Antimicrobial edible packaging based on cellulosic ethers, fatty acids, and nisin incorporation to inhibit Listeria innocua and Staphylococcus aureus

Edible cellulosic films made with hydroxypropylmethylcellulose (HPMC) have proven to be inadequate moisture barriers. To improve its water vapor barri er properties, different hydrophobic compounds were incorporated into the H PMC matrix. Some fatty acids and derivatives were included into the film-fo rming solution prior to film formation. Stearic acid was chosen because of its high capacity to reduce significantly the water vapor transmission rate . Antimicrobial activity of edible HPMC film was obtained by the incorporat ion of nisin into the him-forming solution. Nisin is an antimicrobial pepti de effective against gram-positive bacteria. The inhibitory activity of thi s bacteriocin was tested for inhibition of Listeria innocua and Staphylococ cus aureus. The use of stearic acid was observed to reduce the inhibitory a ctivity of active HPMC film against both selected strains. This phenomenon may be explained by electrostatic interactions between the cationic nisin a nd the anionic stearic acid. Further studies showed that antimicrobial acti vity of film varied with the nature of the hydrophobic compound incorporate d, in decreasing order: film without lipid, methylstearate film, and steari c acid film. This corroborated the idea of electrostatic interactions.