Postharvest Biology and Technology 56 (2010) 223–231 Contents lists available at ScienceDirect Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio UV-C doses to reduce pathogen and spoilage bacterial growth in vitro and in baby spinach Víctor H. Escalona a,∗ , Encarna Aguayo b,1 , Ginés B. Martínez-Hernández b,1 , Francisco Artés b,1 a Centre of Postharvest Studies, Fac. Agricultural Sciences, University of Chile, P.O. Box 1004, Santa Rosa 11315, La Pintana, Santiago, Chile b Postharvest and Refrigeration Group, Department of Food Engineering, Technical University of Cartagena, Paseo Alfonso XIII, 48, 30203 Cartagena, Murcia, Spain article info Article history: Received 7 July 2009 Accepted 21 January 2010 Keywords: Spinacia oleracea L. Fresh-cut Microbial counts Safety Listeria monocytogenes Salmonella enterica abstract The aim of this work was to investigate the use of different doses of UV-C (0, 2.4, 7.2, 12 and 24 kJ m -2 ) radiation treatments to inhibit microbial growth of Listeria monocytogenes and Salmonella enterica. The spoilage bacteria Pseudomonas marginalis (gram negative) was also tested. These bacteria were studied under in vitro conditions and in baby spinach leaves (in vivo conditions) for 13 and 14 d at 5 ◦ C, respectively. All radiation doses were effective in reducing bacterial growth, although contrary to expectations, high doses did not show the highest microbial inhibition in in vitro experiments. UV-C doses (2.4–24 kJ m -2 ) were also used on baby spinach (Spinacia oleracea L.) leaf surfaces, stored under humidified air using perforated plastic film. A clear inhibitory UV-C effect was observed on L. monocytogenes for 14 d at 5 ◦ C. Meanwhile, UV-C radiation reduced S. enterica loads until the first 4 d of storage, after which a significant increase was found on radiated leaves compared to the control. P. marginalis counts were slightly reduced in UV-C treated leaves. In addition, significant decreases in psychrotrophic counts and Enterobacteriaceae were found during the first 4 d of storage. Respiration rates of baby spinach leaves were higher in radiated than in non-radiated leaves. Moreover, no obvious damage on the epidermal surface and to cell shape was detected in radiated and non-radiated leaves by scanning electronic microscopy (SEM). In summary, the use of double-sided UV-C radiation, at low doses, was effective in reducing initial microbial counts of the tested bacteria types and psychrotrophic and Enterobacteria counts, and in keeping L. monocytogenes at low levels during the storage period, without affecting the sensory quality of fresh-cut baby spinach leaves. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Fresh-cut vegetables are very popular for consumption due to their convenience and ready-to-use properties, but they provide an ideal medium for microbial growth due to tissue damage caused by cutting. However, most such material is less contaminated than the original whole vegetable, as they are washed and disinfected (Nguyen-The and Carlin, 1994). Leafy vegetables are highly suscep- tible to mechanical damage, and bacterial and mould growth which drastically reduces shelf-life (Cantwell and Kasmire, 2002). Accord- ing to Nguyen-The and Carlin (1994), fresh-cut products usually contain microorganisms such as psychrotrophic aerobic bacteria, fecal coliforms, yeast, moulds and pectinolytic bacteria. Spinach leaves can harbor high numbers of mesophilic and psychrotrophic aerobic bacteria, identified mainly as pectinolytic ∗ Corresponding author. Tel.: +56 2 9785841; fax: +56 2 9785704. E-mail address: vescalona@uchile.cl (V.H. Escalona). URL: http://www.cepoc.cl (V.H. Escalona). 1 Tel.: +34 968 325750; fax: +34 968 325433. species, such as Pseudomonas which is the major spoilage agent (Babic and Watada, 1996). During cold storage of fresh-cut leaf vegetables, pectinolytic strains of Pseudomonas are responsible for bacterial soft rot (Ahvenainen, 1996). As well as spoilage microor- ganisms, fresh-cut vegetables could harbor pathogens, among which Listeria is of great concern. Listeriosis, caused by Listeria monocytogenes, is of great public health concern due to its clinical severity and high mortality rate, particularly in pregnant women, newborns, the elderly and the immunocompromised people (McLauchlin et al., 2004). L. monocy- togenes is widely distributed in the environment and it is therefore present in a wide variety of raw food materials (Ryser and Marth, 1991). Pre-packaged mixed salads have a high potential for con- tamination by L. monocytogenes due to extensive handling during preparation, or by cross-contamination from the environment. The lack of any heating step prior to the consumption of such products places the emphasis on high-quality ingredients, hygienic manu- facture, appropriate shelf-life, and correct storage for maintaining product safety (Little et al., 2007). Modified atmospheres have to be applied together with other preservative techniques in order to ensure the inhibition of Listeria innocua in fresh-cut vegetables 0925-5214/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2010.01.008