鱼新鲜度对其烤鱼片中晚期糖基化终末产物形成的影响

本文以马面鱼为原料,基于4℃下7 d内挥发性盐基氮的变化判断鱼肉新鲜度,测定生鱼肉及烤鱼片中与晚期糖基化终末产物(Advanced Glycation End-products,AGEs)形成有密切关系的游离氨基酸、核苷酸、乙二醛等的含量变化,探究鱼新鲜度对其烤鱼片中AGEs形成的影响。结果表明:随着鱼肉新鲜度的降低,生鱼肉及烤鱼片中游离氨基酸和核苷酸的含量升高,烤鱼片中总AGEs、羧甲基赖氨酸、荧光性AGEs和戊糖素的含量在总体上均呈上升趋势,至7 d时总AGEs与羧甲基赖氨酸的含量分别达7.24与4.01 μg/g,说明原料鱼肉新鲜度对烤鱼片中AGEs的含量有重要影响;早中期糖基化产物乙二醛的含量在生鱼肉中变化不明显,但在烤鱼片中呈上升趋势,说明烤鱼片的加工过程与糖基化反应存在直接联系。     

Effect of Thermal Treatment on Moisture Transport during Steam Cooking of Skipjack Tuna (Katsuwonas pelamis)

ABSTRACT: Moisture and mass loss were determined during atmospheric steam cooking of skipjack tuna by measurement of muscle moisture content in whole fish and on-line measurement of mass and temperature in fillets. Thermal denaturation temperatures of muscle proteins were measured by differential scanning calorimetry. Muscle moisture content and mass loss were dependent on muscle temperature. Temperature distribution was predicted and mass loss rates were calculated in fillets. A decreasing rate of mass loss was followed by a steady rate period and a resumption of a decreasing rate period. The increased loss of mass during the steady period corresponded to thermal denaturation temperatures of muscle proteins. Changes in mass loss rates resulted from a gradient of muscle changes produced by the temperature gradient created during cooking.     

Using electricity as a tool in quality studies of Atlantic salmon

In order to reveal what role anaerobe muscle activity has on the fillet quality in Atlantic salmon (Salmo salar), 18 rested fish were killed on site and immediately filleted. One fillet was used as control group while the other was electrically exercised using 10 V, 5 Hz pDC for 3 min. Fillet weight and muscle pH was measured before the fillets were wrapped in aluminum foil and stored on ice. After 7 days muscle pH, color, and weight was measured. Texture profile analysis (TPA) was estimated using a 20 mm cylindrical probe compressing either at 40, 60 or 80% into the fillet and the shear force was estimated by slicing standardized muscles samples with a blade. Results show that electrical stimulation forces the muscle to contract and the muscle pH to drop by 0.5 units, leading to higher drip loss and loss of color. Comparing the fillets in pairs (paired t test) strengthens evidence on drip loss and color loss, but revealed also softer texture. Optimum compression rate for detecting differences in salmon muscle is at 60% compression. We conclude that electrical stimulation is a powerful tool for simulating anaerobe muscle activity enabling comparative studies within the same individual, hence isolating the variation amongst individuals and the location of sampling. Furthermore electrical stimulation reduces the need for live animal experimentation in quality studies.     

Texture Properties of Farmed Rainbow Trout (Oncorhynchus mykiss): Effects of Diet,Muscle Fat Content and Time of Storage on Ice

Groups of rainbow trout (Oncorhynchus mykiss) fed diets with low or high fat content were stored on ice for up to 11 days in two separate experiments. After 4, 9 and 11 days storage on ice in the first experiment and after 5, 8 and 11 days in the second experiment the fish were filleted by hand and fillet gaping was evaluated. Texture properties were studied using an Instron compression test. pH was measured in all fillets. In fillets from the second experiment, also fat content and autolytic protease activity were measured. Diet affected fillet fat content and texture properties. Fish fed high fat diet exerted less resistance against compression, indicating a softer consistency. Force at yield point and slope were not significantly affected by diet. The high fat group had higher autolytic protease activity than the low fat group. The results from the Instron measurements indicated that the fish became softer and less tough during 11 days storage on ice. A slight, but statistically significant increase in pH with time was observed in both experiments. In the first experiment a reduction in gaping scores was observed during storage, as opposed to a significant increase in the second experiment. The texture parameters yield point and slope were negatively correlated to gaping in the second experiment.     

