Antioxidants modulate molecular mobility, oxygen permeability, and microstructure in zein films

The effect of octyl gallate and propyl gallate on the molecular mobility, oxygen permeability, and microstructure of zein/glycerol films was studied. Films were cast from 70% ethanol/water containing 20% (w/w) glycerol and different amounts of the antioxidants propyl gallate or octyl gallate. The oxygen permeability and local mobility of these films were measured using phosphorescence from the dispersed triplet probe erythrosin B. Although both antioxidants increased the local mobility of the zein matrix to about the same extent, octyl gallate and to a lesser extent propyl gallate dramatically increased the permeability of the film to oxygen. Atomic force microscopy imaging indicated that propyl gallate induced aggregation of zein complexes, which could lead to a more condensed film. These results indicate that the addition of specific functional ingredients, such as antioxidants, to edible films may significantly affect the physical properties and structure and, thus, functional properties in ways that influence their eventual use.