Comparison of gilthead sea bream (Sparus aurata) and hake (Merluccius merluccius) muscle proteins during iced and frozen storage

Gilthead sea bream (Sparus aurata) and hake (Merluccius merluccius) muscle behave differently during storage, whether in ice or deep frozen. Rapid changes have been observed in the texture of hake muscle during frozen storage, while gilthead sea bream has proved to be more stable. In order to ascertain the role of muscle proteins in the changes observed during storage, parameters related to protein functionality and the properties of extracted natural actomyosin (NAM) were studied initially and during storage in ice or at ?20 °C. Initially, the parameters related to functionality had higher values in hake muscle and extracted NAM than in gilthead sea bream. At the end of iced storage (22 days), less myosin heavy chain (MHC) and actin were extracted from hake, but there was practically no change in gilthead sea bream. This decrease was not accompanied by lower Ca²⁺‐ATPase activity. Freezing produced no drastic changes, with lower values for gilthead sea bream. However, this species was more stable after 1 year, except for the Ca²⁺‐ATPase activity of NAM. This suggests that the changes that hake proteins underwent during storage particularly affected properties related to aggregation, whereas in gilthead sea bream the changes hardly affected the formation of soluble or insoluble aggregates but did affect the active sites of myosin. © 2002 Society of Chemical Industry     

Effect of storing hake (Merluccius merluccius hubbsi) on ice on the viscosity of the extract of soluble muscle protein

The viscosity of high ionic strength muscle extract of hake decreases during storage of whole fish on ice. Linear correlation was obtained when log of reduced viscosity was plotted against days of storage on ice and also in the plot of reduced viscosity against sensory scores.     

Effects of previous frozen storage on chemical, microbiological and sensory changes during chilled storage of Mediterranean hake (Merluccius merluccius) after thawing

The present work aimed to investigate the influence of freezing (−20 °C for 6 months) on the susceptibility of hake to chemical, microbiological and sensory spoilage once thawed and stored in ice. Thus, volatile and biogenic amines, counts of psychrotrophic and mesophilic bacteria, enterobacteria, pseudomonads and Shewanella together with sensory evaluation (of raw and cooked samples) were monitored during 14 days of iced storage in both fresh and frozen-thawed hake (Merluccius merluccius). At the beginning of ice storage, freshness parameters were equivalent in both batches (fresh and frozen-thawed hake), but different behaviour was observed during the iced storage. Overall, levels of volatile and biogenic amines increased much later and then decreased to lower values in frozen-thawed hake in accordance with the delay of microbial development in comparison with fresh hake. On the contrary, sensory spoilage occurred earlier in frozen-thawed hake. Therefore, the usual accepted or regulated limits of acceptability of chemical and microbiological parameters would not be suitable for freshness assessment of frozen-thawed hake.     

Comparison of the effects of four cooking methods on fatty acid profiles and nutritional composition of red mullet (Mullus barbatus) muscle

This study was performed to examine the effects of different cooking methods (frying, steaming, oven cooking, and microwave cooking) on proximate chemical composition, mineral contents, and fatty acids profiles of red mullet (Mullus barbatus) fillets. The frying process caused a significant increase in fat content (from 13.37±0.04 to 34.44±0.20 g/100 g d.w.) and reduced the proportion of the palmitic acid of 50.73% and saturated fatty acids of 56.9%. While, the proportion of polyunsaturated fatty acids (PUFA) increased from 4.04% of total fatty acids for raw fillet to 49.17% of total fatty acids for fried fillets. The steamed, oven-cooked, and microwave-cooked fillets showed the best proportion of fat content, PUFA, and ω-6/ω-3 ratio as compared with fried red mullet fillets. Na, Mg, and Zn contents of cooked fish fillets significantly decreased.     

