Listeria innocua growth in fresh cut mixed leafy salads packaged in modified atmosphere Giovanna O. Scifò, Cinzia L. Randazzo, Cristina Restuccia, Giovanni Fava, Cinzia Caggia * Dipartimento di Orto Floro Arboricoltura e Tecnologie Agro-alimentari (DOFATA), University of Catania, Via S. Sofia, 98, 95123 Catania, Italy article info Article history: Received 23 January 2008 Received in revised form 24 August 2008 Accepted 29 August 2008 Keywords: Fresh cut vegetables Mixed leafy salads Listeria innocua Modified atmosphere packaging PCR–DGGE analysis abstract To investigate Listeria innocua fate in fresh cut mixed leafy salads, packaged both in ordinary (OA) and modified atmosphere (MA), the type strain DSM 20649 was inoculated and its behaviour was monitored by conventional and molecular approaches, during storage at 4 °C. Results indicated that: fresh cut salads packaged under MA (at initial conditions of 6% CO 2 and 3% O 2 ) supported the growth of Listeria spp.; conventional plating technique could not detect L. innocua even into inoculated samples, whereas; PCR–DGGE analysis showed that the L. innocua became one of the dominant species in samples packaged in MA, starting from the 3rd day of storage. The study confirms that modified atmosphere has to be applied together with other preservative tech- niques in order to assure the inhibition of pathogenic micro-organisms in fresh cut vegetables. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction The International Fresh-cut Produce Association (IFPA) defines fresh cut products as fruits or vegetables that have been trimmed and/or peeled and/or cut into 100% usable product that is bagged or pre-packaged to offer consumers high nutrition, convenience, and flavour while still maintaining their freshness (Lamikanra, 2002). The market sales of fresh cut vegetables have expanded tre- mendously in recent decades as a result of changes in consumer attitudes, especially consumption of fresh cut lettuce and carrot due their use in prepared salads (Jacxsens, Devlieghere, Falcato, & Debevere, 1999). Micro-organisms are natural contaminants of fresh produces and fresh cut vegetables may harbour different mi- cro-organisms including bacteria, yeasts, moulds (García-Gimeno & Zurera-Cosao, 1997; Kelly, Asmundson, & Huang, 1996) and even pathogens, such as Salmonella and Shigella spp., Aeromonas hydro- phila, Yersinia enterocolitica and Listeria monocytogenes. These pathogens grow and can cause disease depending on the type of product, condition of storage, and competitive microflora (Brack- ett, 1992). The Modified Atmosphere Packaging (MAP) has been developed over the last decades as a technique to retain high quality of veg- etables and has been successfully applied in extending their shelf-life (Francis, Thomas, & O’Beirne, 1999). The positive effect of MAP on the shelf-life of fresh cut vegetables is due to the reduc- tion of product respiration, as well as of overall rate metabolic and biochemical activities (ethylene production, acid catabolism, changes of pectic substances etc.). Furthermore storage of fresh cut fruits and vegetables at relatively high CO 2 concentrations (5–10%), along with low temperature conditions, results in the inhibition of Gram-negative bacteria such as Pseudomonas spp. or Enterobacteriaceae, considered the most common spoilage bacteria in fresh cut leafy vegetables for their higher growth rate at lower temperatures and their pectinolytic enzymes (Jacxsens, Devlieg- here, & Debevere, 2002; Jacxsens et al., 1999; Nguyen-the & Carlin, 1994). The optimal ranges of O 2 and CO 2 levels have been pub- lished for several commodities, and generally 3–5% O 2 and 3–10% CO 2 (balance N 2 ) is assumed as an optimal gas composition to sup- press the respiration without the danger of hypoxic atmosphere (Jacxsens, Devlieghere, De Rudder, & Debevere, 2000). However, there is still a major concern about the product safety associated with the use of MAP. This is mainly due to the desired suppression of spoilage micro-organisms which extends the shelf-life, creating opportunities for slower growth of psychro- trophic pathogenic bacteria (Jacxsens et al., 1999; Jay, 1995; Ros- nes, Sivertsvik, & Skara, 2003, chap. 14). Studies showed that vegetables (like lettuces, tomatoes, endive, carrots, cabbage, aspar- agus, broccoli, cauliflower) are able to support the growth of L. monocytogenes (Berrada, Soriano, Pico, & Manes, 2006; FDA- USDA-CDC, 1998) and numerous data confirmed that vegetables have been implicated in outbreaks of food-borne listeriosis (Beu- chat, 2002; Farber, Wang, Cai, & Zhang, 1998; Thunberg, Tran, Ben- nett, Matthews, & Belay, 2002). Conventional methods (ISO 11290-1) for the detection of Liste- ria spp. in foods involve use of selective culture enrichment with 0956-7135/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2008.08.017 * Corresponding author. Tel.: +39 095 7580218; fax: +39 095 7141960. E-mail addresses: ccaggia@unict.it, c.caggia@tiscali.it (C. Caggia). Food Control 20 (2009) 611–617 Contents lists available at ScienceDirect Food Control journal homepage: www.elsevier.com/locate/foodcont