Relationship between Muscle pH and Flesh Color of Atlantic Halibut

ABSTRACT:  After 7 d of ice storage, the muscle pH and flesh color (CIE L *, a *, b *) was measured in 118 Atlantic halibut ( Hippoglossus hippoglossus ) slaughtered at different times of the year. All fish originated from the same stock and the fish were farmed under natural and continuous light and slaughtered fed or starved, representing a wide distribution of fish undergoing different stages of growth, maturation, and sizes (1.5 to 5.9 kg). Results show a considerable variation of end pH ranging from 5.7 to 6.8. The color correlated significantly with muscle pH with R  = −0.63, 0.61, and −0.57 for L *, a *, and b *, respectively, while fillet weight and sampling position on the fillet had less influence on color. We conclude that the end pH of the muscle is an important factor for the visual quality of fish, and in particular for Atlantic halibut. Therefore, measures should be taken to avoid high glycogen levels at death, as this will have a large impact on the muscle pH, with negative consequences for flesh color.     

The effects of fish oil-enriched diets on growth,feed conversion and fatty acid content of red hybrid tilapia, Oreochromis sp.

Juvenile, red hybrid tilapia were fed diets containing cod liver oil (0%, 4%, 8%, 12% of total diet) substituted against corn oil. After 10 weeks, no significant differences between treatments were seen in weight gain, specific growth rate, feed conversion ratio, whole body or dorsal muscle (fillet) proximate composition. Gas chromatography revealed significant differences in the total n-3 content and fatty acid profiles of dorsal muscle. The total n-3 content of dorsal muscle increased from 7.6% to 18.6%, total n-6 content fell from 37.5% to 12.9% and docosahexanaenoic acid increased from 5.8–16.1% of total fatty acids, in fish fed 0% and 12% fish oil, respectively. The retention of eicosapentaenoic acid was low in all dietary groups, possibly indicating selective use as a substrate for β-oxidation. The results demonstrate the potential to enhance the total n-3 fatty acids and docosahexaenoic acid in tilapia fillets by increasing dietary fish oil.     

Effect of sexual maturation on thermal stability, viscoelastic properties, and texture of female rainbow trout, Oncorhynchus mykiss, fillets

The nutrient and energy demand of sexual maturation in many fish cultivars causes structural change to key contractile proteins and thereby, affects fillet firmness. Thermal denaturation and viscoelastic properties of white muscle from diploid (2N; fertile) and triploid (3N; sterile) female rainbow trout were investigated at 6 age endpoints from July 2008 through spawning in March 2009. Differential scanning calorimetry showed, in March, that the actin denaturation temperature (T(max,actin)) of 2N females was higher than that observed in 3N females (78.17 versus 77.27 °C). From 35 to 45 °C, viscoelastic measurement revealed that muscle from 2N females and younger fish (July, 16 mo) had greater elasticity (lower tan δ) than muscle from 3N females and older fish (November to March; 20 to 24 mo), respectively. The highest elastic response and the firmest fillets were observed in July. Raw fillets were softer (Allo-Kramer shear; P < 0.05) from September to January (288.77 g/g on average) than those collected in July (475.15 g/g) and March (366.79 g/g). Soft fillets became firmer after cooking except for January samples. Greater cook yield and softer fillets were observed in January compared to December. Lipid accumulation in 3N females may lubricate muscle fibers and protect them from losing functionality during the spawning season for animals on a high plane of nutrition. PRACTICAL APPLICATION: The relationship between fish maturation, measured as egg development, and chemical characteristics of fillets from fertile and sterile fish was evaluated. Thermal denaturation and viscoelastic characterization revealed changes in stability and gelling properties of muscle proteins that were related to changes in fillet texture.     

Influence of different cold storage temperatures during the Rigor mortis phase on fillet contraction and longer-term quality changes of Atlantic cod fillets

Pre rigor produced fillets of Atlantic cod become shorter and more firm than post rigor produced fillets. In pre rigor excised muscle from warm-blooded animals and warm-water adapted fish, cold shortening, extensive contraction during cold storage, is known to occur. The aim of the present work was to study if the extent of fillet shortening in Atlantic cod could be reduced by a slight temperature increase during rigor contraction. The results demonstrate that fillets from this cold-water species showed no cold shortening. On the contrary, the fillets contracted the least when stored at 0 °C during rigor contraction.     

