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3.6. Films morphology
In order to provide a better insight into the structure-property relationships of biocomposite films, scanning electron microscopy(SEM) analysis was performed. SEM micrographs of the surface and cross-section of fish gelatin–chitosan films incorporated with OEO at different levels are illustrated in Fig. 3. The control film (without essential oil) showed relatively rough and continuous surface with grainy structure (Fig. 3A), comparable with the results reported byJeya Shakila et al. (2012) on gelatin–chitosan biocomposite edible films. The formation of covalent and non-covalent bonding between chitosan and protein strands might be causing the surface roughness of gelatin–chitosan films (Prodpran et al., 2007). In contrast, smooth surface was noticed in the films added with essential oil, regardless of oil content (Fig. 3B–D). However, the presence of oregano oil caused discontinuities in the film matrix, probably due 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 deformation forces that acted during the polymer chain aggregation by solvent 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 be separated and centered at the upper surface of film during the drying step.
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