30C-18 |
Luminescence studies of molecular mobility in gelatin films |
K. V. LUKASIK, Department of Food Science, Rutgers University, 65 Dudley Road, New Brunswick, NJ 08901 and R. D. Ludescher. Gelatin is analogous to synthetic polymers in its linear structure, polydispersity and limited monomer composition, making it an appropriate system in which to study the polymeric glass-rubber transition. Gelatin gels form as the result of interchain entanglement; as gelatin gels age, they condense into rubbery films, which vitrify upon drying. Luminescence is a versatile approach to study such protein molecular behavior because of its site specificity and potential application over a wide dynamic range. Our objective was to develop and characterize two diverse types of luminescent probes to study molecular mobility in glassy and rubbery gelatin films. Measurements of fluorescence intensity, lifetime, and polarization were made on two synthetic tryptophan-containing gelatin-like peptides differing only in the location of the intrinsic Trp probe. Disparities in probe relative quantum yields, lifetimes, fluorescence quenching rate constants, and steady state anisotropies indicate dynamically different environments in immediately adjacent parts of the protein chain on the nanosecond time scale. Information about slower motion of larger macrostructural elements was provided by measurements of phosphorescence intensity and lifetime made on a covalent erythrosin B isothiocyanate-gelatin probe. Lifetime decays of probe phosphorescence in glassy and rubbery gelatin films are complex, indicating a multiplicity of dynamic environments on the microsecond time scale in both states. The magnitude of the long-lifetime component of the phosphorescence decreases with increasing relative humidity of film storage, likely a consequence of increased oxygen quencher diffusion through the water-plasticized matrix. These probes provide a variety of molecular information with which we can investigate the effects of film formulation, casting, and storage/use conditions on matrix mobility and micro- and macrostructure. A more thorough understanding of fundamental protein behavior in films will improve our ability to control and manipulate an edible film system’s functionality and stability.
Session 30C, Food Chemistry: Proteins
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