Effect of electrical stunning at slaughter on the quality of farmed turbot (Psetta maxima)

Food quality aspects of farmed turbot (Psetta maxima) were compared following two methods of slaughter: the current commercial method, by immersion in an ice slurry, which is then dewatered after approximately 20 min, or by first humanely, electrically stunning the fish using a prototype commercial stunner, before immersion in an ice slurry, which is dewatered after 20 min. Quality was assessed for up to 10 days of storage on ice following slaughter. No differences were found between the slaughter methods in terms of an overall carcass quality: overall appearance, haemorrhage, damage, burst gall bladder, staining of the body cavity by leakage from the gut or damage to the spine. No detectable difference was found between the treatments using the industry standard freshness scoring system, the Quality Index Method. Both groups of fish were classified as ‘Fresh’ after 10 days of storage on ice. Using objective measurements of colour, no differences between fish from either treatment were found in fillet colour. Changes in flesh pH were similar in electrically stunned and traditionally killed fish with a mean pH (±SE) at 2 h post‐mortem of 6.80±0.027 declining to 6.44±0.032 at 24 h post‐mortem. Humane electrical stunning of turbot at slaughter neither detectably improved nor decreased product quality as measured between 1 and 10 days of storage on ice.     

Electrical stunning of farmed Atlantic cod Gadus morhua L.: a comparison of an industrial and experimental method

An industrial and experimental electrical method for stunning farmed Atlantic cod in air and seawater (SW), respectively, were compared. The impacts of sedation with AQUI‐S^? and exercise to exhaustion before electrical stunning were also assessed to monitor the possible depletion of rested muscle energy levels by electrical stunning. Stress (blood glucose, haematocrit, muscle pH, muscle excitability, high‐energy phosphates and rigor mortis) and flesh quality (fillet texture, colour, liquid leakage (LL), gaping, residual blood and K‐value) were assessed. For the industrial stunning method, an average of 41 V, 0.2 A dc was applied to individual cod for 18–27 s. For the SW method, a bipolar square wave current (170 Hz, 33% duty cycle) was applied for 5 s. After stunning, recovery was prevented by exsanguination in chilled SW. There were no differences (P>0.05) between the two stunning methods except for a higher ultimate fillet pH for cod stunned in air 8 days postmortem. Exercise before stunning depleted muscle energy levels at slaughter, increased LL and fillets had redder and darker flesh after storage on ice for 8 days. Electrical stunning (in air) of AQUI‐S^?‐treated fish partly depleted muscle energy levels (pH 7.3, ATP 18.7 μmol g^?1, PCr 70.1 μmol g^?1). However, flesh quality was not affected. Unless pre‐rigor filleting is the chosen processing strategy, electrical stunning of cod seems to be a promising stunning method.     

不同致死方式对罗非鱼鱼片品质的影响

为了改善鱼肉的品质,文章通过测定样品的挥发性盐基氮（TVB—N）、Ca^2＋-ATP酶活性以及鱼片色泽和质构指标随时间的变化情况分别评价了4种不同致死方式（I．鳃部放血;II．冰激致死;Ⅲ．敲击头部致死;Ⅳ．敲击头部后放血）对罗非鱼（Oreochromissp．）鱼肉品质的影响。结果显示,贮藏期间4个组的TVB—N显著增大,但Ⅱ组和Ⅲ组的TVB—N显著低于I组和Ⅳ组,有利于鱼片冰藏期的保鲜;4个组鱼片的Ca^2＋-ATP酶活性显著下降,Ⅲ和IV2种宰杀方式有利于保持Ca^2＋-ATP酶活性;4个组的亮度（L^＊）、红绿色值（a^＊）和黄蓝色值（b^＊）都随着贮藏时间的延长而增加,I和Ⅳ2种宰杀方法使鱼片L^＊较大而a^＊较小,但4组之间b^＊无显著差异;鱼片的硬度、咀嚼性和胶着性随贮藏时间的延长呈下降的趋势,其中Ⅲ组的质构品质保持得最好。综合以上所有指标,可以认为Ⅲ组最有利于罗非鱼片的保鲜,其次为Ⅱ组。     

