Fresh Cod Fillets Research Articles

Temperature fluctuations in processing and distribution: Effect on the shelf life of fresh cod fillets (Gadus morhua L.)

Low temperature is essential in keeping quality of fresh cod products, and maintaining low temperature is challenging during processing, distribution and storage. In the first step of this study, temperature fluctuations of fresh cod fillets were logged in a commercial cold chain. Short-term temperature rise was observed in the fillets during processing, but in the following distribution, the temperature of the product was approximately 0 °C. In supermarkets, however, fillet temperatures up to 7.0 °C were registered. In the second step, a controlled storage experiment was performed copying time and temperature conditions mapped in the first step. The fillet quality was evaluated with respect to odour and TVB-N at day 7, 10 and 12 after catch. Even a minor rise in temperature by 2 °C reduced the shelf life significantly after 12 days (5 days in ice followed by 7 days at elevated temperature) (p < 0.05). Only fillets stored at 0 °C was below the threshold of 35 mg TVB-N/100 g after 12 days of storage. In this experiment, this threshold was passed at 12 degree-days (DD), and it is suggested that DD should be further explored for generating a rule of thumb for shelf life of cod fillets.

Assisting sustainable food consumption: The effects of quality signals stemming from consumers and stores in online and physical grocery retailing

Increased fish consumption can contribute to a more sustainable food system. This paper explores how signaling affects consumer choices in fresh fish purchasing situations, both in traditional and online retail settings. We examined two different types of market signals; quality signals stemming from consumers as a social proof and authority signals coming from stores. Study 1 showed that quality signals from other consumers (product rating) had the highest importance score in an online setting when compared to traditional attributes in a conjoint experiment. Study 2 again confirmed the prominence of quality signals from consumers by extending the research over to brick and mortar retailing and top-selling items. Study 3 followed up with in-store experiments, using fresh cod fillets as the target product and fresh ground beef as a comparison. The experiments showed increased sales from both types of signaling, with an overall 41.5% increase for fish in our study.

Mathematical models for the trimethylamine (TMA) formation on packed cod fish fillets at different temperatures

The microbial formation of trimethylamine (TMA) can be used as a quality indicator compound to predict the freshness of fish during its shelf life. In a supply chain with fluctuating temperatures, mathematical models will be valuable tools to simulate this formation as a function of temperature and time. These models are essential to link sensor data on the formation of TMA to the actual freshness of fish. Existing models for the formation of TMA in fish needed improvements and secondary models for the effect of temperature on the formation of TMA are lacking in the literature. Three different approaches were evaluated on their ability to simulate the experimental observed TMA formation at 4 different temperatures (0, 5, 10 and 15°C). In the first approach the existing models were improved and the temperature effect was modelled by an empirical model using four parameters. This model is able to simulate the TMA formation at static temperatures. Since TMA is produced on fresh cod fillets by the micro-organisms Shewanella putrefaciens and Photobacterium phosphoreum the microbial Baranyi–Roberts model was initially used for modelling the TMA formation, but this model was found to be too complex (too many correlated parameters that could not be estimated). In the third approach it was seen that a simplified Baranyi–Roberts model with only three parameters could be used to predict the TMA formation with equal accuracy. The influence of the temperature on the parameter μmax was modelled using the extended square root model of Ratkowsky and the differences in TMA formation profiles of different batches could be described by the batch specific parameter N0 representing the initial quality. The presented dynamic model is valuable in predicting the formation of TMA in a fresh fish supply chain with dynamic temperatures. This model has the potential to be used to link sensor data of TMA in the headspace to the actual freshness status of the fish.

Monitoring the Quality of Perishable Foods: Opportunities for Intelligent Packaging

This review paper discusses opportunities for intelligent packaging for monitoring directly or indirectly quality attributes of perishable packaged foods. The possible roles of intelligent packaging as a tool in supply chain management are discussed as well as the barriers to implement this kind of technology in commercial applications. Cases on pasteurized milk and fresh cod fillets illustrate the application of different intelligent packaging concepts to monitor and estimate quality attributes. Conditions influencing quality (e.g., temperature–time) can be monitored to predict the quality of perishable products when the initial quality is known and rather constant (e.g., pasteurized milk). Products with a highly variable initial quality (e.g., fresh fish) require sensors monitoring compounds correlated with quality.

