Freshness Assessment of Thawed and Chilled Cod Fillets Packed in Modified Atmosphere Using Near-infrared Spectroscopy

Near-infrared reflectance (NIR) spectra was recorded of 105 samples of cod mince prepared from chill stored thawed cod fillets of varying quality in modified atmosphere packaging (MAP). Traditional chemical, physical, microbiological and sensory quality methods developed for assessing fresh fish products were determined on the same cod fillets. The purpose was to evaluate the potential of NIR spectroscopy for estimating (i) frozen storage temperature, (ii) frozen storage period and (iii) chill storage period of thawed-chilled MAP Barents Sea cod fillets. Furthermore, the potential for measuring of selected quality attributes as drip loss, water holding capacity and content of dimethylamine by NIR was evaluated. The results of the investigation were presented using multivariate modelling methods such as partial least-squares regression (PLSR) and discriminant partial least-squares regression (DPLSR). Systematic differences in the NIR measurements on minced cod fillets were primarily due to the chill storage duration (days at 2°C) on thawed-chilled MAP fillets. PLSR models based on wavelengths selected by a new Jack-knife method resulted in a correlation coefficient of 0.90 between measured and predicted duration of chill storage period (days at 2°C). The root-mean-square error of cross-validation (RMSECV) was 3.4 d at 2°C. NIR measurements provided promising results for evaluation of freshness for thawed-chilled MAP cod fillets completing the traditionally quality methods. However, it is necessary to study the effect of e.g. sample preparation, season, fishing ground and cod size together with more sophisticated pre-treatments of NIR spectra before the NIR method can be integrated as a method for evaluation of thawed-chilled MAP cod fillets.     

Keeping Quality of Sea-Frozen Thawed Cod Fillets on Ice

The objective was to evaluate the suitability of sea‐frozen, thawed cod fillets for the “chilled” seafood market. Fillets were kept frozen for 17 mo. After thawing, fillets were kept iced and at 4°C. Microbiological research on fillets showed higher initial numbers in post‐rigor than pre‐rigor fillets. Pre‐rigor fillets were judged fresher after 2 mo of storage compared to post‐rigor. With longer freezer storage, lower initial freshness scores were obtained, and formation of trimethylamine in thawed fillets was slowed. Thawed fillets frozen prior to rigor merited higher scores for freshness than fillets frozen post‐rigor. This difference decreased with prolonged freezer storage. The results strongly indicate that fillets should be frozen pre‐rigor.     

Quality of superchilled vacuum packed Atlantic salmon (Salmo salar) fillets stored at −1.4 and −3.6 °C

The most important factor for increasing shelf life is the product temperature, and since fish is more highly perishable than meat, the temperature is even more important. In the present study, portions of fillets of farmed Atlantic salmon (Salmo salar) were superchilled at two temperature levels, −1.4 and −3.6 °C. Texture, drip loss, liquid loss, cathepsin activities and protein extractability were investigated during storage and compared to ice chilled and frozen references. Drip loss was not a major problem in superchilled salmon. Textural hardness was significantly higher in superchilled salmon fillets stored at −3.6 °C compared to those stored at −1.4 °C, ice chilled and frozen references. Cathepsins B and B + L were not deactivated at the selected storage temperatures. The storage time of vacuum packed salmon fillets can be doubled by superchilled storage at −1.4 °C and −3.6 °C compared to ice chilled storage.     

Quality changes during superchilled storage of cod (Gadus morhua) fillets

Superchilling is a method with potential for extending the shelf life of food products by partial freezing. For centuries, Atlantic cod (Gadus morhua) has been the most important commercial species in the North Atlantic fisheries and is now regarded as a very promising species in cold water fish farming. In the present work, superchilled storage at −2.2 °C of fillet portions of farmed cod was investigated. Superchilled cod showed increased shelf life with respect to reduced growth of sulphide producing bacteria compared to ice chilled. Drip loss was lower in superchilled cod. However, liquid loss by low-speed centrifugation was higher in superchilled cod fillets compared to ice chilled. This can be explained by freeze denaturation of muscle proteins, which is supported by the lower extractability of salt soluble proteins. There is a need for process optimization to minimize protein denaturation.     

