Physical and chemical properties of tuna-skin and bovine-hide gelatin films with added aqueous oregano and rosemary extracts

The properties of edible, gelatin-based films with added oregano or rosemary extract (two different concentrations) were studied. Gelatins from different sources (bovine-hides and tuna-skins) were employed with a view to elucidating how inherent gelatin characteristics may affect interaction of the gelatin with the polyphenols in the added extract and hence the properties of the resulting films. The bovine-hide gelatin reacted only slightly with the polyphenols in the extracts as shown by the electrophoretic profile and analysis of the dynamic viscoelastic properties, and consequently the attributes (mechanical properties, water solubility, water vapour permeability) of the films were practically unchanged compared with the film made without any added plant extract. The tuna-skin gelatin did evidence some interactions with the polyphenols in both the oregano and the rosemary extracts, especially for the more concentrated of the two extracts tested, thereby altering the attributes of the corresponding films, namely, a higher glass transition temperature, decreased deformability, and, in particular, increased water solubility. Opacity increased irrespective of gelatin origin and plant extract type and concentration.