Hannes Magnússon

Combined application of modified atmosphere packaging and superchilled storage to extend the shelf life of fresh cod (Gadus morhua) loins.

Development of new technologies and preservation methods to offer conveniently packed fish with sufficient keeping quality is important to meet increasing demand for value-added fresh fish products on the market. The aim of this study was to investigate the effect of combined application of modified atmosphere packaging (MAP) and superchilled storage on the shelf life of fresh cod loins. Fresh cod loins were packed in polystyrene boxes and in MA (CO(2)/N(2)/O(2): 50%/45%/5%) on day 3 postcatch and stored at chilled (1.5 degrees C) and superchilled (-0.9 degrees C) temperatures. Quantitative descriptive analysis (QDA) and physical, chemical, and microbial analyses were carried out during the 21 d of storage. Superchilled storage alone compared with traditional chilled storage in polystyrene boxes increased the total shelf life (days from catch) of cod loins from 9 to 16 or 17 d. Chilled MA packaging increased the shelf life from 9 to 14 d and when MAP and superchilled storage were combined, a synergistic effect was observed and the shelf life was further extended to at least 21 d. It is noteworthy that the characteristic fresh and sweet taste can be maintained longer under such conditions. This could contribute to enhanced eating quality of fresh cod fillets for consumers in distant markets. However, MAP combined with superchilled storage resulted in different textural properties. Superchilled MA packed cod loins had more meaty texture compared to other sample groups after 7-d storage.

Bacterial composition and succession during storage of North-Atlantic cod (Gadus morhua) at superchilled temperatures

BackgroundThe 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.ResultsUnbrined (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 abundant 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.ConclusionThe 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.

Application of Quality Index Method (QIM) Scheme and Effects of Short-Time Temperature Abuse in Shelf Life Study of Fresh Water Arctic Char (Salvelinus alpinus)

ABSTRACT Farmed arctic char were divided into two groups after slaughtering. One group (T1) was stored in ice up to 18 d and the other (T2) was stored at 18°C for 24 h (temperature increased from 3°C up to 12°C), then iced and stored up to 18 d. Changes during storage were observed with sensory evaluation using the Quality Index Method (QIM) and Quantitative Descriptive Analysis (QDA), total viable counts (TVC), and hydrogen sulphide (H2S)-producing bacteria. A high correlation between Quality Index (QI) and storage time in ice was found. Storage time could be predicted within ± 1.3 d. The maximum shelf life, determined with QDA and microbial counts, was 17 and 15 d, respectively, for iced (T1) and temperature-abused (T2) arctic char. At the end of shelf life, TVC was 105–106 CFU/g in the flesh of both groups, with H2S producing bacteria constituting a higher proportion of TVC in T2.

Effect of brining, modified atmosphere packaging, and superchilling on the shelf life of cod (Gadus morhua) loins.

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, CO(2)/O(2)/N(2): 50/5/45) at 0, -2, and -3.6 degrees C. Samples were examined over a 4-wk period. Total viable psychrotrophic counts and counts of H(2)S-producing bacteria reached higher numbers in the air-packed brined fish at -2 and -3.6 degrees 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 degrees 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 degrees C and 14 to 15 d at -2 degrees C. The shelf life of MA-packed unbrined loins was about 14 to 15 d at 0 degrees C but 21 d at -2 degrees C. Thus, synergism of combined superchilling (-2 degrees 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 degrees C was 12 to 15 d but only 13 d under MA. The same synergistic effect did therefore not apply to brined loins as with unbrined ones.

Flavor and quality characteristics of salted and desalted cod (Gadus morhua) produced by different salting methods.

Flavor characterization and quality of salt-cured and desalted cod (Gadus morhua) products was studied using sensory analysis and gas chromatography techniques. The products were produced in Iceland using two different processing methods (filleting and splitting) and three different salting procedures, i.e., the old single-step kench salting or a multistep procedure, and presalting (injection and brine salting or only brine salting), which was followed by kench salting. The main difference observed was between fillets and split fish, where the split fish was darker and had stronger flavor characteristics. Comparison of different salting procedures showed that the use of presalting improved the appearance of the salted products, which can be described as increased lightness and reduced yellowness of the products. In the same products, the intensity of curing flavors was milder, as described by sensory analysis and key aroma compounds. Derivatives from lipid and protein degradation contribute to the characteristic flavor of the salted products.

Process control of lightly salted wild and farmed Atlantic cod (Gadus morhua) by brine injection, brining, and freezing--a low field NMR study.

The aim of this study was to use low-field nuclear magnetic resonance (NMR) and traditional chemical methods to investigate the physical and chemical differences in wild and farmed cod processed pre- and postrigor, and how these properties were affected by brine injection, brining, and freezing. In prerigor processed farmed or wild cod, brine injections followed by brining for 2 d, with brine concentrations up to 5.5% and 4%, respectively, were not sufficient to reach a muscle salt concentration of 2% as aimed for, while wild cod processed postrigor had sufficient salt uptake after the same processing. Low-field NMR gave valuable information about the differences in the muscle structure between wild and farmed cod as well as the state of the water in the muscle during brine injection, brining, and during rigor tension. Low-field NMR is, therefore, a valuable tool that can be used to optimize the salting and storing processes of lightly salted cod products from both wild and farmed cod. For farmed cod to be used in the production of lightly salted products further research is needed. Practical Application: Optimal processing of lightly salted cod products is important to the fish industry, due to an increasing market for this product in southern Europe. Farmed cod, which is seen as a potential steady raw material source for this production, differs considerably from its wild counterparts by having other chemical and physical muscle properties, such as lower water content and lower pH. With the processing procedures used today the farmed cod can, therefore, only be used in some of the products, where wild cod is currently used as raw material. It is, therefore, important that the processing of these products is optimized with regard to these differences in the raw material. This study gives a valuable contribution to further studies about optimal combinations of brine injections, brining, and freezing of pre- and postrigor processed farmed compared to wild cod.

Development of Quality Index Method (QIM) Scheme for Farmed Tilapia Fillets and Its Application in Shelf Life Study

The aim was to develop a Quality Index Method (QIM) scheme for fresh tilapia fillets and evaluate the scheme in a shelf life study. Farmed tilapia fillets were stored at 1 and −1°C for up to 20 days, and changes during storage were observed with sensory evaluation using the QIM scheme and General Descriptive Analysis (GDA), total viable counts (TVC), and hydrogen sulphide (H2S) producing bacteria. The maximum shelf life of fillets stored at1 and −1°C was determined with GDA and microbial counts as 16 and 19 days, respectively. A high correlation of R2 = 0.943 between Quality Index (QI) and storage time at 1C° was found to be 0.843 at −1°C. At the end of shelf life, the QI was 5.3 and 6.5 out of a maximum score of 15 for fillets stored at 1 and −1°C, respectively. Total viable counts and H2S-producing bacteria showed an increasing trend during storage time for both groups. At the end of shelf life, TVC was log 7 cfu/g in the flesh of both groups, with H2S producing bacteria constituting a higher proportion (log 6 cfu/g) of the total. The scheme was modified at the end of the study to better characterize deskinned farmed tilapia fillets.