Effects of slaughtering methods on sensory,chemical and microbiological quality of rainbow trout (<Emphasis Type="Italic">Onchorynchus mykiss</Emphasis>) stored in ice and MAP

The effects of slaughtering methods (percussive stunning and death in ice slurry) on the quality of rainbow trout stored in ice and modified atmosphere packing (MAP) (40% CO₂, 30% N₂ and 30% O₂) were investigated in terms of sensory, chemical and microbiological analysis. Sensory analysis showed that the demerit points of fish slaughtered by percussive stunning were higher than those slaughtered by the ice slurry method, but there were no significant differences in demerit points (P>0.05). In addition, the rate of increase in demerit points in fish in MAP was significantly (P>0.05) higher at 6 and 10 days of storage than that in fish in ice for each slaughter method, which was due to increased drip, the appearance of slime and the odour of the fish in MAP packing. The mean K values of rainbow trout slaughtered by percussive stunning in this study were significantly lower (P<0.05) than those of trout slaughtered according to the ice slurry method. The level of biogenic amines, regardless of the slaughter method, showed a similar trend (P>0.05), but higher concentrations of biogenic amines were found for the ice slurry slaughter method and for fish stored in ice. There were no significant differences (P>0.05) in total viable count of fish stored in ice and MAP, regardless of the different slaughter methods used. However, fish packed in MAP showed reduction in bacterial counts compared to fish held in ice throughout study. The results of this study showed that slaughter by percussive stunning improved the quality of trout compared to the ice slurry method.     

Effect of delayed icing on quality changes of iced rainbow trout (Onchorynchus mykiss)

The effect of delayed icing on quality deterioration of rainbow trout (Onchorynchus mykiss) iced 0, 4 and 8 h after catch was assessed by chemical, microbiological and sensory methods. Total volatile basic nitrogen (TVB-N), free fatty acids (FFA), peroxide value (PV) and thiobarbituric acid (TBA) values increased during the pre-icing duration. Delayed icing led to significant increased (p < 0.05) in total viable counts (TVC) throughout the period of storage. This study showed that sensory analysis of rainbow trout correlated well with microbiological analysis. Results of this study according microbiological and sensory data indicated that the shelf-life of rainbow trout stored in ice immediately after catch was approximately 9–11 days, while delay in icing for 4 and 8 h shortened the shelf-life was around 5–7 and 1–3 days, respectively.     

Microbiological,chemical and sensory assessment of iced whole and filleted aquacultured rainbow trout

The effect of filleting on microbiological, chemical, and sensory properties of aquacultured freshwater trout (Onchorynchus mykiss) stored in ice was studied. Pseudomonads, H₂S-producing bacteria (including Shewanella putrefaciens) and Brochothrix thermosphacta were the dominant bacteria while, Enterobacteriaceae in lower counts were also found in the spoilage microflora of whole ungutted and filleted trout over an 18-day storage period in ice. Bacterial counts of whole ungutted trout were always lower than those obtained for filleted trout samples. Mesophilic counts for filleted and ungutted fish exceeded 7 log cfu/cm² after 10 and 18 days of ice storage, respectively. Of the chemical indicators of spoilage, trimethylamine (TMA) values of ungutted trout increased very slowly whereas for filleted samples higher values were obtained reaching a final value of 4.29 and 6.38 mg N/100 g, respectively (day 18). Total volatile basic nitrogen (TVB-N) values showed no significant increase for whole ungutted trout during storage reaching a value of 20.16 mg N/100 g (day 18) whereas for filleted fish a respective value of 26.06 mg N/100 g was recorded. Thiobarbituric acid (TBA) values of ungutted trout increased very slowly whereas for filleted samples higher values were obtained reaching a final value of 16.21 and 19.41 μg MA/g, respectively (day 18). Of the chemical indices used, none proved useful means of monitoring early freshness for ungutted and filleted trout freshness in ice. Sensory assessment using the EC freshness scale gave a grade E for up to 6 days for the ungutted trout, a grade A for a further 3 days and a grade B for an additional 6 days, after which trout was graded as C (unfit). Acceptability scores for odor, taste and texture of cooked ungutted and filleted trout decreased with time of storage. Results of this study indicated that the shelf-life of whole ungutted and filleted trout stored in ice as determined by sensorial and microbiological data is 15–16 and 10–12 days, respectively.     

