Effects of Concentration, Temperature, and pH on Chain Mobility of Gelatin during the Early Stages of Gelation

This research work focuses on the changes in molecular dynamics of gelatin in the early stages of gelation under temperature variations (273-330 K), pHs (3, 6.5, and 11) and concentrations (1, 3, and 5 %w/w). The early stage of gelation occurs at temperature well above the sol-gel transition point and is accompanied by increasing the viscosity of the solution. The induced variations of the local mobility of the macromolecules are detected by measurements of the spin-spin relaxation time of 1H nuclei of different amino acids. Changes in the rheological characteristics of the gelatin solutions are measured and the effects of acidity, temperature, and concentration on the early stages of the gelatin gelation process are evaluated. The experimental results were analyzed for the mobility of the individual amino acids and of the complete gel network at different temperatures and acidities. Spin-spin relaxation data indicate that the mobility of amino acids in this siane of gelation is not affected by the gelatin concentration, indicating that it is predominantly governed by intra-molecular interactions. As expected, the influence of this interaction on individual amino acids strongly depends on the polarity and their ability to form hydrogen bonds. The variation of the relaxation times reflects the specific role of each individual amino acid during the gelation process. Any deviation from the neutral pH conditions causes a strong increase in the local molecular dynamic, presumably caused by electrostatic repulsion under acidic or basic conditions. At the same time, it leads to decrease in the solution iscosity originally observed under neutral conditions.