Effects of Interactions between the Constituents of Chitosan-Edible Films on Their Physical Properties

The main objective of this work was to evaluate the effect of chitosan and plasticizer concentrations and oil presence on the physical and mechanical properties of edible films. The effect of the film constituents and their in-between interactions were studied through the evaluation of permeability, opacity and mechanical properties. The effects of the studied variables (concentrations of chitosan, plasticizer and oil) were analysed according to a 2(3) factorial design. Pareto charts were used to identify the most significant factors in the studied properties (water vapour, oxygen and carbon dioxide permeability; opacity; tensile strength; elongation at break and Young's modulus). When addressing the influence of the interactions between the films' constituents on the properties above, results show that chitosan and plasticizer concentrations are the most significant factors affecting most of the studied properties, while oil incorporation has shown to be of a great importance in the particular case of transport properties (gas permeability), essentially due to its hydrophobicity. Water vapour permeability values (ranging from 1.62 x 10(-11) to 4.24 x 10(-11) g m(-1) s(-1) Pa-1) were half of those reported for cellophane films. Also the mechanical properties (tensile strength values from 0.43 to 13.72 MPa and elongation-at-break values from 58.62% to 166.70%) were in the range of those reported for LDPE and HDPE. Based on these results, we recommend the use of 1.5% (w/w) chitosan concentration to produce films, where the oil and plasticizer proportions will have to be adjusted in a case-by-case basis according to the use intended for the material. This work provides a useful guide to the formulation of chitosan-based film-forming solutions for food packaging applications.