Food control by applied biochemistry of marine organisms: Comparison of proteins and metabolites from fish and invertebrate muscle

Most fishery products consist of muscle tissue from fish and invertebrates. Differences in the molecular structure and in metabolism of muscles can be utilized to characterize and identify various seafood. Creatine and arginine were found to be useful for the differentiation between imitation crab/shrimp meat and real crustacean meat. Octopine served as an indicator for the meat of cephalopods and mussels. In order to identify the animal species of a fishery product, several electrophoretic methods were used. It depended on the type of product, whether sarcoplasmic or myofibrillar proteins were better suited. Raw products were best analysed by isoelectric focusing of sarcoplasmic proteins. Two types of sarcoplasmic calcium-binding proteins, parvalbumins of fish and soluble calcium-binding proteins of invertebrates, were especially useful for species identification. Due to their thermal stability, these proteins gave species-specific patterns for cooked products, too. Two other techniques were also investigated: urea gel isoelectric focusing, and sodium dodecyl sulphate — polyacrylamide gel electrophoresis. These methods were applied in the analysis of products where the sarcoplasmic proteins had been removed by washing steps, i.e. imitation crab meat made from surimi, and of other raw and cooked products. The myosin light chains gave protein patterns that were characteristic for many species. Paramyosin, which is absent from vertebrate muscle, indicated the presence of mollusc muscle. It was shown that the determination, of arginine kinase activity enabled differentiation between raw fish muscle and invertebrate muscles.