)

ABSTRACT

Livers of Atlantic cod (Gadus morhua) are traditionally used in cod liver oil production or consumed cooked or canned. The farming of cod is a relatively new industry in Norway. The aim of this study was to determine quality and shelf life of fresh liver from farmed cod during chilled storage on ice by hydrolysis and oxidation state and sensory quality and the influence on canned liver. In two experiments, livers from farmed cod were stored chilled and sampled from Days 0 to 13, respectively. Quality, measured as hydrolytic and oxidation degradation, was reduced after 7 days of storage, while sensory quality was reduced after 4 days. Free fatty acids increased from Day 7 in both experiments, while peroxide value and anisidine value showed no change when the livers were single wrapped. Rancid odor was the first sign of oxidation and was registered after three to four days of storage. Canning within 2 days of storage prevented leakage of oil from the canned livers. Sensory analyses of oxidation are recommended as a sensitive and rapid method to detect oxidation of chilled cod liver.     

In-Pack Surface Pasteurization of Capture-Based,Pre-Rigor Filleted Atlantic Cod (Gadus morhua)

In this study, we targeted the surface bacteria of high quality vacuum-packed cod loins to investigate how this affected the shelf life. After heat processing, the storage temperature was kept at 4°C in order to mimic supermarket shelf conditions. Samples that had undergone minimal heating regimes were compared with control samples as well with samples that were heated into the core. Shelf life was assessed based on the findings of a sensory analysis and on microbial growth data and supported by measurements of liquid loss and pH. Surface pasteurization of these samples seems to prolong shelf life only to a limited degree, even for samples with a low initial contamination level. Transportation of some bacteria into the filet, possibly during the intense rigor mortis progress triggered by the heat process, may have created a general flux of water in the samples. Underneath the surface, these bacteria are exposed to a limited thermal load and very little microbial competition. Surface pasteurization is an efficient method to reduce microbial contamination of many foodstuffs. In the case of fresh fish, however, surface pasteurization seems to have a limited effect due to the structure of the muscle and the subsequent storage condition.     

Preliminary Observations on Spoilage Potential of Flora from Desalted Cod (Gadus morhua)

Abstract

Desalted cod products are already marketed, although still presenting some problems. Fresh raw materials and good manufacturing practices during salting, drying and desalting are essential to improve their quality and shelf life. The production of off-odor, hydrogen sulfide, trimethylamine, ornithine, putrescine, cadaverine, histamine, indole, hydrolyzed gelatin and ammonia was investigated in 127 bacterial strains isolated from dried/wet salted cod, later desalted either at 4 or 24°C. Desalting could either introduce or recover off-odor, sulfide hydrogen and/or ornithine producing strains. Cod desalting at 4°C is of great importance in order to improve the shelf life and safety of cod desalted products.     

Instrumental Textural Changes in Raw White Shrimp During Iced Storage

The general objective of this work was to evaluate the changes in the texture of raw white shrimp, stored whole in ice for up to 14 days, by instrumental texture analysis of the flesh after peeling off the carapace. Effect of test method (relaxation, compression, texture profile analysis, cutting, and penetration tests), test speed (0.1, 0.5, and 1.0 mm/s), and test position on sample (second, third, and fourth segments of abdominal musculature) were studied to measure the textural attributes of shrimp. Mechanical parameters (force at yield point, stiffness, toughness, and shear/penetration work) increased significantly during the 14 days of storage. Shrimp muscle maintained firm texture up to 4 days of storage after harvesting. At that time, the texture became soft, stiffness of the skin layer increased, and then pH values in the shrimp reached a value higher than 7 (alkaline). A linear model with a high coefficient of determination (R² > 0.75, for all parameters obtained from the penetration test with the spherical probe) described adequately the mechanical properties of iced shrimp during storage. Comparing several methods, the penetration test on the second flesh segment using a spherical probe at a speed of 0.1 mm/s and using penetration work as a parameter gave the best results to clearly indicate the changes in textural properties of iced shrimp with a high correlation coefficient during storage time (R² = 0.83), while other test methods failed to provide an indication of deterioration.     