Comparison of the effects of six stunning/killing procedures on flesh quality of sea bass (Dicentrarchus labrax,Linnaeus 1758) and evaluation of clove oil anaesthesia followed by chilling on ice/water slurry for potential implementation in aquaculture

The effects of different stunning/killing procedures on flesh quality of European sea bass were investigated: (1) anaesthesia with clove oil, (2) anaesthesia with 2‐phenoxyethanol, (3) percussive stunning, (4) immersion in ice/water slurry, (5) chilling on ice and (6) anaesthesia with clove oil followed by immersion in ice/water slurry. Muscle pH values were significantly lower in sea bass anaesthetized or stunned by a blow to the head compared with fish immersed in ice/water slurry, chilled on ice or immersed in ice/water slurry after clove oil anaesthesia. Lightness was highest in sea bass anaesthetized by 2‐phenoxyethanol or percussively stunned and lowest in ice‐chilled fish. Redness and yellowness were highest in fish chilled on ice and lowest in fish anaesthetized with clove oil. Liquid loss, fat loss and shear values were not significantly different among the procedures. In general, lipid oxidation values during refrigerated or frozen storage did not significantly differ among treatment groups. Combination of clove oil anaesthesia followed by chilling on ice/water slurry appears to improve both flesh quality and welfare of sea bass, although the implementation of further studies is warranted to consolidate this finding.     

Evaluation of electrical stunning of sea bass (Dicentrarchus labrax) in seawater and killing by chilling: welfare aspects, product quality and possibilities for implementation

The objective was to assess neural, behavioural responses and product quality in farmed sea bass (Dicentrarchus labrax) upon electrical stunning in seawater. The electrical sinusoidal 50 Hz or pulse square wave alternating 133 Hz current induced a general epileptiform insult with a current of 3.3±0.2 or 3 A dm^?2, respectively, for 1 s head to tail in seawater. The total duration of the insult was 48±34 and 23±11 s. After stunning, the electro‐cardiogram revealed fibrillation and ceased or showed malfunction. Product quality was assessed in a group electrically stunned, followed by chilling in ice water and the controls were only chilled in ice water. The pH of the fillets was 0.1–0.2 lower (P<0.01) when stunned electrically at days 1, 2, 8 and 10 postmortem, where the colour did not differ. The percentage of sea bass effectively stunned using an electrical sinusoidal or pulse square wave current was above 85% within a confidence level of 95%. A combination of electrical stunning for 10 s, followed by chilling in seawater with ice flakes resulted in the death of all fish. The former method is recommended to be adapted for implementation in practice.     

Change in flesh quality associated with early maturation of Atlantic halibut (Hippoglossus hippoglossus)

To determine the effect of maturation on flesh quality, 20 Atlantic halibut (Hippoglossus hippoglossus) consisting of mature and immature fish of both sexes were killed on site, exsanguinated and stored on ice. After 6 days of storage, the fish was gutted and filleted before colour, texture hardness and shear force were evaluated to determine the effect of maturation. Results show that mature males excreted black mucus from the skin during ice storage, while a greyish mucus was observed from immature fish. Mature fish had approximately 2% lower slaughter yield and 6% lower fillet yield compared with immature fish. The fillets from mature males were significantly harder compared with fillets from immature fish and the muscle structure proved to be stronger as an increased fracturability was observed in mature fish. In colour, fillets from mature fish proved to have a whiter appearance (L^*) than immature fish, while no difference was seen in a^* and b^* values. We conclude that the physiological changes associated with maturation affects the end quality, and may be related to slower growth.     

Slaughtering method and dietary α-tocopheryl acetate supplementation affect rigor mortis and fillet shelf-life of turbot Scophthalmus maximus L.

