Protein isolation from blue mussels (Mytilus edulis) using an acid and alkaline solubilisation technique -process characteristics and functionality of the isolates

BACKGROUND: The pH shift method was developed to isolate proteins from low-value raw materials by solubilisation at high or low pH followed by precipitation. In this paper the application of the pH shift method on isolated mussel (Mytilus edulis) meat and whole mussels is reported. RESULTS: Highest protein solubilisation was achieved at pH values of 2.6 and 12. The optimum precipitation pH values were established as around 5.8 following acid solubilisation and 5.2 following alkaline solubilisation. Protein recoveries were 430 and 580 g kg-1 with the acid and alkaline processes respectively. Using whole crushed mussels, the corresponding recoveries were 310 and 480 g kg-1. Process modifications to further improve protein recovery resulted in only a marginal increase. Lipid oxidation was not induced during pH shift processing, but heavy proteolysis occurred during the acid process version. Proteolysis could not be prevented by porcine plasma protein. Alkali-produced proteins performed better in all functionality tests compared with acid-produced proteins. The acid process removed slightly more lipids, recovered relatively more cysteine, methionine and lysine and resulted in whiter isolates. CONCLUSION: The pH shift method can be successfully used to extract functional proteins from mussels and add value to blue mussels unsuitable for human consumption (with or without shells)

Effect of frozen storage on the quality of whole fish and fillets of horse mackerel (Trachurus trachurus) and Mediterranean hake (Merluccius mediterraneus)

Whole fish and fillets of horse mackerel (Trachurus trachurus) and mediterranean hake (Merluccius mediterraneus) were assessed for quality (physical, chemical and sensory attributes) changes throughout 12 months of frozen storage at - 18 degrees C. The pH; expressible water (EXW), quantities of trimethylamine (TMA), dimethylamine (DMA), formaldehyde (FA), the total volatile base nitrogen (TVB-N) the thiobarbituric acid number (TEA), peroxide value (PV) and amount of free fatty acids (FFA) increased, while sensory attributes (odour, taste, texture) decreased during the frozen storage period. A comparison of quality scores between whole fish and fillets of horse mackerel and mediterranean hake showed that there were no significant differences (P > 0.05) in attribute scores. There were, however, significant differences (P < 0.05) in pH, EXW, TMA, DMA, FA, TVB-N, TEA, FFA and PV

Quality assessment of seven Mediterranean fish species during storage on ice

The following seven Mediterranean fish species, bogue (Boops boops), chub mackerel (Scomber japonicus collias), horse mackerel (Trachurus trachurus), Atlantic mackerel (Scomber scombrus), Mediterranean hake (Merluccius mediterraneus), sardine (Sardine mediterraneus), striped mullet (Mullus barbatus) were assessed for quality changes during a week of ice storage. All fish were stored whole in ice. Fish tester readings of all fish species were found to be below 35 by the end of ice storage. The pH was not significantly changed (p>0.05), while thiobarbituric acid number (TBA) and formaldehyde (FA) content were significantly increased (p less than or equal to 0.05) by the end of ice storage of all fish species. Sensory evaluation showed that better storage life was observed for bogue, sardine and striped mullet by using the European Community (EC) freshness grading scheme of raw fish and for bogue and Mediterranean hake by using sensory panel evaluation of cooked fish fillets. Mediterranean hake may require a different descriptive scheme than the current EC freshness grading scheme. (C) 1998 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved