Methods of stunning freshwater fish: impact on meat quality and aspects of animal welfare

 Taking into account aspects of meat quality and animal welfare, three methods of stunning fish were compared: a manual technique (blow on the head, stab in the neck), one using electricity and one using CO₂. The following results were obtained using eel (n=72), carp (n=120) and trout (n=54). From the viewpoint of animal welfare, the effects on the fish were judged. Excitation and mucus secretion as well as the time taken for the fish to be anaesthetized were recorded. With manual and electrical stunning, all fish were anaesthetized almost immediately, while using CO₂ it took 3.2 min (trout), 9.2 min (carp) and 109.7 min (eel) on average. After slaughter and after 3 and 8 days of storage on ice, the fish meat quality parameters, i.e. pH value, water-holding capacity and rigor mortis, were measured. CO₂ stunning gave rise to the lowest pH values and water-holding capacities. Rigor mortis in carp and eel advanced the most. Testing of raw and prepared fish was performed by a panel assessing organoleptic properties. In many cases, fish anaesthetized manually were ranked to be better than those in the other groups. Received: 4 June 1996 / Revised version: 5 July 1996     

The Effect of Stunning Methods on Rigor Mortis and Texture Properties of Atlantic Salmon (Salmo Salar)

Shear force and rigor mortis were used to evaluate the post‐mortem changes of muscle texture in Atlantic salmon (Salmo salar). The fish were either stunned with carbon dioxide (CO₂), electricity, or percussion prior to slaughter. The pre‐mortem stress during CO₂ stunning resulted in an earlier onset and resolution of rigor mortis, and accelerated post‐mortem softening of the muscle tissue as compared to the other stunning methods. No significant differences, either in development of rigor mortis or shear force, were seen between fish that were stunned with electricity or by percussion. Consequently electricity can be used for stunning fish prior to slaughter.     

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.     

鲢鱼新鲜度对鱼糜凝胶品质的影响

通过对4 ℃条件下鲢鱼死后10 h感官特性、pH值和僵直指数的变化过程以及鲢鱼死后不同时间鱼肉的挥发性盐基氮（total volatile basic nitrogen,TVB-N）值和Ca2＋-ATP酶活性变化的检测,研究鲢鱼肉新鲜度对鱼糜凝胶品质的影响。结果表明：鲢鱼在死后2～3 h开始进入僵直期,鱼体僵直指数升高,pH值下降;随着鲢鱼死后时间的延长,鱼肉的TVB-N值显著升高,Ca2＋-ATP酶活性显著降低。采用死后不同时间的鲢鱼肉制作的鱼糜凝胶,其凝胶强度、保水性和白度均有显著差异,其中以新鲜鲢鱼为原料制作的鱼糜凝胶的凝胶强度最高,而鱼糜凝胶的保水性和白度在鱼肉的僵直期最差。     

Effect of Vacuum and Modified Atmosphere on Enterobacteriaceae Count Determined in Rainbow Trout (Oncorhynchus Mykiss) and Carp (Cyprinus Carpio) Steaks

The aim of our research was to determine the presence and examine the change in total number of Enterobacteriaceae in trout and carp cuts packed in vacuum and modified atmosphere. To conduct the study, three sample groups of cleaned trout and carp cuts were formed. The first two groups were packaged in modified atmospheres with different gas ratios: 60%CO₂+40%N₂ (I group) and 40%CO₂+60%N₂ (II group), whereas the third group of fish cuts were vacuum packaged. Our results suggest that modified atmosphere packaging of fresh fish with an appropriate percentage of CO₂ might reduce the risk of poisoning people with Enterobacteriaceae.     

The determination of flesh productivity and protein components of some fish species after hot smoking

Chemical changes in pike perch (Sander lucioperca L Kottelat 1997), rainbow trout (Oncorhynchus mykiss WALBAUM 1792) and eel (Anguilla anguilla L 1766) after hot smoking were investigated. Some differences in water, protein, lipid, ash and carbohydrate contents of the fish were established as significant (P < 0.01). The flesh productivity of fresh eel and pike perch was found to be very high. Differences in group averages of total microprotein content of fresh, smoked and stored eel, rainbow trout and pike perch were found to be significant (P < 0.01). Using polyacrylamide gel electrophoretic analysis, 18 protein bands in rainbow trout, 12 bands in pike perch and 14 bands in eel were determined. Most of the bands disappeared after smoking and storage owing to denaturation of the fish proteins. © 2001 Society of Chemical Industry     

The Effect of Stunning Methods and Season on Muscle Texture Hardness in Atlantic Salmon (Salmo salar L.)

