Effects of pre-rigour filleting on quality aspects of Atlantic cod (Gadus morhua L.)

Aquaculture is promising in increasing the amount of fresh Atlantic cod available all year around. The aim of this study was to investigate the effects of pre‐rigour filleting on fillet quality of wild and farmed cod. Pre‐rigour filleting resulted in significantly less fillet gaping than in fillets produced post rigour. The pre‐rigour fillets were, however, 12–13% shorter post rigour. In spite of the significantly lower water content of the muscle 6 days post mortem, a significantly higher liquid loss was seen in the pre‐rigour group. Differences in gaping score and muscle pH were dependent on whether the fish were wild or fed. Fillet gaping increased with storage time and was particularly pronounced for well‐fed cod. Fed cod had a significantly higher hydroxyproline (Hyp) content and significantly lower amount of glycosaminoglycans (GAGs) than wild cod. The ratio between GAGs and Hyp was thus significantly lower in fed cod. A connection between connective tissue components and fillet gaping may exist. However, further investigations are required.     

Dietary Trace Metal Supplements Promote Blood Vessel Melanosis in Fillets of Juvenile Farmed Atlantic Cod,Gadus morhua L.

Chronic over‐exposure to diet‐borne copper has been implicated in the development of black stripes caused by melanin deposits (melanosis) around the blood vessels in fillets of farmed Atlantic cod, Gadus morhua L. To test this hypothesis a 6‐mo pilot study using feeds containing controlled amounts of copper has been performed. Cumulative data from each feed group showed that 56% of cod fed a diet containing 10 mg/kg of added copper had black stripe while 58% of cod on a diet containing 5 mg/kg of added copper were affected. Cod on a diet with no added copper had 33% of individuals positive for black stripe, and in a final group on a diet containing no supplementary trace metals and minerals 16% of individuals were affected. Weight gain, increase in length, hepatosomatic index, and condition factor were unaffected by the changes made to mineral supplements. Melanosis has been observed in 24% wild cod of market size (n = 30) whilst 85% of market‐sized farmed cod examined have had black stripe (n = 403).     

Pre-rigor filleting and drip loss from fillets of farmed Atlantic cod (Gadus morhua L.)

Improved slaughtering procedures of farmed fish may provide sufficient time so that filleting can be performed pre‐rigor while the muscle pH is still high. Such filleting not only reduces fillet gaping but also lowers the transportation costs and makes fresh fillets available to the markets at an earlier stage. The aim of our work was to determine the weight reduction of the fillets due to liquid loss and to study the proteins and enzymes in the drip. After 11 days of cold storage, fillets of farmed Atlantic cod produced pre‐rigor had a weight loss of 10% and a fillet contraction of 19% while for fillets produced post‐rigor the values were 5% and 4% respectively. At the same time, approximately twice the amount of proteins had been lost from the pre‐rigor‐produced fillets. Sodium dodecyl sulphate polyacrylamide gel electrophoresis analysis showed that the proteins in the drip were similar to the sarcoplasmatic proteins extracted from the muscle. Specific analysis of proteolytic enzymes indicated that they are less stable in the expelled liquid than in the flesh during storage. The extensive loss of weight and proteins from pre‐rigor‐produced fillets during subsequent storage must be taken into account if such processing is considered for farmed cod.     

Effect of Antarctic krillmeal on quality of farmed Atlantic cod (Gadus morhua L.)

Farmed Atlantic cod with a mean weight of 4.8 kg were maintained for 9 weeks in sea cages and fed diets where the dietary fishmeal component was substituted with increasing proportions (0%, 22%, 63% and 100%) of meal from Antarctic krill, Euphausia superba. Wild‐caught cod were included in the study as external control. At termination of feeding, all fish were slaughtered and muscle pH was immediately recorded. The fish were then stored on ice for three days and assessed for muscle pH and objective (skin and fillet colour, and fillet texture) and subjective (sensory evaluation) quality criteria. Replacement of fishmeal with krillmeal in the diets resulted in the skin colour above and below the lateral line to be more red than the control group without krillmeal substitutions, even though this difference was not significant, and with more yellow hue. Additions of krillmeal increased the muscle whiteness and yellow hue compared with the control group and wild fish. There was no difference in red hue between the groups. Muscle pH, texture or sensory attributes were unaffected by dietary inclusion level of krillmeal. Wild‐caught cod deviated in several aspects from the farmed cod. It is concluded that the replacement of fishmeal with Antarctic krillmeal in the diets two months before slaughter did not move the sensory attributes more towards wild fish.     

