Pre-treatment optimization and properties of gelatin from freshwater fish scales

Enzyme protease A 2G (E.C. 3.4.24.39) was selected to pre-treat grass carp fish (Ctenopharyngodon idella) scales and response surface methodology (RSM) was adopted for pre-treating optimization. The optimal conditions from RSM were hydrolyze temperature 30.73 °C, amount of protease A 2G 0.22% (w/w) and hydrolyze time 5.52 h, and the resulted gelatin gel strength was 276 ± 12 g. The X-ray spectra indicated that the dried fish scales gelatin had tri-helix structure. The isoionic point (pI) value was about 7.0. The gel strength and gel viscoelastic properties of grass carp fish scale gelatin were higher compared to one commercial porcine skin gelatin 180PS8 at lower temperature, while the imino content (16%), gelling and melting points (20.8, 26.9 °C) were lower. At the same concentration, the α-chain and β-component contents of the gelatin made more contributions to the gel viscoelastic properties under gelling or melting points, while the amino acid composition made more effects to the stability of the gel. The gelling process was monitored by circular dichroism (CD) spectra. The results also showed that fish scales also can be a good source for gelatin.