Quality Assessment of Farmed Rainbow Trout (Oncorhynchus mykiss) during Chilled Storage

ABSTRACT:  The quality changes of farmed rainbow trout ( Oncorhynchus mykiss ) stored in ice for a period of up to 20 (0, 4, 8, 12, 16, and 20) d were determined by chemical (total volatile basic nitrogen [TVB-N], free fatty acid (FFA), thiobarbituric acid (TBA), peroxide value (PV), heme iron), microbiological (total viable counts, TVC), and sensory methods. The TVB-N level showed fluctuations during storage, indicating that TVB-N could not be a good indicator of rainbow trout quality. The TBA values remained low and were found to fluctuate during storage. The PV values and the release of FFA increased ( P < 0.05), while heme iron content decreased during storage. The total viable counts of rainbow trout increased ( P < 0.05) from the initial value of 4.0 log CFU/g (day 0) to 7.04 log CFU/g (day 20) over the period of storage. This study showed that sensory analysis of rainbow trout correlated well with the microbiological analysis. The results of this study according to microbiological and sensorial data indicated that the shelf life of rainbow trout stored in ice was approximately 9 to 11 d.     

Modified Atmosphere Packaging and UV-C Radiation on Shelf Life of Rainbow Trout (Oncorhynchus Mykiss)

Effects of modified atmosphere packaging (MAP) in combination to UV-C radiation on rainbow trout fillets were examined. The samples were submitted to two treatments: (T1) aerobic package; (T2) MAP+UV-C radiation (80% CO₂/20% N_2; 106.32mJ/cm²) and were analyzed daily for microbiological (mesophilic and psychrotrophic count) and chemical (biogenic amines) parameters. MAP+UV-C radiation (T2) promoted lag phase formation and lower number of colonies in the stationary phase as well as retarded cadaverine production during storage time. MAP+UV-C radiation retard microbial growth and delay chemical changes enhancing the shelf life of rainbow trout fillets by at least twice.     

Comparison of the shelf lifes of map and vacuum packaged hot smoked rainbow trout (Onchoryncus mykiss)

The objective of this study was to determine the differences of microbiological and chemical quality in MAP and VP packages in refrigerated smoked trout fillets. Such information is important in evaluating the safety of these products. Three groups were constituted: group A – packed in 60%Co₂/40% N₂; group B – packed in 50%CO₂/50% N₂ and group C– vacuum packed. The ratio of fillet to package volume was 1/3 chemical analysis and microbiological analysis were done and also instrumental and sensory analysis were used to determined the shelf life. The observed shelf life of smoked trout was found at least 33 days in vacuum package, 47 days in 60% CO₂/40% N₂ gas mixture and 40 days in 50% CO₂/50% N₂ gas mixture according to results of microbiological analysis. The observed shelf life of smoked trout in MAP group A was determined as 14 days more than VP packs according to results of microbiological and sensory analysis in the study.     

Evaluation of the microbiological safety and sensory quality of rainbow trout (Oncorhynchus mykiss) processed by the sous vide method

