E: Food Engineering & Materials Science Antimicrobial Activity of Nisin and Natamycin Incorporated Sodium Caseinate Extrusion-Blown Films: A Comparative Study with Heat-Pressed/Solution Cast Films Basak Yilin Colak, Pierre Peynichou, Sophie Galland, Nadia Oulahal, Fr´ ed´ eric Prochazka, and Pascal Degraeve Abstract: Antimicrobial edible films based on sodium caseinate, glycerol, and 2 food preservatives (nisin or natamycin) were prepared by classical thermomechanical processes. Food preservatives were compounded (at 65 °C for 2.5 min) with sodium caseinate in a twin-screw extruder. Anti-Listeria activity assays revealed a partial inactivation of nisin following compounding. Thermoplastic pellets containing food preservatives were then used to manufacture films either by blown-film extrusion process or by heat-press. After 24 h of incubation on agar plates, the diameters of K. rhizophila growth inhibition zones around nisin-incorporated films prepared by solution casting (control), extrusion blowing or heat pressing at 80 °C for 7 min of nisin-containing pellets were 15.5 ± 0.9, 9.8 ± 0.2, and 8.6 ± 1.0 mm, respectively. Since heat-pressing for 7 min at 80 °C of nisin-incorporated pellets did not further inactivate nisin, this indicates that nisin inactivation during extrusion-blowing was limited. Moreover, the lower diameter of the K. rhizophila growth inhibition zone around films prepared with nisin-containing pellets compared to that observed around films directly prepared by solution casting confirms that nisin inactivation mainly occurred during the compounding step. Natamycin-containing thermoplastic films inhibited Aspergillus niger growth; however, by contrast with nisin-containing films, heat-pressed films had higher inhibition zone diameters than blown films, therefore suggesting a partial inactivation of natamycin during extrusion-blowing. Keywords: caseinate, edible films, extrusion, natamycin, nisin Practical Application: Milk protein-based films incorporating thermolabile food preservatives such as nisin or natamycin were manufactured by conventional industrial processes used to prepare plastic films. Interestingly, the inactivation of incorporated food preservatives was limited. Therefore, caseinate-based antimicrobial packaging films incorporating food preservatives could be used in the food industry in order to extend shelf life of perishable foods, while maintaining their microbiological safety. Introduction An antimicrobial food packaging system is a film-forming poly- meric matrix incorporating antimicrobial compounds that inhibit the growth of undesirable microorganisms in food during its post- process life. The advantages of these innovative packaging sys- tems over the incorporation of antimicrobial compounds directly in the food matrix are numerous. First, the antimicrobial pack- ages can provide a long-term protection through an increased MS 20151673 Submitted 10/7/2015, Accepted 2/23/2016. Authors Colak and Prochazka are with Univ. de Lyon, Universit´ e Jean Monnet, CNRS UMR (Joined Research Unit) 5223, Ing´ enierie des Mat´ eriaux Polym` eres, 23 rue Paul Michelon. F-42023, Saint-Etienne, France. Authors Colak, Peynichou, Galland, Oulahal, and Degraeve are with Univ. de Lyon, Univ. Claude Bernard Lyon 1 , ISARA Lyon, Laboratoire de Bioing´ enierie et Dynamique Microbienne aux Interfaces Alimentaires (BioDyMIA, EA n°3733), IUT Lyon 1 site de Bourg en Bresse, technopole Alimentec, rue Henri de Boissieu, F-01000, Bourg en Bresse, France. Authors Colak and Prochazka are also with Univ. de Saint-Etienne, F-42023, Saint-Etienne, France. Authors Colak, Peynichou, Galland, Oulahal, and Degraeve are with Univ. de Lyon, Univ. Claude Bernard Lyon 1 - ISARA Lyon, Laboratoire de Bioing´ enierie et Dynamique Microbienne aux Interfaces Alimentaires (BioDyMIA, EA n°3733), IUT Lyon 1 site de Bourg en Bresse, technopole Alimentec, rue Henri de Boissieu, F-01000 Bourg en Bresse, France. Direct inquiries to Author Degraeve (E-mail: pascal.degraeve@univ-lyon1.fr). stability of active agents and their slowed-down release (Hoffman and others 2001; Cao-Hoang and others 2010; Guiga and others 2010). Second, active agents are released from packages/coatings to the superficial zone of foods, that is, precisely where most postprocess microbial contaminations occur. And finally, if the plastic material is made from a biodegradable and/or edible poly- mer, this will not result in any environmental drawbacks (Krochta 2002). Antimicrobial food packaging systems incorporating nisin have been proposed by many authors, most likely because nisin is the only bacteriocin with a food preservative status (labeled as E 234) in the European Union. Nisin is also authorized for certain ap- plications by the Food and Drug Administration in the United States. This cationic peptide produced by numerous strains of Lactococcus lactis subsp. lactis inhibits the germination of a wide- range of spores and is efficient against Gram-positive vegetative bacteria such as Listeria. Its antimicrobial activity is attributed to electrostatic interactions with the phospholipids of the bacterial cell membrane, disturbing normal membrane function and thus leading to cell death (Juneja and others 2012). Nisin has been widely studied by numerous authors due to its conformity to food safety regulations, its commercial availability and its rela- tive heat-stability. Its release from coatings or free-standing films C  2016 Institute of Food Technologists R  doi: 10.1111/1750-3841.13284 Vol. 81, Nr. 5, 2016  Journal of Food Science E1141 Further reproduction without permission is prohibited