Gelatin from skins of several marine species were compared on the basis of their rheological characteristics (viscoelasticity and gel strength) and chemical/structural properties (amino acid composition, molecular weight distribution and triple helix formation). Gelatins from flat-fish species (sole and megrim) presented the best gelling ability and the gels were more thermostable than those from cold-adapted fish (cod and hake). This different behaviour may be explained considering the amino acid composition, the alpha (1)/alpha (2) collagen-chain ratio, and the molecular weight distribution. Thus, cod gelatin presented a lower alanine and imino acid content, and a decreased proline hydroxylation degree; cod and hake gelatins presented a low alpha (1)/alpha (2) ratio (similar to1); hake gelatin showed a highly significant decrease in beta -components and other aggregates. The squid gelatin presented the most significant changes regarding amino acid composition and molecular weight distribution, most of these differences arising from the low solubility of the squid connective tissue. However, the squid gelatin showed viscoelastic properties intermediate between those from flat-fish and cold-adapted fish species. Circular dichroism analysis reveals that gelling involves a refolding of denatured collagen chains into the typical triple helix conformation and, conversely, unfolding upon reheating. Thermal folding and unfolding curves were similar to those of viscoelastic properties but showing a shift towards lower or higher temperatures upon cooling and heating, respectively. The folding process seem to be directly related in the stabilisation of the gels without disregarding its role in triggering the gelation process. Finally, get strength evaluation revealed the importance of slow cold maturation. (C) 2001 Elsevier Science Ltd. All rights reserved.
