Lipid damage during frozen storage of Atlantic halibut (Hippoglossus hippoglossus) in active packaging film containing antioxidants

The use of peroxide value (PV), free fatty acids (FFA), thiobarbituric acid reactive substances (TBARS) and p-anisidine value (PA) proved suitable for studying lipid hydrolysis and primary and secondary lipid oxidation in samples of Atlantic halibut throughout frozen storage. After twelve months, the FFA values in the samples packaged with the film containing natural antioxidants (extracted from barley husks) were similar to the FFA value in the control sample after 9 months. Maximum peroxide value in the samples packaged with the antioxidant-containing film was found one month after the maximum value observed in the control sample. After six months, the concentration of malondialdehyde in the control sample was approximately 30–50% higher than in samples packaged in film containing antioxidants. The results confirm the efficacy of natural antioxidants derived from barley husks and antioxidant active packaging film in slowing down lipid hydrolysis and increasing the oxidative stability of Atlantic halibut flesh.     

Dietary DNA in blood and organs of Atlantic salmon (Salmo salar L.)

The objective of this study was to investigate the uptake of dietary DNA into blood, kidney, and liver of salmon, and to determine the DNA fragment size if dietary DNA was detected. Salmon in groups of five fish were force-fed a feed containing a high copy number of three polymerase chain reaction (PCR) amplified DNA fragments. Tissue samples were dissected from the fish at time intervals starting at 1 h after force-feeding (AFF) and ending at 64 h AFF. Real-time PCR analyses were used to determine the presence or absence of DNA targets. Sensitive methods amplifying small fragments were used to minimise the impact of fragmentation on the detectability of DNA targets. Uptake of dietary DNA was observed and the highest concentrations of dietary DNA in liver and kidney were found 8 h AFF. The results correspond to data published for similar trials performed on other animal species. An additional experiment showed that decontamination of the liver surface by flaming has the potential to decrease DNA contamination from, for example, feed remnants by up to 90%.     

Absence of nematodes in farmed Atlantic salmon (Salmo salar L.) in Norway

In the present study, a total of 1,180 samples of muscle or viscera from Norwegian-farmed salmon (Salmo salar L.) were examined for the presence of nematode larvae. The samples represented all salmon-producing counties in Norway. The method applied was based on the degradation of fish soft tissue in an acidified pepsin enzyme solution. None of the samples examined in this study contained nematodes.     

Visible/near-infrared spectroscopy detects autolytic changes during storage of Atlantic salmon (Salmo salar L.)

Visible (VIS)/near-infrared (NIR) spectroscopy was used to investigate spectroscopic changes occurring during storage of Atlantic salmon fillets with and without bacterial growth. A storage experiment was conducted for 11 d postmortem. Bacterial growth was inhibited by soaking a group of salmon fillets in 3 mM NaN3 prior to storage, while a control group retained its normal bacterial growth. Spectra were obtained by directly applying the spectroscopic probe onto the loin part of each fillet stored under conditions accelerating degradation. Principal component analysis (PCA) was used to monitor and compare spectroscopic development of the 2 groups and the results showed that VIS/NIR spectral changes occurred in the control as well as the treated group of samples within a single day after filleting. After 2 d of storage, stored samples were distinguishable from those fresh in both groups and it was only after the microbial spoilage became pronounced (8 to 9 log colony forming unit [CFU]/g) that the spectra of the spoiled control samples could be differentiated from spectra of the treated samples with no bacterial growth. Microbial growth is therefore not the only explanation for the spectral variations prior to microbial spoilage. Nonmicrobial, autolytic changes including possible changes in the physical properties are also contributing. Our results show that VIS/NIR spectroscopy can detect autolytic changes occurring in salmon muscle during the early stage of storage, independent of microbial growth. PRACTICAL APPLICATION: Important spectroscopic changes occur even when microbial growth is not apparent. This indicates that VIS/NIR spectroscopy may be used to determine the degree of freshness before microbial spoilage becomes relevant.     

Persistence of orally administered Salmonella enterica serovars Agona and Montevideo in Atlantic salmon (Salmo salar L.)

The objective of our experiments was to study the persistence and dissemination of orally administered Salmonella in smoltified Atlantic salmon. In experiment 1, salmon kept at 15 degrees C were fed for 1 week with feed contaminated with 96 most-probable-number units of Salmonella Agona per 100 g of feed and then starved for 2 weeks. Samples were taken from the gastrointestinal tract and examined for Salmonella 1, 2, 8, 9, 15, and 16 days after the feeding ended. In experiment 2, Salmonella Agona and Montevideo were separately mixed with feed and administered by gastric intubation. Each fish received 1.0 x 10(8), 1.0 x 10(6), or 1.0 x 10(4) CFU. The different groups were kept in parallel at 5 and 15 degrees C and observed for 4 weeks. Every week, three fish in each group were sacrificed, and samples were taken from the skin, the pooled internal organs, the muscle, and the gastrointestinal tract and examined for the presence of Salmonella. The results from the two experiments showed that the persistence of Salmonella in the fish was highly dependent on the dose administered. Salmonella was not recovered from any of the fish that were fed for 1 week with the lowest concentration of Salmonella. In the fish given the highest dose of Salmonella, bacteria persisted for at least 4 weeks in the gastrointestinal tract as well as, to some extent, the internal organs. The present study shows that under practical conditions in Norway, the risk of Salmonella in fish feed being passed on to the consumer of the fish is negligible.     