The effects on colour, texture and sensory attributes achieved by washing black tilapia flesh with a banana leaf ash solution

Summary The washing of freshwater fish with clarified solutions of banana leaf ash to remove the muddy odour and flavour is common both in Bangladesh and Indian households. However, no scientific study has been done to evaluate its effectiveness. This study was, therefore, done to show the effect of the washing treatments on the following sensory attributes: odour; flavour; colour and texture. The latter two attributes were also measured by instrumental methods. The experimental animal was black tilapia ( Oreochromis mossambicus ), which was filleted and each fillet washed by a clarified solution of banana ash (either originally 5 or 7% ash). Controls were fillets washed in ice-slush only. Those fillets washed in 5% ash for 5 min were the most acceptable for eating, cooked or uncooked. There were highly significant differences ( p  < 0.01) in the L-colour values (lightness values) when treated fillets were compared to untreated fillets. However cooking the fillets reduced the difference, making it not significant. Texture was significantly affected by washing and this was retained in cooked fillets, however this was particularly significant using a 7% solution which gave a softer fillet.     

Relating instrumental texture, determined by variable-blade and Allo-Kramer shear attachments, to sensory analysis of rainbow trout, Oncorhynchus mykiss, fillets

Texture is one of the most important quality attributes of fish fillets, and accurate assessment of variation in this attribute, as affected by storage and handling, is critical in providing consistent quality product. Trout fillets received 4 treatments: 3-d refrigeration (R3), 7-d refrigeration (R7), 3-d refrigeration followed by 30-d frozen storage (R3F30), and 7-d refrigeration followed by 30-d frozen storage (R7F30). Instrumental texture of raw and cooked fillets was determined by 3 approaches: 5-blade Allo-Kramer (AK) and variable-blade (VB) attachment with 12 blades arranged in perpendicular (PER) and parallel (PAR) orientations to muscle fibers. Correlation between instrumental texture and sensory hardness, juiciness, elasticity, fatness, and coarseness was determined. Muscle pH remained constant at 6.54 to 6.64. Raw fillets lost 3.66% of their original weight after 30-d frozen storage. After cooking, weight loss further increased to 15.97%. Moisture content decreased from 69.11 to 65.02%, while fat content remained constant at 10.41%. VBPER detected differences in muscle sample strength (P= 0.0019) and demonstrated effect of shear direction reported as maximum force (g force/g sample). AKPER detected differences in energy of shear (g × mm; P= 0.0001). Fillets that received F30 treatments were less extensible. Cooking increased muscle strength and toughness. Force determined by VBPER was correlated with sensory hardness (r= 0.423, P= 0.0394) and cook loss (r= 0.412, P= 0.0450). VB attachment is accurate, valid, and less destructive in fillet texture analysis. PRACTICAL APPLICATION: A new shearing device was validated with sensory analysis. Settings and parameters obtained could be used to define fillet texture quality associated with muscle fiber orientation.     

Atlantic salmon skin and fillet color changes effected by perimortem handling stress, rigor mortis, and ice storage

ABSTRACT:  The changes in skin and fillet color of anesthetized and exhausted Atlantic salmon were determined immediately after killing, during rigor mortis, and after ice storage for 7 d. Skin color (CIE L *, a *, b *, and related values) was determined by a Minolta Chroma Meter. Roche Salmo Fan™ Lineal and Roche Color Card values were determined by a computer vision method and a sensory panel. Before color assessment, the stress levels of the 2 fish groups were characterized in terms of white muscle parameters (pH, rigor mortis, and core temperature). The results showed that perimortem handling stress initially significantly affected several color parameters of skin and fillets. Significant transient fillet color changes also occurred in the prerigor phase and during the development of rigor mortis. Our results suggested that fillet color was affected by postmortem glycolysis (pH drop, particularly in anesthetized fillets), then by onset and development of rigor mortis. The color change patterns during storage were different for the 2 groups of fish. The computer vision method was considered suitable for automated (online) quality control and grading of salmonid fillets according to color.     

