Abstract: The effects of γ-polyglutamic acid (γ-PGA) on the kinetic self-assembly of pepsin-solubilized collagen (PSC) from tilapia (Oreochromis niloticus) skin and the microstructure and properties of the resulting hydrogel were investigated. It was found that the self-assembly process of PSC consistently involved the nucleation and growth phases in the presence of various concentrations of γ-PGA, but it prolonged the nucleation time, and decreased the rate constant of the nucleation phase, whereas it firstly rose and then reduced that of the growth phase. After the self-assembly, PSC was formed into a white hydrogel, which showed a three-dimensional fibril network as observed by scanning electron microscopy, but γ-PGA could affect the density of collagen fibrils. The network density displayed an increasing trend with increasing γ-PGA/PSC ratio up to 80%, but significantly decreased as the ratio further increased to 100%. Correspondingly, the gel strength was firstly enhanced and then weakened. Nevertheless, neither the enzymatic resistance nor thermal stability of the collagen hydrogel was improved evidently by γ-PGA, suggesting that further studies are necessary to enhance the gel properties by cross-linking.

Key words: collagen, self-assembly, tilapia, fish skin, γ-polyglutamic acid