Commercially collected records of Atlantic salmon (Salmo salar L.) muscle texture hardness were used to evaluate the effect of slaughter procedures and seasonality on texture quality. A database collected by Marine Harvest® contained flesh hardness records of Atlantic salmon slaughtered at processing plants in Norway from summer 2010 to summer 2011. The fish were slaughtered either by (1) percussion followed by automated bleeding (“Percussive”) or (2) live chilling with exposure to carbon dioxide (CO₂) followed by manual severing gill arches and bleeding (“CO₂”) or (3) live chilling with exposure to CO₂ followed by percussive stunning and at the end automated bleeding (“CO₂·percussive”). Hardness in salmon muscle cutlets was measured in Newtons (N) by Materials Testing Machine Zwick 500N. The hardness in salmon varied significantly over the study period (P < 0.05, mixed effect model) and showed the softest value of 21.2 (± 0.7) Newton (N) in summer 2011 and hardest 24.1 (± 0.2) N in autumn 2010. Slaughter procedures had a significant effect on salmon muscle hardness (P < 0.05, mixed effect model), where percussion followed by automated bleeding resulted in the hardest value (24.0 ± 0.4 N) as compared with CO₂ stunning (21.8 ± 0.2 N) and combination of CO₂ and percussive stunning (23.1 ± 0.15 N). CO₂ is suspected as a causal factor in accelerated postmortem softening of the salmon muscle.     

Water properties and salt uptake in Atlantic salmon fillets as affected by ante-mortem stress,rigor mortis,and brine salting: A low-field H NMR and H/Na MRI study

A low-field (LF) ¹H NMR T₂ relaxation and ²³Na/¹H MRI study was performed on Atlantic salmon to study the effect of ante-mortem handling stress and rigor mortis on muscle water properties and subsequent post-rigor salting. Compared to rested fish, exhausted fish exhibited a more rapid and stronger development of rigor mortis. This resulted in significant differences in post-rigor water-holding capacity and salt uptake. By LF NMR T₂ relaxation analysis significant differences in water distribution according to (1) ante-mortem handling, (2) fillet location, and (3) brine salting were detected. Furthermore, ²³Na MRI revealed differences between the two treatments in fillet salt distribution, where the salt penetration in exhausted fillets was more pronounced. By combining ¹H and ²³Na MR images, the salt diffusion and distribution seemed to be highly affected by the distribution of fat.     

致晕方式对黄羽肉鸡品质的影响

以90日龄的黄羽肉鸡为研究对象,对比二氧化碳(CO2)致晕、电击致晕、不致晕(直接屠宰)3种处理方式对黄羽肉鸡品质的影响.结果表明:CO2致晕组的胴体损伤最小,肌肉僵直进程缩短,沥血量增加,pH值下降速率较快,与其他2组均差异显著(P<0.05);宰后45?min?CO2致晕组的亮度值(L*)、红度值(a*)及黄度值(...     

Effect of Slaughter Method on Postmortem Changes of Grass Carp (Ctenopharyngodon idella) Stored in Icesti

ABSTRACT: The effect of 2 slaughter methods (immersion in ice-water slurry and electrical stunning followed by ice slurry asphyxiation) on the quality of grass carp ( Ctenopharyngodon idella ) stored in ice for 20 d was evaluated using sensory and chemical analysis. Electricity immediately stunned the fish and did not induce blood spots in the flesh. Fish killed by electricity showed a faster initial rate of ATP degradation and entered into rigor mortis earlier, but did not show significant differences in the sensory score when compared with fish killed by immersion in ice-water slurry. Thus, no differences were observed in the shelf life of carps between the 2 slaughter methods evaluated. The limit for acceptability of grass carp stored in ice was around 13 to 16 d. Grass carp accumulated more inosine than hypoxanthine. K, Ki, P , Fr, and H values were highly correlated with storage time and with the TFRU sensory scores in both groups; these could be used to assess the freshness quality of grass carp.     

Adenine Nucleotide Degradation in Modified Atmosphere Chill-stored Fresh Fish

Effects of carbon dioxide modified atmospheres on degradation of adenine nucleotides in chill-stored whitefish (Coregonus clupeafor-mis) and rainbow trout (Salmo gairdneri) were studied. K values were determined during storage up to 26 days. Results indicated CO₂ atmospheres did not alter K values compared to those observed for aerobically held fish. However, both CO₂ atmospheres and potassium sorbate-dipping of fillets caused decreases in hypoxanthine concentrations compared to untreated aerobically held samples.     