Use of microbial transglutaminase and sodium alginate in the preparation of restructured fish models using cold gelation: Effect of frozen storage

Changes in physicochemical properties of raw-appearing restructured models made from hake (Merluccius capensis) muscle, using cold gelation technology by addition of sodium alginate and microbial transglutaminase (MTGase), were studied during frozen storage at ? 15 °C.Among the more interesting results, addition of MTGase produced more protein aggregation in models processed by muscle homogenization and thus the protein network that formed in the gel was better than in samples with added sodium alginate. All samples presented enhanced changes in mechanical properties such as gel strength in the course of frozen storage. The protein network that formed was better organized as shown by the ultrastructure analysis and by protein aggregation data from the beginning of storage, and as a result Water Binding Capacity was greater in restructured models processed by muscle homogenization. Some of the models studied presented lipid oxidation during frozen storage, slightly more in the ones with MTGase added.Industrial RelevanceThe industrial relevance of the present work is to establish bases for using fish fillet trimmings and minced muscle to prepare restructured products that can be commercialized in a raw state and that could also support frozen storage in order to prolong the self-life in the market. The models studied here are not final products but the base with which to prepare them. One possibility of them is to process this kind of products with technologies normally used in whole fish muscle such as smoked fish fillets, carpaccios or marinated products. In addition, these raw restructured products can be commercialized to be cooked as a normal fresh fish fillet or pieces of fillet in a variety of preparations, and also products that contain a high amount of salt. Samples elaborated by binding larger muscle fragments imitate well the original fibrousness of the muscle so that it could be used to elaborate products similar to hamburgers or others that will be fried in batter.     

The connective tissues of fish

Summary. 'Gaping'is a phenomenon in which slits or holes appear between the muscle blocks, so that in a bad case the fillet falls to pieces and cannot be processed or sold. the gaping in whole fish frozen in rigor mortis, thawed and filleted was shown to be related to the biological condition of the fish, strong healthy fish gaping a great deal, while spent or starving fish did not gape at all. It is postulated that when fish are frozen in rigor mortis the ice growing in the connective tissue weakens it, so that it may break under the rigor mortis contraction. the contraction of spent or starving fish appears to be too weak to break the connective tissue. No gaping was shown by similar fish frozen before rigor mortis. the practical importance of the findings is discussed.     

The texture of Atlantic salmon (Salmo salar) muscle as measured instrumentally using TPA and Warner–Brazler shear test

Muscle texture measurements were performed on Atlantic salmon (Salmo salar) using two different instrumental methods; The Texture Profile Analysis, which is a uniaxial compression test, and the Warner–Brazler shear test. The performances of the two tests were evaluated as to their ability to differentiate between recently killed salmon and salmon stored on ice for up to 24 days. Both tests performed well, but the shear test was slightly more sensitive than the compression test. Further, salmon were either starved or fed for two weeks prior to slaughter. The muscle from fed salmon lost its strength slightly faster than that from starved salmon, but this difference was only detectable during the first two days of chilled storage. The effects of temperature, fish size and degree and mode of deformation on the instrumental test results were studied and were found to be significant. Also, the sample geometry, ie the thickness of the fillet was found to have a very significant effect on the TPA-test results. © 1999 Society of Chemical Industry     

Post-mortem degradation of myosin heavy chain in intact fish muscle: Effects of pH and enzyme inhibitors

Fish muscle is rapidly degraded during post-mortem storage, due to proteolytic enzymes acting probably both on muscle cells and connective tissue. In this work we have developed a model system which may be used to study the enzymatic degradation occurring in intact post-mortem fish muscle. Degradation of myosin heavy chain (MHC) was monitored in muscle with pH adjusted to 6.05, 6.3 and 6.9 and in the presence of the enzyme inhibitors PMSF, EDTA, phenanthroline, pepstatin A, antipain, E-64 and the cysteine proteinase activator dithiothreithol (DTT). After storage, myofibrillar proteins were isolated and MHC-specific antibodies used to study the degradation in the different samples. MHC from muscle with pH 6.05 and 6.3 was degraded, while no severe degradation was observed at pH 6.9. Introduction of enzyme inhibitors into the muscle tissue clearly showed that mainly cysteine and aspartic proteinases are responsible for the in situ MHC degradation. This is supported by the severe breakdown of MHC in the muscle samples containing DTT.     

Freshness assessment of ray fish stored in ice by biochemical,chemical and physical methods

Ray fish were caught, filleted, and stored in ice. Fillets were analysed for 18 days to determine the chemical, biochemical and physical changes and their relation to the muscle eating quality. Trimethylamine (TMA-N), total volatile bases (TVB-N), ATP content and breakdown products, K value, pH, texture, water-holding capacity (WHC) and colour changes were monitored. At the beginning of the study, the ray fish muscle showed a low concentration of ATP and a high value of inosine 5′-monophosphate (IMP). Regarding to the signs of freshness and deterioration, K value presented an exponential increase (r2 = 0.95) with an initial value of 4.7% and a final value of 47.5%. Furthermore, the TBV-N and TMA-N significantly increased (P < 0.05) during the storage in ice. As for the physical analysis whereas the texture changed (P < 0.05); pH and the WHC were not affected (P < 0.05). The overall results of this study indicated that the edible quality of ray fish muscle was maintained during at least 15 days of ice storage.     