Non-destructive sensing of the freshness of packed cod fish using conductivity and pH electrodes

The use of pH and conductivity electrodes as non-destructive methods for monitoring changes in the freshness status of packed fish is explored. The electrodes monitor changes in the electrical properties of an aqueous phase positioned in the headspace of the fish package. Volatile compounds produced in/on the packed fish and released in the headspace dissolve into this aqueous phase. Several compounds affect the electrode signals. The signals of the electrodes were compared with the volatile amines content of fresh cod fillets stored at 0–15°C. The changes in the pH signal were strongly temperature dependent and not suitable as quality indication for practical storage temperatures. The conductivity signal showed a characteristic pattern, that correlated with the increasing volatile amines content at all temperatures. The non-destructive measurement of conductivity establishes the proof of principles for monitoring the freshness of packed fish and paths the way towards new developments of intelligent packaging concepts.

The influence of labelling on consumers' evaluations of fresh and thawed cod fillets in England

PurposeThe purpose of this study was to investigate the effect of information on English consumers' evaluation of fresh and thawed cod fillets which in English retail stores is referred to as “chilled” seafood.Design/methodology/approachAfter the exploration of consumers' impressions of thawed fish, this study followed a pair‐wise comparison approach in a central location consumer test. Fish fillets were evaluated on liking, smell and texture by means of a questionnaire with additional behavioural and attitudinal questions.FindingsThis study showed that consumers in England may prefer thawed over fresh cod fillets without information. However, consumers' evaluations increased for labelled fresh cod fillets and decreased for thawed. Finally, consumers reported positive expectations about fillets labelled “fresh” or “frozen at sea”.Research limitation/implicationsThis study involved testing cod fillets in a central location test. Consumers do not usually evaluate cod fillets in this way in their daily life. The quality of the two types of fillets made especially for this test may vary compared to the ones usually sold and consumed.Practical implicationsThis study can inform producers and retailers about what to expect by means of sales of fresh and thawed cod products with or without information.Social implicationsIt was shown that consumers are positively influenced by information and are willing to consume more fish if they know that the fish is fresh or thawed properly.Originality/valueThis is the first paper to present English consumers' evaluations of thawed cod.

How fresh is fresh? Perceptions and experience when buying and consuming fresh cod fillets

From January 1st 2010 it was mandatory for all retail stores selling fresh fish in Norway to provide their customers with capture date information for wild fish and slaughter date for farmed fish. The objectives of this study were to: (a) evaluate how many days after capture are consumers willing to buy fresh fish stored on ice, (b) once they have bought the fish how many days are they willing to keep it at home before eating it, and (c) estimate the shelf life of fresh cod using consumer acceptance/rejection data, with and without capture-date information. To cover (a) and (b) a survey was conducted in Norway among 419 respondents visiting retail stores asking them to evaluate how many days after capture they were willing to buy fresh Atlantic cod (Gadus morhua) stored on ice. The respondents were also asked how many days after purchase they were willing to keep the fresh cod at home before cooking and eating it. To cover objective (c), fillets of wild Atlantic cod were evaluated by a total of 389 consumers from three Norwegian cities in three different stages: raw and cooked without information on capture data, raw with capture date information. Survival analysis statistics were used to analyze the data with the inclusion of respondents’ age, self-reported degree of fresh fish expertise and frequency of fresh fish consumption. When respondents were asked for the last day they would buy fresh cod after capture, there was a 75% probability that this would be approximately 3days and 5days for elder and young respondents, respectively. There was a 75% probability that these respondents would have the fish approximately 1day at home before cooking and eating it. The shelf life (as measured in an acceptability test) corresponding to a 25% rejection probability was approximately 7days and 11days, with and without capture-date information, respectively. Thus, in general, when respondents were asked which was the last day they would be willing to buy cod after capture, this time (3–5days) was shorter than the shelf life (7–11days).

A non-destructive ammonium detection method as indicator for freshness for packed fish: Application on cod

This paper introduces a non-destructive method for monitoring headspace ammonium as an indicator for changes in the freshness status of packed fish. Electrodes in an aqueous phase in the package monitor changes in the concentration of ammonia produced in/on the packed fish and released in the headspace. The outputs of an ammonium ion-selective electrode (NH4+-ISE) were compared with the volatile amines content of the fish fillets. The method was tested in triplicate with fresh cod fillets stored between −0.5 and 1.9°C. Changes in the ammonia content of the fish could be monitored in the aqueous phase with the NH4+-ISE. The changes in the NH4+-ISE signal correlated with the content of volatile amines (TVB-N) in the cod fillets. This non-destructive method might be the basis for the development of an intelligent packaging for monitoring freshness of packed fish.

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.

Development of Quality Index Method (QIM) scheme for fresh cod ( Gadus morhua) fillets and application in shelf life study

The aim was to develop and evaluate a Quality Index Method (QIM) scheme for fresh cod fillets. Cod fillets were stored at 0–1 °C on ice up to 14 days. Total viable counts (TVC) and counts of H 2S-producing bacteria were done. A QIM scheme for fresh cod fillets to evaluate freshness was proposed. A high correlation between the Quality Index (QI) and storage time on ice was found. The remaining storage time could be estimated with accuracy of ±1.3 days when the cod fillets were evaluated with QIM. The maximum storage time was estimated 8 days based on Quantitative Descriptive Analysis and H 2S-producing bacteria counts.