Blood vessel melanosis: a physiological detoxification mechanism in Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>)

Melanin deposits in white muscle represent a potentially serious quality problem for farmed cod. Black lines of deposited melanin are associated with blood vessels and consist of layers of melanin-filled cells. Despite numerous anecdotal reports of melanosis in farmed cod no detailed investigations into the underlying mechanisms have been undertaken. In this study we have confirmed that melanosis is present in both farmed and wild cod. However, the incidence of melanosis in wild fish is much lower than that in farmed fish. In addition, we have demonstrated that tyrosinase, a copper-dependent metalloenzyme that is the primary enzyme of melanin synthesis, is present in cod tissues. Copper levels are significantly different in the white muscle of farmed (0.5 ± 0.03 mg/kg wet weight) and wild (0.34 ± 0.01 mg/kg wet weight) cod (P < 0.05) and in the blood vessels of farmed (2.23 ± 0.37 mg/kg wet weight) and wild (0.32 ± 0.02 mg/kg wet weight) cod (P < 0.05). Similarly, differences in the levels of tyrosinase activity were observed in both muscle and blood vessels. Melanised tissues contain higher copper concentrations than tissue containing little or no melanin. Furthermore, we have shown that the addition of copper to protein extracts from fish muscle causes an increase in tyrosinase activity in vitro. Our results suggest that overabundance of copper in commercial feeds leads to increased melanin synthesis via increased tyrosinase activity. We propose that melanin is deposited at sites of high copper exposure and subsequently sequesters copper as a means of reducing the overload stress on other homeostatic mechanisms.     

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.     

Microstructure and texture of fresh and smoked Atlantic salmon, Salmo salar L., fillets from fish reared and slaughtered under different conditions

This study was carried out to examine differences in microstructure and texture of fresh and smoked farmed Atlantic salmon Salmo salar L. fillets with different biological characteristics. The left fillet was analysed fresh and compared with the salted and smoked right fillet from each individual fish. Light microscopy and image analysing techniques were used to study both transversal and longitudinal sections of the muscle. The fish muscle fibres shrank during the salting and smoking process, but sarcomere length did not change. After smoking, a considerable number of fat globules were dispersed among the muscle fibres. The biological characteristics studied were based upon diploid and triploid fish held in both sea cages and land‐based tanks. Different starvation times were used and one group was stressed during slaughter. The cross‐sectional area of muscle fibres from triploid fish was found to be larger than from diploid fish, both in fresh and smoked fillets.     

Changes in trimethylamine oxide and trimethylamine in muscle of wild and farmed cod (Gadus morhua) during iced storage

Trimethylamine oxide (TMAO) is found at high levels in wild Atlantic cod. Trimethylamine oxide is reduced to trimethylamine (TMA) during iced storage. In this study, the levels of TMAO and TMA in wild and farmed cod and the impact of storage, gender and season on these levels were investigated. Wild cod had higher levels of TMAO than farmed cod. Wild cod also had higher levels of TMA after 15 days of iced storage. Farmed cod were found to have levels of TMA‐N <5 mg/100 g after 15 days of iced storage, which is below the maximum permitted level for fresh fish. Therefore, TMA appears to be an unsuitable measure of freshness in farmed cod. Female farmed cod had higher levels of TMAO than male farmed cod; no such difference between genders was found in wild cod. Female and male farmed cod had similar levels of TMA after post‐mortem iced storage. The hepatosomatic index (HSI) of female farmed cod was higher than that seen in male cod and this may be the underlying reason for the differences in muscle TMAO. Levels of TMAO in male farmed cod were higher during the autumn and were correlated with a larger HSI during the same period.     

Performance of intensively farmed Murray cod Maccullochella peelii peelii (Mitchell) fed newly formulated vs. currently used commercial diets, and a comparison of fillet composition of farmed and wild fish

