Effects of gamma irradiation on cytotoxicity and phenolic compounds of Thymus vulgaris L. and Mentha x piperita L. Eliana Pereira a, b , Andreia I. Pimenta c , Ricardo C. Calhelha a , Amilcar L. Antonio a , Sandra Cabo Verde c , Lillian Barros a, d, * , Celestino Santos-Buelga b , Isabel C.F.R. Ferreira a, ** a CIMO-Escola Superior Agr aria, Instituto Polit ecnico de Bragança, Campus de Santa Apol onia, 1172, 5301-855 Bragança, Portugal b GIP-USAL, Facultad de Farmacia, Universidad de Salamanca, Campus Miguel de Unamuno, 37007 Salamanca, Spain c C 2 TN e Centro de Ci^ encias e Tecnologias Nucleares, Instituto Superior T ecnico, Universidade de Lisboa, Portugal d Laboratory of Separation and Reaction Engineering (LSRE), Associate Laboratory LSRE/LCM, Polytechnic Institute of Bragança, Campus de Santa Apol onia, 1134, 5301-857 Bragança, Portugal article info Article history: Received 12 January 2016 Received in revised form 1 April 2016 Accepted 2 April 2016 Available online 4 April 2016 Keywords: Food irradiation Cytotoxicity Phenolic compounds Aromatic herbs abstract The aim of the present study was to evaluate the effects of gamma irradiation on cytotoxicity and phenolic compounds of Thymus vulgaris L. and Menta  piperita L. (methanolic extracts), used in tradi- tional medicine. Thirteen and fourteen phenolic compounds, including caffeoyl derivatives and flavonoid glycosides, were detected in T. vulgaris and Mentha piperita, respectively, none of which was affected by the irradiation dose used (10 kGy). Furthermore, the irradiation up to 10 kGy did not change the cytotoxic properties of peppermint samples on tumor cell lines (MCF-7, NCI-H460, HeLa and HepG2), whereas thyme samples irradiated at 10 kGy increased their cytotoxicity in the assayed tumor cell lines compared with samples submitted to 2 and 5 kGy. All in all, the dose of 10 kGy was considered as suitable to be applied for the purpose of disinfestation and microbial decontamination of these plants without modifying their phenolic composition and bioactive properties. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Phytochemicals present in medicinal plants have revealed to be beneficial for the prevention of various diseases due to its capacity to act in multiple biological mechanisms (Zhang et al., 2011). Its antioxidant potential acts in the neutralization of reactive oxygen species (ROS) that cause damaging changes in the cells (Bajpai, Agrawal, Bang, & Park, 2015; Jain, Jain, Jain, Jain, & Balekar, 2010). The increasing interest in the use of phytochemicals is due to their natural origin, the possibility to be ingested through the diet, easy acquisition and also due to their reduced adverse effects (Dillard & German, 2000). The use of medicinal plants for the treatment of different diseases dates back to ancient times, revealing satisfactory results as anti-inflammatory, antimicrobial, antimutagenic, anti- cancer and antioxidant agents. These effects are in part explained by the presence of phyto- chemicals such as phenolic compounds (Wojdylo, Oszmia nski, & Czemerys, 2007). Phenolic compounds are secondary metabolites ubiquitously distributed in plants (Jabri-Karoui, Bettaieb, Msaada, Hammami, & Marzouk, 2012; Wojdylo et al., 2007). They include a large group of biologically active compounds, with over 8000 individual mole- cules described, having at least one aromatic ring with one or more hydroxyl groups attached, being able to vary from small molecules to large and complex ones. These compounds usually appear in their natural sources as esters and glycosides (Roby, Sarhan, Selim, & Khalel, 2013; Vallverdú-Queralt et al., 2014). Many species of plants recognized for their medicinal properties and beneficial impact on health contain these metabolites, such as e.g., Thymus vulgaris L. (thyme) and Mentha  piperita L. (pepper- mint) (Zgorka & Glowniak, 2001; Kapp et al., 2013), belonging to the Lamiaceae family. Thyme is a plant widely used in folk medicine and its essential oil has shown bioactive properties because of its composition in bioactive metabolites (mixture of monoterpenes, being the main compounds thymol), such as antimicrobial, anti- * Corresponding author. CIMO-Escola Superior Agr aria, Instituto Polit ecnico de Bragança, Campus de Santa Apol onia, 1172, 5301-855 Bragança, Portugal. ** Corresponding author. CIMO-Escola Superior Agr aria, Instituto Polit ecnico de Bragança, Campus de Santa Apol onia, 1172, 5301-855 Bragança, Portugal. E-mail addresses: lillian@ipb.pt (L. Barros), iferreira@ipb.pt (I.C.F.R. Ferreira). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt http://dx.doi.org/10.1016/j.lwt.2016.04.004 0023-6438/© 2016 Elsevier Ltd. All rights reserved. LWT - Food Science and Technology 71 (2016) 370e377