Study on antimicrobial activity of a food packaging material containing potassium sorbate

The feasibility of EVA/LLDPE films containing 1, 2 and 5% (w/w) K-sorbate to inhibit microbial growth and as a consequence prolong shelf-life of foods was investigated. Based on weight loss experiments it was shown that K-sorbate is very suitable for incorporation in LLDPE because of its heat stability during extrusion. After 3 weeks, resp. 6.4, 2.8 and 5.7% of the incorporated sorbic acid was released into distilled water from films containing resp. 1, 2 and 5% (whv) K-sorbate. The very limited migration of K-sorbate may be explained by the incompatibility of the polar salt with the apolar LLDPE. This limited migration could explain the very small inhibitory effect of the K-sorbate films on the growth of Candida spp., Pichia spp., Trichosporon spp, and Penicillium spp. During storage at 7 degrees C of cheese packaged in a 5% (w/w) K-sorbate film, no significant differences could be observed for yeast and mould growth on the cheese cubes compared to a reference film. The concentration of sorbic acid in the cheese did not exceed 14 ppm. This is much lower than the 1000 ppm K-sorbate needed to inhibit microbial growth. The results of this study confirm that the K-sorbate incorporated LLDPE film is not able to inhibit microbial growth in vitro on inoculated media and in vivo on cheese due to the insufficient release of K-sorbate from the film.