Combined effect of oregano essential oil and glycerol on physicochemical properties of antimicrobial films based on chitosan and acetylated cassava starch

The effect of levels of glycerol (GLY) and oregano essential oil (OEO) in casted films based on acetylated cassava starch (AAc) was evaluated using a Response Surface Methodology. It was possible to select the optimal levels of GLY (0.46% w/w) and OEO (0.7% v/w) to produce more resistant (stress at break 25±2 MPa) and less soluble (20 ± 1 %) films. In addition, the effect of OEO addition or the biopolymer type used on film properties was studied. It was observed that AAc and chitosan (CH) contributed to the reinforcement and stretchability of the selected matrix, respectively, while the addition of an optimal level of OEO generated a more resistant film probably as a result of changes in the microstructure and interactions among components according to microscopy, thermal analysis and FTIR results. The water vapor permeability was improved in films based only on AAc. A trend towards higher degradation temperatures for the AAc, AAc/CH and AAc/CH/OEO systems, concerning the CH films, was observed. On the other hand, AAc promoted the hydrophobicity of the surface, CH increased the brown color and OEO improved the solubility in water and introduced an effective antimicrobial barrier action against external food contamination by E. coli and L. innocua. Therefore, the modification of starch and OEO incorporation allowed improvements in the properties of the developed films, making them attractive to be proposed as an active food packaging material.