Identification of tetrodotoxin and fish species in a dried dressed fish fillet implicated in food poisoning

There were five victims of neurotoxic food poisoning from a dried dressed fish fillet in Changhua County, Taiwan, in February 2000. The toxicity of the dried dressed fish fillets was 243 mouse units per g according to a tetrodotoxin bioassay. The partially purified toxin was identified as tetrodotoxin and anhydrotetrodotoxin. The sequence of the 376-nucleotide region in the cytochrome b gene of the mitochondrial DNA exhibited the same genotype as that of the toxic puffer fish Lagocephalus lunaris. The same single restriction site for Hinfl was found in the polymerase chain reaction (PCR) products from the dried dressed fish fillet and the muscle of L. lunaris, yielding two DNA fragments of 170 and 206 bp. However, no restriction site for Hinfl was found in the PCR products from other toxic puffer fishes, including Takifugu niphobles, Takifugu oblongus, and Takifugu rubripes. Therefore, the species of the dried dressed fish fillet was identified as L. lunaris and its causative agent was identified as tetrodotoxin.     

Survival of Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella spp. on Catfish Fillets Exposed to Microwave Heating in a Continuous Mode

Microwave (MW) heating using continuous power output with feedback control and a modified ingredient formulation may provide better and consistent cooking of foods. Currently, household units with build-in inverter power supply units are available. These new generation MW ovens provide continuous, adjustable output and cooking, in contrast to the traditional rectifier-based ovens that rely on the on-off mechanism for control. This study attempted to apply a feedback power control (termed as modified or "smart" MW oven) and phosphate treatment to further improve heating uniformity and enhance food quality and safety. Listeria monocytogenes (Lm, 4-strain cocktail), Escherichia coli O157:H7 (Ec, 5-strain cocktail), and Salmonella spp. (Sal, 6-strain cocktail), surface inoculated onto catfish fillets (75 × 100 × 15 mm; weight 110 g), were heated using the modified MW oven to study the inactivation of the pathogens. The sensitivity of these 3 bacteria to MW heating was in the order of Ec (most), Lm, and Sal (least). Greater than 4 to 5 log CFU reductions of Ec, Lm, or Sal counts on catfish fillet surfaces were inactivated within 2 min of 1250 W MW heating, where the fillet surface temperature increased from 10 to 20 °C to 80 to 90 °C. MW heating caused degradation of catfish fillet texture, which was noticeable as early as 10 to 15 s after the heating started, as evidenced by bumping sounds. Bumping can be significantly reduced by soaking fillets in phosphate solution. However, the results may need verification if applied in different MW ovens and/or with foods positioned away the geometric oven center. This study successfully demonstrated the feasibility of applying MW energy to eliminate foodborne pathogens on fish fillets. Practical Application: The results demonstrated in this report with the "smart" microwave oven design may enhance microwaveable food safety and quality, and therefore promote the microwaveable food business.     

Development of lipid oxidation and flesh colour in frozen stored fillets of Norwegian spring-spawning herring (Clupea harengus L.). Effects of treatment with ascorbic acid

Frozen stored fillets from Norwegian spring spawning herring (Clupea harengus L.) become discoloured. Based on the hypothesis that lipid oxidation in the fillets caused discoloration, we designed an experiment where ascorbic acid was added to the water (2 g l⁻¹) in RSW-tanks on board a fishing vessel and/or by spray (20 g l⁻¹) after filleting but before freezing. Treatment with ascorbic acid on board and on the fillet line led to 8- and 17–24-fold increases, respectively, in the ascorbic acid concentration in the herring fillets. Ascorbic acid treatment on the fillet line, but not the treatment on board, protected the herring fillets against oxidation during freezing, an effect that could be detected until 9 weeks of storage at −30 °C. Between 9 and 14 weeks of storage there was a new burst of lipid oxidation where the treatments had no effect. There was a large variation in colour within each fillet and between fillets in the same group. During freezing, the amount of yellow colour increased substantially and the amount of red colour increased in the posterior end of the fillets, causing a visible change in appearance. Thereafter only minor changes occurred until week 10 but, in week 30, the fillets had become less red, causing a less fresh and more grey appearance. Compared to the within fillet and within group variations, there were only minor effects of ascorbic acid treatment on colour. It is suggested that shelf life of frozen herring fillets should be set at between 9 and 14 weeks at −30 °C. Treatment with ascorbic acid will not alleviate the discoloration of frozen herring fillets.     

