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.

     

Shelf life modelling of frozen shrimp at variable temperature conditions

The objective of this study was to investigate the effect of variable storage conditions on shelf life and quality characteristics of frozen shrimp. Colour change measured both instrumentally and visually was modelled by apparent zero order equations and showed high dependence on temperature. TVB-N and TMA values increased with storage time and were modelled with apparent first order equations. Taste and overall acceptability scores of frozen shrimp had high correlation with TVB-N and TMA values. The temperature dependence of quality deterioration was adequately modelled by the Arrhenius equation and activation energy ranged from 118 to 156 kJ/mol for the different indices measured. The developed models were validated in fluctuating time-temperature conditions in order to establish their applicability in the real cold chain.     

预调理冷藏罗非鱼片保藏技术

为提高冷鲜罗非鱼的保藏货架期,文中采用化学保鲜剂对罗非鱼进行宰前减菌化处理,再用生物保鲜剂结合香辛料对鱼片进行预调理,并于冷藏(10℃)条件储藏8 d,期间测定鱼片的菌落总数、挥发性盐基氮、pH值,并进行感官评价。实验结果表明:罗非鱼宰杀前用50 mg/L的稳定态ClO2浸泡10 min可将罗非鱼体表肉菌落总数由8.6×104CFU/g降低至2.4×103CFU/g,减菌率达97.21%;3种生物保鲜剂均可延长鱼片的货架期,其中,0.01%的纳他霉素的保鲜效果较好,鱼片较对照组延长了2～3 d。香辛料预调理不能显著延缓鱼肉的腐败变质,但与生物保鲜剂有一定的协同作用,尤其是在改善鱼肉色泽等感官指标的劣变方面较明显;经香辛料调理后的冷鲜罗非鱼片具有自然、纯正的鱼香味,无鱼腥味,麻辣适中,口感鲜美。     

Effects of chilled storage on quality of vacuum packed meagre fillets

The aim of this study was to experimentally assess several quality indices of meagre Argyrosomus regius (Asso, 1801) fillets packed in air (AP) and vacuum (VP) stored chilled (+4 °C) for up to 13 days. Considering our experimental data on concentration of bacterial counts, shelf-life is estimated at ca. 6 days for AP fillets and an additional 3–5 days for VP meagre fillets. Total volatile basic nitrogen (TVB-N) and trimethylamine (TMA-N) did not reach the regulated limits (25–35 mg/100 g chilled fish). The models implemented in the software Seafood Spoilage and Safety Predictor predicted a relatively shorter shelf-life of 4.8–6.9 days for fish stored in air at +4 °C when compared to AP and VP fillets. Empirical data and the models implemented in the software were used to predict the shelf-life of fillets if packaged under different modified atmospheres (MAP). Chilled, MAP fillets are likely to have a longer shelf-life than AP or VP samples if equilibrium CO₂ concentration is substantially high.     

A new approach to modelling the shelf life of Gilthead seabream (Sparus aurata)

A total of 217 Gilthead seabreams were subdivided in four groups, according to four different storage conditions. All fish were evaluated by both Quality Index Method (QIM) and microbiological analysis, sampling skin, gills and flesh, separately. A QIM score predictive system was set by modelling the growth of microflora of skin, gills and flesh and coupling these predictions to each related partial QIM score (QIM_Skin, QIM_Gills, QIM_Flesh). The expression of QIM score as a function of bacterial behaviour was carried out by the employment of two coefficients. The predicted mean bacterial concentrations corresponding to the QIM score at 14 days were always near to Log 8 CFU g^?1 in the case of ‘S’ (skin) and ‘G’ (gills) series. Moreover, predicted QIM scores were in a good agreement with observed data, reproducing the observed mean time of rejection as well as the bacterial spoilage level (Log 8 CFU g^?1), for all kinds of storage condition.     

冷冻处理的熟制虾肉在保鲜条件下的货架期

以熟制克氏原螯虾(Procambarus clarkia)虾肉为原料,分别进行缓慢冷冻和快速冷冻处理后,于4℃下贮藏,通过感官评价、理化指标和微生物指标的测定,研究冷冻处理的熟制虾肉的货架期和品质。研究发现:快速冷冻处理虾肉的品质优于缓慢冷冻处理,但两者的货架期均为5d,6d为可接受的限值,未经冷冻处理的虾肉货架期为2d。感官评分值与TVB-N,MDA含量和菌落总数均有极显著的负相关,R2均在-0.947以上(P<0.01)。快速冷冻组虾肉在贮藏期间失重率和pH值稳定。TVB-N和菌落总数有望作为评价熟制虾肉品质的化学指标,TVB-N值为30mg/100g和菌落总数为6logcfu/g可作为熟制虾肉可接受的限值。冷冻处理有效的延长了熟制虾肉在4℃贮藏条件的货架期,可作为一种处理手段应用于熟制水产品的保鲜。     

Numerical modelling of temperature fluctuations of chilled and superchilled cod fillets packaged in expanded polystyrene boxes stored on pallets under dynamic temperature conditions

