The amino acid spectra of fish protein concentrates as a function of processing

Studies on the amino acid contents (spectra) of fish protein concentrates (FPC) prepared by various techniques from different fishes have been reported. The concentrations of the essential amino acids were used as criteria in evaluating the relative quality or nutritional value of the protein (nitrogen x 6.25) present in each of the FPC preparations. Carp (Cyprinus carpio), a fresh water fish and three marine fishes - golden croaker (Micropogon undulatus), hake (Merluccius productus) and anchoveta (Chalcinus angulatus) were used as experimental fishes for the investigation. The amino acid spectra of bones and scales fractions were significantly lower in the essential amino acids than the original fish or fillets prepared from the fish. Based on the essential amino acid data, it was postulated that the quality of the protein (N x 6.25) of the bones and scales fraction would be inferior to that of either the total fish or the fillets. The essential amino acid spectra of FPC prepared by the isopropanol (IPA) extraction process were equal to or only slightly better than those of the raw fish. It was suggested that the losses of both soluble non-protein nitrogen and sarcoplasmic protein nitrogen to the extracting solvent were compensating. Thus, the essential amino acid concentrations of the FPC and the fish were approximately the same. Results obtained on FPC prepared by an enzymatic process were similar to those obtained with the IPA method. That is, the essential amino acid values for the Enzyme-FPC were approximately equal to those of the original fish. This was true despite the absence of bones and scales in the final FPC. The insoluble bones and scales are removed prior to the production of FPC from the supernatant protein digest. These results are not entirely in keeping with results obtained with deboned products. However, the enzymatic digestions were not complete and protein was lost to the residue. Also, the enzyme process, initiated at pH 10, could have extracted non-protein nitrogen from the bones and scales.