The Effects of Essential Oils Addition on the Quality of Wild and Farmed Sea Bream (<Emphasis Type="BoldItalic">Sparus aurata</Emphasis>) Stored in Ice

The preservative effect of laurel (Laurus nobilis) and cumin (Cuminum cyminum) essential oils (EOs) on fresh vacuum-packed (VP) wild and farmed sea bream (Sparus aurata) fillets was evaluated during ice storage by microbiological, physicochemical and electrophoretic analyses. In the present study, wild (W) and farmed (F) fillet treatment included the following lots: control vacuum-packaged samples (WV and FV), VP with added EOs (0.5% v/w) of cumin (WVC and FVC), and of laurel (WVL and FVL). Wild and cultured fish were found to differ significantly in their muscle proximate compositions irrespective of fillet treatments with particularly higher fat and carbohydrate contents in farmed sea bream (4.82 and 0.32 g/100 g, respectively, vs. 1.53 and 0.22 g/100 g in wild fish). The treatment of wild and farmed sea bream fillets with laurel or with cumin EOs induced a decrease in bacterial growth by ca. 0.5 to 1 log cfu/g and in lipid oxidation by ca. 40% of TBA value, extending the shelf life of fish fillets by approximately 5 days of ice storage. However, the addition of EOs to VP fillets resulted in a reduced liquid holding capacity (LHC) throughout ice storage suggesting an early proteolysis initiation confirmed by the myofibrillar and sarcoplasmic electrophoretic profiles. Laurel and cumin EOs as natural and efficient antibacterial and antioxidant compounds can be used in conjunction with VP to enhance ice-stored sea bream quality.     

Computer vision-based evaluation of pre- and postrigor changes in size and shape of Atlantic cod (Gadus morhua) and Atlantic salmon (Salmo salar) fillets during rigor mortis and ice storage: effects of perimortem handling stress

The present study describes the possibilities for using computer vision-based methods for the detection and monitoring of transient 2D and 3D changes in the geometry of a given product. The rigor contractions of unstressed and stressed fillets of Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua) were used as a model system. Gradual changes in fillet shape and size (area, length, width, and roundness) were recorded for 7 and 3 d, respectively. Also, changes in fillet area and height (cross-section profiles) were tracked using a laser beam and a 3D digital camera. Another goal was to compare rigor developments of the 2 species of farmed fish, and whether perimortem stress affected the appearance of the fillets. Some significant changes in fillet size and shape were found (length, width, area, roundness, height) between unstressed and stressed fish during the course of rigor mortis as well as after ice storage (postrigor). However, the observed irreversible stress-related changes were small and would hardly mean anything for postrigor fish processors or consumers. The cod were less stressed (as defined by muscle biochemistry) than the salmon after the 2 species had been subjected to similar stress bouts. Consequently, the difference between the rigor courses of unstressed and stressed fish was more extreme in the case of salmon. However, the maximal whole fish rigor strength was judged to be about the same for both species. Moreover, the reductions in fillet area and length, as well as the increases in width, were basically of similar magnitude for both species. In fact, the increases in fillet roundness and cross-section height were larger for the cod. We conclude that the computer vision method can be used effectively for automated monitoring of changes in 2D and 3D shape and size of fish fillets during rigor mortis and ice storage. In addition, it can be used for grading of fillets according to uniformity in size and shape, as well as measurement of fillet yield measured in thickness. The methods are accurate, rapid, nondestructive, and contact-free and can therefore be regarded as suitable for industrial purposes.     

