Bioactive packaging materials from edible chitosan polymer - Antimicrobial activity assessment on dairy-related contaminants

The inhibitory activity of chitosan-based edible coatings was assessed against 2 food pathogens (Staphylococcus aureus and Listeria monocytogenes) and I strain involved in food alteration (Pseudomonas aeruginosa) on model agar medium and on a real cheese food product. Colony counting and epifluorescence microscopy methods were conducted, and the results show a nonsignificant influence of the components of the food matrix in the protection of the microbial population against chitosan activity. Numeration on model agar medium showed 100% inhibition of the development of selected Gram-positive bacteria and 77% inhibition on Pseudomonas growth. Chitosan is thought to act through binding to the cytoplasmic membrane surface, and it is possible that the outer membrane protects the Gram-negative cells. Moreover, epifluorescence microscopic results showed a possible chitosan action during a short time duration on the synthesis of nucleic acids and especially on the relative proportion of RNA compared with DNA. This impact was followed by an adaptative mechanism of the cells. Edible chitosan coating could thus be used to increase the microbial lag phase while decreasing the maximum density of selected microorganisms and could have potential application for dairy products preservation.