This work evaluates the microbiological quality and sensorial characteristics of rainbow trout processed by the sous vide method under different time/temperature conditions and stored at 2°C and 10°C.The equivalent heat treatments applied in core were: 3.3 min at 90°C (PV₇₀ in core 331.64), 1.04 min at 90°C (PV₇₀ in core 104.5) and 5.18 min at 70°C (PV₇₀ in core 5.18). The product stored at 2°C or 10°C was periodically evaluated to investigate its sensory quality, microbiological condition and proximate composition. The batches stored at 2°C had lower growth counts of mesophiles and psychrotrophs. Moreover, these counts decreased by increasing the heating temperature and time. Staphylococcus aureus, Bacillus cereus, Clostridium perfringens and Listeria monocytogenes were not found in any of the samples. Neither aerobic nor anaerobic spores were detected in the trout samples processed at 90°C for 3.3 min in core and stored at 2°C after 45 days. A heat treatment of 90°C for 3.3 min in core was the most effective to extend the shelf-life of trout (>45 days).Therefore, it can be concluded that the treatment at 90°C for 3.3 min in core is the most effective to ensure the safety and extend the shelf-life of sous vide trout preserving its sensory characteristics.This study establishes the microbiological quality of sous vide trout and emphasizes the relevance of the microbiological quality of the raw materials, heat treatment and storage temperature to ensure the safety of the product, since this fatty fish is not eviscerated and high counts can be found in the raw fish.     

The impact of strawflower and mistletoe extract on quality properties of rainbow trout fillets

Many plants, including strawflower and mistletoe, contain antioxidants and antimicrobials, which can increase the shelf life of seafood. The main aim of this study was to investigate the effect of mistletoe and strawflower extracts at doses of 0.5% (w/v) on the sensory, chemical and microbiological properties of rainbow trout fillets during 27 days of storage at 2 ± 1 °C. The phenolic compounds in these plants have been studied, but their effects on food quality and storage properties have not been reported. We found that extract of mistletoe did not extend the shelf life of the fillets; however, the strawflower extract show high antimicrobial activity in fish fillets. The shelf life of rainbow trout was 20 days for the control and fish treated with mistletoe extract and 23 days for fish treated with strawflower extract. The antioxidant effect of extracts on fish fillets was weak, whereas strawflower extract had high antimicrobial effect. Peroxide value (PV) and thiobarbituric acid (TBA) values fluctuated during storage periods around main values below 14 meq O₂ kg^?1 and 0.6 MA kg^?1, respectively. Putrescine, cadaverine, spermine, spermidine, serotonin, tyramine and dopamine were main amine, whereas histamine accumulated at low levels (<2 mg per 100 g). Strawflower suppressed biogenic amine accumulation in fish fillets. At the limit of acceptability, total viable count (TVC), Enterobacteriaceae and lactic acid bacteria count remained below 7.6, 6.83 and 8.01 log CFU g^?1, respectively. The results of this study show that ethanol extracts of strawflower improve the shelf life of rainbow trout.     

Effects of ozonation on microbiological,chemical and sensory attributes of vacuum-packaged rainbow trout stored at 4±0.5°C

The effects of ozone in aqueous solution on the shelf life of whole, vacuum-packaged rainbow trout, stored under refrigeration (4±0.5°C) were studied by monitoring the microbiological, chemical and sensory changes for a period of 15 days. Vacuum-packaged non-ozonated trout served as the control sample. Ozonation affected populations of bacteria namely, mesophilic aerobic bacteria, Pseudomonas spp. and H₂S-producing bacteria until day 11 of storage, Brochothrix thermosphacta, lactic acid bacteria and Enterobacteriaceae until day 8 of storage. Trimethylamine (TMA) values of all rainbow trout samples remained low (<3 mg N/100 g) until day 11 of storage, and then increased to 12.2, 8.9 and 4.7 mg N/100 g for the control and the samples ozonated for 60 and 90 min, respectively on day 15 of storage. Total volatile basic nitrogen (TVB-N) values remained relatively constant (20–25 mg N/100 g) until day 11 of storage, but increased to 61.1, 37.6 and 39.4 mg N/100 g flesh for the control and ozonated specimen for 60 and 90 min, respectively on day 15 of storage. Thiobarbituric acid (TBA) values remained relatively constant (1–3 mg MA/kg flesh) until day 12 of storage but increased to 8.4, 6.4 and 3.8 mg MA/kg flesh on day 15 of storage for the control and the ozonated trout for 60 and 90 min, respectively. Sensory evaluation (odor, taste and texture) of cooked rainbow trout showed a very good correlation with bacterial populations. On the basis of both sensory and microbiological data, a shelf life of 10 and 12 days was obtained for ozonated, vacuum-packaged and refrigerated rainbow trout at 60 and 90 min, respectively.     