Estimating packaging atmosphere–temperature effects on the shelf life of cod fillets

The behaviour of the natural microflora (total bacterial count, psychrotrophic bacteria, total coliforms, and lactic acid bacteria) of fresh cod fillets packaged in air, under vacuum, in a modified atmosphere with low oxygen concentration (5%) and in a modified atmosphere with high oxygen concentration (80%) was monitored during storage at different isothermal conditions from 4 to 12 °C. The growth data of the total bacterial count and total coliforms were used to model kinetically the shelf life of the samples in order to check the effects of storage temperature and packaging atmosphere. The acceptability times were compared with the stability times to establish if the shelf lives predicted were correlated. At 4 °C, cod fillets packaged under vacuum and in a modified atmosphere with low oxygen concentration had a higher shelf life (6.00 and 5.42 days), calculated from the growth of the total bacterial count, than the samples packaged in other atmospheres (1.96 and 2.62). Kinetic modelling could be valuable for the prediction of microbial fish quality loss.

Distribution of Water in Fresh Cod

Low-field 1H nuclear magnetic resonance (NMR) transverse relaxation was used to measure water mobility and distribution of water in fresh cod fillets. The NMR relaxations were analysed with the so-called SLICING method giving uni-exponential profiles from which the transverse relaxation time (T2-values) and the relative sizes of the water populations were calculated. Two water populations with the T2-values of 50 and 94 ms were obtained. The shortest relaxation time was primarily found near the head, and water with the longest relaxation time was primarily found near the tail. This variation can be explained by the smaller muscle cells and muscle fibers in the tail, which may influence the distributions of water into the different pools. The amount of one of the water populations was correlated to the overall water content with a correlation coefficient of −0.94.

Shelf-life extension of cod fillets with an acetate buffer spray prior to packaging under modified atmospheres

Fresh cod fillets (Gadus morhua) were sprayed with a 10% acetate buffer (pH 5.6), packed with an industrial gas-flushing packaging machine under modified atmospheres (50% CO2-45% O2-5% N2, 2cm3/1g gas/ product ratio) and stored at 7°C for 12 days. Control cod fillets were directly packed and stored under the same conditions. A reduction of the aerobic plate counts was observed immediately after the cod fillets had been sprayed. During storage under modified atmospheres, there was complete inhibition of H2S-producing bacteria and Enterobacteriaceae in the treated cod fillets. Production of total volatile bases and trimethylamine (TMA) was inhibited in treated fillets for 10 days' storage under modified atmospheres. Inhibition of TMA production can be attributed to growth inhibition of H2S-producing bacteria, inhibition of the trimethylamine oxide (TMAO)-dependent metabolism of TMAO-reducing bacteria and the stable pH during storage. The shelf-life, at 7°C, of treated cod fillets, based on cooked flavour score, was almost 12 days, ca 8 days more than shelf-life of the control fillets.

Thawed Cod Fillets Spoil Less Rapidly Than Unfrozen Fillets When Stored under Modified Atmosphere at 2°C

The effect of two months of frozen storage at −20°C on the spoilage characteristics and shelf life of thawed and modified atmosphere packed (MAP) cod fillets stored at 2°C was studied. Thawed MAP cod fillets were compared with fresh cod fillets stored in CO2-containing modified atmospheres with and without added oxygen. The shelf life of 11 to 12 days in the fresh MAP cod was extended to more than 20 days in the thawed MAP cod at 2°C. This shelf life extension was most likely due to the inactivation of the spoilage bacterium Photobacterium phosphoreum during frozen storage as reflected both in Chemical analyses and sensory evaluation. In contrast to fresh MAP cod fillets no significant production of trimethylamine occurred and almost no amine odor and taste were detected during 20 days of chill storage of thawed MAP cod fillets. The use of frozen fillets as raw material not only provides a more stable product in MAP but also allows much greater flexibility for production and distribution. However, a slightly increased concentration of dimethylamine, a larger drip loss, and detection of weak frozen storage flavor were observed in the thawed MAP cod fillets.

