Graduate Thesis Or Dissertation
 

Edible food coatings to control potassium sorbate diffusion from surface into food bulk : characterization of the diffusion process in polysaccharide based films

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  • 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.
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file details VOJDANIFAKHRIEH1987.pdf 2017-08-03 Pubblico Scaricare