Murray cod is a top‐order carnivore with high culture potential. Currently, there are no commercial diets formulated specifically for Murray cod. In this study, results of two growth trials on Murray cod (80–83.5‐g mean initial weight), conducted in commercial settings, using two laboratory‐formulated diets (DU1 and DU2; 48.9% and 49.1% protein, and 16.9% and 16.1% lipid, respectively, on a dry matter basis), and two commercial diets, formulated for other species (salmon – CD/S and barramundi – CD/B) but used in Murray cod farming are presented. The two commercial diets had less protein (46.6% and 44.4%) but higher lipid (21.7% and 19.5%). The energy content of the feeds tested was similar (about 20–22 kJ g^?1). The growth performance and feed utilization of Murray cod did not differ significantly amongst the diets, but the food conversion ratio and % protein efficiency ratio in fish fed the DU1 and DU2 diets were consistently better. There was significantly less carcass and muscle lipid deposition in fish fed with the latter diets. Of the fatty acids in muscle, the lowest amounts (in μg mg lipid^?1) of n‐3 (262.5±2.9), n‐6 (39.8±0.9) and polyunsaturated fatty acid (PUFA) (302.3±3.8) were observed in fish fed CD/S, and the highest in fish fed DU2 and CD/B. Fatty acids 16:0 and 18:0, 18:1n‐9 and 16:1n‐7, and 22:6n‐3, 20:5n‐3, 22:5n‐3 and 18:2n‐6 were the dominant fatty acids amongst the saturates, monoenes and PUFA, respectively, and accounted for 80.8–88.7% of all identified fatty acids (23) in muscle of Murray cod. The study showed that Murray cod could be cultured successfully on a diet (DU2) containing 20% soybean meal without compromising growth and/or carcass quality. Differences in the proximate composition and fatty acid composition of muscle of wild and farmed Murray cod were observed, the most obvious being in the latter. Wild Murray cod had significantly less (P<0.05) saturates (192.6±1.84 vs. 266.3±3.51), monoenes (156.5±8.7 vs. 207.6±6.19), n‐3 (145.2±5.24 vs. 261.8±3.2) but higher n‐6 (144.3±2.73 vs. 48.3±1.38) in muscle (all values are in μg mg lipid^?1) than in farmed fish. Wild fish also had a much lower n‐3 to n‐6 ratio (1.0±0.03 vs. 5.4±0.09).     

Effects of dietary oxidized oil and vitamin E on the growth,blood parameters and body composition of juvenile Atlantic cod Gadus morhua (Linnaeus 1758)

The effects of oxidized dietary lipid and the role of vitamin E on the growth performance, blood parameters and body composition of juvenile Atlantic cod (Gadus morhua) were evaluated over a 9‐week feeding period. Four isonitrogenous experimental diets containing fresh or oxidized fish oil with or without added vitamin E (α‐tocopherol or mixed tocopherols) were fed to juvenile cod. The oxidized lipid used had a peroxide value of 94 mEq kg^?1 oil. No significant (P>0.05) differences in growth performance (weight gain and specific growth rate) or feed utilization (feed consumption and feed efficiency ratio) were observed when oxidized dietary lipid was used. The hepatosomatic index (HSI), viscerosomatic index (VSI) and haematocrit did not show any significant (P>0.05) differences among the treatments. However, erythrocyte osmotic fragility (EOF), referred to as susceptibility to haemolysis, of fish fed oxidized oil without added vitamin E was high in comparison with those fed unoxidized oil. Supplementation with α‐tocopherol appeared to decrease haemolysis, but mixed tocopherols had no significant (P>0.05) effect on EOF. The proximate composition of fish whole body was also affected by diet treatment. Fatty acid composition of liver total lipid reflected that of dietary lipid. Variations in tissue (liver and muscle) fatty acid composition among the treatments followed the same trend as those of the dietary fatty acids. Fish fed fresh oil had a higher proportion of polyunsaturated fatty acids (PUFA) in muscle and liver lipid than those fed oxidized oil. The results suggest that oxidized dietary oil affected juvenile Atlantic cod in certain tissues and that these effects could be alleviated by supplementation of sufficient amounts of vitamin E in the diet.     

Urea in feeds for sea water farmed Atlantic salmon: effect on growth, carcass quality and outbreaks of winter ulcer

The main objective of the present study was to evaluate whether dietary supplementation of urea might reduce the incidence of winter ulcer in sea water-farmed Atlantic salmon. Salmon destined to be S0 smolt were fed with a urea-supplemented diet (0 or 20 g kg⁻¹ urea) over an 8-week period prior to sea water transfer and were then fed supplemented diet (0, 5, 10 or 20 g kg⁻¹ urea) during the first and second winters in the sea. During the first winter positive relationships between dietary urea and plasma urea and between plasma urea and plasma osmolality were observed. Further, plasma osmolality displayed a negative relationship to mortality. Of the salmon that died during the first winter in the sea 90% had one or more skin ulcers. Both during the first and second winter there were fewer salmon with ulcer among fish fed with the diets supplemented with urea. Salmon fed with 20 g kg⁻¹ urea tended to have higher percentage water in the muscle. Mortality and incidence of salmon with ulcer seemed to relate to plasma osmolality amongst fish fed on diets that differed in levels of urea supplementation, suggesting that an osmotic imbalance may contribute to the development of winter ulcer in farmed salmon. Salmon fed with 20 g kg⁻¹ urea showed significantly greater body weight during the second winter in sea. Fish killed without prior starvation had significantly higher level of muscle urea in the 20 g kg⁻¹ urea group compared with fish fed with the unsupplemented diet. However, a 13-day starvation period reduced urea content in the muscle to the level of the control. No effects of dietary urea supplementation on the sensory quality of market size Atlantic salmon were observed.     

