Mercedes Careche

Estimation of freezing storage time and quality changes in hake (Merluccius merluccius, L.) by low field NMR.

The potential of low field NMR (LF NMR) as a fast monitoring technique to estimate the quality of hake (Merluccius merluccius) frozen stored at -10°C for up to 6months was evaluated. LF NMR clearly detected three populations of water: water strongly bound to macromolecules (T(2b)), trapped water (T(21)) and free water (T(22)). As storage time increased, and concomitant with an increase in the T(22) and a decrease in the T(21) water populations, the water holding capacity (WHC) and apparent viscosity values decreased and the shear strength increased, reflecting the characteristic loss of juiciness and tougher texture developed by hake during frozen storage. Two mathematical models were constructed: a simple regression using the biexponential analysis of the relaxation times (T(21), T(22)) and amplitudes (A(21), A(22)) and a partial least square regression (PLS) of CONTIN analysis. Both models seemed suitable to estimate the quality of the product.

The effect of neutral and oxidized lipids on functionality in hake (Merluccius merluccius L.): A dimethylamine- and formaldehyde-forming species during frozen storage

Abstract The effect of added cod liver oil and oxidized cod liver oil on protein solubility, apparent viscosity and emulsifying capacity was measured during frozen storage of vacuum packed minced hake ( Merluccius merluccius L.), a species which forms dimethylamine (DMA) and formaldehyde (FA) during frozen storage. The results indicate that the samples with oxidized lipids added showed the best functionality during storage and the untreated control produced the worst. The DMA content was found to be inversely related to the degree of oxidation of lipids as measured by the TBA index, suggesting that the apparent protective effect of unoxidized and oxidized cod liver oil on protein functionality is due to a lower rate of FA and DMA formation. Electrophoretic studies indicated that differences existed in the types of interactions responsible for aggregation in the different treatments.

Low field nuclear magnetic resonance (LF-NMR) relaxometry in hake (Merluccius merluccius, L.) muscle after different freezing and storage conditions.

Low field NMR T2 transverse relaxation measurements were performed on muscle samples from sixty hake (Merluccius merluccius, L.). Fish fillets from hake stored in ice for 3 and 14 days were subjected to different freezing methods (air blast, liquid nitrogen or walk-in freezer) and storage conditions (-20 and -10°C for 5 days, 8 and 18 weeks). Distribution analysis of T2 data of unfrozen muscle displayed a major band (T21), accounting for 90-92% of the total signal, with a relaxation time centred at 47-60 ms and a broad band with protons of higher mobility between 300 and 800 ms, accounting for 3-5% of the signal. Upon freezing, T21 became wider and an extra band appeared within the range 120-360 ms. Whereas no changes were detected at -20°C, the T21 time constant decreased during frozen storage at -10°C in a similar way for all three freezing methods. The relative abundance of T21 declined with storage time but differences were found as a function of freezing. Results are discussed in the light of morphological alterations and protein denaturation, and it is concluded that LF NMR relaxometry is sensitive to different freezing and frozen storage conditions which can have important implications for the quality of fish muscle.

Vibrational spectroscopic analysis of hake (Merluccius merluccius L.) lipids during frozen storage

Vibrational spectroscopy (mid FTIR and FT-Raman) was used to monitor lipids extracted from hake fillets during frozen storage. Kramer shear resistance was used as a marker of texture changes and lipid damage was also investigated by following the development of conjugated dienes and free fatty acids by spectrophotometric methods. Results show that the intensity of the free fatty acid carboxylic ν(CO) band measured by ATR-FTIR spectroscopy can be used for monitoring the development of lipid hydrolysis in hake lipids. Changes in the Raman ν(CC) stretching region (1658cm(-1) band), partially attributed to conjugated dienes development, were the only observed spectroscopic alterations related to lipid oxidation of hake lipids during frozen storage at -10°C. The high correlation of free fatty acids with instrumental texture and the disappearance of the νas(PO2(-)) band are consistent with membrane lipid hydrolysis being one of the factors directly related with toughening of lean fish flesh.

Anchovy shelf life as affected by different chilling methods during distribution.