Temperature variations in cod fillets packaged in four levels of EPS boxes stored on pallets under thermal load were studied numerically and experimentally. In the experiment the fillet temperature along with environmental temperature were monitored at 39 positions on the pallets during 9-h dynamic temperature storage between 7 and 23 °C. A three-dimensional time-dependent heat transfer model was developed using the ANSYS FLUENT Computational Fluid Dynamics (CFD) software. The overall mean absolute error of the model was 0.3 °C and the maximum error obtained at a single position over the whole period was 2.4 °C. The model was further developed in order to simulate temperature evolution inside a fully loaded, 12-level pallet under the same dynamic temperature conditions as a four-level pallet studied before. The mean temperature after 9-h thermal load was 1.0 °C lower in the 12-level pallet but the maximum temperature evolution was similar in both pallets. Finally, the model was used to investigate the temperature-maintaining effect of superchilling fish before the thermal load.     

Effect of harvesting stress and storage conditions on protein degradation in fillets of farmed gilthead seabream (Sparus aurata): A differential scanning calorimetry study

A trial was undertaken to evaluate Differential Scanning Calorimetry (DSC) as a fast analytical tool to differentiate gilthead seabream subjected to variable conditions of slaughter stress and post-mortem storage. Fish were subjected to different harvesting stress conditions: profound anaesthesia (PA, low stress) and net crowding (NC, high stress). Fish were slaughtered in an ice-salt water slurry, and subsequently stored on ice (7 days). Additional NC fish were frozen (−20 °C) and subjected to a freeze–thaw cycle. Dorsal muscle was assessed for cathepsins activity, liquid loss and DSC analysis. It is demonstrated that DSC analysis is capable of differentiating fresh, frozen and thawed-re-frozen fish, while liquid loss and cathepsin B activity are good markers to distinguish fresh from frozen fish. Harvesting stress had little effect on myosin and actin enthalpy transitions, as observed by DSC at 49 and 74 °C, respectively, but a lower ΔH actin/myosin ratio was found in PA fish, suggesting that intense exercise prior to slaughter promoted partial denaturation of muscle myosin.     

Vacuum frying process of gilthead sea bream (Sparus aurata) fillets

Vacuum frying was tested as an alternative technique to develop low oil content fried gilthead sea bream fillets. Three oil temperatures for vacuum frying (90, 100, and 110 °C) were considered. For each temperature the times investigated were 1, 2, 3, 4, 5, 6, 8 and 10 min. To compare the effect of vacuum frying to atmospheric frying on the characteristics of gilthead sea bream fillets and frying rate, treatment at 165 °C was considered. The effect of oil temperature and pressure conditions on the drying process and oil absorption of sea bream fillets was investigated. Other product attributes such as shrinkage and colour were analyzed. Atmospheric frying (165 °C) produces a greater decrease in the mass of the fillets than vacuum frying treatment. Compared with atmospheric frying, oil content of vacuum-fried fish fillets was lower. After ten minutes of treatment the values obtained for vacuum frying were 0.14 ± 0.01 g_oil/g_{dry solid}, 0.18 ± 0.02 g_oil/g_{dry solid} and 0.12 ± 0.01 g_oil/g_{dry solid} for 90 °C, 100 °C and 110 °C respectively and 0.27 ± 0.01 g_oil/g_{dry solid} for traditional frying at 165 °C. Atmospheric frying was the treatment that produced the greatest shrinkage in the fillets reaching values of 36.8% with respect to the fresh sample after ten minutes of treatment. For vacuum treatments shrinkage values ranged between 23.7% and 33.0% at 100 °C and 110 °C respectively after 10 min of frying. According to the results, the vacuum treated samples became lighter, less greener and more yellow.

Industrial relevance

Healthy products are a tendency in the international market. Vacuum frying offers some advantages that can include: the preservation of natural colour and flavours of the products due to low temperature and low oxygen content during the process (better than with conventional deep fat frying), and has less adverse effects on oil quality. The use of this technology on fish products can improve the problems of market saturation at the present time for some species like gilthead sea bream (Sparus aurata).     

Use of time-temperature integrators and predictive modelling for shelf life control of chilled fish under dynamic storage conditions

A systematic approach for fish shelf life modelling and Time Temperature Integrator (TTI) selection in order to plan and apply an effective quality monitoring scheme for the fish chill chain was developed. The temperature behaviour of the natural microflora of the Mediterranean fish boque (Boops boops) was studied and growth of the specific spoilage bacteria Pseudomonas spp. and Shewanella putrefaciens was modelled and correlated to organoleptic shelf life. Arrhenius and square root functions were used to model temperature dependence of maximum growth rates. Bacterial growth and shelf life models were validated under dynamic storage conditions with independent variable temperature experiments. The response of several TTIs from similar storage experiments was also modelled. The reliability of the TTI monitoring was cumulatively expressed by the error in the TTI derived effective temperature (Teff) for different variable temperature distributions. Teff was directly translated to shelf life of the fish.     

