The aim of these experiments was to evaluate the effect of brining, modified atmosphere packaging (MAP), and superchilling on the quality changes of cod loins as measured by microbial, sensory, and chemical analysis. Unbrined and brined (2.5 ± 1.0% NaCl) cod loins were kept in styrofoam boxes (air) and under modified atmosphere (MA, CO2/ O2/ N2: 50/5/45) at 0, −2, and −3.6 ° C. Samples were examined over a 4-wk period. Total viable psychrotrophic counts and counts of H2S-producing bacteria reached higher numbers in the air-packed brined fish at −2 and −3.6 ° C than in comparable unbrined groups, being significantly different (P <0.05) at the lower temperature. However, lower counts of these bacteria were obtained in the brined MAP fish than in comparable unbrined fish. Counts of Photobacterium phosphoreum increased most rapidly in air- and MA-packed loins kept at 0 ° C. Lower counts were found at superchilled temperatures. According to sensory analysis the shelf life of unbrined air-packed loins was about 11 d at 0 ° C and 14 to 15 d at −2 ° C. The shelf life of MA-packed unbrined loins was about 14 to 15 d at 0 ° C but 21 d at −2 ° C. Thus, synergism of combined superchilling (−2 ° C) and MA led to a considerable shelf life increase for unbrined loins despite the fact that processing and packaging took place 4 to 5 d post-catch. The shelf life of air-packed brined loins at −2 ° C was 12 to 15 d but only 13 d below MA. The same synergistic effect did therefore not apply to brined loins as with unbrined ones.
Category: Branches
A collection of 376 golden redfish (Sebastes marinus) from several fishing grounds in the North Atlantic in late 2001 was genotyped at nine microsatellite loci to provide preliminary information on the possible genetic structure in this species. Landscape genetic analysis revealed the presence of two distinct genetic pools within the North Atlantic, suggesting that S. marinus might be structured within the North Atlantic and should be the subject of more investigation.
Background
The bacteriology during storage of the North Atlantic cod has been investigated for the past decades using conventional cultivation strategies which have generated large amount of information. This paper presents a study where both conventional cultivation and cultivation independent approaches were used to investigate the bacterial succession during storage of cod loins at chilled and superchilled temperatures.
Results
Unbrined (0.4% NaCl) and brined (2.5% NaCl) cod loins were stored at chilled (0 ° C) and superchilled (-2 and -3.6 ° C) temperatures in air or modified atmosphere (MA, % CO2/ O2/ N2: 49.0 ± 0.6 / 7.4 ± 0.2 / 43.7 ± 0.4). Discrepancy was observed between cultivation enumeration and culture independent methods where the former showed a general dominance of Pseudomonas spp. (up to 59%) while the latter showed a dominance of Photobacterium phosphoreum (up to 100%).
Gas chromatography-mass spectrophotometry (GC-MC) showed that trimethylamine was the most abundantly volatile in mid- and late storage periods. Terminal restriction polymorphism (t-RFLP) analysis showed that the relative abundance of P. phosphoreum increased with storage time.
Conclusion
The present study shows the bacteriological developments on lightly salted or non-salted cod loins during storage at superchilled temperatures. It furthermore confirms the importance of P. phosphoreum as a spoilage organism during storage of cod loins at low temperatures using molecular techniques. The methods used compensate each other, giving more detailed data on bacterial population developments during spoilage.
Atlantic herring (Clupea harengus) is an important commercial fish and shows to be more and more demanded for human consumption. Therefore, it is very important to find good methods for monitoring the freshness of the fish in order to keep it in the best quality for human consumption. In this study, the fish was stored in ice up to 2 weeks. Quality changes during storage were assessed by the Quality Index Method (QIM), quantitative descriptive analysis (QDA) and Torry scheme, by texture measurements: puncture tests and Texture Profile Analysis (TPA) tests on texture analyzer TA.XT2i, and by electronic nose (e-nose) measurements using FreshSense instrument. Storage time of herring in ice could be estimated by QIM with ± 2 days using 5 herring per lot. No correlation between instrumental texture parameters and storage time or between sensory and instrumental texture variables was found. E-nose measurements could be used to detect the onset of spoilage.
In 2006, we sampled the anoxic bottom waters of a volcanic lake beneath the Vatnajökull ice cap (Iceland). The sample contained 5 × 105 cells per ml, and whole-cell fluorescent in situ hybridization (FISH) and PCR with domain-specific probes showed these to be essentially all bacteria, with no detectable archaea. Pyrosequencing of the V6 hypervariable region of the 16S ribosomal RNA gene, Sanger sequencing of a clone library and FISH-based enumeration of four major phylotypes revealed that the assembly was dominated by a few groups of putative chemotrophic bacteria whose closest cultivated relatives use sulfide, sulfur or hydrogen as electron donors, and oxygen, sulfate or CO2 as electron acceptors. Hundreds of other phylotypes are present at lower abundance in our V6 tag libraries and a rarefaction analysis indicates that sampling did not reach saturation, but FISH data limit the remaining biome to <10–20% of all cells. The composition of this oligarchy can be understood in the context of the chemical disequilibrium created by the mixing of sulfidic lake water and oxygenated glacial meltwater.