The effects of dietary α‐tocopheryl acetate supplementation and different slaughtering methods were investigated on the flesh quality of farmed market‐size turbot Scophthalmus maximus (L). Turbot were divided into three groups and fed commercial diets, supplemented with different levels of α‐tocopheryl acetate at the following dietary inclusion levels: 72 (100), 547 (500), 969 (1000) (mg of α‐tocopheryl acetate kg^?1 diet, analytical values with diet codes in brackets). After 5 months, fish (mean weight 1056 ± 19.7 g) from each dietary treatment were sampled, applying three different slaughtering methods: (A) bleeding in ice water; (B) thermal shock, no bleeding; (C) percussion followed by bleeding in ice water. The time course of rigor mortis was evaluated, using pH, rigor index and mechanical compression tests. The results showed that the three parameters corresponded very well. Percussive stunning resulted in higher initial post‐mortem pH (P < 0.01) and a significantly delayed onset of rigor mortis (P < 0.05). Diet significantly affected shelf‐life, with fillets from fish fed diets 500 and 1000 having lower TBARS (thiobarbituric acid reactive substances) numbers from day 2 (P < 0.001) and less colour deterioration from day 7 of storage on ice onwards (P < 0.05). These results suggest that an increase in dietary α‐tocopheryl acetate before slaughter as well as careful selection of the slaughtering method may greatly enhance the flesh quality of market‐size turbot.     

Optimal Conditions for Long-distance Transportation of Live Black Rockfish (Sebastes schlegeli) and Changes in their Characteristics during Transport

Optimal transport conditions for the live black rockfish and changes in their characteristics during long-distance transport were investigated. Oxygen consumption by black rockfish was lowest at 4°C and increased as the water temperature increased up to a maximum at 10°C. At a water temperature of 8°C and 10°C, the plasma glucose concentration of the fish was 36.2 and 38.2 mg/dL, respectively. The mean weight of the fish reduced to approximately 2.8% of initial weight after 16 days of storage at 8°C. The fish did not feed, and the survival rate of fish stored for 16 days at 8°C was 98.4%. The longer the live fish were stored in the container, the quicker the onset of rigor mortis after the slaughter was reached. Compared with fillets from control fish, the chewiness of fillets was somewhat lower (17.3%) after storage of fish for 16 days, but the softness of the fillets was slightly higher (21.6%). From these results, it was suggested that the optimum temperature for long-distance transport of the live fish was 8°C and that the long transport period of live fishes decreased their fillet quality more rapidly after fish death.     

Changes During Chilled Storage of Whole Tilapia and Short-Term Frozen Storage of Tilapia Fillets

This study evaluated the physicochemical changes in Nile tilapia (n = 82, 373.71 ± 61.91 g) refrigerated for up to 92 h and in the frozen fillets. The tilapias were captured with nets, slaughtered by ice and water shock (1:1) in a temperature of approximately 2°C for 30 min, and stored refrigerated at 4°C in polystyrene boxes containing ice. The fish were filleted, and filets were weighed and frozen. The drip loss and protein were determined after 23 days of frozen storage. After 4 h of storage, all fish were in full rigor mortis. The pH of the muscles decreased for up to 45 h of the storage period. The fillets obtained from tilapia stored for more than 72 h lost more weight and protein. Thus, the filleting or processing of tilapia should be done before 72 h of cold storage, since deterioration of the fish starts to occur after this period.     

Is humane slaughter of fish possible for industry?

Abstract The objective was to evaluate industrial and research slaughter methods for Atlantic salmon (Salmo salar), gilt‐head seabream (Sparus auratus) and eel (Anguilla anguilla) with respect to welfare and quality. As a general term of reference, an optimal slaughter method should render fish unconscious until death without avoidable excitement, pain or suffering prior to killing. For Atlantic salmon, commercial slaughter methods (carbon dioxide stunning followed by gill cutting, and gill cutting alone) are not in conformity with the general term of reference, as the fish are not rendered unconscious immediately and possibly experience stress. Evaluation of automated percussive stunning remained unconclusive. More research should enable us to ascertain whether loss of consciousness is instantaneous. Electrical stunning can be humane if applied properly. However, because flesh of electrostunned fish was characterized by occasional bloodspots, optimization of the electrical parameters is required. Prototypes for percussive and electrical stunning of salmon have been recently developed. This implies that humane slaughter of salmon is feasible for industry. For gilt‐head seabream, neither aphyxia in air nor transfer of the fish to an ice slurry were considered to be humane: the methods did not induce immediate brain dysfunction and vigorous attempts to escape occurred. Percussive and electrical stunning can be in conformity with the general term of reference. However, conditions for stunning whole batches of seabream have not been established. Quality of the fish slaughtered by percussive stunning was similar to that obtained by the industrial method, i.e. immersion in an ice slurry. Further work is required to establish optimal stunning conditions and to develop prototypes. For eel, desliming in a salt‐bath followed by evisceration, electrical stunning performed under the conditions prescribed by the German legislation, and live chilling and freezing were not considered to be humane. In contrast, it was established that a 10–20 kg batch of eels in fresh water could be rendered unconscious immediately and until death by applying electricity in combination with nitrogen gas. The conditions used were 0.64 A dm^?2 for 1 s, followed by 0.17 A dm^?2 combined with nitrogen flushing for 5 min. A preliminary assessment of flesh quality suggests that it may be improved by application of the latter method, compared with the salt bath. The results clearly indicated that humane slaughter of eels is possible in practice.     

