The role of pulsed light spectral distribution in the inactivation of Escherichia coli and Listeria innocua on fresh-cut mushrooms Ana Y. Ramos-Villarroel a , Nicoleta Aron-Maftei b , Olga Martín-Belloso c, * , Robert Soliva-Fortuny c a Department of Biology and Animal Health, University of Oriente, Núcleo Monagas, Av. University, Los Guaritos, 6201 Maturín, Venezuela b Department of Applied Microbiology, “Dunarea de Jos” University of Galati, Street Domneasca No.111, 800201 Galati, Romania c Department of Food Technology, TPV-XaRTA, University of Lleida, Av. Alcalde Rovira Roure 191, 25198 Lleida, Spain article info Article history: Received 5 July 2011 Received in revised form 14 September 2011 Accepted 20 September 2011 Keywords: Fresh-cut mushroom Pulsed light treatments Listeria innocua Escherichia coli Quality parameters abstract Pulsed light (PL) treatments have emerged as a non-thermal method for microbial decontamination on foods surfaces. The aim of this work was to evaluate the bactericidal effect of PL by identifying the spectral range with antimicrobial activity and its effect on the quality of fresh-cut mushrooms (Agaricus bisporus). The mechanism responsible for their action on bacterial cells was also studied using Transmission Electron Microscopy (TEM). Results show that the effectiveness of PL-treatment decreases when the UV (ultraviolet) spectral region is blocked (particularly UV-C). PL treatments of full wavelength spectrum (180e1100 nm) and a fluence of 12 J/cm 2 caused 3 and 2 log reductions in the initial counts of inoculated Escherichia coli and Listeria innocua, respectively. TEM showed significant damage in cell cytoplasm and cytoplasmic membrane after treatments with full spectrum pulses and a total fluence of 12 J/cm 2 . In contrast, mushroom cells treated with 6 J/cm 2 did not exhibit apparent changes in their cytoplasmic membrane. Full spectrum treatments had a more pronounced impact on color, texture and headspace gas composition than treatments without UV spectrum profile. This work contributes with new information regarding the effects of the spectral range of PL treatments that the whole UVeVis range of the spectrum accounts for the lethal effect against microorganisms. On the other hand, it also provides increased knowledge regarding the antimicrobial action of this technology, showing that a photophysical effect exists, leading to changes in the bacterial cytoplasmic membrane and cell content. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Changes in the consumers’ lifestyle with a preference for more natural, fresh and ready-to-eat products have increased the market of minimally processed foods (Soliva-Fortuny & Martín-Belloso, 2003). Production of sliced mushrooms is growing but there is little information available on their quality, shelf life or safety (Brennan & Gormley, 1998; Brennan, Le Post, & Gormley, 2000). In addition, most research has been carried out with whole mush- rooms. Sliced mushrooms are usually marketed in trays over- wrapped with plastic films, which reduce dehydration, and stored under refrigeration temperatures (González-Fandos, 2006). Slicing operations cause spreading of bacteria over cut surfaces, further bruising due to additional handling and disruption of hyphal cells, enabling substrates and enzymes to initiate enzymatic browning reactions (Brennan & Gormley, 1998). Initial microbial counts on mushrooms are very high, ranging from 6.2 to 7.2 log CFU g 1 at harvest time (Simón, González-Fandos, & Tobar, 2005). Therefore, they are highly perishable and tend to lose quality right after harvest (Kim, Ko, Lee, Park, & Hanna, 2006). Pulsed light (PL) treatments have been proposed as a feasible alternative to thermal treatments for killing pathogenic and spoilage microorganisms in foods, thus extending their shelf life. Several studies have shown the ability of PL to inactivate Salmonella spp., Escherichia coli, E. coli O157:H7, Listeria monocytogenes and Listeria innocua in some products (Bialka & Demirci, 2008; Ozer & Demirci, 2006; Palgan et al., 2011; Sauer & Moraru, 2009; Uesugi & Moraru, 2009). The variability of results (2e8 log reductions) is most likely due to the different target microorganisms, the inten- sity of the treatment, and the properties of the substrates (MacGregor et al., 1998; Paskeviciute, Buchove, & Luksience, 2010; Sharma & Demirci, 2003; Woodling & Moraru, 2005). In PL treatments, broadband radiation is emitted ranging from ultraviolet (UV) to near-infrared (NIR). UV wavelengths range from 180 to 400 nm, while visible (VIS) from approximately * Corresponding author. Tel.: þ34 973 702593; fax: þ34 973 702596. E-mail addresses: ay2170@tecal.udl.cat (A.Y. Ramos-Villarroel), nicoleta.aron@ ugal.ro (N. Aron-Maftei), omartin@tecal.udl.cat (O. Martín-Belloso), rsoliva@tecal. udl.cat (R. Soliva-Fortuny). Contents lists available at SciVerse ScienceDirect Food Control journal homepage: www.elsevier.com/locate/foodcont 0956-7135/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2011.09.029 Food Control 24 (2012) 206e213