Modeling the inhibition kinetics and the mass transfer of controlled releasing potassium sorbate to develop an antimicrobial polymer for food packaging
Potassium sorbate inhibited the growth of yeast (Saccharomyces cerevisiae) through a mechanism of uncompetitive inhibition. Heating decreased the antimicrobial effect of potassium sorbate in a manner consistent with the Arrhenius relationship in terms of temperature, while heating time inactivated it by first order kinetics. Therefore, thermal processing of foods containing potassium sorbate may reduce antimicrobial activity and cause microbial spoilage of the food products. The diffusivity and diffusion profile of potassium sorbate in plastic films and cheese were determined both experimentally and using mathematical models and computer simulations. Low density polyethylene (LDPE) had the lowest diffusivity among common commercial plastic films. The results of diffusion tests suggested that the LDPE film is good as a reservoir layer for releasing the preservative. The other common films, such as high density polyethylene, polypropylene and polyethylene terephtalate, are good films for use as control layers for slow release or barrier layers. An overall diffusion model for the preservative release in a plastic film/cheese packaging system was suggested and simulated by computer programming for predicting the shelf-life of cheese. The tensile strength of a LDPE film was not changed by the addition of potassium sorbate into the film. These results can be explained by a model of the polymer structure which assumes that the huge amorphous regions of the polymer incorporated the small potassium sorbate molecules. However, the transparency of the film, an optical property, was reduced due to the incorporation of potassium sorbate. A migration test of the preservative-releasing LDPE sheet showed good fit with model simulations, and was used in determining the diffusivity of potassium sorbate from the LDPE sheet to water. The LDPE film containing potassium sorbate released its preservative and inhibited the yeast growth on agar plates. Therefore, it is possible that the antimicrobial polymer could prevent microbial spoilage of food products and prolong the shelf life of the products when it is used as a packaging material during food packaging.
Floros, Purdue University.
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