Barrier properties and mechanical strength of bio-renewable, heat-sealable films based on gelatin, glycerol and soybean oil for sustainable food packaging

In this work we studied the mass transfer of renewable films based on gelatin (Ge), glycerol (Gly) and epoxidized soybean oil (ESO) for application in food packaging. Films were tested for water vapor absorption and diffusion at various water activities (aw), oxygen and water vapor permeability. The absorbed vapor mass increased with aw, as expected, to 0.25-0.3 g/gpol (aw = 0.8). The isotherms were fitted by five different mathematical models. The apparent diffusion coefficient showed an increasing tendency with humidity, up to aw = 0.6-0.7, where a maximum was reached. Oil addition caused a reduction in the diffusion coefficient of Ge based films, associated to a greater amount of dispersed hydrophobic phase. Moreover, heat seal and tear of Ge based films were studied. All films were able to be thermosealed. The partial replacement of Gly by 20% ESO increased significantly the heat seal strength, reaching values higher than those reported for synthetic polymers. Gelatin sample containing 20% Gly and 20% ESO presented an appropriate balance between gas barrier properties as well as the resistance of the heat sealing and the tearing.