Combined effect of freeze chilling and MAP on quality parameters of raw chicken fillets

The effect of short-term frozen storage prior to thawing on the quality of freeze-chilled chicken fillets was investigated, as was the effect of modified atmosphere packaging (MAP). Four process treatments were used: (1) fresh chicken chilled at 4 degrees C without previous freezing, (2) freeze-chilled for 7 days and thawed at 4 degrees C, (3) chilled at 4 degrees C packaged under MAP (70% N(2)-30%CO(2)), and (4) packaged under MAP, freeze-chilled for 7 days and thawed at 4 degrees C. Microbiological, chemical and sensory analyses were conducted on samples for a period up to 15 days. Freeze-chilled fillets gave a lower total viable count (TVC) at a given sampling day than chilled fillets. MAP, as expected, delayed microbial growth. The Pseudomonads were the dominant microbial species in fillets under aerobic conditions. MAP reduced the populations of Pseudomonads by 2-4 log cfu/g. Lactic acid bacteria (LAB) and Enterobacteriaceae increased progressively for all treatments throughout storage. Yeasts and molds were inhibited by MAP and by freeze chilling. Total volatile basic nitrogen (TVB-N) values increased rapidly for the chilled fillets but remained significantly lower for the freeze-chilled and the MA-packaged samples. MAP and especially freeze chilling enhanced drip loss. MAP did not affect redness or yellowness of product while freeze chilling decreased product redness. Lightness was not affected by either MAP or freeze chilling. Based on taste, which proved to be the most sensitive sensory attribute, shelf life of product ranged from 6 to 7 days for all treatments leading to the conclusion that freeze chilling is a suitable technology for fresh chicken fillets enabling their distribution as a frozen product and upon subsequent thawing at their final destination, their retail display as chilled products. MAP in combination with freeze chilling had a negligible effect on product quality.     

Methods for phosphate addition in heavy salted cod (Gadus morhua L.)

Headed and gutted fresh or frozen and thawed cod (Gadus morhua L.) from the same net catch were hand filleted post rigor before carrying out small-scale salting trials. Fillets were heavy salted using three different methods introducing phosphate during injection, brining, or during pickle salting. For all salting methods, treatment with 0, 4.5, 9 or 18 g/L of the pyro and tri polyphosphate blend Carnal 2110 was carried out. Quality and chemical parameters were analyzed after 5 weeks and 6 ± 1 months of chilled storage of heavy salted fillets.     

Effect of freezing on the physicochemical, textural and sensorial characteristics of salmon (Salmo salar) smoked with a liquid smoke flavouring

This study reports the effect of different refrigeration/freezing treatments on the physicochemical, textural and sensorial properties of farmed Atlantic salmon (Salmo salar) treated with a commercial liquid smoke flavouring. Observations were made on three groups of fillets - group RFS: salted, smoked and stored at 4 °C; group BFS: frozen at −25 °C for 24 h, thawed, salted, smoked and stored at 4 °C; and group AFS: salted, smoked and frozen at −25 °C for 24 h and stored at −18 °C - over a period of 45 days. Scores (on a scale of 1-9) were provided for different sensorial attributes by a panel of 10 trained tasters. Sixty percent of the panellists consistently preferred the AFS fillets. The maximum shelf life associated with each treatment was defined as the last sampling day on which a mean score of ≤5 was awarded for the fillet sensorial attributes by ≥50% of the panellists. Freezing the salmon for 24 h before smoking (BFS) did not increase its shelf life (30 days) over that of refrigerated smoked salmon (RFS). In addition, the former treatment had a negative effect on the adhesiveness, cohesiveness, smoke odour intensity and colour intensity of the flesh. However, maintaining the fish frozen at −18 °C (AFS) increased its shelf life (>45 days) and invested the flesh with greater firmness, cohesiveness and colour intensity.     

