Received: 1 October 2013 Accepted for publication: 13 May 2015 Slov Vet Res 2016; 53 (1): 5-12 UDC 579.67.08:615.331:637.513.14:636.5 Original Scientific Article EFFECTS OF OREGANO ESSENTIAL OIL, GRAPEFRUIT SEED EXTRACT AND THEIR COMBINATION ON THE GROWTH AND SURVIVAL OF Salmonella Typhimurium AND Listeria monocytogenes IN POULTRY FILLETS UNDER MODIFIED ATMOSPHERE PACKAGING Tolga Kahraman 1 , Ghassan Issa 4 , Sema Sandikci Altunatmaz 2 , Beren Basaran Kahraman 3 , Filiz Aksu 2 , Ali Aydin 1 *, Harun Aksu 1 1 Department of Food Hygiene and Technology, 2 Food Technology Programme of Vocational High School, 3 Department of Microbiology, Faculty of Veterinary Medicine, Istanbul University, 34320 Avcilar, Istanbul, 4 Culinary Programme, Avrupa Vocational School, 34010 Zeytinburnu, Istanbul, Turkey *Corresponding author, E-mail: aliaydin@istanbul.edu.tr Summary: The antimicrobial effect of oregano essential oil (OEO), grapefruit seed extract (GSE) and their combination on the growth and survival of foodborne pathogens (Salmonella Typhimurium and Listeria monocytogenes) were determined in poultry fillets under modified atmosphere packaging (30% CO 2 /70% N 2 ). In a preliminary experiment, OEO and GSE were used at concentrations of 0.05%, 0.1%, 0.5%, 0.8%, 1.0%, 1.5%, 2.0% and of 0.01%, 0.02%, 0.04%, 0.08%, 0.1%, respectively. Paper disc diffusion testing showed that OEO at 0.05%, 0.1% and GSE at 0.01%, 0.02%, 0.04%, 0.08% had weak antibacterial activity. In addition, due to the very strong odour and taste, poultry samples treated with OEO at 1.0%, 1.5%, 2.0% and the combinations were assessed with scores below the limit of acceptance. Thus, the levels of 0.5% and 0.8% of OEO and 0.1% of GSE were further used in poultry fillets. In this study, the pathogens were affected by OEO and GSE. L. monocytogenes was the most sensitive pathogen. In conclusion, the results of this study confirmed the possibility of using natural products with MAP in food production to prevent the growth of foodborne bacteria. Key words: oregano essential oil; grapefruit seed extract; poultry; foodborne pathogens Introduction Poultry is a very popular food commodity worldwide, and its consumption has increased over the last decades in many countries due to its relatively low cost of production, low fat content and its high nutritional value (1). Increased demand for fresh poultry and a desire to transport to more distant markets have increased the need to extend the shelf life of poultry products (2). Nowadays, consumers increasingly demand the use of natural products as alternative preservatives in foods, as the safety of synthetic additives has been questioned. The most abundant groups of natural compounds are represented by essential oils and plant extracts (3). Oregano and Grapefruit Seed Extract (GSE) have frequently been used successfully for food preservation (4, 5). The practical application of several essential oils in foods is limited due to the strong flavour they impart to foods and also to their interaction with some food ingredients. The preservative effect of essential oils and extracts may be achieved by