With the growing concern of the accumulation of plastic-based food packaging waste, the search for biodegradable packaging materials is on the rise. However, through the lifetime of their usage and storage, appreciable changes in the material’s properties due to physical ageing are apparent. Aromatic aminoacids (e.g., tyrosine or tryptophane) within protein-based biomaterials and food grade dyes added to packaging exhibit photophysical properties sensitive to the physical properties of their surrounding media. These Intrinsic luminescent probes could provide a ubiquitous method to noninvasively follow local solvation and structural integrity of biodegradable food packaging as a function of time.<br/><br/>Gelatin (2%) was used as the main biodegradable material to prepare films using a solvent casting procedure with Glycerol (0.5%) as a plasticizer. The casting solutions were doped with Fast Green -FG- (0.1uM), an edible food dye with luminescent properties sensitive to changes in molecular crowding. The films were stored under controlled relative humidities (2.5, 25, 33, 53, or 75 %RH) for at least five weeks. The photophysical properties of tyrosine and FG within the films were evaluated using front face luminescence spectroscopy. Moisture content was assessed under vacuum at 60 C for 24 h. Tensile strength was determined with a Universal Testing Machine following the ASTM standard method D882. Data collection was performed every week at least in quadruplicate.<br/><br/>The peaks of the luminescent probes (Tyr or FG) were differentiable from background noise. Fluorescence intensity of Tyr and FG were sensitive to changes in solvation and structural rigidity as verified from the moisture content and tensile strength measurements. An increase in rigidity during ageing was observed for all samples, particularly those stored at low and intermediate RHs. The FG fluorescence intensity showed a linear correspondence with the tensile properties of the biodegradable material during ageing. These findings could act as a base to develop a quick, inexpensive, and more universal system to test structural strength of biomaterials for use in food packaging.

Intrinsic luminescent probes as sensors to monitor structural properties and solvation in biodegradable films

256th National Meeting (2018)

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