Mercury and selenium concentrations in muscle tissue of different species of predatory freshwater fish and correlation between these elements

Concentrations of total mercury and selenium were determined in 49 and 42 muscle tissue samples, respectively, of six species of predatory freshwater fish, dace (Leuciscus leuciscus), pike perch (Sander lucioperca), pike (Esox lucius), European catfish (Silurus glanis), rainbow trout (Oncorhynchus mykiss) and asp (Aspius aspius). Muscle selenium concentration did not correlate with the corresponding total mercury concentration (R ^2?<?0.198) in all examined predatory fish species. There was an inverse correlation between the ratio Se/Hg content and the total mercury content in the muscle tissues of dace, pike perch, pike, European catfish and asp. The muscle tissue of rainbow trout exhibits a linear correlation between the ratio Se/Hg content and the total mercury content. The total mercury concentration of all examined samples did not exceed the hygienic limit for Hg for predatory fish.     

Thawing, Refreezing and Frozen Storage Effects on Muscle Functionality and Sensory Attributes of Frozen Cod (Gadus morhua)

Thawing and re-freezing of cod fillet blocks did not necessarily result in greater deterioration (relative to a ‘once frozen’ control) of cooked fish sensory attributes after 9 months frozen storage at –22°C. Thawed and refrozen fish muscle displayed a faster decline in myofibril protein solubility than once frozen controls and had reduced water-holding capacity but analysis of proton spin-spin relaxation times indicated no change in water location. The decline in protein solubility was not caused by complete protein unfolding. Long thawing times (30 hr) before re-freezing and storage resulted in cooked fish with more gray appearance and more stale flavor. Changes in fish muscle functionality did not enable direct inference of sensory attributes.     

Metals (major,essential to non-essential) composition of the different tissues of three demersal fish species from İskenderun Bay,Turkey

This study was performed to investigate certain major and toxic metal concentrations in different tissues of three demersal fish species (Triglia lucerna, Lophius budegassa, Solea lascaris). Generally, skin and liver exhibited higher metal concentrations than did muscle. Sodium and arsenic concentrations were found at higher levels in muscle tissues than in livers and skin, while zinc and nickel in different organs were classified as follows: skin > liver > muscle tissues. The concentrations of trace metals in fish samples indicated that S. lascaris was more contaminated than were other fish species, followed by L. budegassa and T. lucerna. It may be concluded that consumption of these species from this region is not likely to pose a threat for human health. However, although the concentrations are below the limit values for fish muscles, a potential danger may emerge in the future, depending on domestic waste waters and industrial activities in the region. Therefore, further monitoring programmes should be conducted.     

Effects of brine concentration on shelf-life of hot-smoked tilapia (Oreochromis niloticus) stored at 4 °C

This work evaluated the effect of brine concentration on the shelf-life of hot-smoked tilapia (Oreochromis niloticus) stored at 4 °C. The fish were brined in solutions of 5%, 10%, and 15% NaCl and unsalted fish were used as controls. The fish were then smoked, cooled and stored at 4 °C. Oxidative rancidity measured by the peroxide value (PV), and thiobarbituric acid number (TBA) showed increases with the storage time and also as a result of the increasing salt content in fish muscle. Hot smoked tilapia can be stored safely under refrigerated conditions for over 35 days, and 5% brine was found to be optimal for storage.     

The impact of dietary oil source and frozen storage on the physical,chemical and sensorial quality of fillets from market-size red hybrid tilapia, Oreochromis sp.

Red hybrid tilapia (Oreochromis sp.) were fed one of four diets containing either fish oil, crude palm oil, palm fatty acid distillates or refined palm olein as the only added oil. Post-harvest fillet quality was then evaluated at 1, 10 and 30 weeks of frozen storage. Dietary oil source did not significantly (p > 0.05) influence the liquid holding capacity and texture of fillets but both these parameters were increased by frozen storage. Fillets from fish fed palm oil-based diets exhibited significantly higher oxidative stability during frozen storage, compared to fish fed the fish oil diet. Dietary oil source and frozen storage had little impact on sensory attributes. Unlike fillet proximate composition, fillet fatty acid composition was significantly affected by both diet and frozen storage. Total n-3 polyunsaturated fatty acids decreased significantly in the fillet lipids of all fish after 30 weeks of frozen storage.     