The impact of high-temperature, short-time thermal treatment on texture and weight loss of green asparagus

 The kinetics of the degradation of texture and loss of weight of green asparagus heated to between 100 and 130 °C was studied. The texture of the asparagus was evaluated with two types of cells fitted to a universal texturometer: one cell measured resistance to cutting with a wire and the other was a Kramer cell. The two methods enabled distinction between the different thermal treatments, although the Kramer cell gave information about the behaviour of parts of the spear further away from the tip. The thermally induced degradation of the texture and loss of weight followed first-order kinetics. With respect to the texture, the parameters obtained with the wire cell 2.5, 5 and 7.5 cm from the tip were activation energy (E _a)=19, 20 and 23 kcal/mol, respectively, and those obtained with the Kramer cell were E _a=18.3, 20.9 and 24 kcal/mol, depending on the section of asparagus investigated. For loss of weight an E _a of 8.9 kcal/mol was obtained; thus, it is an important quality factor to be taken into account when optimizing the process of canning green asparagus. Received: 7 November 1996     

The impact of high-temperature, short-time thermal treatment on texture and weight loss of green asparagus

 The kinetics of the degradation of texture and loss of weight of green asparagus heated to between 100 and 130 °C was studied. The texture of the asparagus was evaluated with two types of cells fitted to a universal texturometer: one cell measured resistance to cutting with a wire and the other was a Kramer cell. The two methods enabled distinction between the different thermal treatments, although the Kramer cell gave information about the behaviour of parts of the spear further away from the tip. The thermally induced degradation of the texture and loss of weight followed first-order kinetics. With respect to the texture, the parameters obtained with the wire cell 2.5, 5 and 7.5 cm from the tip were activation energy (E _a)=19, 20 and 23 kcal/mol, respectively, and those obtained with the Kramer cell were E _a=18.3, 20.9 and 24 kcal/mol, depending on the section of asparagus investigated. For loss of weight an E _a of 8.9 kcal/mol was obtained; thus, it is an important quality factor to be taken into account when optimizing the process of canning green asparagus. Received: 7 November 1996     

Maltase activity and dough rising ability of baker’s yeasts obtained at different growth conditions during the maturation stage

 The effects of temperature, pH and dissolved oxygen (DO) at the final production stage on the quality of baker’s yeast were studied. It was noted that an increase of temperature above 37 °C worsened dough-rising ability; nevertheless, at the same time, a good value of maltase activity – 26.0 nmol⋅min^-1⋅mg^-1 was found. Dough-rising ability and maltase activity are strongly influenced by pH. The highest maltase activity, 68 nmol⋅min^-1⋅mg^-1, was obtained at pH 6.0, which improves the dough-rising ability to 55 cm³ CO₂. The concentration of DO affects the fermentation activity of the strain Saccharomyces cerevisiae 3: the metabolism became oxido-fermentative at less than 40% DO and maltase activity and dough-rising ability increased up to 43.5 nmol⋅min^-1⋅mg^-1 and 56 cm³, respectively. The results indicate that dough-rising ability and maltase activity increased as the temperature increased, and as the concentration of DO decreased. A direct correlation between maltase activity and dough-rising ability was found. Received: 24 October 1996     

Changes in cell-wall-degrading enzyme activities in stored olives in relation to respiration and ethylene production Influence of exogenous ethylene

 The activity of various enzymes (α-D-galactosidase; β-D-galactosidase; α-L-arabinofuranosidase; α-D-mannosidase, β-D-N-acetylglucosaminidase, cellulase and polygalacturonase) associated with the cell wall during olive storage was assayed in order to establish the behaviour of the enzymes as a function of the ripening stage and in relation to the production of ethylene. The effect of exogenous ethylene (100 mg/l for 24 h) was also evaluated. In addition, gaseous emissions of CO₂ and ethylene during olive storage were monitored. The results obtained indicate that the high initial CO₂ level in the green olive coincides almost exactly in time with the climacteric maxima when the fruit is on the tree. After the rapid decrease in the respiration rate of green olives during storage, the CO₂ production rate increases as the stage of maturity advances. The results also indicate that ethylene is not capable of stimulating the activity or synthesis of enzymes in green olives, but can produce such a stimulation in black olives. Furthermore, during the first day of storage there were very marked decreases in enzyme activities. Small variations in the conditions of aerobiosis in post-harvest ripening were shown to have notable effects on the normal metabolism of the fruits. Received: 29 January 1996 / Revised version: 1 July 1996     

Distribution of microbes in supercritical CO2 extraction of sea buckthorn (Hippopha? rhamnoides) oils