Yield and Gel Strength of Gelatin Extracted from Smoked Salmon (Salmo salar) Skins

The gelatin yield and gel strength of gelatin extracted from the skins of smoked salmon were determined. The skins had a crude protein content of 43.5 ± 1.2% and an estimated collagen content of 23.6 ± 1.0%. Following an alkali extraction process under varying extraction conditions, the protein content varied from 2.78% to 32.1%, and the gelatin yield ranged from 2.23% to 22.4% of the initial skin weight. The gelatin purity (gelatin/protein) ranged from 55.4% to 100%, with the highest Hyp/protein sample arbitrarily designated as being 100% pure, i.e., an assumption of pure gelatin. Statistical analysis showed that HCl concentration, pretreatment temperature, and extraction temperature significantly affected the protein yield and gelatin yield. The wide range of gel strengths indicates that the gelatin might have been hydrolyzed to different extents during the different extraction and cooling processes. Statistical analysis did not show that any of the factors studied affected the gel strength. However, the data indicated that low NaOH concentrations and HCl concentrations might not prevent hydrolysis during the extraction process. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS–PAGE) showed that the gelatins contained α- and β-chains and that the gelatins composed of higher concentrations of larger molecular weight polypeptide chains had higher gel strengths.     

Growth of Atlantic Salmon,Salmo salar,Fed Diets Containing Barley Protein Concentrate

A 16-week feeding trial was conducted with juvenile Atlantic salmon (123 g/fish initial weight) to determine the effects of adding either 11% or 22% barley protein concentrate (BPC) to the diet compared to salmon fed a reference diet (0% BPC) containing mostly fishmeal. The fish were stocked into twelve 0.264 m³ tanks, providing 40 fish per tank with an average density of 18.55 kg/m³. Temperature was maintained at ?12°C and salinity at ?2 ppt using ground water during the study. There were no significant differences in specific growth rate (0.62 basal, 0.60 11% BPC, 0.72 22% BPC), feed conversion (1.06, 1.37, 1.09), weight gain (124.3 g, 113.5 g, 155.3 g), proximate composition of the salmon for lipid (8.4%, 7.8%, 9.8%), protein (17.3%, 17.1%, 18.6%), moisture (71.4%, 72.3%, 69.4%), and ash (6.5%, 6.1%, 6.9%) among any of the treatment groups. Salmon fed the diet containing 22% barley protein concentrate, however, had significantly greater energy retention (34%) compared to the fish fed the other diets (23%–28%). The results of this study indicate that barley protein concentrate is an acceptable feed ingredient for Atlantic salmon that should provide performance similar to fishmeal at inclusion rates below 22%.     

The Effects of Light Salting on Physicochemical Characteristics of Frozen Cod (Gadus morhua) Fillets

Abstract

The effects of light salting by brine injection and brine immersion on physicochemical and textural properties of cod fillets were evaluated. Light salting significantly increased yield and water holding capacity. Adding brine injection to the process can be used to shorten the process time needed to obtain the desired salt content and increase yield. The effects on chemical composition were most significant in salt content, but water and protein content were also affected. Water content decreased from the tail to head direction of the fillets, both in unsalted and light salted fillets. Changes in protein content were in opposite proportion to changes in water content. This could be seen in the fresh fish and also after freezing, both in unsalted and light salted fillets. Texture of the fish was not significantly affected by salting and freezing.     

Review of morphological and behavioural differences between reared and wild individuals: Implications for sea-ranching of Atlantic salmon, Salmo salar L., Atlantic cod, Gadus morhua L., and European lobster, Homarus gammarus L.

Abstract The main question which must be raised when planning to enhance natural populations through sea ranching is whether reared organisms are fit for a life in the wild, or more specifically, whether there are differences between reared and naturally resident individuals. The causes and effects of these differences are reviewed, and results from the Norwegian enhancement programme, which compared reared and wild individuals of Atlantic salmon, Salmo salar L., Atlantic cod, Gadus morhua L., and European lobster, Homarus gammarus L., are discussed with emphasis on morphological and behavioural differences. It was concluded that exposure to an artificial rearing environment during ontogeny can affect both the phenotype and the behaviour of the reared individuals, and thereby, their potential for survival after release into the wild as well. Suggestions are made as to how to diminish observed differences, and thereby, improve the survival potential.     

