Structure of fish proteins as modified by salting procedures: A rheological and ultrastructural analysis of hake (Merluccius hubbsi) fillets.

Salting is a technique used for preserving fish meat and allows obtaining added value products. The salting process provokes several structure modifications, which in turns cause changes in the fish texture. Thus, the objective of this study was to investigate the effect of three salting procedures (dry salting [DS], mixed salting [MS] and brining [BS]) on the rheology and structure of Merluccius hubbsi (Argentine hake). Rheological properties were evaluated using dynamic oscillatory and thermorheology tests, and the structure changes by scanning electron microscopy. DS samples showed the highest values of salt concentration referred to liquid phase (zNaCl ), while BS showed the lowest ones. In all cases, elastic (G') and loss (G″) modulus increased with salting time. G' values exceeded G″ values, indicating a predominant solid behavior. DS samples presented the greatest increase in rheological parameters (G', G″ and η*). Thermomechanical spectra allowed to identify an increase in denaturation temperature (Td) of proteins (myosin and actin) for DS and MS, and to a lesser extent for BS (Td = 46.7 ± 0.4°C, Td = 50.3 ± 0.8°C, Td = 58.8 ± 0.6°C and Td = 58.2 ± 0.9°C for fresh, BS, MS and DS, respectively). Ultrastructural images evidenced conformational changes on the myofibrillar proteins and the connective tissue (collagen). BS caused the least superficial damage to hake tissue. Based on the results, BS could be the method recommended for the industrial production of salted M. hubbsi. PRACTICAL APPLICATION: During salting of hake, variations in water and salt content have a significant effect on the myofibrillar and connective tissue proteins. The study of rheological properties and microstructure allows a better understanding of the conformational changes induced by the salting process. The least surface damage exhibited by brining fillets is consistent with the mass transfer mechanism that leads to the formation of a film on the muscle surface that dilutes the salt; for this reason, compared to dry and mixed salting, brining could be the method recommended for the industrial production of salted (>15% w/w) Merluccius hubbsi.

Effect of different preservation processes on chemical composition and fatty acid profile of anchovy (Engraulis anchoita).

The effects of salting-ripening, canning and marinating processes on chemical composition and fatty acid profile of anchovy (Engraulis anchoita) were evaluated (p = 0.01), with emphasis on long-chain polyunsaturated fatty acids. Fresh anchovy showed a high proportion of PUFAs (∼45 g/100 g total lipid) with an eicosapentaenoic (EPA) + docosahexaenoic (DHA) content of 27.08 g/100 g total lipid. The salting-ripening process led to the largest changes in the chemical composition and the fatty acid profile, which resulted in a reduction of ∼70% on the total EPA and DHA contents (g/100 g edible portion). Contrary, canned and marinated anchovy presented a fatty acid profile similar to that of fresh anchovy. The use of vegetable oil as covering liquid led to final products with increased ω-6 PUFAs content. Despite the modifications observed, the total amount of essential EPA and DHA fatty acids provided by these products remained high compared with values reported in literature for other foods.

Molecular characterization of Shewanella and Aeromonas isolates associated with spoilage of Common carp (Cyprinus carpio).

Storage in ice is a common way of preserving commercial fish species but some microorganisms can still contaminate and participate in the spoilage of the product; therefore, identification of potential harmful microbes is important. Thirteen colonies were isolated from common carp (Cyprinus carpio) that had been stored in ice, whose phenotypic identification revealed that they belonged to the genera Aeromonas (n = 5) and Shewanella (n = 8). Molecular genotyping with ERIC-PCR showed clonality only among two of the five Aeromonas isolates and for two groups (n = 3; n = 2) of the eight Shewanella isolates. Sequencing the rpoD gene showed that four Aeromonas isolates belonged to the species Aeromonas salmonicida and one to A. sobria. Of the eight Shewanella, seven isolates cluster with Shewanella putrefaciens and one with Shewanella profunda in the 16S rRNA phylogenetic tree. However, analysis of the gyrB gene showed that these eight isolates could constitute a new species closely related to S. baltica. The Shewanella and A. salmonicida isolates produce off-odours and reduce trimethylamine oxide, indicating that they might contribute to the spoilage of the fish.

Ripening of salted anchovy (Engraulis anchoita): development of lipid oxidation, colour and other sensorial characteristics.

BACKGROUND: Changes in lipids are in general associated with quality deterioration, though earlier studies in anchovy indicate that the volatile compounds of importance to the characteristic flavour could be generated by lipid oxidation. The aim of the present paper was to study the changes in the fatty acid composition and the lipid oxidation of Engraulis anchoita during ripening and their relationship with the development of the typical sensorial characteristics. RESULTS: As a result of ripening, polyunsaturated fatty acids decrease from 4.27 to 2.42 and 2.00 g kg(-1) fatty acids in gutted fish and fillet, respectively. The most affected class of fatty acids was the n-3 fatty acids, especially docosahexaenoic acid. Moreover, saturated fatty acids were the most stable to the process. 2-Thiobarbituric acid reactive substances (TBARS) increased throughout ripening, and the use of fillets instead of gutted fish reduced this value. The a value was the parameter most modified, showing a marked increase which correlates with the acquisition of a uniform pink colour. Sensory analysis did not show development of off-odour or undesirable changes in colour during ripening. CONCLUSION: As a result of ripening, the fatty acid profile was modified and an increment of TBARS was observed. However, these changes did not lead to deterioration in the quality of the product.