Anchovies are a very labile fish and deteriorate fast under chilling conditions. In the South of Spain, fishing boats land their catches in wooden boxes with ice (12 to 14 kg). For some years now, fish processors have prepared this species for market distribution by placing about 7 kg fish in expanded polystyrene (EPS) boxes containing water and ice. Then, in the distribution market, boxes are dewatered and re-iced. Transportation of the fish in EPS boxes containing water and ice was recently forbidden on the grounds that boxes for transportation of fish in ice must have holes to let melted ice drain away. In this paper, the effect of preserving the anchovy in water and ice from landing to the distribution market was studied and compared with the more traditional methods of storing the fish in ice in either wooden or EPS boxes. Physical, chemical, microbiological, and sensory analyses were carried out over three different storage trials to account for the effect of seasonality. Little differences were found among lots, but some of the parameters showed that fish transported in water and ice did present less spoilage than fish stored in ice, especially when compared to the wooden boxes. According to these results, chilling of this fish in water and ice can be used as an alternative preserving method during transport.

Effect of neutral and oxidized lipids on protein functionality in megrim (Lepidorhombus whiffiagonis W.) and sardine (Sardina pilchardus R.) during frozen storage

The effect of added cod liver oil and oxidized cod liver oil on protein solubility, apparent viscosity and emulsifying capacity was measured during frozen storage (−18°C) of vacuum packed minced muscle of two non-dimethylamine (DMA)-forming species, megrim (Lepidorhombus whiffiagonis W) and sardine (Sardinia pilchardus R.). The aim was to establish the role of both unoxidized and oxidized lipids in protein functionality in the absence of interference due to the effect of formaldehyde on the proteins. The results showed that, with the addition of cod-liver oil (CLO), the three protein functional properties were equal to, or slightly lower than, the untreated controls in both species. Samples with oxidized cod-liver oil (OCLO) added showed lower protein solubility and viscosity, whereas the emulsifying capacity values were higher than in the controls. Hence, in non-DMA-producing fish species, no protective effect on fish protein can be attributed to neutral lipids.

Role of formaldehyde in formation of natural actomyosin aggregates in hake during frozen storage

ZusammenfassungWährend der Lagerung gewisser Magerfische in gefrorenem Zustand bildet sich Formaldehyd (FA), was die Bildung von Aggregaten myofibrilärer Proteine verursacht. Diese Aggregate wurden im Modell mit Actomyosin (NAM) (5 mg/mL) und wachsenden Formaldehydkonzentrationen untersucht. Die Muster wurden zwei Monate in gefrorenem Zustand bei -20 °C gelagert. Während dieses Zeitraums wurden die Löslichkeit in 0,6 M NaCl, die Ca2+ATPase-Aktivität, die cis-Parinarsäure-(CPA)-Hydrophobie und SH-Gruppen gemessen sowie SDS-Polyacrylamid-Gel Elektrophoresen (PAGE) durchgeführt. — FA verursachte einen sofortigen Verlust von Ca2+ATPase-Aktivität sowie einen Rückgang löslicher Proteine und in der CPA-Hydrophobie. Dieser Effekt verstärkte sich bei eingefrorenen Mustern. Die elektrophoretischen Profile derjenigen Proteine, die löslich blieben, zeigten sowohl in frischen als auch in gefrorenen Mustern, daß das erste Protein, das bei einer Reaktion von FA mit NAM gelöst wird, Myosin ist, darauf folgen Actin, die Troponine und leichten Myosinketten und schließlich Tropomyosin, was wiederum von der FA-Menge und Reaktionszeit abhängt. In den Anfangsstadien wurden hochmolekulare Aggregate gefunden, die wahrscheinlich das Ergebnis gleichwertiger Bindung von Myosinmolekülen sind. Bei Erhöhung der FA-Menge oder Verlängerung der Lagerzeit bildeten sich hochmolekulare Strukturen, die im löslichen Teil nicht gefunden werden konnten.AbstractDuring frozen storage of certain lean species of fish, formaldehyde (FA) is formed, giving rise to changes in texture related to the formation of aggregates of myofibrillar proteins. In order to study these aggregates a model system was prepared with natural actomyosin (NAM) (5 mg/ml) and increasing concentrations of formaldehyde. The system was stored frozen at-20° C for 2 months during which solubility in 0.6 M NaCl, Ca2+ATPase activity,cis-parinaric acid (CPA) hydrophobicity, SH groups and sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis (PAGE) were measured. — FA caused an immediate loss of Ca2+ATPase activity and a decline in soluble protein and CPA hydrophobicity, an effect that was enhanced when the samples were frozen. The electrophoretic profiles of the proteins that remained soluble showed that in both fresh and frozen samples, when FA reacts with NAM the first protein to be insolubilised is myosin, followed by actin, then the troponins and myosin light chains and lastly tropomyosin, depending on the amount of FA and the reaction time. Aggregates of high molecular mass were found at early stages, probably as a result of covalent binding of myosin molecules. When the amount of FA or the frozen storage time was increased, these aggregates became insoluble, forming high-molecular-mass structures and hence were not found in the soluble fraction.

