Mechanical, water vapor barrier and thermal properties of gelatin based edible films

Edible films are thin materials based on a biopolymer. The objectives of this work were to determine the water vapor permeability and the mechanical and thermal properties of edible films based on bovine hide and pigskin gelatins. These films were prepared with 1g of gelatin/ 100 ml of water; 15-65 g sorbitol/100 g gelatin; and at natural pH. The samples were conditioned at 58% relative humidity and 22 degreesC for 4 days before testing. The mechanical proper-ties were determined by the puncture test and the water vapor permeability by gravimetric method at 22 degreesC. For DSC analysis, samples were conditioned over silica gel for 3 weeks. Samples (similar to 10 mg) were heated at 5 degreesC/min, between - 150 and 150 degreesC in a DSC TA 2010. A second scan was run after cell cooling with liquid nitrogen. As expected, the puncture force decreased and the puncture deformation and water vapor permeability increased with the sorbitol content. The origin of gelatin was important only above 25 g sorbitol/100 g gelatin. The DSC traces obtained in the first scan of samples with 15-35 g sorbitol/100 g gelatin, showed a well visible glass transition followed by a sol-gel transition. However, with the increase of sorbitol concentration, the glass transition became broader, typical of the system presenting a phase separation. The model of Couchman and Karazs for ternary system, was used to predict the Tg values as a function of sorbitol concentration. (C) 2001 Elsevier Science Ltd. All rights reserved.