Fillet shelf-life of Atlantic halibut Hippoglossus hippoglossus L. fed elevated levels of α-tocopheryl acetate

Fish fillet quality may be influenced by the antioxidant level in preslaughter diet. Thus, the effects of dietary α‐tocopheryl acetate supplementation and feeding time on the flesh quality of farmed Atlantic halibut Hippoglossus hippoglossus L. were investigated. Halibut of mean initial weight of 312 ± 12.3 g were divided into two groups and fed commercial diets, supplemented with different levels of α‐tocopheryl acetate at the dietary inclusion levels of 189 and 613 mg kg^?1 diet. Fish were sampled after 6,9,12 and 24 weeks. Over the experimental period, they reached a final mean weight of 1320 ± 108.4 g. Tissue α‐tocopherol of fillet and liver was significantly affected by the levels of α‐tocopheryl acetate given with the diets (P < 0.001). In storage on ice, fillets of fish fed the diets high in α‐tocopheryl acetate exhibited significantly lower (P < 0.001) levels of lipid oxidation. The colour of fillets in all groups deteriorated slightly, but diet did not affect this process. Halibut fed the supplemented diets for longer periods were better protected against lipid oxidation (P < 0.001) and colour deterioration (P < 0.01) than those fed for shorter periods. However, after 9 days of storage, lipid oxidation levels were still extremely low [< 0.6 µg malondialdehyde (MDA) g^?1 fillet], even in fillets of fish fed the low α‐tocopheryl acetate diet for a short period preslaughter. Different slaughtering methods tested at the end of the trial showed that percussive stunning can delay the onset of rigor mortis by 8–12 h compared with bleeding of the fish. These results suggest that halibut fillets have enhanced shelf‐life stability even at low doses of dietary α‐tocopheryl acetate, and that other factors in the antioxidant defence mechanisms of the species might play a major role in the prevention of lipid oxidation.     

Preslaughter Anesthesia with Lippia alba Essential Oil Delays the Spoilage of Chilled Rhamdia quelen

This study evaluated whether anesthesia with essential oil (EO) of Lippia alba (300 mg L^?1 for 4 min) prior to electronarcosis (128 V m^?1 × 300 Hz for 5 s) or hypothermia (ice/water slurry) could delay fish spoilage during chilled storage of whole fish. Silver catfish (Rhamdia quelen) were subjected to two different pre-stunning treatments (water or anesthesia with EO of L. alba) followed by two different stunning procedures (hypothermia or electrical stunning), yielding four groups (n = 32/group): water (control) + hypothermia, water (control) + electrical stunning, EO of L. alba + hypothermia, and EO of L. alba + electrical stunning. After stunning, fish were slaughtered by percussion and stored in ice. Preslaughter anesthesia with the EO of L. alba extended fish shelf life by delaying the loss of freshness (nucleotide degradation), growth of Enterobacteriaceae, and fish deterioration (sensory evaluation). Such preservative effect was most remarkable for fish that were subsequently submitted to electrical stunning, as they had the lowest demerit scores and greatest shelf life in the sensory evaluation. Our results showed that preslaughter anesthesia with EO of L. alba followed by electrical stunning can delay the loss of freshness and extend fish shelf life during chilled storage.     

花鲈冰藏过程中肌原纤维蛋白生化特性与新鲜度变化的相关性

为研究冰藏期间花鲈鱼片的品质及蛋白质生化特性的变化,通过感官评分、pH、质构、色差、硫代巴比妥酸值(TBA值)、挥发性盐基氮(TVB-N)值、菌落总数(TVC)和肌原纤维蛋白含量、巯基、羰基含量的测定及十二烷基硫酸钠—聚丙烯酰胺凝胶电泳(SDS-PAGE)确定了冰藏花鲈鱼片理化指标变化,并对肌原纤维蛋白生化特性与主要的...     

