Extraction, microstructural, and FTIR characterization of elastin from skin and swim bladder of Caspian white fish Rutilus kutum

The Caspian white fish or Caspian kutum Rutilus kutum is only found on the Iranian coastline of the Caspian Sea. This study investigated the extraction process of soluble/insoluble elastin from skin/swim bladder of Rutilus kutum on the basis of organic acid hydrolysis and hot alkali methods. Fourier-transform infrared (FTIR) spectroscopy analysis exhibited typical peaks at low frequency for amide I centered at ∼ 1633 cm⁻¹ and amide II at ∼ 1538 cm⁻¹. The comparative spectra indicated similar α-helix and β-sheet content of soluble/insoluble elastin in skin and swim bladder. The high content of amide I/II and increased polarity of soluble elastin can improve their reactivity in food matrices/textures or biopolymer design, whereas insoluble elastin powder, containing less amide I/II content and weaker dipoles, may be an alternative source for cell culture and tissue engineering. The purity of the soluble elastin from skin/swim bladder was confirmed through SDS-polyacrylamide gel electrophoresis (SDS-PAGE) analysis with an apparent molecular weight of 40 kDa, and hydrolyzed insoluble elastin generated an individual protein band at the same molecular mass containing some diffused ground proteins in the 35–45 kDa range and no contamination with collagen. Scanning electron microscopy (SEM) images of elastin presented fibrillar bundles with different diameters and peripheral beta sheets, with such constructions being appropriate features for the design of diverse biomimetic scaffolds.