Microstructural characterization of edible films by microscopy techniques and textural features

The microstructural study of edible films is of great importance because it provides information about the structural arrangement and morphology of the films. Several microscopy techniques are employed for structural characterization of edible films; however, most of these only provide qualitative information. The aim of this study was to characterize the surface microstructure of alginate, chitosan and alginate/chitosan films by using of Optical Microscopy, Environmental Scanning Electron Microscopy and Atomic Force Microscopy as well as through the extraction of textural parameters based on image analysis techniques in order of developing a quantitative analysis of microstructure. The alginate, alginate/chitosan and chitosan films were produced by a casting/solvent evaporation method. Small parts of films were used for obtaining surface films micrographs using the microscopy techniques mentioned above. The micrographs were obtained under the same conditions and resolution in each technique. Textural features (Homogeneity, Contrast, Entropy) and fractal dimension values were extracted from grayscale micrographs by means of Gray Level Co-Occurrence Matrix and Shifting Differential Box Counting algorithms, respectively. The Image J program was used to develop the image analysis. Surface micrographs of edible films were obtained with different microscopy techniques, where alginate and chitosan films showed smooth surfaces compared with alginate/chitosan films that showed rough surfaces. The high degree of roughness observed in alginate/chitosan films is due to the formation a branched structural arrangement. Homogeneity, contrast, entropy and fractal dimension parameters described adequately the surface morphology of the films and significant differences between samples were found. We conclude that the use of GLCM and SDBC algorithms to determine textural features and fractal dimension values from images, permit characterizing at a quantitative manner the surface microstructure of edible films and that methodology could be applied as a complementary tool for microscopy techniques.