Detection of antibacterial activity of an enzymatic hydrolysate generated by processing rainbow trout by-products with trout pepsin.

Trout by-product hydrolysates, generated using trout pepsin, were characterized and studied in terms of their antibacterial effects against food contaminants and fish farming pathogens. After a hydrolysis time of 25 min, the hydrolysates demonstrated inhibitory activity against several gram-positive and gram-negative bacteria. The degree of hydrolysis (DH) was found to exert a considerable influence on antibacterial activity, with a significant increase in the observed inhibitory effect at the beginning of hydrolysis. The highest antibacterial activity was obtained at a DH of 30% (enzyme/protein ratio 0.04 U/mg of protein, enzyme activity 6.5 U/mg protein, hydrolysis conditions 37°C, pH 3.0). The highest antibacterial activity detected was against the fish farming bacteria Flavobacterium psychrophilum and Renibacterium salmoninarum, with minimal inhibition concentrations of 2mg/ml and 5mg/ml, respectively. The amino acid determination of the hydrolysate (DH 30%) revealed that lysine, leucine, alanine, arginine, glycine, aspartic acid and glutamic acid residues represented the major amino acids.

The differentiation of tuna (family: Scombridae) products through the PCR-based analysis of the cytochrome b gene and parvalbumin introns.

BACKGROUND: In spite of the many studies performed over the years, there are still problems in the authentication of closely related tuna species, not only for canned fish but also for raw products. With the aim of providing screening methods to identify different tuna species and related scombrids, segments of mitochondrial cytochrome b (cyt b) and nuclear parvalbumin genes were amplified and sequenced or subjected to single-strand conformation polymorphism (SSCP) and restriction fragment length polymorphism (RFLP) analyses. RESULTS: The nucleotide diagnostic sites in the cyt b gene of five tuna species from Indonesia were determined in this study and used to construct a phylogenetic tree. In addition, the suitability of the nuclear gene that encodes parvalbumin for the differentiation of tuna species was determined by SSCP and RFLP analyses of an intron segment. RFLP differentiated Thunnus albacares and from T. obesus, and fish species in the Thunnus genus could be distinguished from bullet tuna (Auxis rochei) by SSCP. CONCLUSIONS: Parvalbumin-based polymerase chain reaction systems could serve as an additional tool in the detection and identification of tuna and other Scombridae fish species for routine seafood control. This reaction can be performed in addition to the cyt b analysis as previously described.

Applying population genetics for authentication of marine fish: the case of saithe (Pollachius virens).

The number of fishery products with a quite detailed description of the origin is increasing. This trend is driven by the interest of consumers and the fight against illegal unregulated and unreported fisheries. Unfortunately, there is a lack of methods to prove this information experimentally besides the document-based traceability assessments. For marine fish population genetics is a promising strategy, but research is concentrated only on a few species. Saithe is a commercially important fish species, despite the fact that genetic knowledge is scarce regarding the specification of populations. For a comparative study cost- and time-effective strategies were tested: We found RAPD-PCR to be a useful method for low-budget research or prestudies. Adoption of microsatellites from closely related species turned out to be possible with limited success quota. Our results suggest a clustered structure of populations within the Northeast Atlantic, probably overlapping in the northern North Sea.

Meat Composition and Quality Assessment of King Scallops (Pecten maximus) and Frozen Atlantic Sea Scallops (Placopecten magellanicus) on a Retail Level.

An enlarged range of scallop products on the market allows the consumer to buy lower priced alternatives, which often raises the question of quality and control. Frozen meat of king scallops (Pecten maximus) and Atlantic sea scallops (Placopecten magellanicus) were purchased on the German market and compared with fresh shell-on king scallops of various origin. The approximate composition, inclusive citric acid and phosphates, minerals, free amino acids (FAA) and fatty acid profiles were examined in the muscle to identify changes as a result of processing. The FAA glycine and taurine as well the fatty acids 20:5n-3 (EPA) and 22:6n-3 (DHA) were the most abundant, but were reduced in processed samples. Di- and triphosphate contents were not detectable (<0.01 g·kg-1) in untreated meats. Most frozen scallop products contained added citrates and polyphosphates and had distinctly higher water contents (up to 89%) and an increased moisture to protein ratio (M/P) (up to 9) compared with the fresh king scallops (78%, M/P < 5). Labelling of species, verified by PCR-based DNA analysis, and ingredients were not correct in each case. Overall results indicated no relevant differences in mineral content, except high sodium contents, resulting from additives. Labelling does not readily allow the consumer to recognize the extent of processing effects.

Differentiation of Sparidae species by DNA sequence analysis, PCR-SSCP and IEF of sarcoplasmic proteins.

The increasing global trade of fishery and aquaculture products makes it necessary to develop methods for species identification in case of fish fillets or other highly processed seafood with external morphological characteristics (e.g. gills, fins) of the original fish being removed. Species identification methods based on DNA- or protein-analysis, like DNA sequencing of PCR products, PCR-SSCP (polymerase chain reaction - single strand conformation polymorphism), and isoelectric focusing (IEF) of water-soluble proteins of fish fillet were applied successfully to distinguish between various sparid species including Sparus aurata, Spondyliosoma cantharus, Boops boops, Acanthopagrus bifasciatus, Argyrops spinifer, Pagellus bogaraveo and Lithognathus mormyrus of the family Sparidae available on European markets. Indication of the presence of parvalbumins in light muscle of all of the studied species is presented by the location of heat-stable proteins in the anodic range of the IEF gels.