2.2. Test for antimicrobial efficacy
The antimicrobial efficacy of the developed active films was investigated via the Japanese Industrial Standard Method JIS Z 2801:2000. The applied test strains were E. coli DSM 498, Listeria monocytogenes DSM 15675 and Saccharomyces cerevisiae DSM 70449. All test strains were obtained from “Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany (DSM)”. For each test strain an aliquot of an overnight culture was added to a 500-fold diluted nutrient broth in order to adjust
a concentration of at least 1 x 105 colony forming units per ml (cfu/mL). Triplicates of each test film were cut to a size of 5 x 5 cm, inoculated with 400 μL of the test inoculum and covered with a sterile PET-film. Two uncoated films were used in triplicates; one for the determination of the initial cell count directly after inoculation, the other was treated according to the test samples as a reference. All samples were incubated for 24 hours at the specific growing temperature of the germs (E. coli and Listeria monocytogenes at 37 °C, Saccharomyces cerevisiae at 25 °C) and 90 % relative humidity. A colony count after 24 h showed the number of the surviving cells.