## 1 Introduction  
_Salmonella_ is one of the main microorganisms identified as a cause of food-borne outbreaks in the EU/EEA (87.9 cases/100.000 population). Animal-based food, especially poultry meat, is the main source of human salmonellosis [1]. Positive samples of _Salmonella_ originate from different food products, mostly from meat and meat products, and notably from fresh meat from broilers and turkeys [2].  
In the European Union (EU), and concretely in Spain, specific regulations have been developed for the control of food-borne zoonoses [3; 4; 5]. In turkey meat production, the focus has mainly been on the control of _Salmonella_ spp. [6; 7], with particular concern regarding _Salmonella_ Enteritidis and _Salmonella_ Typhimurium [2]. High prevalence rates can only be combatted through holistic management of the entire process. In slaughterhouses, all the processes must emphasize avoiding contamination of carcass and reaching the maximum hygienic standards, and the _Salmonella_ prevalence should be decreased in various slaughtering steps. European regulations (R 2073/2005) and different international recommendations have established that the absence of _Salmonella_ in a 125 mL sample is required.  
Scalding is performed to loosen the feathers prior to the defeathering step, and this process is conducted by immersing the slaughterned birds in warm water or through the use of a newly developed process that involves exposure to steam [8]. According to this author, turkeys are usually subjected to a process called soft scalling/semicsalling, which is performed at a water temperature of 50-53 \({}^{\circ}\)C for 1-3 min. The scalling and defeathering steps can support contamination. Ideally, a poultry scalder prepares carcasses for defeathering and reduces the bacterial and debris load on the skin of the carcass [9].  
Controlling the temperature in a conventional water tank scalder is also a key aspect of keeping the bacterial load under control [8]. Indeed, scaling is considered both an important and troublesome step regarding contamination [10]. [PERSON] and [PERSON] [11] report that careful equipment design is required for meat hygiene, since 1 g of soil material (e.g., dirt, fecal material) attached to the feathers can contain 10\({}^{8}\)-10\({}^{9}\) microorganisms. It is important to minimize cross-contamination in the common bath used for scalding [12]. Physical variables to control this contamination are time and temperature, which influence washing and antimicrobial effects; the chemical variable is pH, which also influences the antimicrobial effect [11]. According to these authors, for quality pork and poultry meat production, methods of scalding and temperature selection need to be studied. In fact, places where cross-contamination occurs frequently in slaughterhouses include the scalding, defeatinging, evisceration, and chilling steps [13]. Also, [PERSON] [14] reports that time, temperature, pH, and the use of antimicrobial chemicals, among other factors involved in this step, are critical both in terms of maintaining product quality and minimizing the occurrence of enteric pathogens. Furthermore, the scalding water adheres to the feathers and to skin pores. For this reason, it is not strange to find different genera of microorganisms in scalding tank water [15]. In this sense, [PERSON] and [PERSON] [16] summarized reports demonstrating that in addition to water temperature, carcass contamination during scaling may be reduced by several measures, with the inclusion of approved chemicals to maintain pH at values which do not allow for _Salmonella_ growth being among them [17; 18; 19; 20; 21].  
This work deals with two of the factors with notable influence on bacterial growth: temperature and pH. The objective of our work is to test different treatments based on these factors in scaling tank water throughout the day in a pilot line of a turkey slaughterhouse under real conditions in order to decrease the occurrence of _Salmonella_.