Evaluation of Egg White Protein-Based Coatings to Improve the Protection of Frozen Atlantic Salmon (Salmo salar)

ABSTRACT

The effects of different egg white protein coatings on Atlantic salmon quality preservation after 4 months of frozen storage were evaluated. These coatings increased the yield of the fillets and protected them from lipid oxidation, providing better protection than glazing. Egg white protein coatings were better options than glazing to preserve salmon color during frozen storage. The best results were obtained with the application of coatings before freezing. No clear effects of the type and concentration of plasticizer in most quality parameters were found. Egg white protein + glycerol 2:1 applied before freezing was the best coating for frozen Atlantic salmon protection.     

Triploid Induction in Atlantic Cod (Gadus morhua L.) by the Use of Different Pressure Levels

Different levels of pressure were investigated to see if it was possible to induce triploidy at a lower pressure than previously used (600 bar) for Atlantic cod (Gadus morhua). Newly fertilized eggs were exposed to different levels of pressure: 400, 500, and 600 bar, and one control group (no pressure). Induction of triploidy occurred at each pressure level used in this experiment. Mean weight and length at the termination of the trial period was significantly lower, in the 400 bar group, compared to the other treatment groups. Microsatellite loci analysis revealed over 90% triploid outcome in each experimental group. Lower incidence of deformities was seen in the 400 bar group compared to the 500 and 600 bar groups. Overall this study demonstrated successful triploid induction at both low (400 bar) and medium (500 bar) pressures.     

A multivariate approach to optimization of macronutrient composition in weaning diets for cod (Gadus morhua)

Atlantic cod, initial weight 0.26 g, were fed diets varying in added protein from 530 to 830 g kg^?1, lipid from 50 to 300 g kg^?1 and carbohydrate from 0 to 150 g kg^?1 of dry weight, according to a three‐component mixture design. Analysed values of protein and lipid were 500–770 g kg^?1 and 30–270 g kg^?1, respectively. Analysed carbohydrate levels were as added. Increasing levels of both lipid and carbohydrate had a positive effect on fish growth (P < 10^?3), whereas protein levels above 600 g kg^?1 gave a reduction in growth (P < 10^?4). The effects on growth were evident in fish less than 4 g, whereas fish growth between 4 and 6 g was unaffected by the dietary variation. It is hypothesized that the reduction in growth at high protein levels in fish of less than 4 g could be owing to incomplete utilization of protein, as the stomach of cod is not fully developed before the fish is approximately 1 g. Mortality and cannibalism were high in fish less than 4 g but low when the fish grew from 4 to 6 g. There was a significant decrease in cannibalism with increasing dietary lipid during the first half of the experiment (P < 0.05) and cannibalism was consistently high in fish fed less than 150 g kg^?1 lipid. The lipid level in whole fish increased with increasing dietary levels of lipid (P < 10^?6) and carbohydrate (P < 10^?4), whereas the liver lipid level increased with increasing dietary lipid up to 200 g kg^?1 (P < 10^?6) and decreased thereafter (P < 10^?4). Whole body glycogen increased slightly with increasing levels of dietary carbohydrate (P < 0.05) and was not affected by the other dietary variables. Liver glycogen increased in response to increasing dietary carbohydrate (P < 10^?5) and decreasing levels of dietary lipid (P < 10^?5). An abrupt increase in liver glycogen was seen with the reduction in dietary lipid from 100 to 50 g kg^?1. The hepatosomatic index increased in response to both dietary lipid and carbohydrate (P < 10^?6). It is concluded that the protein requirement of young cod is less than 500 g kg^?1 of dry diet. Fish of less than 4 g should not be given more than 620 g kg^?1 protein and should be supplemented with 150–200 g kg^?1 lipid. Carbohydrate up to 150 g kg^?1 of dry diet promoted growth and did not seem to affect the fish negatively. Fish above 4 g can be given diets varying in protein and carbohydrate over the wide range of concentrations used in the present study, but lipid supplementation should be restricted to between 100 and 200 g kg^?1.     

