Original article Antimicrobial activity of nisin incorporated in pectin and polylactic acid composite films against Listeria monocytogenes Tony Jin, 1 * LinShu Liu, 2 Howard Zhang 1 & Kevin Hicks 2 1 Food Safety Intervention Technologies Research Unit, Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA 2 Crop Conversion Science and Engineering Research Unit, Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA (Received 5 July 2007; Accepted in revised form 3 January 2008) Summary An extruded composite food packaging film containing pectin, polylactic acids (PLAs) and nisin was developed to inhibit Listeria monocytogenes. The mechanical properties and surface structure of the film were also examined. Cells of L. monocytogenes were reduced by 2.1, 4.5 and 3.7 log units mL )1 by the pectin plus PLA (pectin ⁄ PLA) film containing nisin (1000 IU mL )1 of tested liquid) in Brain Heart Infusion (BHI) broth, liquid egg white and orange juice, respectively, after 48 h at 24 °C. Pectin played an important roll in embedding nisin into the film. The pectin ⁄ PLA film had a similar stiffness but lower tensile strength, elongation and fracture energy than the pure PLA film. These data suggested that nisin incorporated into the pectin ⁄ PLA film was an effective approach to reducing L. monocytogenes in a typical growth medium (e.g. BHI broth) as well as in foods (e.g. orange juice and liquid egg). Keywords Films, liquid egg, Listeria monocytogenes, nisin, orange juice, packaging, pectin, polylactic acids. Introduction In recent years, there has been a growing interest in the use of natural antimicrobials, especially nisin, in food packaging applications. Nisin is a bacteriocin produced by Lactococcus lactis ssp. lactis. It is effective against gram-positive bacteria and ineffective against fungi and gram-negative bacteria (Jay, 1996). Nisin was affirmed GRAS by Food and Drug Administration in 1988 (FDA, 1988), and now used as a biopreservative in 57 countries around the world. Because it is non-toxic, heat stable and does not contribute to off-flavours, nisin is commercially used in a variety of foods including dairy, eggs, vegetables, meat, fish, beverages and cereal-based products to inhibit growths of foodborne pathogens including Listeria monocytogenes (Schillinger et al., 1996). Listeria are a concern in food with extended shelf life because they tolerate salt, pH changes, inadequate thermal pasteurisation and refrigerated temperatures (Conner et al., 1986; Cole et al., 1990; Harris et al., 1991). They are ubiquitous and can contaminate many foods and beverages (Adams & Moss, 2000). Some strains can grow in the pH range of approximately 4.1– 9.6 and in the temperature range of approximately 1– 45 °C (Yuste & Fung, 2002). Cells of L. monocytogenes have been implicated in several fatal outbreaks of foodborne illness (Ryser & Marth, 1991; Mead et al., 1999). The presence of L. monocytogenes in ready-to-eat foods is a special concern for at-risk populations. The USDA’s Food Safety Inspection Service has set a zero- tolerance level for L. monocytogenes in ready-to-eat food products (Klima & Montville, 1995). Cells of L. monocytogenes have been isolated from commercially processed liquid whole egg in the United States (Leasor & Foegeding, 1989) and Northern Ireland (Moore & Madden, 1993). Although no outbreaks of listeriosis have been attributed to eggs, the potential exists for survival and growth of L. monocytogenes in egg prod- ucts. Acidic foods such as fruit juices were not recog- nised as vehicles for organisms causing foodborne illness until their survival in acidic fruit juices was demon- strated recently (Mazzotta, 2001). No outbreaks involv- ing L. monocytogenes in fruit juices have been reported; however, this pathogen can survive in the presence of *Correspondent: E-mail: tony.jin@ars.usda.gov Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture. International Journal of Food Science and Technology 2009, 44, 322–329 322 doi:10.1111/j.1365-2621.2008.01719.x Ó 2008 Institute of Food Science and Technology