Carboxylated styrene acrylate latex samples have been functionalized by the immobilization and entrapment of the enzyme glucose oxidase (GOx), which can be used as an oxygen scavenger in food packaging. GOx was covalently immobilized both on the surface of already formed fi lms and on the latex particles in dispersion, as well as entrapped within the polymer matrix. In the latter two cases, polymer fi lms were formed after the enzyme had been added to the latex dispersion. The storage stability of the enzyme and the infl uence of adding clay were also studied. For a given amount of enzyme, the enzyme immobilized on the fi lm surface showed an enzyme activity about 10 times higher than that of the enzyme present within the polymer matrix. This is probably due to the diffusion limitations of the substrate in the polymer matrix. The fi lms with the enzyme present within the polymer matrix, however, showed a higher total oxygen-removal capacity than fi lms with the enzyme immobilized on the surface. Entrapped enzyme showed a slightly higher activity than enzyme immobilized in the dispersion due to the negative effect of the activating chemicals used during the immobilization and on conformational constraints upon covalent bonding. Low amounts of clay added to the dispersion decreased the enzyme activity, but with higher amounts of clay the enzyme activity increased, probably because of the increased porosity and thus higher substrate accessibility. The most suitable storage condition for all the enzyme-containing fi lms was +8°C, which is just above the glass transition temperature of the polymer used.

The potential of various latex grades to take up, retain and release different types of aroma compound has been explored. The latex grades used included two styrene-acrylate latices and two styrene-butadiene latices, of which one contained talc. The aroma compounds used were ethyl butyrate, 1-hexanol, heptanal, 3-octanone, a-pinene and limonene dissolved in propylene glycol. It was shown that talc improves both the uptake of aroma compounds in the dispersion phase and the retention during the film formation process. However, the styrene-acrylate latex had a greater ability than the styrene-butadiene latex to hold the aroma compounds once the films were formed. These results have been compared to calculated solubility parameters. The uptake of 1-hexanol and propylene glycol in the latex dispersions were higher than expected from the theoretical calculations, probably because of the amphiphilic nature of these molecules. In addition, the influence of aroma compounds on the film formation was evaluated.