Biochemical and structural characterisation of thermostable acid- and pepsin-soluble collagens from South African Geelbek (Atractoscion aequidens) scales and its potential application in film formation

Abstract

Fish processing typically generates large amounts of non-edible by-products, which contain collagen protein as one of the principal constituents. In this study, the biochemical properties, in vitro fibril-forming potential and film-forming potential of acid (ASC)- and pepsin (PSC)-soluble collagens extracted from the scales of geelbek (Atractoscion aequidens) were evaluated. Based on ultraviolet absorption spectroscopy, electrophoretic pattern, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) analysis, both ASC and PSC were classified as type I collagen. Further, amino acid composition analyses confirmed the presence of 326 and 319 glycine residues/1000 residues in ASC and PSC, respectively, which is characteristic of collagen. The collagens were thermally stable, with a maximum transition temperature of 112.27 °C for ASC and 113.41 °C for PSC. The collagens also demonstrated excellent fibril-forming potential, as indicated by SEM analysis. Being a bioactive material, the extracted collagen was further utilised to prepare collagen–chitosan films. The presence of collagen–chitosan interaction was revealed by FTIR spectra examination of the films, confirming a favourable modification of collagen’s secondary structure. Colour, differential scanning calorimetry and dynamic mechanical analysis demonstrated that the collagen–chitosan films had moderate colour indices and enhanced thermal properties. Overall, this study offers insights into biomaterial fabrication using geelbek collagen that could potentially be useful in the biomedical and food industries. Graphical abstract