Effect of gamma-irradiation on the survival of Listeria monocytogenes and allergenicity of cherry tomatoes Setsuko Todoriki a,Ã , Latiful Bari a , Kazumi Kitta a , Mika Ohba a , Yasuhiro Ito a , Yuka Tsujimoto a , Norihito Kanamori b , Erika Yano c , Tatsuya Moriyama c , Yukio Kawamura c , Shinichi Kawamoto a a National Food Research Institute, Tsukuba, Ibaraki 305-8642, Japan b Japan International Research Center for Agricultural Science, Tsukuba, Ibaraki 305-8686, Japan c School of Agriculture, Kinki University, Nara-city, Nara 631-8505, Japan article info Keywords: Listeria monocytogenes Allergenicity Cherry tomatoes Gamma-irradiation abstract The presence of Listeria monocytogenes in fresh produce is a growing concern because of the possibility of food-borne illness. Ionizing radiation is an effective non-thermal means of eliminating pathogenic bacteria in fresh produce; however, the effect of ionizing irradiation on the allergenic properties of the host commodities remains unknown. This study aimed (i) to determine the effective dose of gamma- irradiation in eliminating L. monocytogenes on whole cherry tomatoes and (ii) to evaluate the effect of gamma-irradiation on the allergenic properties of tomato proteins. Cherry tomatoes that were inoculated with a mixture of five L. monocytogenes strains were treated with gamma-rays from a 60 Co source. A 1.25 kGy dose of gamma-irradiation was found to be sufficient to eliminate L. monocytogenes on whole cherry tomatoes. The immunoblot profile of serum samples obtained from two patients with tomato allergy revealed that gamma-irradiation did not affect the allergenicity of tomato proteins for up to 7 days after irradiation when the tomatoes were stored at 20 1C. Additionally, the m-RNA levels of b-fructofuranosidase, polygalacturonase, pectin esterase, and superoxide dismutase, the main allergenic proteins in tomato, were not affected by the applied irradiation dose. Thus, this study demonstrated that a 1.25 kGy dose of gamma-irradiation effectively eliminates L. monocytogenes on cherry tomatoes without affecting the expression of allergenic proteins in the fruits. & 2009 Elsevier Ltd. All rights reserved. 1. Introduction Contamination with Listeria monocytogenes has been primarily associated with the consumption of dairy products, beef, pork, poultry, and seafood. However, a growing body of data suggests that salad vegetables such as cabbage, celery, lettuce, cucumber, radish, and tomatoes are very often contaminated with L. monocytogenes, and some of these products have been implicated in outbreaks of food-borne listeriosis (Kornacki, 2005). Ionizing radiation can effectively eliminate L. monocytogenes in processed meat products and a variety of fresh and frozen products of animal origin (Bari et al., 2006; Sommers and Boyd, 2006). Ionizing radiation can penetrate protected areas of produce (surface, subsurface, and interior regions) and destroy the bacteria; however, the extent to which a biofilm habitat may influence the radiation sensitivity of bacteria, either both native non-pathogens and pathogenic contaminants, is not well under- stood. Recently, several studies have reported on the allergenicity of tomato (Lycopersicon esculentum) in relation to pollenosis and oral allergy syndrome (OAS) (Kondo et al., 2001). Current studies have shown that pathogenesis-related proteins (PR-Ps) are common allergenic proteins in plants (Midoro-Horiuti et al., 2001; Ebner et al., 2001). Thus, the allergenicity of tomato fruits is expected be affected by its physiological response to various types of environmental stresses. The effects of ionizing radiation on the allergenic properties of foods of animal origin have been studied and several researchers have reported that the antigenicity of egg and milk proteins is modified by ionizing radiation (Lee et al., 2001; Byun et al., 2004; Seo et al., 2004). These studies demonstrated a novel application of radiation processing: the alteration of antigenicity and IgE- binding ability of irradiated proteins owing to radiation-induced modifications in protein conformation. While no adverse effects of irradiation on allergenic properties of food products have been reported as yet, the biochemical effects of radiation on allergens in fresh produces remains to be elucidated. The objectives of this study were (i) to determine the effective dose of gamma-irradiation in eliminating L. monocytogenes on ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/radphyschem Radiation Physics and Chemistry 0969-806X/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2009.03.060 Ã Corresponding author. Tel.: +81298 38 8047; fax: +81 298 39 1552. E-mail address: setsuko@affrc.go.jp (S. Todoriki). Radiation Physics and Chemistry 78 (2009) 619–621