Fatty acid profiles of commercially important fish species from the Mediterranean, Aegean and Black Seas

The fat content and fatty acid compositions in the flesh of eight commercially important fish species from the seas of Turkey were evaluated. The fatty acid compositions of wild fish species ranged from 25.5% to 38.7% saturated (SFA), 13.2–27.0% monounsaturated (MUFAs) and 24.8–46.4% polyunsaturated acids (PUFAs). Among them, those occurring in the highest proportions were myristic acid (C14:0, 1.70–10.9%), palmitic acid (C16:0, 15.5–20.5%), palmitoleic acid (C16:1, 2.86–17.0%), stearic acid (C18:0, 3.32–8.18%), oleic acid (C18:1n9 cis, 6.11–20.8%), linoleic acid (C18:2n6, 0.93–4.03%), octadecatetraenoic acid (C18:4n3, 0.02–4.55%), cis-5, 8, 11, 14, 17-eicosapentaenoic acid (EPA, C20:5n3, 4.74–11.7%) and cis-4, 7, 10, 13, 16, 19-docosahexaenoic acid (DHA, C22:6n3, 7.69–36.2%). The proportions of PUFAs-n3 (ranging from 21.7 for mullet to 43.7 for scad) were higher than those of PUFAs-n6 (ranging from 1.24 for bogue to 4.34 for red scorpion fish). EPA and DHA were high in all fish species, increasing the value of these fish species.     

Influences of bioavailability, trophic position, and growth on methylmercury in hakes (Merluccius merluccius) from Northwestern Mediterranean and Northeastern Atlantic

Methylmercury (MeHg) determinations in hake, its food-chain, and the surrounding waters and sediments allowed us to show that the higher length or age normalized mercury concentrations of Northwestern Mediterranean (Gulf of Lions: GoL) muscle hakes compared to its Northeastern Atlantic (Bay of Biscay: BoB) counterpart are due to both biotic and abiotic differences between their ecosystems. Bioenergetic modeling reveals that the slower growth rate of Mediterranean hake favors the MeHg bioaccumulation in the fish muscle and explains most of the difference between GOL and BoB hake populations. In addition, the waters of the Mediterranean hake habitat favor a higher MeHg exposition, due to the upper position of the thermohalocline, where MeHg is formed. Furthermore, we show that, within the Mediterranean hake population, a major increase in the biomagnification power (the slope of the relationships between logMeHg and δ(15)N), from 0.36 up to 1.12, occurs when individuals enter adulthood, resulting from the combined effects of lowering growth rate and change in feeding habits. Finally, δ(15)N normalized Hg concentrations indicate that the highest Hg concentrations are for hake from the shelf edge and the lowest are for hake from the Rh?ne prodelta area, suggesting a lower Hg bioavailability in inshore environments, consistent with MeHg distributions in water, sediment, and preys.     

Gel properties of collagens from skins of cod (Gadus morhua) and hake (Merluccius merluccius) and their modification by the coenhancers magnesium sulphate,glycerol and transglutaminase

The gel properties of two different kinds of fish gelatins prepared from cod (Gadus morhua) and hake (Merluccius merluccius) and modified by the coenhancers glycerol, salt and microbial transglutaminase, were examined. Gel strength was substantially increased by the addition of coenhancers although results varied, depending on the species. In gelatin from hake (M. merluccius) skin, the highest values were obtained with 10 mg/g of transglutaminase, whereas magnesium sulphate was more effective at both concentrations (0.1 and 0.5 M) in gelatin from cod (G. morhua) skin. Although, in both gelatins, the addition of any ingredient increased the viscosity modulus (G″), the elastic modulus (G′) was only increased by the addition of glycerol 15% (w/v) and MgSO₄ 0.5 M in hake (M. merluccius) gelatins; in cod (G. morhua) it was increased by all ingredients. The gelling and melting points, very important properties in fish gelatin, showed a notable improvement, the behaviour being different, depending on the species.     

Study of two different cold restructuring processes using two different qualities of hake (Merluccius capensis) muscle,with addition of microbial transglutaminase

BACKGROUND: Microbial transglutaminase (MTGase) can improve the mechanical and functional properties of restructured fish products without the need of thermal gelation. The present study seeks to determine whether, for different setting times, MTGase activity in restructured hake muscle made with pieces or with homogenised muscle can be affected by the quality of the protein in the raw materials. RESULTS: As regards mechanical properties, samples of both qualities subjected to the two different processes attained a suitable consistency after setting for 24 h at 5 °C. The quality of the protein in the sample is important when pieces are used for restructuring, but not when sample is homogenised. Also, there were strong correlations between residual MTGase activity up to 12 h and mechanical properties and electrophoretic band density. Water binding capacity (WBC) was not significantly altered by MTGase addition. CONCLUSION: The experimental combination of 10 g kg^?1 of MTGase, 15 g kg^?1 of sodium chloride and 7.5 g kg^?1 of sodium caseinate was suitable for the production of minimally processed raw restructured fish products made with two different qualities of fish protein and two different restructuring processes. In the restructured products made with pieces, the protein quality significantly affected final properties, but in finely homogenised product the protein quality was less important. Copyright © 2009 Society of Chemical Industry     