Effects of different freezing treatments on physicochemical responses and microbial characteristics of Japanese sea bass (Lateolabrax japonicas) fillets during refrigerated storage

In order to establish an effective freezing method for quality control, the present research evaluated the effects of the different freezing treatments on the quality of Japanese sea bass (Lateolabrax japonicas) over a period of 20 days storage at 0 ± 1 °C. Fish pH value, total volatile basic nitrogen (TVB-N), K-value, trimethylamine nitrogen (TMA-N), drip loss, hardness, color, biogenic amines, microbiological characteristics were measured. Sea bass fillets were stored at −18 °C (T1), −55 °C for 24 h and then −18 °C (T2), −55 °C (T3) for 3 months prior to refrigerated storage. T2 showed lower TVB-N, pH value, biogenic amines and drip loss than T3 and T1 did. Significant lower value of bacterial loads, b* value and hardness were observed in T1, T2 and T3 than those of control group. No significant differences were observed among T1, T2 and T3 for TMA-N and a* value. The study demonstrated that Japanese sea bass fillets treated with −55 °C for 24 h and then −18 °C up to 3 months maintain better quality during refrigerated storage.     

Effect of frozen storage on the proteolytic and rheological properties of soft caprine milk cheese

Freezing and long-term frozen storage had minimal impact on the rheology and proteolysis of soft cheese made from caprine milk. Plain soft cheeses were obtained from a grade A goat dairy in Georgia and received 4 storage treatments: fresh refrigerated control (C), aged at 4°C for 28 d; frozen control (FC), stored at −20°C for 2 d before being thawed and aged in the same way as C cheese; and 3-mo frozen (3MF), or 6-mo frozen (6MF), stored at −20°C for 3 or 6 mo before being thawed and aged. Soft cheeses had fragile textures that showed minimal change after freezing or over 28 d of aging at 4°C. The only exceptions were the FC cheeses, which, after frozen storage and aging for 1 d at 4°C, were significantly softer than the other cheeses, and less chewy than the other frozen cheeses. Moreover, after 28 d of aging at 4°C, the FC cheeses tended to have the lowest viscoelastic values. Slight variation was noted in protein distribution among the storage treatment, although no significant proteolysis occurred during refrigerated aging. The creation and removal of ice crystals in the cheese matrix and the limited proteolysis of the caseins showed only slight impact on cheese texture, suggesting that frozen storage of soft cheeses may be possible for year-round supply with minimal loss of textural quality.     

High Dietary Vitamin E Affects Storage Stability of Frozen-refrigerated Trout Fillets

Fillets were processed from trout fed a diet containing either 200 (low vitamin E [LVE] diet) or 5000 (high vitamin E [HVE] diet) mg a‐tocopheryl acetate/kg for 0, 4, and 9 wk. These fillets were evaluated fresh and after 6 mo of frozen storage. Frozen fillets were thawed and stored 3 d at 1 °C before analyses. Muscle α‐tocopherol of fish fed the HVE diet continuously increased through 9 wk of feeding. Reduced muscle α‐tocopherol and moisture, and increased muscle redness and fat were observed in frozen‐refrigerated fillets compared with fresh fillets. Thiobarbituric acid‐reactive substances were lower in frozen‐refrigerated fillets produced from fish fed the HVE diet. Proportion of unsaturated fatty acids and omega‐3 fatty acids increased as feeding duration increased from 0 to 9 wk.     

Histamine production by Enterobacter aerogenes in tuna dumpling stuffing at various storage temperatures

Enterobacter aerogenes was studied for its growth, and promoting the formation of total volatile base nitrogen (TVBN) and histamine in tuna dumpling stuffing stored at various temperatures from −20 °C to 37 °C. The bacterial number rapidly increased in low (2.0 log CFU/g) or high (5.0 log CFU/g) inoculated concentrations at temperature above 15 °C and reached the highest bacterial count at 37 °C. In addition, the low spiked sample stored at 37 °C for 12 h and the high spiked sample stored at 25 and 37 °C for 12 h, formed histamine at above 50 mg/100 g of the potential hazard level in most illness cases. However, bacterial growth was controlled by cold storage of the samples at 4 °C or below, but histamine formation was stopped only by frozen storage. Once the frozen stuffing samples were thawed and stored at 25 °C, histamine started to accumulate rapidly.     

