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. / Graduation date: 1990
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27083 |
| Date | 15 January 1990 |
| Creators | Rico-Pena, Delmy del Carmen |
| Contributors | Torres, J. Antonio |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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