 The distribution of vegetative microbial cells and their spores in a supercritical CO₂ extraction process was studied. The seed and flesh/skin fractions of the press residue of sea buckthorn berries (Hippopha? rhamnoides) from a juice factory were used as raw materials. A pilot-scale extraction plant was operated at 30 MPa at temperatures of 40 and 60°C. The number of yeasts, moulds and bacteria in the pulp/skin fraction, in the extraction residues, in the extracted oils as well as in the water phases separated from the extracted oils was estimated by the spread plate technique. The microbial content of the flesh/skin material was increased in some extractions by the addition of bacterial spores. In general, the extraction process led to a decrease in the bacterial count of the extracted material, whereas no microbial growth was detected in the oils extracted or in the water phases separated from them. Neither yeasts nor moulds were found in any samples after the extraction process. The microbial status of seed oil and flesh/skin oil obtained by industrial-scale CO₂ extraction at 40°C and at 30 MPa before and after gelatine encapsulation remained unchanged. This proves that supercritical CO₂ can be used to manufacture edible oil products free of living micro-organisms and their spores. Received: 14 May 1996     

Influence of smoking parameters on the concentration of polycyclic aromatic hydrocarbons (PAHs) in Danish smoked fish

A new method for the analysis of 25 polycyclic aromatic hydrocarbon (PAH) compounds in fish was developed, validated, and used for the quantification of PAHs in 180 industrially smoked fish products. The method included pressurized liquid extraction, gel-permeation chromatography (Bio-beads S-X3), solid-phase extraction (silica gel), and gas chromatography-mass spectrometry analysis. The sum concentration of 25 PAHs (∑PAH₂₅) was highest in smoked herring (n = 3) and mackerel fillets (n = 13), with an average concentration of 320 and 235 µg kg^?1, respectively. Lowest average ∑PAH₂₅ concentrations were obtained for indirectly smoked trout (26 µg kg^?1). Principal component analysis was used to correlate processing parameters to PAH concentrations and to identify the effects of these parameters. The analysis showed that for salmon hot-smoking conditions lead to higher ΣPAH₂₅ than cold smoking, and for other fish species direct smoking leads to higher ΣPAH₂₅ than indirect smoking. Also, the usage of common alder increases the PAH contamination compared with beech. The effects of smoking time, combustion temperatures, and two types of smoke-generating material on the ∑PAH₂₅ were also tested in a pilot plant study with smoked trout as a model fish. In addition to confirming that increased combustion temperatures and usage of common alder in comparison with beech increased ∑PAH₂₅, it was also revealed that the PAH concentration decreased in the order fish skin ? outer layer of the fish muscle > inner part of the fish muscle.     

Physicochemical,micro-structural,and textural properties of different parts from farmed common carp (Cyprinus carpio)

The fish body of cultured common carp (Cyprinus carpio) was divided into six sections, including the upper back, lower back, jaw, chest, belly, and tail. Differences in the physicochemical, micro-structural, and textural properties of different muscle tissues were investigated. The upper and lower back, with high content of protein, low content of fat, high water-holding capacity, and desirable textural properties, was proven to be the most valuable part of common carp from both a nutritional point-of-view and an organoleptic perspective. This could provide a theoretic basis for the comprehensive utilization of freshwater fish.     

草鱼和鳗鱼内脏发酵鱼露的理化成分比较

以草鱼鱼露和鳗鱼鱼露为研究对象,研究鱼露发酵过程中理化成分(TVB-N、AA-N、pH、NaCl、脂肪、总糖等)含量的变化。在发酵的过程中,pH呈现下降趋势,鳗鱼鱼露略高于草鱼鱼露;AA-N呈先上升后略微下降的趋势,鳗鱼鱼露的含量高于草鱼鱼露;TVB-N呈先增加后趋于平稳的趋势,鳗鱼鱼露的含量略高于草鱼鱼露;NaCl略微有所上升,草鱼鱼露和鳗鱼鱼露相差不大;脂肪含量呈现下降趋势,草鱼鱼露和鳗鱼鱼露相差不大;总糖的含量呈现先上升后下降的趋势,草鱼鱼露的含量高于鳗鱼鱼露。     

Nitrogen stunning of rainbow trout

This study examined the use of nitrogen gas for stunning of Rainbow Trout. It was found that nitrogen could be used as an effective stunning method and that the strong aversive reaction reported for carbon dioxide stunning was not observed. Measurement of ATP, its metabolites and pH were carried out to evaluate the effects of nitrogen stunning on post mortem muscle biochemistry. This treatment was compared to percussive stunning and air asphyxiation. Post mortem ATP levels in nitrogen stunned fish (1.96 ± 0.36 μmol g^?1) were significantly higher than for asphyxiated fish (0.2 ± 0.11 μmol g^?1) but lower than values for percussively stunned fish (5.9 ± 0.89 μmol g^?1). This work indicates that the use of gasses other than carbon dioxide for stunning of fish deserves further study.