17E-22 |
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K. V. LUKASIK and R. D. Ludescher. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, 65 Dudley Rd., New Brunswick, NJ 08901-8520 Edible gelatin films act as ingredient carriers and GRAS barriers to mass transfer because of the molecular interactions occurring within. An understanding of solid-state matrix dynamics that underlie macromolecular behavior is necessary to exploit edible film technology most effectively. Our objective was to study effects of plasticizer content (e.g. water, glycerol, etc.) and casting conditions (above or below the gelatin triple-helix melting temperature Tm) on oxygen diffusion and dynamic heterogeneity in amorphous gelatin films. Porcine gelatin was covalently labeled with erythrosin (oxygen-sensitive probe) and used to make thin films, cast under varying conditions, on an impermeable substrate. Matrix molecular mobility was studied with phosphorescence measurements of probe emission. Intensity decays were collected and analyzed with a stretched exponential model to determine probe lifetime. Oxygen desorption, observed by monitoring the phosphorescence signal increase over time, was analyzed for the oxygen diffusion coefficient (D~10-8cm2/s). In films cast below Tm, a dependence of lifetime on emission wavelength exists, and the temperature effect on lifetime differs at 0 and 75% relative humidity (RH), suggesting water-modulated sub-millisecond dynamic heterogeneity. Lifetime trends in air and in nitrogen were comparable for water-plasticized films cast above and below Tm, but lifetimes were ~15-20% shorter and D was up to two times larger in films cast below Tm at comparable RH, indicating a difference in the probe’s molecular environment related to triple-helical crosslink content. Probe lifetime was greater in glycerol-plasticized films than in water-plasticized films, but a similar dependence of lifetime on emission wavelength exists. Oxygen diffusion within the erythrosin excited state lifetime was immeasurable, even at levels of 50% (w/w), suggesting that diffusion-related dynamics may occur on a different time scale in glycerol-plasticized films. Further characterization of the small molecule effect on biopolymer dynamics is critical to modulation of edible film matrix functionality.
Session 17E, Food Chemistry: Proteins
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