Detection of nematodes in cod (Gadus morhua) fillets by imaging spectroscopy

ABSTRACT:  A promising method for detection of parasites in whitefish fillets has been developed. By use of imaging spectroscopy it is possible to record both spectral and spatial information from an object. In this work it is shown that by applying a white light transmission setup and imaging spectroscopy to cod ( Gadus morhua ) fillets, it is possible to make spectral images containing information to differentiate between fish muscle and parasites. The spectral images are analyzed by discriminant partial least square regression as well as image-filtering techniques. The method identifies parasites on the surface of the fillets as well as embedded parasites. One parasite was detected at 0.8 cm below the fillet surface, which is 2 to 3 mm deeper than what can be found by manual inspection of fish fillets. The method is nonintrusive and should thus be feasible for industrial purposes.     

Low detection efficiency of candling as a commonly recommended inspection method for nematode larvae in the flesh of pelagic fish

The third-stage larvae of the parasitic nematode Anisakis simplex commonly occur in most commercially important fish species from the North Atlantic. In this study, the occurrence and site distribution of Anisakis larvae in various size groups of Norwegian spring spawning herring (Clupea harengus), blue whiting (Micromesistius poutassou), and mackerel (Scomber scombrus) from the Northeast Atlantic was investigated. Although most of the larvae were found in the abdominal cavity, the small proportion lodged in the flesh was sufficient to affect food quality and safety. However, the prevalence of Anisakis larvae in fish fillets varied considerably among the size groups of each species: 15 to 60% in herring, 32 to 77% in mackerel, and 89 to 100% in blue whiting. The commonly recommended nematode detection method in the fish processing industry is candling, i.e., a brief visual inspection on a light table. Comparison of successively more accurate detection methods, i.e., candling, enzymatic degradation, and UV illumination, for fillets of each fish species revealed that only 7 to 10% of the nematode larvae present in the fillets were detected by candling. The candling efficiency was apparently independent of fillet thickness. Thus, candling is not sufficient to detect the majority of the nematodes that are actually present in the fillets of pelagic fish from the Northeast Atlantic. These findings emphasize the importance of adequate deep-freezing of any fresh pelagic fish product, especially if it is intended for consumption in a raw or semiraw state.     

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.     

The connective tissues of fish.

'Gaping' is a phenomenon in which the connective tissues of fish fillets fail to hold the blocks of muscle together. Slits appear across the surface of the muscle which cannot then be mechanically skinned, or, in the case of smoked salmon fillets, sliced.
Seasonal increases in the gaping of salmon fillets coincide with a fall in the postmortem pH of the flesh, occurring in June-July.
Extensive gaping can be caused by fish entering rigor mortis at too high a temperature. In trout, this temperature is considerably higher than in gadoids, suggesting that gaping from high-temperature rigor may in practice be fairly rare in salmonids.
The thermal denaturation temperature ( T _D) of acid-soluble collagen isolated from the turbot farmed in warmed water does not differ significantly from that of the connective tissues of those reared at normal temperatures. This observation is discussed in relation to gaping.     

STRUCTURE AND COLOR CHANGES DUE TO THERMAL TREATMENTS IN DESALTED COD

Cod (Gadus morhua) has a great importance in some European countries, either due to fish production and exportation volume or because of its high consumption. Desalted cod (3.94 ± 0.04% salt content and 73.49 ± 0.06% water content) has a limited shelf-life due to the microbial activity and the autolytic proteolysis affecting product texture. Thermal treatments can be used to preserve the cod, but these can cause changes in color, fish muscle tenderization through protein denaturation and collagen breakdown. In this research, steam blanching (5 min), water blanching (1 min) and microwave heating (5 W/g, 2 min) were applied to desalted cod. The effect of these treatments on color (CIEL*a*b* coordinates), mechanical properties (shear and TPA tests) and microstructure of cod were analyzed. Thermally treated cod were lighter, slightly yellowed and softer. From color data and microstructural observations, heat induced changes in cod were a little smaller than in microwave heated cod.     