The effects of stress and storage temperature on the colour and texture of pre-rigor filleted farmed cod (Gadus morhua L.)

This experiment deals with the effects of pre‐slaughter stress and storage temperature on muscle pH, fillet contraction, colour and texture in pre‐rigor filleted farmed cod fillets. The fish were either sedated with a low dose of MS‐222 (14.3 mg L^?1) (unstressed groups) or exposed to the air for 3 min (stressed groups) before being submerged in a benzocaine bath (150 g L^?1). The fish were then killed by a blow to the head, their gills cut, filleted and finally stored at either 4 or 20°C. The stressed groups had significantly lower pH values after slaughter (pH=7.0) than the unstressed groups (pH=7.3). This difference was maintained until post rigor for the fish stored at 4°C, but at 20°C it was immediately overshadowed by a decrease in pH caused by temperature‐dependent processes. The length contraction and changes in registered colour values were more pronounced at both the higher temperature and the higher level of pre‐slaughter stress. Again temperature dominated, but significant and consistent effects were registered from stress. No significant effects of stress on texture post rigor were observed. It is concluded that high storage temperature masks the majority of effects caused by pre‐slaughter stress on the measured variables. Stress management protocols, however, are important when the fillets are kept at the common storage temperature of 4°C.     

Stress assessment,quality indicators and shelf life of three aquaculture important marine fish,in relation to harvest practices,water temperature and slaughter method

The objective of this study was to evaluate the effect of harvest practices and slaughter method on stress, quality and shelf life of whole fish (gilthead sea bream, European sea bass and red sea bream) towards the development of a humane slaughter practice. The use of hook and line resulted in significantly lower plasma cortisol and glucose in European sea bass and gilthead sea bream. Water temperature at harvest affected significantly the concentrations of stress indicators (plasma cortisol and glucose), mainly in European sea bass and gilthead sea bream. No significant differences were observed between the harvesting methods, regarding fish appearance, microbial spoilage and sensory scoring and subsequently shelf life. However, significantly lower hardness was recorded in fish harvested using the electric stunner, compared to the fish killed with slurry ice of the same harvesting period. Shelf life ranged between 13–18 days for gilthead seabream, 10–16 days for European sea bass and 10–14 days for red sea bream, depending on harvesting period.     

Effect of the slaughter method on the quality of raw and smoked eels (Anguilla anguilla L.)

Eels (Anguilla anguilla L.) were slaughtered using two procedures. The commercial method consisted of desliming the fish in dry salt followed by evisceration. The alternative method consisted of stunning and killing in water with a combination of electricity and oxygen removal. Eels slaughtered as commercially exhibited aversive reactions and consequently a higher level of muscular activity before death. In raw fillets, differences appeared clearly between the two batches. The alternative slaughter by electricity and gas led to redder, firmer flesh with a higher pH. Myofibrillar proteolysis, lipid oxidation and loss of freshness (as evaluated by K‐value) were reduced. After hot‐smoking, which is a process that greatly modifies the fish flesh properties, differences between batches were less pronounced. However, eels slaughtered by the alternative method were characterized by a higher pH and a redder colour of the dark muscle, a desirable property form a commercial point of view. When assessed by sensory difference tests, appearance seemed to be the only attribute that allowed panellists to discriminate the two batches. Overall, it is concluded that slaughter by electricity and gas improved the quality of raw and smoked eels compared with the commercial method.     

Contribution of Bleeding to Total Handling Stress During Slaughter of Atlantic Salmon

White muscle high-energy phosphate levels showed that the bleeding procedure applied during slaughter of Atlantic salmon (Salmo salar) did not overshadow the total pre-slaughter handling stress. The energy status of the muscle seemed to increase as a result of bleeding and the bleeding per se did not have adverse effects on flesh freshness resulting from excessive handling stress. The time for onset of rigor mortis and rigor strength were clearly related to the initial stress level and the rate of ATP depletion. The onset of rigor in stressed fish occurred about one day earlier compared with rested fish and the stressed fish also became stiffer.     

