3.2. Film solubility
Water insolubility or resistance is a substantial characteristic of edible films for use in food protection, where water activity ishigh, or when the edible film must be in contact with water during processing of the coated food, to avoid the exudation of fresh or frozen products (Gontard et al., 1992). All the prepared films maintained their integrity after incubation in water with gentle motion for 24 h. The control film displayed a low solubility value of about38%, similar to that reported by Jeya Shakila et al. (2012) (∼40%)in composite films from fish gelatin and chitosan. The lower solu-bility of biocomposite films in the present study may result fromthe protein-polysaccharide interactions mainly via hydrogen bonding which plays an important role in film formation as reported by Gómez-Estaca et al. (2010). A significant (p < 0.05) increase in water solubility was observed by adding OEO to the film (Table 1).The higher solubility of oil incorporated-films may be assigned to the re-emerging protein-polysaccharide interactions with this essential oil which weaken the interactions that had stabilized theprotein-polysaccharide network structure (Gómez-Estaca et al.,2010). The presence of essential oil may also limit the interaction ofglycerol with protein matrix which would allow an increase in itsleaching phenomenon (Pires et al., 2013). Likewise, the inclusion of clove essential oil to gelatin–chitosan film matrix increased their solubility in water (Gómez-Estaca et al., 2010).