A comparison of selected quality features of the tissue and slaughter yield of wild and cultivated pikeperch<Emphasis Type="Italic"> Sander lucioperca</Emphasis> (L.)

The study focused on the comparison of carcass and fillet yields, fillet color, the content of basic components, and the fatty acid composition of tissue from cultivated and wild pikeperch. There was no variation in yield between carcasses and fillets. The brightness and redness of the color of the fillet surfaces of both types of fish were comparable, although the yellowness, chromaticity and shade of color differed. The tissue of cultivated fish had three times more fat (2.87%) than did that of wild fish; the difference was compensated for by water content. The protein and mineral component contents did not vary significantly. The total levels of saturated and monounsaturated acids in the tissue lipids in 1 g of fat varied. No differences were observed between the total amount of polyunsaturated fatty acids (PUFA), PUFAn-3, PUFAn-6, or in the n-3/n-6 proportion. One consequence of the higher fat content in cultivated pikeperch tissue was that the contents of eicosapentaenoic (EPA; 20:5n-3) and docosahexaenoic (DHA; 22:6n-3) acids per 100 g of fillet were significantly higher than in the tissue of wild pikeperch.     

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.     

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.     

Change in attachment of Salmonella Typhimurium, Yersinia enterocolitica, and Listeria monocytogenes to pork skin and muscle after hot water and lactic acid decontamination

The attachment of Salmonella enterica subsp. enterica serovar Typhimurium, Yersinia enterocolitica, and Listeria monocytogenes to pig skin and muscle tissue decontaminated with 80 °C water or 55 °C, 1% lactic acid for 5 and 15 s was investigated. Attachment properties differed between skin and muscle surfaces. A significantly higher number of firmly attached bacteria was found on the decontaminated skin surface compared to the non-treated skin surface, both on hot water (P < 0.0001) and on lactic acid treated skin (P < 0.001). At the muscle surfaces, no such difference in attachment were shown between hot water treated surfaces and non-treated surfaces. In contrast, for lactic acid decontamination, significantly fewer bacteria attached to the treated muscle surfaces (P < 0.0001). The study did not show significant differences in surface attachment, between Salmonella, Yersinia and Listeria, which indicate that surface and environmental factors may influence attachment more than bacterial properties. A more profound location of attached bacteria at muscle compared to skin was indicated. Confocal laser scanning microscopy studies showed that bacteria located in deep tissue structures of non-decontaminated and decontaminated skin and muscle surfaces. In the latter, bacteria tended to “hide” between the muscle fibres and may be entrapped at those sites. The finding of changed attachment properties at skin after decontamination may play a role in cross- and recontamination, during subsequent meat processing.     

Zinc and copper content in marine fish samples collected from the eastern Mediterranean Sea

Zinc and copper contents in the edible parts (muscle, fillet) of 49 commercially used fish species from the eastern Mediterranean Sea (Izmir Outer Bay, Homa Lagoon/Izmir and Mersin Bay) were determined by differential pulse stripping anodic voltammetry. In the sample preparation step, all frozen fish samples were lyophilized, milled in a ball mill and finally decomposed in an oxygen plasma ashing chamber. Among the three sampling locations, the highest zinc concentration was found in Mediterranean shad (Alosa fallax nilotica) from Izmir Outer Bay with 9.73 mg/kg wet weight and the highest copper content was found in derbio (Trachinotus ovatus) from Homa Lagoon with 1.14 mg/kg wet weight. The accuracy of the concentrations determined in this study was checked by the measurements of certified reference material no. 422 cod muscle from the Commission of the European Communities, Community Bureau of Reference. All zinc and copper concentrations observed in species of the eastern Mediterranean Sea showed that fish from this area are good sources of these essential elements.     

Chemical and biochemical changes of hybrid catfish fillet stored at 4 °C and its gel properties

Chemical and biochemical changes of aquacultured hybrid catfish fillet (Clarias macrocephalus × Clarias gariepinus) and its gel-forming ability as affected by age and sex of fish along with storage time were investigated. Fillets were stored at 4 °C for 0, 3, 6, 9, 12 and 15 days. There was no significant effect of sex and age of fish as well as storage time on fat, moisture and ash contents (P > 0.05). The total protein, water soluble protein, and salt soluble protein contents of the fillets significantly decreased with storage time (P < 0.05). On the other hand, pH, total volatile base nitrogen (TVB-N) and autolytic degradation products (ADP) increased as storage time continued (P < 0.05). Decreases in Ca²⁺-ATPase activity and gel properties were observed as storage time increased. However, there was no significant effect of either sex or age of fish on textural properties of gel (P > 0.05). Hybrid catfish fillet stored at 4 °C should be processed within 6 days.