Extraction and Characterization of Gelatin from Skin By-Products of Seabream, Seabass and Rainbow Trout Reared in Aquaculture

The expansion of fish filleting, driven by the increasing demand for convenience food, concomitantly generates a rising amount of skinning by-products. Current trends point to a growing share of aquaculture in fish production, so we have chosen three established aquaculture species to study the properties of gelatin extracted from their skin: rainbow trout, commonly filleted; and seabass and seabream, marketed whole until very recently. In the first case, trout skin yields only 1.6% gelatin accompanied by the lowest gel strength (96 g bloom), while yield for the other two species exceeds 6%, and gel strength reaches 181 and 229 g bloom for seabass and seabream, respectively. These results are in line with the proportion of total imino acids analyzed in the gelatin samples. Molecular weight profiling shows similarities among gelatins, but seabass and seabream gelatins appear more structured, with higher proportion of β-chains and high molecular weight aggregates, which may influence the rheological properties observed. These results present skin by-products of seabream, and to a minor extent seabass, as suitable raw materials to produce gelatin through valorization processes.

Mechanistic insights into the dual activities of the single active site of l-lysine oxidase/monooxygenase from Pseudomonas sp. AIU 813

l-Lysine oxidase/monooxygenase (l-LOX/MOG) from Pseudomonas sp. AIU 813 catalyzes the mixed bioconversion of l-amino acids, particularly l-lysine, yielding an amide and carbon dioxide by an oxidative decarboxylation (i.e. apparent monooxygenation), as well as oxidative deamination (hydrolysis of oxidized product), resulting in α-keto acid, hydrogen peroxide (H2O2), and ammonia. Here, using high-resolution MS and monitoring transient reaction kinetics with stopped-flow spectrophotometry, we identified the products from the reactions of l-lysine and l-ornithine, indicating that besides decarboxylating imino acids (i.e. 5-aminopentanamide from l-lysine), l-LOX/MOG also decarboxylates keto acids (5-aminopentanoic acid from l-lysine and 4-aminobutanoic acid from l-ornithine). The reaction of reduced enzyme and oxygen generated an imino acid and H2O2, with no detectable C4a-hydroperoxyflavin. Single-turnover reactions in which l-LOX/MOG was first reduced by l-lysine to form imino acid before mixing with various compounds revealed that under anaerobic conditions, only hydrolysis products are present. Similar results were obtained upon H2O2 addition after enzyme denaturation. H2O2 addition to active l-LOX/MOG resulted in formation of more 5-aminopentanoic acid, but not 5-aminopentamide, suggesting that H2O2 generated from l-LOX/MOG in situ can result in decarboxylation of the imino acid, yielding an amide product, and extra H2O2 resulted in decarboxylation only of keto acids. Molecular dynamics simulations and detection of charge transfer species suggested that interactions between the substrate and its binding site on l-LOX/MOG are important for imino acid decarboxylation. Structural analysis indicated that the flavoenzyme oxidases catalyzing decarboxylation of an imino acid all share a common plug loop configuration that may facilitate this decarboxylation.

Characteristics of Pepsin-Solubilised Collagen from the Skin of Splendid Squid (Loligo formosana)

Pepsin-solubilised collagen from the skin of splendid squid (SC) was isolated, partially purified by salt precipitation and dialysis prior to characterisation. The yield of SC was 75.3% (dry weight basis). SC with high purity was obtained as shown by the distinct UV absorption peak at 232 nm and high hydroxyproline content. Total sugar content of SC was 4.70% (dry weight basis), which was higher than that of collagen from calf skin (CC) (1.45% dry weight basis) (P<0.05). Based on SDS-PAGE and elution profile, SC might contain the mixed types of collagen (type SQ-I and type SQ-II), in whichα- andβ-chains were the major components. SC was rich in glycine and had high content of imino acids (189 residues/1000 residues). The degradation induced by chymotrypsin and lysyl endopeptidase was more pronounced in CC, compared with SC. The maximum transition temperature (Tmax) of SC was 34.1°C, which was about 7°C lower than that of CC. Fourier transform infrared spectra revealed that the triple-helical structure of SC was predominant with the copresence of carbohydrate moieties. Therefore, the skin of splendid squid, a byproduct from squid processing, can be an alternative source for collagen production.

Effect of sulphite ions on the proline and polyamine content in the bean Phaseolus vulgaris

The influence of sulphite (0.0125-0.2%) on changes in the levels of free proline, protein bound proline and hydroxyproline and of free polyamines in the roots and leaves of two cultivars of beans (<i>Phaseolus vulgaris</i>) differing in sensitivity to these ions was investigated. It was found that both cultivars reacted similarily, the response of the seedlings of the more sensitive cultivar occuring at lower concentrations of sulphite.The observed changes in the content of imino acids and polyamines are discussed.

The Characteristics of Gelatin from Scales of Tilapia (Oreochromis spp.)

Gelatin was extracted from tilapia (Oreochromis spp.) scale after decalcification. The content of protein in the gelatin was 92.5% (w/w). The amount of imino acids (proline and hydroxyproline) was 167 residues per 1000 residues. Its gel strength, melting point and degradation temperature were 271 g, 27.0 °C and 59.7 °C, respectively. Fourier transform infrared spectroscopy spectra showed that the intensity of major absorption bands in the gelatin was higher than that in bovine bone gelatin. The gelatin had visible β-component and degradation fragments.