Molecular mobility and oxygen permeability in amorphous beta-lactoglobulin films

Edible films and coatings are developed to extend the shelf life of food products. Our overall objective is to understand how molecular mobility modulates diffusion rates and thus chemical reactivity in films made from amorphous beta-lactoglobulin. The phosphorescence emission spectra and lifetimes of the triplet probe erythrosin B embedded in the beta-Lg films provide measures of the modes, rates, and distribution of molecular mobility in the film, providing the molecular detail necessary to connect food quality and stability to molecular structure and mobility. The mobility contours generated from this research provided us with information about the onset temperature and level of molecular mobility required to support permeability of atmospheric oxygen. In beta-Lg --based binary matrices, sugars (sucrose, trehalose, maltose), plasticizers (glycerol, sorbitol, maltitol and PEG-400), fatty acids (palmitic acid, caprylic acid) and protein (BSA) were selected to investigate how variations in composition influence the molecular mobility and oxygen permeability in amorphous beta-Lg matrix. Further more complicated beta-Lg -- based ternary matrices (maltose and maltitol) and (PEG and sucrose) were generated in order to gain a deeper understanding of edible films.In pure beta-Lg films there was linear correlation between molecular mobility and oxygen permeability. Various additives showed different results with respect to mobility and permeability. The addition of sucrose, maltose, maltitol and trehalose greatly reduced the mobility and the permeability of the beta-Lg matrix. Glycerol exhibited an anti-plasticization effect and showed decreased mobility at a molar ratio of 1:1 glycerol/beta-Lg. PEG greatly enhanced the permeability of beta-Lg matrix. Fatty acids palmitic acid and caprylic acid had a rigidification effect on the matrix with no change in permeability. We were able to detect dynamic synergies in beta-Lg maltose and maltitol mixtures, whereby these sugar-polyol mixtures at equal ratios anti-plasticized the beta-Lg matrix and at unequal ratios plasticized the matrix. The tertiary matrix comprising of beta-Lg, PEG 400 and sucrose brought about a substantial reduction in the permeability. A better understanding of the mobility in these complex matrices will help improve the effectiveness of beta-Lg in barrier applications in real food systems.