Impact of ghosts on the mechanical, optical, and barrier properties of corn starch films

Ghosts are insoluble materials remaining after the gelatinization of starch dispersions. The role of ghosts on the properties of starch films has not been fully characterized. Thus, the aim of this work was to study the impact of ghosts on the mechanical, optical, and barrier properties of starch films. To this end, an aqueous corn starch dispersion (5% w/w), with glycerol added as plasticizer (1.5% w/w), was formed, and heated at 90 degrees C for 20min. The resulting gelatinized starch dispersion (GSD) was sonicated (0, 1, 2, 4, and 8min). The amount of ghosts phase fraction (GPF) in the GSD decreased with sonication time (ca. 80% after 8min). The sonicated GSDs were cast and dried, and the resulting films were characterized by means of SEM, TGA, FTIR, elongation at break, and WVP techniques. The results showed that GPF affected positively and negatively the films. The elongation at break and tensile strength were enhanced, the higher was the GPF in the starch films, whereas film opacity and water vapour permeability decreased as GPF decreased. Thus, the presence of ghosts imposes a trade-off problem between mechanical stability and other film properties (e.g., opacity and WVP). It was found that GPF of about 20-30% provided films with good overall properties.