Investigation of the sensory properties of the flesh of rainbow trout (Oncorhynchus mykiss) fed diets with astaxanthin, shrimp waste meal and red pepper meal

Sensory properties (colour, general appearance and taste) were investigated in rainbow trout, Oncorhynchus mykiss, fed standard diets supplemented with either 60 mg/kg astaxanthin, shrimp waste meal or red pepper meal. The fish were divided into three experimental groups (fed diets supplemented with pigments) and one control group, and fed experimental and control diets for 100 days. After the feeding period, the fish were evaluated for sensory properties. Colour was evaluated using a colour card for salmonids. General appearance and taste were evaluated using hedonic scaling. Significant differences between the fish fed diets with and without pigment supplementation were found. Feeding of rainbow trout with diets supplemented with pigments affected their sensory properties.     

Effect of chitosan coatings enriched with cinnamon oil on the quality of refrigerated rainbow trout

The effects of a chitosan (Ch) coating enriched with cinnamon oil (Ch + C) on quality of rainbow trout (Oncorhynchus mykiss) during refrigerated storage (4 ± 1 °C) were examined over a period of 16 days. A solution of Ch (2%, w/v) and Ch + C (2%, w/v Ch + 1.5%, v/v C) was used for the coating. The control and the coated fish samples were analysed periodically for microbiological (total viable count, psychrotrophic count), chemical (TVB-N, PV, TBA), and sensory (raw and cooked fish) characteristics. The results indicated that the effect of the Ch + C coating on the fish samples was to enable the good quality characteristics to be retained longer and to extend the shelf life during the refrigerated storage.     

Chilled storage of golden gray mullet (Liza aurata)

This study determined quality changes of whole ungutted golden gray mullet (Liza aurata) while stored in ice or in a refrigerator (without ice). Changes in microbiological quality (total viable and psychrophilic counts, lactic acid bacteria and Enterobacteriaceae), chemical quality (pH, total volatile basic nitrogen, trimethylamine, peroxide value, thiobarbituric acid, and free fatty acids), and raw fish sensory attributes were evaluated during 16 days of storage. The sensory attributes of golden gray mullet correlated well with the microbiological analyses (r = 0.92). Based on the overall raw acceptability sensory scores and the microbiological tests, the shelf life of the raw golden gray mullet was 10 days in ice and about 14 days in a refrigerator.     

Influence of salting and gamma irradiation on the shelf-life extension of threadfin bream in ice

Fresh, eviscerated threadfin bream (Nemipterus japonicus) packaged in polyethylene pouches were dipped in 10% (w/w) sodium chloride for 1 h and subjected to gamma irradiation at 0, 1 or 2 kGy at ice temperature. The treated fish were stored under ice. At periodic intervals, quality of the fish was determined by sensory, chemical and microbiological parameters. The unsalted and unirradiated fish was acceptable up to 8 days in comparison to a storage life of 12 and 22 days for the unsalted fish irradiated at 1 and 2 kGy, respectively. Salting prior to irradiation at 0, 1 or 2 kGy gave a shelf life of 9, 14 and 28 days, respectively. Salting gave a firmer texture to the fish and prevented drip formation in the pouches during storage. The results suggested that while irradiation could significantly (P< 0.05) extend the refrigerated shelf life of threadfin bream, salting prior to irradiation could enhance the acceptability of the irradiated fish.     

