Permeability properties of an edible methylcellulose-palmitic acid film Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/z029p8332

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  • The use of edible coatings in combination with antimicrobial agents enhances the microbial stability of foods. In this study we evaluated the potassium sorbate and sorbic acid permeability of an edible methylcellulose (MC) - palmitic acid (PA) film with a MC:PA ratio of 3:1. Permeability cell measurements were used to evaluate the effect of pH and water activity (a [subscript w]) on the film permeation rate by sorbic acid and potassium sorbate. For films with a thickness of 55-66 pm, potassium sorbate permeability increased from 2.3x10⁻¹⁰ to 2.0x10⁻⁸ (mg/sec cm²)/(cm)/(mg/mL) as a [subscript w] increased from 0.65 to 0.80. Films were not stable at a [subscript w] levels above 0.80. The permeability of the film to sorbic acid decreased from 3.3x10⁻⁸ to 9.1x10⁻¹⁰ (mg/sec cm²) (cm)/(mg/mL) when pH in the permeability cell was increased from 3 to 7. This permeability decrease with pH could balance the loss of effectiveness of sorbates due to the lowering of the percentage of undissociated molecules at high pH. Another characterization of the MC-PA film was the evaluation of the effect of relative humidity (RH) on its oxygen transmission rate (OTR). In general, the film was highly permeable to oxygen (OTR values at 24°C, 660 to 1400 mL O₂ (STP)/m² 24h atm, average film thickness of 55 μm). Therefore, there is no risk to develop anaerobic conditions on food surfaces coated with the MC-PA film. There was no relative humidity effect on OTR in the 0-60% RH range; whereas, the OTR doubled when the RH was increased from 60 to 80%. These results agree well with the moisture uptake of the MC-PA film. Its moisture sorption isotherm shows a large moisture content increase at RH levels larger than 60%. The application of methylcellulose-based films as moisture permeability barriers in simulated sundae ice cream cones showed that a MC-PA film practically stopped moisture transfer from the ice cream to the sugar cone. Sugar cone crispness was retained for a period longer than three months when stored coated at -10°F and +10°F. The crispness of commercial sundae ice cream cones is retained for periods much less than three months.
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