Persistence and distribution of intravenously injected DNA in blood and organs of Atlantic salmon (Salmo salar L.)

In a recent study it was reported that DNA could be taken up from the feed and transferred to the blood of Atlantic salmon (Nielsen CR, Berdal KG, Bakke-McKellep AM, Holst-Jensen A, Eur Food Res Tech, 2005). In the present study the transport in blood and accumulation in some organs of intravenously injected DNA was studied. Intravenous injection was used as an alternative to feeding to ensure that the quantity of target DNA would permit a quantitative study of the distribution and degradation of the DNA in the fish. Three DNA fragments of different length were administered by injection to 40 salmon, each in a copy number of 10¹⁰. Blood and tissues were sampled at different time intervals after injection. To ensure the use of a sensitive and reliable detection system, real-time PCR methods with TaqMan chemistry were applied in this study. Target DNA was observed in blood and all investigated tissues, with peak levels observed at 0.5–1 h after injection. Some tissue samples were positive for the target DNA up to 24 h after injection. Results of the present study indicate that dietary DNA taken up in the blood may be transported to organs like liver and kidney, as well as muscle and gonads.     

Cloning, pharmacological characterization, and expression analysis of Atlantic salmon (Salmo salar L.) nuclear progesterone receptor

To better understand the role(s) of progestogens during early stages of spermatogenesis, we carried out studies on the nuclear progesterone receptor (Pgr) of the Atlantic salmon. Its open-reading frame shows the highest similarity with other piscine Pgr proteins. When expressed in mammalian cells, salmon Pgr exhibited progestogen-specific, dose-dependent induction of reporter gene expression, with 17α,20β-dihydroxy-4-pregnen-3-one (DHP) showing the highest potency. We then analyzed testicular pgr mRNA and DHP plasma levels in animals during the onset of spermatogenesis, which were exposed to natural light or to constant light, to induce significant differences in testis growth. Grouping of the animals according to their progress through spermatogenesis showed that testicular pgr mRNA levels as well as DHP plasma levels first increased when germ cells had reached the stage of late type B spermatogonia and further increased when entered meiosis, i.e. when spermatocytes were present. However, in situ hybridization studies revealed that pgr mRNA expression was restricted to Sertoli cells, with a strong signal in Sertoli cells contacting type A/early type B spermatogonia, while Sertoli cells contacting larger germ cell clones with further differentiated stages (e.g. late type B spermatogonia) were less intensely/not stained. We conclude that the increase in pgr mRNA levels per pair of testis reflects, at least in part, the increased number of Sertoli cells enveloping type A and early type B spermatogonia. We propose that Sertoli cell-expressed Pgr may mediate DHP-stimulated early steps in spermatogenesis in Atlantic salmon, such as an increase in the number of new spermatogonial cysts.     

Collagen content in farmed Atlantic salmon (Salmo salar,L.) and subsequent changes in solubility during storage on ice

To elucidate whether collagen is an important factor for fish flesh quality, the collagen content and its changes in solubility during storage on ice in muscle of farmed Atlantic salmon (Salmo salar, L.) were measured. The contents of acidsoluble, pepsin-soluble and insoluble collagen in white muscle were determined in fresh fish muscle and at the end of 5, 10 and 15 days storage on ice. Total collagen was found to be 0.66% of fresh weight, with a relative distribution of 6% acidsoluble, 93% pepsin-soluble and 1% insoluble collagen. During storage on ice, a progressive change in solubility of muscle collagen was found. For insoluble collagen, significantly lower values were detected at day 15 compared to day 0. A minor, but even increase in acid-soluble collagen was found from day 0, while no changes were seen in pepsin-soluble collagen during storage. These results show that collagen fibres of farmed Atlantic salmon have a high solubility in acid and salt solutions and contain few cross-links. Some cleavage of intermolecular cross-links seems to occur during storage on ice.     

Toxicokinetic model assessment on the dechlorination of dietary toxaphene CHB-62 into CHB-44 in Atlantic salmon (Salmo salar L.)

European Union legislation on the upper limits of toxaphene in feed and food include the congeners CHB-26, CHB-62 and CHB-50 and is set at 50 µg kg^?1 feed for the sum of these three congeners. However, due to their elevated presence in fish, the congeners CHB-40 and CHB-41, CHB-44, and CHB-42 should also be included according to the European Food Safety Authority (EFSA) in 2005. Earlier trials with model zebra fish have shown in vivo dechlorination of dietary CHB-62 to CHB-44 and, to a lesser degree, of CHB-50 to CHB-40. Biomagnification patterns of Atlantic salmon, fed with technical toxaphene-enriched feeds, indicated that Atlantic salmon have a similar dechlorination. In the present study, a serial one-compartment physiological kinetic model, which includes differentiated growth of body components, is used to quantify the contribution of dechlorination to the congener-specific fillet accumulation of a mixture of dietary toxaphene congeners in Atlantic salmon. The model is assessed from experimental uptake and elimination kinetics of Atlantic salmon smolt fed with technical toxaphene for 122 days followed by a depuration period of 75 days in which the fish were fed toxaphene-free control feed. The serial one-compartment model shows that about 31% of CHB-44 that accumulated in the fillet originated from dietary CHB-62. In contrast, dechlorination of CHB-50 into CHB-40 is not significant. The results show that previously demonstrated in vivo dechlorination of CHB-62 into CHB-44 in zebra fish also occurs in the farmed fish species Atlantic salmon. This dechlorination can at least partly explain the relatively elevated CHB-44 observed in toxaphene fish surveys.     