Quality of wild-captured saithe (Pollachius virens L.) fed formulated diets for 8 months

Fish farms may attract wild fish that feed on waste feed from the cages. Saithe, Pollachius virens L., are particularly numerous around salmon cages in northern Europe and may obtain a significant proportion of their diet from waste feed. It has been claimed that these fish are of inferior quality to saithe that feed on natural diets; differences are said to include soft muscle tissue and a different taste. In order to document such changes in quality we performed a feeding experiment. Young wild saithe were collected and fed either a lipid-rich salmon diet or a lean cod diet for 8 months. All fish were individually tagged and growth was monitored throughout the experiment. Parameters related to flesh quality were measured. Diet clearly influenced the growth rate of the fish, and many fish reached a very high hepatosomatic index when fed on a salmon diet. However, many fish had a low feed intake and thus a low rate of growth. There were some differences in skin and muscle colour, pH and in sensory parameters between wild-caught and artificially fed saithe at the end of the experiment. Those fed the cod diet were more similar to wild saithe than those fed the salmon diet.     

Dietary fishmeal levels affect the volatile compounds in cooked muscle of farmed large yellow croaker Larimichthys crocea

A comparative study on the volatile compounds in cooked muscle of wild and farmed large yellow croaker (LYC) was conducted. The two farmed LYC groups were fed with diets containing 44% (CF) and 25% (LF) of fish meal (FM) respectively. Results showed that 48 volatiles, including aldehydes, alcohols, ketones, hydrocarbons, aromatics, acids, esters, furans and miscellaneous compound, were detected in cooked fillets. The LF group had significantly lower amounts of total aldehydes and ketones, higher content of miscellaneous compound in cooked fillets than that in the CF and wild groups (p < .05). Compared with the wild group, the LF group had significantly lower amounts of total alcohols, acids and esters, while the CF group had significantly lower amounts of total aldehydes, higher content of total ketones in cooked muscle (p < .05). According to the principal component analysis (PCA), some volatiles (propanal, nonanal, etc.) could be considered as sensitive indicators to classify cooked muscle samples. In conclusion, differences in the volatiles in the cooked muscle between the wild and farmed LYC have been found. Low level of dietary FM (25%) changed the volatile profiles in cooked fillets of farmed LYC. A PCA may be useful to screen potential volatiles to classify cooked muscle samples in this study.     

The Effects of Sodium Alginate on Quality of Rainbow Trout (Oncorhynchus mykiss) Fillets Stored at 4 ± 2°C

Edible coating is a novel food packaging technology for controlling the growth of spoilage bacteria and chemical changes in ready-to-eat food products. Fresh fish are highly perishable foodstuffs and are very susceptible to spoilage. A sodium alginate coating was used to maintain the quality of rainbow trout fillets in chilled storage over a period of 20 days. Fillet samples were coated with an aqueous solution of 3% sodium alginate and then stored at chilled temperature (4 ± 2°C). The control and coated samples were analyzed periodically (every 5 days) for microbial (aerobic plate count and psychrotrophic count), chemical (total volatile basic nitrogen, thiobarbituric acid, peroxide value), and sensory characteristics. The results indicated that the sodium alginate coating helped protect the quality characteristics of treated fresh fish fillets and prolonged the shelf life during chilled storage of rainbow trout fillets.     

腌制鳙鱼片在冷藏过程中品质变化规律的研究

文章研究了腌制鳙（Aristichthys nobilis）鱼片在冷藏过程中的品质变化规律.将鱼片用质量分数为2％的食盐进行腌制处理,置于4 ℃下冷藏,通过测定感官指标和硫代巴比妥酸（TBA）值、色泽、脂肪酸组成等理化指标,探究腌制对鳙品质的影响.结果显示,腌制组鱼片的货架期为15 d,对照组为9d;腌制组和对照组的pH分别在第9天和第3天达到最低值,分别为6.73和6.81;腌制组TBA值的增长速度显著高于对照组;与对照组相比,腌制鱼片的亮度低,肉色偏红、偏蓝;腌制组鱼片的总多不饱和脂肪酸（∑PUFA）,尤其是n-3系列多不饱和脂肪酸的含量明显低于对照组（P＜0.05）.结果表明,腌制虽然能够延长鳙鱼片冷藏时的货架期,但是会加速鱼片变色,促进脂肪酸尤其是n-3系列多不饱和脂肪酸的氧化.     

