3.6. Films morphologyIn order to provide a better insight into the structure-propertyrelationships of biocomposite films, scanning electron microscopy(SEM) analysis was performed. SEM micrographs of the surface andcross-section of fish gelatin–chitosan films incorporated with OEOat different levels are illustrated in Fig. 3. The control film (withoutessential oil) showed relatively rough and continuous surface withgrainy structure (Fig. 3A), comparable with the results reported byJeya Shakila et al. (2012) on gelatin–chitosan biocomposite edi-ble films. The formation of covalent and non-covalent bondingbetween chitosan and protein strands might be causing the sur-face roughness of gelatin–chitosan films (Prodpran et al., 2007). Incontrast, smooth surface was noticed in the films added with essen-tial oil, regardless of oil content (Fig. 3B–D). However, the presenceof oregano oil caused discontinuities in the film matrix, probablydue to weaker protein-polysaccharide interaction in film network(Bonilla et al., 2012). As the oil content increased from 0.4 to 1.2%(w/v), lipid droplets were slightly enlarged maybe due to the defor-mation forces that acted during the polymer chain aggregation bysolvent evaporation (Sánchez-González et al., 2009). Consequently,the increased size of the oil droplets could enhance creaming andphase separation. Oregano essential oil at high content might beseparated and centered at the upper surface of film during thedrying step.