Freshness assessment of cultured sea bream (Sparus aurata) by chemical,physical and sensory methods

The quality changes of cultured sea bream (Sparus aurata) stored in ice for a period of up to 23 days were determined by K and related values, sensory assessment and texture by texturometer. Sensory schemes, based on the Tasmanian Food Research Unit (TFRU) scheme for raw fish and on the Torry scheme for cooked fish were modified to be appropriate for whole cultured sea bream, according to the trained panellists’ perceptions, during the storage period in ice. The TFRU sensory score of fish showed good agreement with K value and texture results throughout the storage period. The limit for acceptability of cultured sea bream stored in ice was about 17–18 days. Generally, K, K_i and G values had good correlation with the degree of freshness and can be used as freshness indicators.     

Microbiological,chemical and sensory assessment of mussels (<Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis>) stored under modified atmosphere packaging

Wild mussels (Mytilus galloprovincialis), were packaged aerobically under vaccum packaging(VP) and modified atmosphere packaging (MAP (50%/50% CO₂/N₂: M1, 80%/20% CO₂/N₂: M2, 65%/35% CO₂/N₂: M3), and stored at 2 ± 1 °C. Quality evaluation was carried out using microbiological, chemical and sensory analyses. Microbiological results revealed that M2 and M3 delayed microbial growth compared to M1. Of the chemical indices determined, the TVB-N and TMA-N values of M2 remained lower than the proposed acceptability limits of 35 mg N/100 g and 8 mg N/100 g, respectively, up to 8 days of storage. All of the MAP and VP mussel samples exceeded these limits after 12 days of storage. All samples retained desirable sensory characteristics during the first 8 days of storage. Based on microbiological and chemical analyses along with sensory evaluation, M2 and M3 gave a longer shelf-life compared with VP and M1. M2 gas mixture was the most effective for mussel preservation.     

Quality assessment of wild European eel (Anguilla anguilla) stored in ice

The quality assessment of wild European eel (Anguilla anguilla) stored in ice and in boxes without ice (3 ± 1 °C) was investigated by the sensory analysis, levels of nucleotide breakdown products and biogenic amines for up to 19 days. Sensory analysis was assessed using the Tasmanian Food Research Unit Scheme. K and related values (K_i, G, P, H and F_r) were used as freshness indicators. Linear regressions (r²) obtained from K, K_i, G, P, H and F_r were 0.95, 0.96, 0.83, 0.96, 0.99 and 0.96, respectively, for eel stored in ice whereas, for eel kept in boxes without ice, the values were 0.86, 0.86, 0.96, 0.91, 0.98 and 0.86, respectively. When eel stored in ice and in boxes without ice were considered at the limit of acceptability by assessors at ∼12–14 days and ∼5–7 days, respectively, the average K, K_i and P values were ∼70–85%, H values were ∼60% and F_r values were ∼10% for both storage conditions. The level of histamine exceeded the legal limit (5 mg/100 g fish) in eel stored without ice after 6–7 days and, in ice, after 13–14 days of storage, at which time eels were rejected by the sensory panel. The concentrations of biogenic amines were higher in eel stored in boxes without ice than in eel kept in ice. The levels of histamine in the muscle of eel kept in boxes without ice and in ice increased to the maximum levels of 17.9 mg/100 g on day 12 and 12.6 mg/100 g on day 19, respectively.     

Application of superchilling to prolong the keeping time of rainbow trout

The paper deals with refrigeration at peri-cryoscopic temperatures as a measure to preserve rainbow trout. Effects of superchilling and storage at -2 °C on sensory, physico-chemical, and microbiological changes in the fish are analysed.     

Quality assessment of whole and gutted sardines (Sardina pilchardus) stored in ice

The quality and shelf life of whole ungutted and gutted sardines ( Sardina pilchardus ) stored in ice were studied. The changes in the fish were investigated by sensory assessments, chemical analyses and microbiological analyses. The sensory scores of uneviscerated and gutted sardines stored in ice at +4 °C were 7 days. The chemical indicators of spoilage, total volatile basic nitrogen and trimethylamine values of gutted sardine increased very slowly, whereas for whole ungutted samples higher values were obtained reaching a final value of 15.03–29.23 mg per 100 g and 2.36–4.16 mg per 100 g, respectively (day 9). Peroxide and thiobarbituric acid values remained lower for whole ungutted sardine samples until day 9 of storage, whereas for gutted fish were higher. The level of histamine exceeded the legal limit in whole ungutted sardine after 7 days of storage in ice, during which sardines were rejected by the sensory panel. Mesophilic aerobic bacteria count, H₂S-producing bacteria, sulphide reducing anaerobe Clostridias, Enterobacteriaceae count of whole ungutted sardine samples are higher than gutted sardine samples during the storage. Psychrotrophic bacteria counts of the two groups were not different. The limits of microbiological data were not exceeded throughout the storage in both the groups' samples.     

