| The functionality of gelatin, a biopolymer derived from animal collagen, as a gelling and binding agent and film-former is heavily influenced by its structure and dynamics in solution and in the solid state. Luminescence spectroscopy is a non-perturbing approach to probe elements of macromolecular structure and mobility that is site specific and potentially applicable over a wide dynamic range.; Measurements of fluorescence intensity, lifetime, and polarization were made on two synthetic tryptophan (Trp)-containing gelatin-like triple-helical peptides known to differ only in the location of the intrinsic Trp probe. The probe in one peptide had a smaller fluorescence quantum yield, a slightly shorter lifetime, a larger bimolecular rate constant for quenching by iodide, a smaller value of steady state anisotropy, and different apparent hydrodynamic dimensions than in the other. These data indicate structurally and dynamically different environments on the nanosecond time scale in immediately adjacent parts of the gelatin protein chain, and suggest a differential exposure to solvent and range of motion for neighboring amino acids. Characterization of gelatin's structure on the amino acid residue level is important in understanding events in protein folding and molecular interaction.; Measurements of the phosphorescence intensity and lifetime of Erythrosin B probe were made in amorphous gelatin films plasticized by water or glycerol, and cast above or below gelatin's melting temperature. Trends in probe lifetime indicated active modes of molecular mobility affecting the ability of oxygen to permeate the plasticized protein matrix, and suggest dynamic heterogeneity on the sub-millisecond time scale, even in minimally plasticized films. Emission data indicate that solvent relaxation occurs in the film matrix within the lifetime of the probe. Oxygen diffusion, as monitored by changes in probe intensity, has been modeled with a single diffusion coefficient in films plasticized in the intermediate moisture range.{09}However, films plasticized at higher humidity show considerably more complex behavior. Also, glycerol, even at very high levels, does not appear to promote mobility affecting oxygen diffusion. A better understanding of the mobility in the plasticized amorphous solid state will help improve the effectiveness of gelatin films in barrier applications in complex food systems. |
