International Journal of Research Studies in Microbiology and Biotechnology (IJRSMB) Volume 2, Issue 2, 2016, PP 25-29 ISSN 2454-9428 (Online) http://dx.doi.org/10.20431/2454-9428.0202005 www.arcjournals.org ©ARC Page| 25 Inhibition of Salmonella Enterica and Listeria Monocytogenes in Tofu by Activated Plastic Films Pilar Martínez Viedma 1 , Maria José Grande Burgos 1 , Rubén Pérez Pulido 1 , Belén Soriano 2 , Antonio Gálvez 1 *, Rosario Lucas 1 1 Department of Health Sciences, University of Jaen, 23071-Jaén, Spain. 2 ANDALTEC, Centro Tecnológico del Plástico; Martos, Jaén, Spain 1* agalvez@ujaen.es Abstract: Transmission of food borne pathogens through the food chain is a matter of concern. In the present study, tofu sausage slices were used as model for testing the antimicrobial activity of low-density polyethylene (LDPE) films surface-activated with tyrosol singly or in combination with p-hydroxybenzoic acid or a bacteriocin preparation from Enterococcus faecalis. Tofu slices challenged with cocktails of Listeria monocytogenes and Salmonella enterica strains were vacuum packaged in LDPE films activated with antimicrobials and stored at 10 ºC for one month. Best results against the two foodborne pathogens tested were obtained when tyrosol (1.5%) was used in combination with p- hydroxybenzoic acid (0.5%). Results from the present study highlight the potential of tyrosol for development of active packaging with antibacterial activity. Keywords: Active packaging; Tyrosol; Bacteriocin; Listeria; Salmonella. 1. INTRODUCTION Tofu (soybean curd) is a popular food in Asian countries. Its consumption has been increasing in Western countries in recent years, especially by people with health concerns. Tofu is considered a healthy part of a well-balanced diet, as it is low in calories and rich in protein, iron, calcium, magnesium, and group B vitamins [1]. Usually, packaged tofu is sold in supermarkets, where it is normally found refrigerated (4 − 10 ℃). In Western countries, packaged tofu is also sold in other formats such as sausages for vegetarian consumers. Unpackaged tofu is sold only in open markets, typically by independent vendors who usually display the product under conditions prone to microbial contamination [2, 3]. Transmission of food borne pathogens through the food chain is a matter of concern. A recent study reported the presence of Salmonella spp. in 7% of unpackaged tofu samples in Bangkok [4]. Several incidents of tofu recalled due to Listeria monocytogenes contamination were also reported [5, 6]. The application of films or coatings activated with antimicrobial substances is an attractive approach to avoid transmission of food borne pathogens through the food chain. A large variety of materials, ranging from plastic films to coating solutions based on cellulose, pectin, starch, alginate, chitosan, or proteins have been tested against food borne pathogens in different food systems [7-10]. The activated materials allow a gradual release of antimicrobial compounds into the food surface and at the same time act as a barrier against cross contamination of the packaged or coated food product. Natural antimicrobial compounds (such as essential oils or bacteriocins) are good candidates for preparation of activated films or coatings since they have a good acceptance by the consumers [11, 12]. Films based on methylcellulose or hydroxymethylcellulose activated with the bacteriocin nisin achieved a decrease in viable counts of Listeria in refrigerated tofu that was dependent on the bacteriocin concentration applied [13]. Yet, we have found no other reports in the scientific literature on application of activated films for preservation of tofu. Antimicrobial compounds found in essential oils have the advantage over bacteriocins of being naturally active on both gram-positive and gram-negative bacteria [11]. Tyrosol is a phenolic compound resulting from hydrolysis of the olive fruit main bitter compound, oleuropein [14-16], and is found in byproducts from table olives and olive oil industry. The aim of the present study was to determine the efficacy of plastic films activated with tyrosol (an antimicrobial compound naturally