Effect of fatty acids and 'Brazilian elemi' on composite films based on gelatin

Composite edible/degradable films produced with hydrocolloids and lipids can result in better functionality than films produced with the components, especially with respect to their barrier properties. Of the lipids, waxes produce the best water vapor barrier properties, but produce fragile/brittle films. The problem of incorporating lipids into a hydrocolloid in a homogenous way has still to be solved. The objective of this research was the incorporation of 'Brazilian elemi', a highly hydrophobic resinous exudate of the botanical family Burseraceae, into gelatin films, using a blend of stearic and palmitic acids to dissolve the elemi, and subsequent emulsification of the filmogenic solution using triacetin as plasticizer. Films with the addition of acids, the blend and the blend and the elemi presented better water vapor barrier properties as compared to the gelatin/triacetin film. The mechanical resistance decreased with the addition of the lipids and the opacity and soluble matter increased. The confocal laser scanning microscopy showed the size distribution of the lipid drops and their localization in the matrix. They were not homogeneously incorporated despite the improvement in the water barrier property and the fact that the films appeared to be homogenous and malleable. The analyses by differential scanning calorimetry showed additional melting points besides that characteristic of the protein rich fraction, representing melting of the part of the lipid not incorporated into the filmogenic matrix. Dynamic mechanical calorimetry also showed the presence of more than one glass transition temperature (Tg), indicating the occurrence of phase separation.