ORIGINAL PAPER Effects of gallotannin treatment on attachment, growth, and survival of Escherichia coli O157:H7 and Listeria monocytogenes on spinach and lettuce Christina Engels • Agnes Weiss • Reinhold Carle • Herbert Schmidt • Andreas Schieber • Michael G. Ga ¨nzle Received: 14 January 2012 / Revised: 20 March 2012 / Accepted: 25 March 2012 / Published online: 12 April 2012 Ó Springer-Verlag 2012 Abstract Food-borne illness outbreaks are increasingly associated with fresh produce. Their high prevalence may reflect the lack of methods to effectively remove patho- genic bacteria from the surface of fruits and vegetables. This study evaluated the effect of antimicrobial gallotan- nins on attachment, growth, and survival of food-borne pathogens on green leafy vegetables. Spinach leaves and interior leaves of lettuce harboring high and low cell counts of background microbiota, respectively, were washed with tap water with and without added gallotannins. To account for the variability among organisms, green leafy vegetables were inoculated with strain cocktails of Escherichia coli O157:H7 and Listeria monocytogenes. Cell counts of L. monocytogenes were significantly reduced by the gal- lotannin treatment. Lower cell counts after storage for 8 days at 4 °C demonstrated antimicrobial effects of gallotannins retained on the surface of green leafy vege- tables. Gallotannin treatments with 1 g/L did not inhibit E. coli O157:H7 but hindered their attachment to filter paper by up to 94 %. The addition of gallotannin-containing extracts from mango (Mangifera indica L.) kernels to the washing water did neither alter color nor texture of bagged fresh-cut products. In conclusion, gallotannin treatment significantly reduced surface contamination of green leafy vegetables with L. monocytogenes and reduced the attachment of cells of E. coli O157:H7. Keywords EHEC Á Listeria Á Gallotannins Á Pentagalloylglucose Á Lettuce Á Spinach Introduction Fresh-cut produce has increasingly been identified as a source of food-borne outbreaks, particularly with Listeria monocytogenes and enterohemorrhagic Escherichia coli (EHEC) [1]. Surveillance of retail products of leafy greens showed a high prevalence of L. monocytogenes [2, 3]. L. monocytogenes survives in the food-processing environ- ment and grows at refrigeration temperature. L. monocyt- ogenes causes meningitis, septicemia, or fetal death in pregnant women. Young, elderly, and immunocompromised people as well as pregnant women are susceptible to infec- tion. Serotypes of L. monocytogenes associated with human listeriosis include 4b, 1/2a, and 1/2b [4]. L. monocytogenes causes less than one percent of food-borne illness but liste- riosis has a high hospitalization and mortality rate [5]. EHEC also caused major produce-associated outbreaks [for reviews, see 2, 6]. In 2011, a severe outbreak of hemolytic-uremic syndrome (HUS) caused by a Shiga toxin-producing E. coli (STEC) was reportedly linked to C. Engels Á A. Schieber Á M. G. Ga ¨nzle (&) Department of Agricultural, Food and Nutritional Science, University of Alberta, 4-10 Ag/For Centre, Edmonton, AB T6G 2P5, Canada e-mail: mgaenzle@ualberta.ca A. Weiss Á H. Schmidt Institute of Food Science and Biotechnology, Food Microbiology, Hohenheim University, Garbenstrasse 28, 70599 Stuttgart, Germany R. Carle Institute of Food Science and Biotechnology, Plant Foodstuff Technology, Hohenheim University, Garbenstrasse 25, 70599 Stuttgart, Germany Present Address: A. Schieber Institut fu ¨r Universita ¨t Bonn, Institut fu ¨r Erna ¨hrungs- und Lebensmittelwissenschaften, Universita ¨t Bonn, Ro ¨merstrasse 16, 53117 Bonn, Germany 123 Eur Food Res Technol (2012) 234:1081–1090 DOI 10.1007/s00217-012-1727-6