Alcalase-assisted production of fish skin gelatin rich in high molecular weight (HMW) polypeptide chains and their characterization for film forming capacity

Gelatin rich in high molecular weight (HMW) polypeptide chains exhibit superior film forming capacity. Alcalase enzyme was used to produce gelatin rich in HMW polypeptide chains from shark (spiny dogfish) skin. The optimum conditions were established as 1.15 U/g alcalase pretreatment for 2.1 h followed by water extraction at 50.4 °C for 4.6 h and produced gelatin with 33% HMW polypeptide chains of total protein. There was significant interaction (p < 0.1) between alcalase treatment and water extraction to control the HMW polypeptide chain content in gelatin. Optimized gelatin had 31.6% of glycine, 10% of proline and 7.9% of hydroxyproline. Gelatin rich in HMW polypeptide chains had strong capacity to form films from solutions with low gelatin concentrations (0.5–4%, w/v). Films formed by 3% gelatin solution (GF3) had low opacity and showed no difference with films formed by 4% gelatin solution (GF4), in terms of water solubility, water vapor permeability, as well as tensile strength and elongation at break (p > 0.05). FTIR spectrum of the GF3 film disclosed five characteristic amide bands, and the TGA trace showed GF3 film was stable up to 225 °C. Microstructure of GF3 using SEM displayed a smooth and compact film network.