Total lipid content and fatty acid composition of commercially important fish species from the Mediterranean, Mar Grande Sea

The fatty acid (FA) profiles of 11 commercially important fish species from the sea of Southern Italy (Mar Grande Sea) were investigated.The results showed significant differences among the fatty acid profiles of the examined fish (p < 0.05). A relatively high proportion of n − 3 polyunsaturated fatty acids (PUFAs), of which more than 70% were accounted by docoesahexaenoic acid (DHA) and eicoesapentaenoic acid (EPA) in salema, bogue, common two-banded seabream and sand smelt, and lower proportions of oleic acid (C18:1n − 9) and palmitic acid (C16:0) also dominating. The percentages of EPA and DHA were between 5.03-8.61% and 9.85-17.39% of total lipid, respectively.The results showed that the fish examined are a good source of n − 3 PUFAs, resulting in a very favourable n3 - n6 ratio, especially in salema, sand smelt, common two-banded seabream and picarel.     

Polychlorinated biphenyl residues in the golden grey mullet (Liza aurata) from Tunis Bay,Mediterranean sea (Tunisia)

Concentrations of polychlorinated biphenyls (PCBs) were determinated in the muscle tissues of mullets (Liza aurata) caught from two coastal marine areas in Tunis bay, “Raoued” and “Radès”. Twenty congeners were detected in all the fish samples analyzed, among which were 4 congeners recommended by the European Union for assessing pollution and 4 “dioxin-like” congeners. Residue levels of total PCBs ranged from 45 to 194 ng/g wet wt in the mullet from “Radès” and from 43 to 65 ng/g w wt in specimens from “Raoued”. Hexachlorobiphenyls were predominant in fishes caught from both “Raoued” and “Radès” areas, accounting for 43% and 40%, respectively. The individual PCB profiles were dominated by congeners 153 in mullet from “Raoued” and PCB 200 in fishes from “Radès”. The levels of TEQs of “dioxin-like” congeners were 3.4 pg/g w wt for fishes from “Raoued” and 2.5 pg/g w wt for specimens from “Radès”.     

Mercury(II) sorption to two Florida Everglades peats: evidence for strong and weak binding and competition by dissolved organic matter released from the peat

The binding of mercury(II) to two peats from Florida Everglades sites with different rates of mercury methylation was measured at pH 6.0 and 0.01 M ionic strength. The mercury(II) sorption isotherms, measured over a total mercury(II) range of 10(-7.4) to 10(-3.7) M, showed the competition for mercury(II) between the peat and dissolved organic matter released from the peat and the existence of strong and weak binding sites for mercury(II). Binding was portrayed by a model accounting for strong and weak sites on both the peat and the released DOM. The conditional binding constants (for which the ligand concentration was set as the concentration of reduced sulfur in the organic matter as measured by X-ray absorption near-edge structure spectroscopy) determined for the strong sites on the two peats were similar (Kpeat,s = 10(21.8 +/- 0.1) and 10(22.0 +/- 0.1) M-1), but less than those determined for the DOM strong sites (Kdom,s = 10(22.8 +/- 0.1) and 10(23.2 +/- 0.1) M-1), resulting in mercury(II) binding by the DOM at low mercury(II) concentrations. The magnitude of the strong site binding constant is indicative of mercury(II) interaction with organic thiol functional groups. The conditional binding constants determined for the weak peat sites (Kpeat,w = 10(11.5 +/- 0.1) and 10(11.8 +/- 0.1) M-1) and weak DOM sites (Kdom,w = 10(8.7 +/- 3.0) and 10(7.3 +/- 4.5) M-1) were indicative of mercury(II) interaction with carboxyl and phenol functional groups.     

A new pest of dried fish from the Orient, Lardoglyphus angelinae new sp. (Acarina:Acaridae)

Lardoglyphus angelinae new species (Acarina:Acaridae) is described from material found in packaged dried fish (pollack) imported from Hong Kong. The male genitalia are compared for two other species, Lardogyphus konoi (Sasa and Asanuma) and Lardoglyphus zacheri Oudemans. Keys for the adults and hypopi of Lardoglyphus Oudemans are given.