SUMMARY: As a means of effective utilization of fish water‐soluble proteins (FWSP), which are mostly discarded into the waste water of seafood processing plants, the development and characterization of edible films from FWSP of blue marlin meat were investigated. The film‐forming solutions were prepared from 3% FWSP solutions at pH 10 with 1.5% glycerol as a plasticizer, followed by heating at 70°C for 15 min. Edible films were successfully prepared by drying the film‐forming solutions at 25°C for 20 h. It was revealed that FWSP had to be denatured somehow to unfold the protein structure, and the interaction of FWSP molecules, particularly through disulfide linkages, was attributed to the formation of films. Transparent edible films thus formed had better flexibility and lower water vapor permeability compared with most of the other protein films.

Natural actomyosin (NAM) of P. tayenus exhibited higher turbidity and storage modulus (G') upon heating, compared to that of P. macracanthus, suggesting the higher protein aggregation and rigidity. At temperature above 35 Њ Њ Њ Њ ЊC, P. tayenus NAM had higher surface hydrophobicity and disulfide bond formation than P. macracanthus NAM. The ␣ ␣ ␣ ␣ ␣-helix content of NAM from both fish species decreased as the temperature increased, indicating changes in structural conformation during heating. NAM gel from P. tayenus rendered more three-dimensional network than that from P. macracanthus. These results indicated that P. tayenus NAM possessed superior gelling characteristic to P. macracanthus NAM due to the higher aggregation of protein caused by both hydrophobic interaction and disulfide bond.

The fish dark muscle is less allergenic than the white muscle, because the same allergen molecule (parvalbumin) is contained at much lower levels in the dark muscle than in the white muscle. Thus, the dark muscle is less implicated in fish allergy than the white muscle.

Although tropomyosin is known to be a major allergen of crustaceans, its structural information is limited to only five species. In this study, tropomyosin was confirmed to be a major allergen in six species of crustaceans (black tiger prawn, kuruma prawn, pink shrimp, king crab, snow crab, and horsehair crab) by immunoblotting. Then, the amino acid sequences of tropomyosins from these crustaceans were elucidated by a cDNA cloning technique. Sequence data for crustacean tropomyosins including the obtained results reveal that fast tropomyosins are contained in shrimps (or prawns) and lobsters, slow tropomyosins in crabs, and both tropomyosins in crayfishes and hermit crabs. Although fast and slow tropomyosins share a high sequence identity (about 90%) with each other, significant differences are observed in specific regions between both tropomyosins.

Fish skin mucus contains a variety of antimicrobial proteins and peptides that seem to play a role in self defense. We previously reported an antibacterial protein in the skin secretion of the rockfish, Sebastes schlegeli, which showed selective antibacterial activity against Gram‐negative bacteria. This study aimed to isolate and structurally and functionally characterize this protein. The antibacterial protein, termed SSAP (S. schlegeli antibacterial protein), was purified to homogeneity by lectin affinity column chromatography, anion‐exchange HPLC and hydroxyapatite HPLC. It was found to be a glycoprotein containing N‐linked glycochains and FAD. Its molecular mass was estimated to be 120 kDa by gel filtration HPLC and 53 kDa by SDS/PAGE, suggesting that it is a homodimer. On the basis of the partial amino‐acid sequence determined, a full‐length cDNA of 2037 bp including an ORF of 1662 bp that encodes 554 amino‐acid residues was cloned by 3′ RACE, 5′ RACE and RT‐PCR. A blast search showed that a mature protein (496 residues) is homologous to l‐amino acid oxidase (LAO) family proteins. SSAP was determined to have LAO activity by the H2O2‐generation assay and substrate specificity for only l‐Lys with a Km of 0.19 mm. It showed potent antibacterial activity against fish pathogens such as Aeromonas hydrophila, Aeromonas salmonicida and Photobacterium damselae ssp. piscicida. The antibacterial activity was completely lost on the addition of catalase, confirming that H2O2 is responsible for the growth inhibition. This study identifies SSAP as a new member of the LAO family and reveals LAO involvement in the innate immunity of fish skin.