# Plant Extracts for the Control of _Listeria monocytogenes_ in Meat Products
## 1 Introduction  
The need to produce healthy and safe food without the use of chemical additives has led to the development of technologies for the control of both pathogenic and spoilage microorganisms and consequently high-quality standards. This requirement comes from the consumers demanding safe and quality food products but, at the same time, little processing, with a low content of chemical additives and with an extended shelf-life [1]. The main innovative conservation techniques optimized and available for food applications are based on the implementation of high pressure [2], active packaging [3; 4; 5] and natural antimicrobial compounds [6; 7; 8; 9; 10]. The growing interest in food bio-conservation has led to the use of new antimicrobial compounds of various origins, including those based on the use of microorganisms, their metabolites and natural extracts of plant origin [11; 12; 13]. A wide range of hams and sausages can be found on the market, with their characteristics deriving from different product recipes, raw materials and processing conditions, which are also related to the climatic conditions and to the specific origin of the raw meals. Consequently, different recipes and processing methods give the products different organoleptic characteristics. Italian Salami and hams are made with fresh, carefully selected Italian pork, with spices added to refine the taste of the meat: this is a fundamental step to enhance the scent of the final product, and is essential to shape the different tastes, which are typical of specific territories [14]. The spices are added during the preparation of foods with the aim of improving their organoleptic characteristics. Furthermore, the antioxidant action carried out by the molecules that compose the spices can contribute significantly to the prevention of natural food alteration phenomena (oxidative phenomena) with anadvantage for the final consumer as well [15]. Since ancient times, spices have been used for the control of microbial alterations and for their antimicrobial activity in food [16; 17; 18]. Spices such as cinnamon, cloves, garlic, mustard and onion can increase the commercial life of foods thanks to the content of some biologically active compounds consisting of phenols, aldehydes, ketones, ethers and hydrocarbons. Several studies carried out using other spices, such as laurel, coriander, rosmear, thymme, oregano and sage, have shown their significant bacteriostatic effect [19; 20; 21]. Some authors have described the use of these natural extracts for the preservation of fresh meat, fish products and fresh cheeses [15; 20]. Some extracts are not only able to control the development of altering microorganisms but, by prolonging the shelf-life, they allow for a general increase in quality itself [22; 23; 24; 25; 26]. Spices, in addition to exhibiting antimicrobial action against certain foodborne pathogens, have a stimulating action towards lactic acid bacteria, used as starters in seasoned meat products and fundamental protagonists of fermentation processes. In fact, the presence of lactic acid bacteria has a positive impact on fermented products only, whereas in non-fermented or cooked meat products, they can be involved with food spoilage if a cross-contamination post thermal process happens [27]. The stimulus action seems to be dependent not only on the type of spices and their origin, but also on the different types of microbial population present in the food [28; 29]. Different extracts of spices can be effectively used as natural additives alone or in combination with other conservation technologies. They can act on food preservation with an inhibitory effect on the spoilage microbial population, both Gram-positive and Gram-negative bacteria. However, their effectiveness changes according to pH, storage temperature, oxygen presence and the concentration of biologically active components responsible for antimicrobial activity [30].