The effects of natural antioxidants and lighting conditions on the quality of salmon (Salmo salar) fillets packaged in modified atmosphere

The effect of lighting conditions (darkness, a low‐UV colour‐balanced lamp and supermarket fluorescents), along with the application of natural antioxidants (rosemary extract and ascorbic acid) on shelf‐life of salmon (Salmo salar) fillets packaged in modified atmosphere and stored at 1 ± 1 °C was studied. Darkness and lighting with low‐UV colour‐balanced lamps led to an extension of shelf‐life compared with conventional light, as assessed by a* values, lipid oxidation (TBARS value) and sensory evaluation. The application of natural antioxidants on the surface of MAP salmon fillets gave rise to a delay of lipid oxidation as well as an improvement of the sensory quality, mainly in the case of conventional lighting conditions. Copyright © 2005 Society of Chemical Industry     

Lipase-Assisted Concentration of n-3 Polyunsaturated Fatty Acids from Viscera of Farmed Atlantic Salmon (Salmo salar L.)

ABSTRACT: In fish processing, viscera are generally considered waste products and often discarded. Our research objective was to use Atlantic salmon ( Salmo salar L.) viscera as a source of fish oil and to increase its concentration of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) by lipase-assisted hydrolysis. Lipids from fillets and viscera had similar fatty acid compositions. After the enzymatic hydrolysis, acylglycerols were isolated from free fatty acids, therefore increasing the concentrations of EPA and DHA in the acylglycerols. Among the 6 commercial lipases investigated, lipases from Pseudomonas cepacia and Candida rugosa were the most effective following incubation of viscera oil at 35 °C for 20 h. Salmon viscera were a good source for fish oil, and the concentration of DHA and EPA was doubled by using microbial lipases.     

Antioxidants from barley husks impregnated in films of low-density polyethylene and their effect over lipid deterioration of frozen cod (Gadus morhua)

BACKGROUND: The changes in quality of cod fillets packaged in films with and without antioxidants during 12 months of frozen storage at ? 20 °C were investigated in the present study. The following parameters were determined in order to study lipid hydrolysis and primary and secondary lipid oxidation in the samples during frozen storage: peroxide value, conjugated dienes, conjugated triene hydroperoxides, free fatty acids, totox value, thiobarbituric acid‐reactive substances and p‐anisidine value. RESULTS: Films containing antioxidants isolated from barley husks were effective in slowing down lipid hydrolysis and primary and secondary lipid oxidation processes. Secondary lipid oxidation reached maximum values in the 12th month of storage in control samples and samples packaged with antioxidant‐containing film. Maximum lipid hydrolysis and lipid oxidation values for control cod samples were significantly higher than the maximum values found in samples packaged with antioxidant‐containing film. CONCLUSION: The results confirm the efficacy of natural antioxidants derived from barley husks in slowing down lipid hydrolysis and increasing the oxidative stability of cod flesh. They also demonstrate the potential usefulness of natural antioxidants extracted from barley husks in the development of active packaging films for food preservation. Copyright © 2011 Society of Chemical Industry     

Temporal variation in muscle fibre area,gaping, texture,colour and collagen in triploid and diploid Atlantic salmon (Salmo salar L)

Diploid and triploid Atlantic salmon were reared for 32 months in seawater, from October 1998 to January 2000. During this period of time, four samplings were taken to study differences in quality traits and chemical components in the flesh between diploid and triploid Atlantic salmon. Season was found to be the dominant factor explaining the variation in flesh quality traits in both triploid and diploid fish. Ploidy affected the majority of investigated variables while body size had lesser impact. Triploid Atlantic salmon had fewer small muscle fibres and up to 23% larger mean cross‐sectional muscle fibre area than diploids. Triploids also displayed more gaping, softer fillet texture, lower post mortem end pH, darker (L value) and redder (a value) flesh colour, and more soluble and less insoluble collagen compared with diploid fish. No effect of ploidy was found on crude chemical composition. Furthermore, a negative relationship was found between gaping score and muscle fibre area, and a weak positive correlation was found between fibre density and texture firmness. However, when body size and sampling time was included in the statistical model, this relationship between gaping and fibre area became very weak, and the relationship between texture and fibre area was completely negated. This suggests that intra‐species variation in both texture and gaping is more related to season and body size than to average muscle fibre area size. Copyright © 2004 Society of Chemical Industry