真空包装羊肉货架期初步研究

研究了真空包装和热缩处理对冷却羊肉货架期的影响,结果表明,真空包装羊肉的货架期可达25d,热缩处理可延长冷却肉的货架期。     

Shelf life of Stracciatella cheese under modified-atmosphere packaging

The aim of this work is to evaluate the shelf life of Stracciatella cheese packaged in a protective atmosphere, using 4 different CO₂:N₂:O₂ gas mixtures [50:50:0 (M1), 95:5:0 (M2), 75:25:0 (M3), and 30:65:5 (M4) vol/vol] and stored at 8°C. Cheese in traditional tubs and under vacuum were used as the controls. Results showed that the modified-atmosphere packaging, in particular M1 and M2, delayed microbial growth of spoilage bacteria, without affecting the dairy microflora, and prolonged the sensorial acceptability limit.     

Chlordane and toxaphene residues following cooking of treated channel catfish fillets

The reduction in residues of chlordane and toxaphene following cooking (frying, baking, and smoking) of fillets obtained from treated Channel catfish (Ictalurus punctatus) was determined. On average, cooking reduced moisture content by 17% and increased fat content by 28 to 274%. Frying reduced chlordane residues by 56 to 86% on a dry basis (db) or 84 to 92% on a percent fat basis (fb) when raw fillets were compared to cooked fillets. Baking and smoking reduced chlordane significantly less (P < 0.05) than frying with reductions in residues of 12% and 9% (db) or 30% and 33% (fb), respectively. Frying reduced toxaphene residues by 40 to 49% (db) or 65 to 77% (fb), while baking and smoking reduced toxaphene by 35% and 24% (db) or 51% and 59% (fb), respectively.     

The storage life of chilled pork packaged under carbon dioxide

Pork cuts of longissimus dorsi muscle with overlaying fat and skin were packed under vacuum in film of low oxygen transmission rate, or under CO₂ in gas impermeable aluminium foil laminate. Cuts were stored at +3 or −1·5°C. Vacuum packaged cuts were grossly spoiled by Brochothrix thermosphacta after 2 weeks' storage at 3°C and after 5 weeks at −1·5°C. Cuts packaged under CO₂ were grossly spoiled by B. thermosphacta after 5·5 weeks' storage at 3°C. Growth of B. thermosphacta was suppressed when CO₂ packaged cuts were stored at −1·5°C. At that temperature, slow growth of enterobacteria was detected after a lag of about 18 weeks. The enterobacteria caused gross spoilage of an increasing proportion of cuts between 18 and 26 weeks. Muscle tissue with pale, soft, exudative (PSE) characteristics tended to lose colour after long storage periods, apparently because of loss of myogglobin with exudate. Until spoilage, the eating qualities of pork appeared little affected by prolonged storage.     

Storage life of chilled Patagonian hake (Merluccius hubbsi)

The storage life of iced Patagonian hake ( Merluccius hubbsi ) was studied. Seasonal changes were investigated by means of organoleptic assessments (raw and cooked), total volatile bases (TVB) and pH.
During summer-time (December to March) the keeping time, from the edibility point of view, for round hake in ice is not more than 9 to 10 days; in the remaining months the storage life under the same conditions is up to 14 to 15 days.
The difference could be due to the biological condition of hake during and after the spawning time (end of spring-beginning of summer), the shallow and temperate waters of the fishing grounds in summer, and the heavy feeding after spawning.
Comparison trials between gutted and ungutted hake in ice, and between ungutted hake in ice and in chilled sea water (CSW) were also performed.
The duration of rigor mortis of whole hake stored in ice, and the feasibility of quality assessment by an electronic device were also studied.     

Microwave assisted air drying of osmotically treated pineapple with variable power programmes

Variable power programmes for microwave assisted air drying of pineapple were studied. The pineapple pieces were pre-treated by osmotic dehydration in a 55° Brix sucrose solution at 40 °C for 90 min. Variable power output programmes were designed and ran with different inlet air temperatures between 30 and 70 °C. Results indicated that the use of variable microwave power combined with low air temperatures can result in a fast drying process without significant charring of pineapple pieces. High microwave powers need to be reduced quickly, faster than the decrease in water content would suggest, to minimize charring. In this study an inlet air temperatures of 70 °C was found to be excessive when combined with microwave energy (5 W/g - after compensating for the moisture loss), resulting in fast temperature increase. Microwave power was found to be most effective in the first hour to 1.5 h of processing. It should then be reduced to 0.1 W/g (initial product weight) in the final stages of drying to avoid charring of the fruit pieces. The best microwave programme tested lead to 20% water content with just 1% losses due to charring, but the results allow to conclude that charring could be completely reduced by switching off microwave energy altogether after 1.5 h and then finish off drying with higher air temperatures. The use of low air temperatures (30-50 °C) is advantageous with microwave energy in the first stages of drying as it limits the peaks of specific energy absorption, but it slows down drying towards the end probably because of a too low point of equilibrium (saturation humidity of air). Microwave energy did not significantly influence the drying process towards the end, although drying rates showed a “memory effect”, that is, drying rates in processes with the same conditions after a given time depended on the conditions up to that point.