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Potassium Sorbate Diffusion in Whey Protein Isolate and Lipid Emulsion Films
By,
L.R. Franssen and J.M.Krochta
Department of Food Science & Technology
University of California, Davis
Because of good oxygen, aroma and oil barrier properties, whey protein isolate (WPI) films are potentially useful in food preservation applications. With the incorporation of preservatives, such as potassium sorbate, the usefulness of edible WPI films could be extended to providing microbiological protection to food products. Determining the ability of potassium-sorbate-containing WPI films to retard sorbate diffusion into food products would assess their usefulness as antimicrobial films.
Our objective was to determine the diffusion characteristics and coefficients of potassium sorbate in WPI films and in WPI:beeswax (BW) emulsion films.
WPI and WPI-BW films (20 and 40% BW dry solids basis) with 1.6% potassium sorbate and 1:1 WPI:glycerol were cast. The films were conditioned to 94% relative humidity at 23C. Sorbate diffusion in the films was measured by immersing the films in a stirred 20% glycerol solution (water activity = 0.94) and measuring sorbate concentration in the solution at various time intervals. Sorbate concentration was determined by UV spectroscopy and diffusion coefficients were calculated using Fick's second law and appropriate boundary conditions.
Potassium sorbate diffusion in WPI films exhibited Fickian behavior. The diffusion coefficients in WPI films were found to be larger than those of corn zein and wheat gluten films reported in the literature. The diffusion coefficients in WPI films increased with increasing BW content, opposite to the effect of lipid in corn zein and wheat gluten film.
The results indicate that WPI films without lipid have slower potassium sorbate diffusion and therefore would be better antimicrobial films because of their ability to retard potassium sorbate migration. WPI films, which are hydrophilic, showed increased diffusion coefficients upon addition of BW. This indicates that the permeability of potassium sorbate through the more hydrophobic and non-polymeric beeswax is greater than diffusivity through the plasticized whey protein film matrix.
For more information on Dr. Krochta’s work and the Food Science and Technology Department at UC Davis, please visit Dr. Krochta's Web site - http://foodscience.ucdavis.edu/fst/faculty/KrochtaWeb/index.htm.