The effects of soluble gas stabilisation on the quality of packed sardine fillets (Sardina pilchardus) stored in air,VP and MAP

Sardine (Sardina pilchardus) is a species that for its abundance assumes great importance in the Portuguese fishing sector. In order to contribute for a better utilisation of this species, the aim of this study was to investigate the effect of the pre‐treatment with soluble gas stabilisation (SGS) (100% CO₂ at 2 bar, during 15 and 30 min) on the quality and shelf‐life of sardine fillets, packed in air (AP), vacuum (VP) and modified atmosphere (MAP: 5% O₂/35% CO₂/60% N₂). During the chilled storage, the quality changes were evaluated by sensory evaluation, chemical and microbiological analysis. The total volatile basic nitrogen content remained almost constant, between 16 and 19 mg N/100 g muscle, during the storage period, for all samples. The TBARs values increased with storage time, for all batches and storage conditions. The application of SGS treatment to sardine fillets, resulted in a bacteriostatic effect, contributing to the improvement of the microbiological quality of fillets. Considering a sensory criteria, the shelf‐life of SGS pre‐treated sardine fillets was found to be 5 days in AP and MAP while in VP‐treated fillets a shelf‐life of 8 days was reported. At sensory rejection, sardine fillets presented a K‐value of 30% in AP and MAP batches and 40% in VP batch.     

Biochemical,sensory and microbiological attributes of wild turbot (Scophthalmus maximus), from the Black Sea,during chilled storage

Freshness of wild turbot (Scophtalmus maximus) stored in ice was assessed by chemical, sensory and microbiological methods. The limit for sensory acceptability of wild turbot stored in ice was ∼12–15 days. The quality of turbot decreased on day 15 (B) and they were no longer acceptable on day 19 (C). The TVB-N level showed fluctuations during storage, indicating that TVB-N could not be a good indicator of turbot quality. The release of FFA increased from an initial value of 6.33 (expressed as % of oleic acid) to a final value of 20.6 during the storage period. The initial PV value was 5.60 meq/kg for turbot stored in ice and it started to increase to 21.6 meq/kg on day 12 and then started to decrease to 13.6 meq/kg at the end of storage period. The level of TMA in wild turbot increased sharply from an initial value of 9.36 mg/kg to a final value of 38.9 mg/kg. Linear regressions (r²) obtained from K, K_i, G, P, H and F_r were 0.92, 0.89, 0.99, 0.89, 0.96 and 0.89, respectively, for the wild turbot stored in ice. Turbot maintained high (E) and good quality (A) during the first 12 days of chilled storage when the average K, K_i and P values were ∼78–85%, and H, F_r and G values were ∼45%, 15% and 149%, respectively. Eight biogenic amines were investigated, namely, histamine, putrescine, cadaverine, spermidine, spermine, tryptamine, tyramine, and 2-phenylethylamine, three amines (histamine, tyramine, and tryptamine) were not detected in any of the fish samples during the storage period. As storage time progressed, putrescine and cadaverine became the dominant amines, reaching 22.7, and 16.9 mg/kg, respectively, at 19 days of storage in ice. Total viable counts of whole gutted turbot increased from the initial value of 3.3 log cfu g⁻¹ (day 0) to 7.87 log cfu g⁻¹ (day 19) over the period of storage. If 10⁶ microorganisms/g are considered to be the TVC limit of acceptability, the shelf life of turbot was approximately ∼13–14 days.