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.     

Bleeding of Farmed Atlantic Cod: Residual Blood,Color, and Quality Attributes of Pre- and Postrigor Fillets as Affected by Perimortem Stress and Different Bleeding Methods

The main objectives of the study were to (a) assess the effect of perimortem stress on blood drainage, (b) compare the efficiency of gill cutting and direct gutting as bleeding methods, and (c) compare pre- and postrigor filleting strategies for presence of residual blood in Atlantic cod fillets. Anesthetized cod had significantly higher drainage of blood compared to stressed fish. Nevertheless, the visual assessments of residual blood were not affected by stress or bleeding method. Some minor, but significant, differences between pre- and postrigor fillets were found. Stressed fish were initially less light in color than those unstressed, but after ice storage there was no noticeable difference. However, initially, the largest difference in fillet color was due to different bleeding methods. Fillets cut from fish subjected to gill cutting were lighter and less red in color than those bled by direct gutting. After 7 and 21 days of storage, the color differences observed in fresh and salted fillets, respectively, were mainly due to the different rigor status when they were filleted, indicating that fillets cut postrigor were superior to fillets cut prerigor. Prerigor filleting resulted in lower water holding capacity after ice storage in anesthetized, direct gutted cod.     

Effects of Dietary Vitamin E Enrichment on Frozen Channel Catfish, (Ictalurus punctatus) Fillets

The storage quality of channel catfish (Ictalurus punctatus), following long term frozen storage, fed diets containing 5 and 10 times the normal level of vitamin E for 45 or 60 days prior to harvest, was evaluated. There were no unusual effects of treatment on fish weight, survival or feed conversion ratios. Muscle vitamin E content was higher (P < 0.05) from fed diets containing supplemental vitamin E than in the control. Oxidation as measured by TBARS and sensory analysis values did not differ (P > 0.05) in response to vitamin E supplementation. Lipid oxidation increased as storage time increased. Lack of change in phospholipid and neutral lipid fractions during storage indicated that autoxidations was the major cause of oxidation in catfish. Vitamin E levels up to 10 times the normal amount did not improve the overall quality of catfish fillets.     

Assessment of Fatty Acid Composition and Technological Properties of Northern Pike (Esox lucius) Fillets: The Effects of Fish Origin and Sex

The aim of the study was to investigate the effects of northern pike origin (wild vs. farmed) and sex (female vs. male) on chemical composition, including fatty acids, and technological properties of fresh fillets. Fish origin influenced moisture, protein, fat, and ash contents, pH and color of the fillets, and the proportion of 22 out of 25 determined fatty acids, whereas sex affected expressible water, pH, lightness and redness of fillets, and only a single fatty acid (C20:0) proportion. Farmed pike had higher protein and fat content and lower moisture and ash than wild pike. Higher proportion and content of total polyunsaturated and n-3 fatty acids, as well as lower n-6/n-3 ratio, were found in farmed pike. Thus, it can be concluded that the commercial feed positively affected fatty acid proportion and content in the fish tissue and increased its nutritional value.     

Electrical stunning of farmed Atlantic cod Gadus morhua L.: a comparison of an industrial and experimental method

An industrial and experimental electrical method for stunning farmed Atlantic cod in air and seawater (SW), respectively, were compared. The impacts of sedation with AQUI‐S^? and exercise to exhaustion before electrical stunning were also assessed to monitor the possible depletion of rested muscle energy levels by electrical stunning. Stress (blood glucose, haematocrit, muscle pH, muscle excitability, high‐energy phosphates and rigor mortis) and flesh quality (fillet texture, colour, liquid leakage (LL), gaping, residual blood and K‐value) were assessed. For the industrial stunning method, an average of 41 V, 0.2 A dc was applied to individual cod for 18–27 s. For the SW method, a bipolar square wave current (170 Hz, 33% duty cycle) was applied for 5 s. After stunning, recovery was prevented by exsanguination in chilled SW. There were no differences (P>0.05) between the two stunning methods except for a higher ultimate fillet pH for cod stunned in air 8 days postmortem. Exercise before stunning depleted muscle energy levels at slaughter, increased LL and fillets had redder and darker flesh after storage on ice for 8 days. Electrical stunning (in air) of AQUI‐S^?‐treated fish partly depleted muscle energy levels (pH 7.3, ATP 18.7 μmol g^?1, PCr 70.1 μmol g^?1). However, flesh quality was not affected. Unless pre‐rigor filleting is the chosen processing strategy, electrical stunning of cod seems to be a promising stunning method.