Thermal gelation of chicken, pork and hake (Merluccius merluccius, L) actomyosin.

Response surface methodology compared the effects of protein concentration (PC, 5-15 mg mL(-1)), ionic strength (NaCl concentration, IS, 0.1-0.7 M) and pH (5.2-7.5) on the gelation properties (penetration test) of natural actomyosin (NAM) from chicken, pork and hake muscle. Results indicated that, for Ln work of penetration (Ln WP), models had r(2) of 0.705 (p < 0.01) for NAM from pork, 0.813 (< 0.001) for NAM from chicken and 0.264 from hake (p > 0.05). The maximum work of penetration did not differ widely among the three samples, regardless of the fact that pH, NaCl level and protein concentration were different in each case. It was found that hake NAM only formed gels within a very narrow range of PC, pH and IS compared with chicken and pork NAM. In the latter two, maximum WP levels were found in gels formed within a pH range of 5.5-6.0 and ionic strength of 0.1-0.2 (NaCl, M). This suggests that hake protein is more sensitive to changes in environmental factors than that from pork or chicken.

Freezing and frozen storage of actomyosin from different species

A comparative study was made of the influence of freezing (−24°C) and frozen storage (−12°C) on the functional properties (viscosity, solubility) and physico-chemical characteristics (aliphatic and aromatic hydrophobicity, ATPase activity) of actomyosin (AM) from myosystems (chicken and hake) of differing freezing and frozen stability. The difference in functional behaviour between chicken and hake AM as a consequence of freezing and frozen storage suggests that, for hake AM, denaturation and aggregation occur essentially through direct aggregation of AM molecules to produce AM aggregates, whereas in chicken proteins, AM first dissociates into myosin and actin to produce myosin and myosin-actin aggregates.

Effect of added lipids on the texture of minced hake (Merluccius merluccius L.), megrim (Lepidorhombus whiffiagonis W.) and sardine (Sardina pilchardus W.) during frozen storage.

ZusammenfassungDer Einfluß von zugesetztem Kabeljauleberöl (CLO) und oxidiertem Kabeljauleberöl (OCLO) auf die Konsistenz von zerkleinertem Fischfleisch aus Seehecht (Merlucdus merlucdus L.), Flügelbutt (Lepidorhombus whiffiagonis W.) und Sardine (Sardina pilchardus W.) wurde während der Gefrierlagerung (bei−18 °C) gemessen. Die Ergebnisse zeigen, daß weder der Zusatz von neutralem noch der von oxidiertem Öl, selbst bei erheblicher Ranzigkeit, den Scherwiderstand im Fisch beeinflußt, wenn kein Formaldehyd gebildet wurde. Bei der Fischart aber, die während der Gefrierlagerung Formaldehyd bildet, wie z. B. Seehecht, können die Werte des Scherwiderstandes in Gegenwart von neutralen und oxidierten Lipiden gegen Ende der Lagerperiode niedriger sein als bei Abwesenheit der Lipide; wahrscheinlich wegen verminderter Formaldehydbildung. Obwohl es sehr schwierig ist, die Bedeutung einer einzelnen Verbindung zu bewerten, scheinen diese Ergebnisse zu zeigen, daß Formaldehyd für die Konsistenzveränderungen in tiefgefrorenem Fisch einen viel wichtigeren Faktor darstellt als oxidierte Lipide.SummaryThe effect of added cod liver oil and oxidized cod liver oil on the measurement of texture in minced hake (Merlucdus merlucdus L.), megrim (Lepidorhombus whiffiagonis W.) and sardine (Sardina pilchardus W.) has been measured during frozen storage (−18° C). The results show that added neutral and oxidized lipids, even at high rancidity levels, do not affect shear resistances measured by the Kramer shear-compression cell in non-formaldehyde forming species such as megrim and sardine, over the frozen storage period. However, in a formaldehyde-forming species such as hake, in the presence of neutral and oxidized lipids at the end of the storage period, the values of shear resistances may be lower than in the absence of these lipids, probably owing to formation of less formaldehyde in these cases. Although it is very difficult to estimate the importance of a single compound or group of compounds on texture, these results seem to indicate that formaldehyde is a much more important factor than oxidized lipids in changes of texture in fish.