Insight into the mechanism of the decrease in mechanical strength and water-holding capacity of gels made from oxidized gelatin

The purpose of this study was to investigate the effect of oxidation on the physicochemical properties of gelatin and gelatin gels. Porcine skin gelatin was oxidized with different concentrations of H2O2 (0-30 mM). Upon oxidation of gelatin, a significant modification of amino acid residues including glycine, proline, hydroxyproline, and hydroxylysine occurred. Zeta-potential, ordered secondary structure and the fraction of triple-helix decreased, while particle size and surface hydrophobicity increased. Gels made from oxidized gelatin showed a looser network structure indicated by scanning electron microscope, and the gels had a weakened mechanical strength and water-holding as compared to non-oxidized gelatin gels. Based on these results, a mechanism of how oxidation affects the gelatin gel properties was proposed: Oxidation-induced increase of hydrophobicity and decrease of net charges promoted aggregation between gelatin molecules, thereby limiting the formation of triple-helix, which subsequently leads to a loose network structure and eventually a weakened gel strength and water-holding capacity.