Casein/wax blend extrusion for production of edible films as carriers of potassium sorbate-A comparative study of waxes and potassium sorbate effect

Organic acids as potassium sorbate (KS) have a long history as being generally recognized as safe food preservatives. In this work, KS was incorporated in rennet casein sheets containing waxes (beeswax, candelilla and carnauba waxes) and its release and antimicrobial potential against Escherichia coli were analysed. KS was studied at 15 degrees C for its antimicrobial properties against Escherichia coli ATCC 10536. 15 degrees C is a non-common incubation temperature for E. coli but is often used for food storage of cheeses (in ripening cellars) or dry foods for example. Waxes are well studied blended to hydrocolloids to make coatings or films by solvent casting method but the novelty of this work is the use of a twin screw extruder to produce films. Morphological, barrier, tensile and antimicrobial properties were compared for casein/wax blends material produced by twin screw extrusion. The presence of KS significantly inhibits E. coli and that even at low concentration and even after 20 days at 15 degrees C, which suggests effect of casein matrix as preservative carrier. Besides, a plasticizing action of KS was demonstrated at 10% addition on mechanical properties (decrease of TS and increase of % E) and on water barrier properties. Concerning water vapor permeability, only beeswax among waxes introduced in sheets was efficient to reduce WVP (by 20%). No significant impact on sheet color parameters was observed especially due to wax addition. Finally, the work provided here might help researches on edible biopolymer as preservative carriers that can be produced by an easily industrial process (twin screw extrusion).