Influence of different cold storage temperatures during the Rigor mortis phase on fillet contraction and longer-term quality changes of Atlantic cod fillets

Pre rigor produced fillets of Atlantic cod become shorter and more firm than post rigor produced fillets. In pre rigor excised muscle from warm-blooded animals and warm-water adapted fish, cold shortening, extensive contraction during cold storage, is known to occur. The aim of the present work was to study if the extent of fillet shortening in Atlantic cod could be reduced by a slight temperature increase during rigor contraction. The results demonstrate that fillets from this cold-water species showed no cold shortening. On the contrary, the fillets contracted the least when stored at 0 °C during rigor contraction.     

Efficacy of freezing, frozen storage and edible antimicrobial coatings used in combination for control of Listeria monocytogenes on roasted turkey stored at chiller temperatures

The presence and growth of Listeria monocytogenes on ready-to-eat (RTE) turkey is an important food safety issue. The antilisterial efficacy of four polysaccharide-based edible coatings (starch, chitosan, alginate and pectin) incorporating sodium lactate (SL) and sodium diacetate (SD) as well as commercial preparations Opti.Form PD4, NovaGARD™ CB1, Protect-M and Guardian™ NR100 were compared against L. monocytogenes on roasted turkey. Pectin coating treatments incorporating SL/SD, Opti.Form PD4 with or without Protect-M, and NovaGARD™ CB1 displayed higher antimicrobial efficacy against.L. monocytogenes than the other antimicrobials and coating materials. In the second phase of the study, it was investigated whether frozen storage could enhance the antilisterial effectiveness of pectin coating treatments on chilled roasted turkey. Inoculated roasted turkey samples coated with pectin-based treatments were frozen for up to 4 weeks and subsequently stored at 4 °C for 8 weeks. Frozen storage significantly enhanced the antilisterial activity of various coating treatments; with selected treatments reducing the L. monocytogenes populations by as much as 1.1 log CFU/cm² during the subsequent 8-week chilled storage. This study demonstrates that pectin-based antimicrobial edible coatings hold promise in enhancing the safety of RTE poultry products and frozen storage has the potential to enhance their effectiveness.     

Storage Quality of Fresh and Frozen-thawed Fish in Ice

The objective was to determine whether traditional quality indexes of fresh (unfrozen) fish like sensory analysis, bacterial counts and trimethylamine content could be applied to thawed whole cod, cod fillets and ocean perch fillets kept in ice. Freezing and short-term freezer storage (≤5 wk at ?25°C) had very little effect on bacterial counts. During long-term freezer storage (≥14 wk at ?25°C) total counts were reduced as well as counts of trimethylamine oxide-reducing bacteria in cod fillets but not in ocean perch fillets. When the thawed fish was unacceptable the trimethylamine was <1 mgN/100g. Trimethylamine as a spoilage indicator was of no value when evaluating spoilage of thawed whole cod, cod fillets and ocean perch fillets kept in ice.     

Predictive modelling and selection of Time Temperature Integrators for monitoring the shelf life of modified atmosphere packed gilthead seabream fillets

The objective of the present study was to validate a kinetic model for growth of spoilage bacteria in modified atmosphere packed (MAP) gilthead seabream fillets and to select a Time Temperature Integrator (TTI). The temperature and CO₂ dependence of the growth of lactic acid bacteria in MAP gilthead seabream fillets was expressed by an Arrhenius-type model for the range of 0-15 °C and 20-80% CO₂, which was validated at isothermal, variable and chill chain conditions. A new UV activatable photochemical TTI, was kinetically studied and the influence of the level of activation on the response of the TTI was modelled. Applying the developed models, the required charging levels were estimated so that the TTI response was tailored to monitor the shelf life of fish fillets at selected MAP conditions, during the chill chain storage. A simulation experiment of the product distribution and storage in various chill chain conditions showed the applicability of the TTIs as shelf life monitors.     