Microbiological quality and shelf‐life of chilled cod fillets in vacuum‐skin and modified atmosphere packaging

AbstractThe microbiological quality and shelf‐life of fresh cod fillets (Gadus morhua) packed under modified atmospheres (CO2/N2/O2, 40:20:40) were compared to air and vacuum‐skin packed fillets. Packed fillets were kept at 0 ± 1°C and chemical and microbiological analyses as well as sensory assessment were carried out after 4, 6 and 8 days. The decomposition process was evaluated through microbial and enzymatic proteolysis by means of total volatile nitrogen measurement, acetic acid values, surface pH and organoleptic tests. The microbiological quality was established by evaluating the growth of microbial species responsible for spoilage (total bacteria count. Gram‐negative bacteria, H2S‐producers) and identifying isolated species. Modified atmosphere packaging gave the best results and the high oxygen content did not affect the microbiological quality in the presence of 40% carbon dioxide. Vacuum‐skin packed fillets gave less satisfactory results owing to poor chemical and microbiological indices, even if they we‐e always better than fillets maintained in air.

Effect of Sodium Polyphosphates on Frozen Cod Fillets (Gadus morhua)

Fresh cod fillets were exposed to water or to one of four polyphosphate solutions: sodium hexametaphosphate (HX), sodium tripolyphosphate (TP), tetrasodium pyrophosphate (PP), or FREEZ-GARDR FP-19 (FP). Exposure times of 30, 60, and 120s were used. The fillets were frozen and evaluated after 5 and 31 weeks of storage at −18°C. Fillets were assessed for pick-up weight, thaw drip, cooking loss, pH, and expressible moisture as well as for sensory properties.No significant differences were found in pick-up weight or thaw drip. Among the fillets stored for 5 weeks, fillets dipped in HX, TP, and FP yielded less cooking loss and were found to be more tender and juicy. Among the fillets stored for 31 weeks, fillets treated with PP tended to have a higher pH, less expressible moisture, and better sensory properties. The extended frozen storage resulted in significantly less thaw drip and significantly more expressible moisture than the 5-week storage period. Overall, the beneficial effects of exposing cod fillets to polyphosphate solutions prior to freezing appeared to be minimal in comparison to exposing fillets to water.

Microbial Flora of Cod Fillets (Gadus morhua) Stored at 2°C in Different Mixtures of Carbon Dioxide and Nitrogen/Oxygen

Cod fillets were stored in different combinations of carbon dioxide and oxygen/nitrogen at 2°C and the development of the microflora was studied during storage. The shelf life, expressed as the time for the microflora to reach 1 × 106 CFU/g, successively increased as the CO2 concentration increased. No significant effects were noted whether oxygen or nitrogen was used together with CO2 to comprise the gas mixtures. In 100% CO2, the total aerobic count did not exceed 1 × 106 CFU/g during the storage period. The microflora of the fresh cod fillets consisted of Flavobacterium spp., Alteromonas putrefaciens, Moraxella-like organisms and Pseudomonas spp. After 6 d of storage in air, the total aerobic count had reached 5 × 107 CFU/g and the microflora was dominated by A. putrefaciens (62%) and non-fluorescent Pseudomonas spp. (28%). After 26 to 34 d of storage, Lactobacillus spp. and A. putrefaciens dominated the spoilage flora in the different gas mixtures and the total count amounted to 3 × 105 to 2 × 107 CFU/g. The ratio of Lactobacillus spp. at the termination of storage in the different gas mixtures increased in the order of air <50%CO2/50%N2 <50%CO2/50%O2 <90%CO2/10%N2 <100%CO2 <90%CO2/10%O2, whereas the ratio of A. putrefaciens decreased in the same order. Considering the technical difficulties in using an atmosphere at 100% CO2 and the microflora developing during storage in the different gas mixtures, it is suggested that a suitable gas mixture for retail packages should be 50% CO2/50% O2.

Effects of ethylene oxide on the tissue and flora of fresh and freeze dried cod fillets.

Summary. Attempts to sterilize fresh cod fillets with ethylene oxide resulted in protein denaturation with the commensurate exudation of soluble tissue materials. The bacterial colony forming units were reduced to a level of between zero and 100/g of tissue, but sterilization was never achieved. Freeze dried cod fillet sections treated with ethylene oxide and reconstituted with sterile Ringer's solution gave a sterile product which when inoculated with a natural bacterial flora produced normal spoilage odours.

Nitrite-Reducing Bacteria on Cod Fillets

Nitrite-reducing bacteria are present on fresh cod fillets; the proportion increases during storage and they shortly become the predominating flora.Nitrite-reducing bacteria decrease the retarding action that small amounts of nitrite have on the bacterial reduction of trimethylamine oxide.

Effect of Trimethylamine Oxide on the Growth of Bacteria

It has been shown that the addition of 1% trimethylamine oxide to culture media reduces the total counts from fresh cod fillets approximately fifty per cent when the plates are incubated at 25 °C. or lower.By plating out pure cultures it has been shown that the inhibiting action of the oxide is on gram positive organisms and has either no effect or a slight stimulating action on gram negative organisms.