Volatile compounds in cold smoked salmon products were identified by gas chromatography to study their suitability for rapid detection as indicators to predict sensory quality evaluated by quantitative descriptive analysis. Smoked salmon odor contributed by guaiacol, boiled potato- and mushroom-like odors characteristic of fish lipid degradation and sweet odors associated with the microbial metabolites 3-methyl-butanal and 3-hydroxybutanone were the most intense odors. Other key volatiles were present in high levels but contributed less to the odors. These included furan-like compounds originating from the smoking, spoilage compounds like ethanol, 3-methyl-1-butanol, 2-butanone, and acetic acid along with oxidatively derived compounds like 1-penten-3-ol, hexanal, nonanal and decanal . Partial least square regression models based on data from storage studies of cold smoked salmon from Iceland and Norway verified that selected key volatile compounds performed better as predictors to explain variation in sensory attributes (smoked, sweet / sour rancid and off odor and flavor) than traditional chemical and microbial variables.
During the past decade, genetic markers have been used increasingly to improve stock discrimination and to aid fisheries management. Today, the Icelandic and Faroese Plateau cod (Gadus morhua) are managed as separate units, belonging to ICES Subareas Va and Vb1, respectively. There is little information on the genetic connectivity of the two units, however, except in terms of tagging experiments which revealed limited adult migration between the two areas, and few genetic studies describing genetic differentiation among Faroese and East Icelandic cod. Here, previously published data on the genetic structure of Icelandic cod were combined with new data from the Faroe Plateau to assess the level and the source of genetic variability of Atlantic cod around the Iceland – Faroe Ridge and the potential sources of genetic variation. In all, 771 cod were genotyped at nine microsatellite loci and at the Pantophysin locus (Pan I). The genetic markers employed were congruent and showed that South Icelandic and East Icelandic – Faroese Plateau populations have limited genetic connectivity. Diversifying selection associated with restricted gene flow is likely to explain the observed pattern with the Pan I locus. Further analyzes detected historical imprints in the microsatellite data, suggesting that the divergence could be due to isolation of different cod populations during the last glacial maximum.
Most studies of the genetic structure of Atlantic cod have focused on small geographical scales. In the present study, the genetic structure of cod sampled on spawning grounds in the North Atlantic was examined using eight microsatellite loci and the Pan I locus. A total of 954 cod was collected from nine different regions: the Baltic Sea, the North Sea, the Celtic Sea, the Irish Sea and Icelandic waters during spring 2002 and spring 2003, from Norwegian waters and the Faroe Islands (North and West spawning grounds ) in spring 2003, and from Canadian waters in 1998. Temporal stability among spawning grounds was observed in Icelandic waters and the Celtic Sea, and no significant difference was observed between the samples from the Baltic Sea and between the samples from Faroese waters. F-statistics showed significant differences between most populations and a pattern of isolation-by-distance was described with microsatellite loci. The Pan I locus revealed the presence of two genetically distinguishable basins, the North-west Atlantic composed of the Icelandic and Canadian samples and the North-east Atlantic composed of all other samples. Permutation of allele sizes at each microsatellite locus among allelic states supported a mutational component to the genetic differentiation, indicating a historical origin of the observed variation. Estimation of the time of divergence was approximately 3000 generations, which places the origin of current genetic pattern of cod in the North Atlantic in the late Weichselian (Wisconsinian period), at last glacial maximum.
The identification of North Atlantic redfish has been controversial and remains a difficult task due to overlapping of meristic and morphological characters. Here we used nine microsatellite loci to assess the level of genetic differentiation among these species and assess the resolution power of these microsatellite loci for individual assignment-based analyzes. Conventional analyzes as well as individual Bayesian assignment methods clearly separated the four species of North Atlantic redfish as well as the giant form of Sebastes marinus and the so-called “oceanic” and “deep-sea” types of Sebastes mentella. Locus-by-locus analyzes revealed that only five microsatellite loci out of nine used could discriminate the species concerned. The advantage of the Bayesian methods relies in the individual information retrieved. It therefore gave additional information on the interrelationship among species. Indeed, we provide evidence of potential hybridization among species as well as individual misclassification based on morphological identification. We provide a powerful tool to discriminate North Atlantic redfish species, which might be useful for legal issues such as poaching, unintentional harvesting and control label.