Shelf life of thawed cod fillets kept in ice

Summary Fillets of cod (Gadus morhua) were vacuum packed, frozen in an air-blast freezer and stored at –28°C. After 1 week, 3, 6 and 12 months, samples were thawed and stored in ice. Fresh fillets from the same batch were taken for reference and iced immediately. Organoleptic tests showed an extension of shelf life for the thawed fish of 2 days (1 week frozen storage) to 3–4 days (3 to 12 months storage) compared to the fresh fillets. The increase of pH, total volatile bases, trimethylamine and volatile acids was significantly retarded in the thawed fish. Relationships of these last three determinations with sensory assessment, however, were poor.

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Haltbarkeit aufgetauter und in Eis gelagerter Kabeljaufilets

Zusammenfassung Kabeljaufilets (Gadus morhua) wurden vakuumverpackt, in einem Luftfroster tiefgefroren und bei –28°C gelagert. Nach 1 Woche bzw. 3, 6 und 12 Monate wurden die Proben aufgetaut und in Eis gelagert.Sensorische Analysen zeigten, daß der aufgetaute Fisch ca. 2 Tage (1 Woche Gefrierlagerung) bis 3–4 Tage (3 bis 12 Monate Lagerung) länger haltbar war als die frischen Filets.Die Erhöhung der pH-Werte, des flüchtigen Basenstickstoffs, des Trimethylamins und der flüchtigen Säuren war in den aufgetauten Filets wesentlich verzögert. Jedoch korrelierten die drei letzten Befunde wenig mit den sensorischen.

     

Brining of cod fillets: effects of phosphate,salt, glucose,ascorbate and starch on yield,sensory quality and consumers liking

In order to study how triphosphate, salt, glucose, ascorbate and starch, both separately and in mixture, could affect the quality and the yield of brined cod fillets, an experimental design was applied. Salt was the variable with highest pronounced effect on yield and appearance, followed by triphosphate, glucose, starch and sodium ascorbate. By treating skinless frozen/thawed cod fillets with brine consisting of 25 g salt/l, 10 g triphosphate/l, 5 g glucose/l, 5 g sodium ascorbate/l and 5 g starch/l in a vacuum tumbler for 15 min, a 35% weight increase was obtained. The products retained a natural appearance with a homogenous surface. Next, an experiment was carried out to assess the effect of this brining mixture on sensory properties and consumers liking of both fresh and frozen/thawed cod fillets. Sensory analyses showed that the intensity of the sensory attributes cod taste, cod smell, juiciness, whiteness and glossiness could be heightened by brining, while the intensities of old/stale taste and smell could be lowered. The effects were prominent for products subjected to freezing before and/or after processing, while the characteristics of the fresh products were little influenced by brining. Using an in-house consumer panel, it was shown that the frozen/thawed products were the less preferred products. However, brining considerably enhanced the preferences for frozen and thawed cod fillets, obtaining preferences similar to the fresh, nonbrined product (F).     

Control of Growth of L. monocytogenes in Fresh Salmon using Microgard and Nisin

Pathogens like Listeria monocytogenes in fresh, or even in cold smoked salmon, have become a major public health concern for the salmon processing industry and government agencies. The effect of bacteriocin solutions (Microgard^™ and Nisin) on reducing total microbial counts, inhibiting Listeria monocytogenes, and prolonging the shelf-life was evaluated. Listeria monocytogenes was inoculated onto chilled and on frozen and thawed salmon samples. The combination of Nisin and Microgard reduced the total aerobic bacteria populations of fresh chilled salmon by 2 log (P<0.05) and increased its shelf-life, at 6 °C, by 3-4 d, as compared with the control. The above bacteriocin combination also reduced the growth of inoculated Listeria monocytogenes in frozen-thawed salmon and increased its shelf-life from 5 to 10 d at 6 °C. The bacteriocin treatment did not affect surface pH values or color of the fish.