Preslaughter stress and subsequent effect on flesh quality in farmed cod

The aim of this study was to investigate the effect of prehandling stress on the flesh quality of Atlantic cod (Gadus morhua). In order to stress the animal, water was reduced in the tank before a total of 30 fish were caught five at a time using a dipnet and held for 3 min, causing stress by hypoxia. This fish was compared with a control group (n=30) of fish exposed to anaesthetics directly in the tank. All fish were killed by a percussive blow to the head and exsanguinated and stored on ice before flesh quality was measured. Immediately after death and after ice storage for 3 and 8 days, 10 fish per group were measured for muscle pH, texture, fillet gaping, colour, drip loss and cathepsin D. Handling stress resulted in an initial increased fillet lightness, drip loss and decreased fillet shear force, although these differences did level off during ice storage. Stress caused by handling resulted in earlier onset of rigour mortis as compared with the control group, which reached maximum rigour tensions within 26 and 36 h postmortem respectively. We conclude that handling before harvest results in reduced time before entering rigour. After 8 days of ice storage, no effect of handling stress was seen on the muscle pH, flesh colour, fillet shear force, gaping score, drip loss or cathepsin D activity.     

Interactions between ice storage time, collagen composition, gaping and textural properties in farmed salmon muscle harvested at different times of the year

Atlantic salmon were sampled in June, September and February of the consecutive year and were stored on ice for up to 14 days in order to test the effect of harvest time and subsequent ice storage on meat quality. Texture and gaping frequency were analysed and were related to colour, protein degradation, collagen solubility, collagen types and final pH as well as lipid oxidation in the fillets to test possible interactions between harvest time and quality degradation during storage. In February, the connective tissue contained more soluble collagen and less insoluble collagen, as well as more of both types I and V collagen, than in the samples collected in June. During ice storage, fish became softer with a concomitant increase in the number of fish displaying very high gaping. pH increased during ice storage and fillet colour became lighter and redder, while yellowness changed in the fattier fillets upon ice storage. Ice storage resulted in changes in pepsin-soluble collagen (PSC) depending on harvest time as did both types I and V collagen. The softer the fish, the higher the gaping score and the more insoluble collagen, the less gaping occurred.     

琼胶寡糖及EGCG对冰藏花鲈鱼片新鲜度与蛋白质生化特性的影响

花鲈贮运期间易受微生物与内源酶的联合作用,导致新鲜度及蛋白质生化特性改变,影响其食用价值。因此,采用适当的保鲜方式对花鲈贮运流通过程中的品质变化加以调控,以保证其品质安全显得尤为重要。为探究表没食子儿茶素没食子酸酯(EGCG)及琼胶寡糖(AO)对冰藏花鲈鱼片的保鲜效果,对硬度值、色差及新鲜度指标(硫代巴比妥酸值、K值、挥发性盐基氮、菌落总数、感官评分)进行测定,并对蛋白质生化特性(肌原纤维蛋白含量、二级结构、巯基、羰基含量)进行分析。结果显示,对照组在第16天时感官得分低于8,且菌落总数和K值已分别高达(6.78±0.15) lg(CFU/g)与67.37%±1.75%,不可食用,而EGCG组(EG)、琼胶寡糖组(AO)及复合组的样品仍具有较好的硬度、色泽及新鲜度。贮藏至20 d时对照组的TBA值高达(0.81±0.03) mg/kg,而EG组、AO组及复合组的TBA值在贮藏期间均未出现大幅度增加,且始终低于对照组。另外,贮藏至12 d时对照组的羰基含量已显著高于其他保鲜处理组,对照组在贮藏末期的羰基含量上升至(1.63±0.04)nmol/mg,而EG组、 AO组及复合组的羰基含量仅为(1.14±0.03)、(1.28±0.08)与(0.99±0.09) nmol/mg。贮藏末期复合组的蛋白含量、α螺旋、巯基均高于对照组和单一保鲜组。研究表明,EGCG及琼胶寡糖均能较好地维持鱼片的新鲜度,能显著抑制蛋白质变性与氧化,且二者复合后的保鲜效果优于单一保鲜剂,延长鱼片保质期至20 d以上。该研究为EGCG及琼胶寡糖的保鲜机理提供了理论基础,为开发高效的新型生物保鲜剂提供参考。