Edible coatings controlling preservative migration from
surface to food bulk could inhibit surface microbial growth
which is often the main cause of spoilage for many food
products. In this project we focused our attention upon
methylcellulose, hydroxypropyl methylcellulose, and chitosan as
the structural component for such edible films. These films
were generally transparent and effective at thicknesses in the
order of 20 to 100 μm. We expect them to have little impact
on the sensory properties of a food.
Permeability cell measurements were used to evaluate the
effect of coating composition. Further film characterization included film thickness and electron microscopy studies. To
gain an understanding of the permeation process, the
permeability tests were done at 5, 24, 32, and 40°C.
Among these polysaccharide films, methylcellulose was the
most promising diffusion barrier with a permeability constant of
3.4 and 1.4xl0⁻⁸ (mg/sec cm²)(cm)/(mg/ml) at 24 and 5°C,
respectively. These barrier properties were enhanced by the
incorporation of lipids into the film formulation.
The permeability of sorbates in methylcellulose and
hydroxypropyl methylcellulose emulsified with lauric, palmitic,
stearic and arachidic acid was found to depend upon the
polysaccharide, the fatty acid chain length, and the number of
fatty acid double bonds. Potassium sorbate permeation increased
in the following order lauric>palmitic>stearic>arachidic acid.
The effect of the double bond type, i.e. cis vs. trans was also
determined. The permeability rate of potassium sorbate
increased in the order of oleic>elaidic>stearic acid.
The effect of temperature on potassium sorbate permeability
was analyzed using an Arrhenius activation energy model for the
permeation process. Permeability determinations at four
different temperatures showed excellent agreement with this
model and suggest that the permeation process is diffusion
controlled. Electron microscopy studies showed the absence of
pores, channels or other defects which might be introduced
during casting, drying, handling or permeability determination.
This observation is consistent with our hypothesis that potassium sorbate permeation is diffusion controlled.
Furthermore, our experimental data suggest that the diffusion is
controlled by the properties of the solvent embedded in the
film. Further studies are required to confirm this hypothesis.
The effect of casting technique was examined by coating a
pure polysaccharide film with a fatty acid mixture or bees wax
and by laminating a fatty acid mixture or hydrogenated palm oil
between two layers of pure polysaccharide films. Unfortunately,
most of these films cracked easily and could not be tested in
our permeability cell. On the other hand, hydroxypropyl
methylcellulose films coated with bees wax showed exceedingly
low potassium sorbate permeability values.
These modifications of the polysaccharide film properties
reduced the potassium permeability down to 10⁻⁹ to 10⁻¹¹
(mg/sec cm²)(cm)/(mg/ml) depending upon temperature, film
composition and film casting technique. A simplified procedure
previously published was used to evaluate surface microbial
stability enhancement. With this information a food processor
can select the appropriate film, application procedure and film
thickness to achieve the desired shelf life under ambient or
refrigerated storage conditions. / Graduation date: 1988
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27066 |
| Date | 23 September 1987 |
| Creators | Vojdani, Fakhrieh |
| Contributors | Torres, J. Antonio |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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