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Use of phosphorescence spectroscopy to probe oxygen permeability of glassy and rubbery gelatin films |
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 film technology has emerged as a significant method for extending the shelf life of certain foods. The bulk protein matrix of an edible film can be an effective GRAS barrier to detrimental environmental factors, including oxygen gas and water vapor. Functional differences in edible film systems arise from differences in composition, and conditions of preparation, casting, storage and use. These differences are fundamentally the result of small-scale molecular changes in the matrix. The objective of this study was to correlate these subtle modes of macromolecular mobility with a macroscopic effect, i.e. changes in the gelatin film’s permeability to oxygen. Phosphorescence spectroscopy is a sensitive, site-specific method that can address this relationship, unlike more traditional techniques of assessing properties of polymer-like films. Porcine gelatin was labeled with phosphorescent dye (erythrosin B) and was used to make thin (~0.035mm) films on quartz supports. Films were equilibrated at a range of relative humidity (RH) values in preparation for phosphorescence emission and lifetime measurements. Desorption of oxygen was observed by monitoring the dye phosphorescence signal over time; values of the oxygen diffusion coefficient and permeability were determined from this data. Phosphorescence lifetime data suggest that both glassy and rubbery films have heterogeneous molecular microenvironments on the sub-microsecond time scale. However, oxygen diffusion appears to be negligible in environments <57% RH. Diffusion coefficients in rubbery films were determined to be on the order of 10-8cm2/sec, and increased with RH above 57%. Gelatin is a versatile food material with diverse functionality. As a biomolecule, it is an excellent model for studying the polymer-like behavior of food materials. A better understanding of the molecular structure and dynamics of this protein film system will be helpful in effectively using gelatin as a component of food coatings and in developing further related novel applications.
Session 11, Food Chemistry: Proteins I
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