Lactococcus lactis ssp. lactis as Protective Culture in Vacuum-Packed Raw Salmon (Salmo salar)

This study evaluates the potential use of protective cultures to improve the microbial quality of vacuum-packed raw Atlantic salmon. The inhibitory properties of 16 selected lactic acid bacteria and bifidobacteria against 32 spoilage organisms were characterized. As the food matrix and natural microflora of the product can affect the inhibitory effect, the best inhibitory strain, Lactococcus lactis ssp. lactis, was also tested in vacuum-packed salmon. As a result, L. lactis treated products had 3-days prolonged shelf life when compared to nontreated fish. In addition, the usage of L. lactis did not change the organoleptical and textural properties of the fish. This study shows that Lactococcus lactis might be applied to increase shelf life of vacuum-packed raw fish stored at refrigeration temperatures.     

Storage of lipids in the myosepta of Atlantic salmon (Salmo salar)

Storage of lipids in the myosepta of Atlantic salmon (Salmo salar) was determined by dissection of myosepta from both white and dark muscle, by analyzing lipid classes of myosepta, and by analysis of muscle tissues with and without myosepta. By using Iatroscan-TLC/FID it was found that triglyceride was the only major lipid class present in the myosepta. In a sample pooled from three fish, 39.1% of white muscle lipids were found to be stored in the associated myosepta. In the dark muscle up to 62.4% of the total lipids were located in the associated myosepta.After removal of the myosepta, the ratio of the total lipid content of dark muscle to white muscle decreased from 5.25 to 3.66. The proportion of polar lipids increased in both white muscle and dark muscle after removal of the myosepta; however the ratio of phosphatidyl choline (PC) to phosphatidyl ethanolamine (PE) in both muscle types remained constant. This suggests that neutral lipids accounted for most of the lipids in the myosepta. It is concluded that this type of connective tissue, not the actual muscle fibres, stores most of the muscle lipids in Atlantic salmon.     

The Effect of Photoperiod on Sexual Maturation,Appetite and Growth in Wild Atlantic Cod (Gadus morhua L.)

An experiment was conducted to examine (a) the effects of photoperiod on timing of sexual maturation (b) the relationship between plasma steroid levels, appetite and growth in male and female Atlantic cod (Gadus morhua L.). Wild caught Norwegian coastal cod were subjected to either a 6L/18D photoperiod typical of January at 60° N-(Short day group) or a simulated natural photoperiod (Normal day group) from June 2000 until spawning started. Appetite of individual fish were measured twice weekly, while weight, length and plasma levels of the sex steroids testosterone (T), 11 keto-testosterone (11-KT) and estradiol-17β (E2) were monitored bimonthly. Cod in the Short day group matured 3 months ahead of the cod in the Normal day group and started spawning in early November. Appetite decreased in both sexes 2–3 months prior to spawning in both groups, but this reduction was stronger among males. In both sexes, length growth was reduced concurrently with the appetite loss. Overall, females had significantly higher somatic growth, put relatively less energy into length growth and had developed larger livers compared to males at the time of spawning in the Short day group. Plasma steroid levels increased in both groups throughout the experiment, reaching peak levels of ca 10 ng ml⁻¹ (T) and 15–20 ng ml⁻¹ (11-KT) in males, and 1.5–2 ng ml⁻¹ (T) and 12–18 ng ml⁻¹ (E2) in females at the onset of spawning. Steroid levels increased more rapidly among Short day cod verifying the earlier onset of maturation. These results confirm that photoperiod is a major cue to maturation in cod and imply that the high cost of spawning for females incur differences in appetite between the sexes.     

Characterization of Acid-Soluble Collagen From Bone of Pacific Cod (Gadus macrocephalus)

Acid-soluble collagen (ASC) was isolated from Pacific cod (Gadus macrocephalus) bone. The ASC was rich in glycine. The amount of imino acid was lower than that of calf skin collagen, as was the transition temperature (48.6°C). Electrophoresis revealed two different α chains (α₁ and α₂), β-component, and γ-component. Fourier transform infrared spectroscopy measurement showed that ASC was in triple-helix structure. ASC had a solubility greater than 90% in a very acidic pH range (pH 1–4), and the solubility decreased with increasing NaCl concentrations up to 3%. Lyophilized ASC had a network ultrastructure with lace-like fibers, similar to calf skin collagen sponge.