Atlantic salmon (Salmo salar,L) as raw material for the smoking industry. II: Effect of different smoking methods on losses of nutrients and on the oxidation of lipids

The changes in total fat content, fatty acid composition, tocopherol, ascorbic acid, pH and oxidation were analysed in Atlantic salmon (Salmo salar, L.) in response to either cold smoking (20 or 30 °C) or electrostatic smoking. Both fresh and frozen fillets were dry-salted before smoking. The fish smoked were the lean ocean-ranched salmon caught off Iceland in June 1998 and farmed Norwegian salmon, slaughtered in either November 1998 or April 1999, differing in fresh fillet fat content from 84 to 169 g·kg⁻¹ wet weight. The fresh material used in smoking significantly affected the smoking loss of nutritive components in the fillets. The leaner the fish the higher percentile loss in fillet fat. Ascorbic acid decreased about 80 percent from the fresh value, independent of smoking temperature (20 or 30 °C). The fish that were dry-salted and electrostatically smoked only lost about 10 percent of the fresh ascorbic acid content, independent of the type of raw material used, indicating a conserving effect on ascorbic acid by the electrostatic process. Also, the electrostatically smoked fish showed a smaller drop in fillet pH than cold-smoked fillets, while tocopherol was little affected by the smoking methods tested.     

Injection-salting of pre rigor fillets of Atlantic salmon (Salmo salar)

ABSTRACT:  The effects of temperature (−1, 4, and 10 °C), brine concentration (12% and 25% NaCl), injection volumes, and needle densities were investigated on fillet weight gain (%), salt content (%), fillet contraction (%), and muscle gaping in pre rigor brine-injected fillets of Atlantic salmon ( Salmo salar ). Increased brine concentration (12% to 25%) significantly increased the initial (< 5 min after injection) and final contraction (24 h after injection) of pre rigor fillets. Increased brine concentration significantly reduced weight gain and increased salt content but had no significant effect on muscle gaping. The temperatures tested did not significantly affect weight gain, fillet contraction, or gaping score. Significant regressions ( P < 0.01) between the injection volume and weight gain (range: 2.5% to 15.5%) and salt content (range: 1.7% to 6.5%) were observed for injections of pre rigor fillets. Double injections significantly increased the weight gain and salt content compared to single injections. Initial fillet contraction measured 30 min after brine injection increased significantly ( P < 0.01) with increasing brine injection volume but no significant difference in the fillet contraction was observed 12 h after brine injection (range: 7.9% to 8.9%). Brine-injected post rigor control fillets obtained higher weight gain, higher salt content, more muscle gaping, and significantly lower fillet contraction compared to the pre rigor injected fillets.
Injection-salting is an applicable technology as a means to obtain satisfactory salt contents and homogenously distribute the salt into the muscle of pre rigor fillets of Atlantic salmon before further processing steps such as drying and smoking.     

预制调理低嘌呤大菱鲆鱼片的制备及品质研究

为满足痛风患者对高蛋白、多不饱和脂肪酸鱼片的需求,研制预制调理低嘌呤鱼片。本研究在单因素研究的基础上优化工艺条件,对鱼片进行浸泡-水煮处理,从而对嘌呤进行有效脱除,制得低嘌呤调理鱼片,并采用高效液相色谱法检测嘌呤含量。结果表明,花椒粉水溶液浸泡鱼片的最佳条件为:浸泡时间为45 min,花椒粉添加量为2%（w/V）,加工方式为水煮,水煮时间为8 min。与新鲜大菱鲆相比,清水对大菱鲆鱼片进行浸泡-水煮处理之后,嘌呤含量减少58.07%;而利用花椒粉对大菱鲆进行浸泡并且水煮处理能够使嘌呤含量减少79.50%,花椒粉浸泡-水煮处理可显著降低大菱鲆中的嘌呤含量,表明浸泡结合水煮处理可用于脱除鱼片中的嘌呤,为预制调理低嘌呤大菱鲆鱼片的制备以及高尿酸人群的健康饮食提供指导意见。