Modifying the physical properties of dairy protein films for controlled release of antifungal agents

The effect of sodium chloride (NaCl) and pH of sorbitol-plasticized whey protein isolate (WPI) and sodium caseinate (NaCas) films on their mechanical and physical properties were examined. Moreover, antimicrobial films were prepared by incorporating different levels of potassium sorbate and natamycin in WPI films, plasticized with sorbitol, and the diffusion rates of the antimicrobial agents in a liquid medium were evaluated. The addition of NaCl resulted in a decline of Young modulus (E) of the edible films and an increase of the elongation at break upon extension (%EB). For WPI films, reducing the pH of the casting solution down to 5.0 resulted in creation of WPI films with greater flexibility than those at pH 7.0, while the highest %EB values were observed at pH 6.0. The moisture uptake behavior increased with the addition of sodium chloride and the films made from casting the WPI-sorbitol solution containing 200 mM NaCl showed a greater moisture adsorption capacity at a given aw. The addition of NaCl did not affect significantly the water vapor permeability with the exception of 300 mM NaCl. Whey protein films, made by casting a solution of pH 5.0 showed a significant increase in water vapor permeability (WVP), compared with films originated from solutions with pH 7.0 or 6.0. The addition of sodium chloride and the pH reduction of edible WPI films containing potassium sorbate resulted in reduction of the diffusion coefficient of the antimicrobial. In the case of films containing natamycin, adding sodium chloride did not affect the diffusion coefficient, whereas reducing the pH values of the film forming solution decreased this parameter. The diffusion rate of the two antifungal agents was inversely affected by the molecular shape/size of the component.