Use of a Scald Additive to Reduce Levels of Salmonella Typhimurium During Poultry Processing S. R McKee,1 J. C. Townsend, and S. F. Bilgili Department of Poultry Science, Auburn University, Auburn, AL 36849 ABSTRACT This study was conducted to evaluate the efficacy of a scald additive, RP scald, to reduce Salmonella Typhimurium (ST) levels on inoculated poultry carcasses. The RP scald (contains sodium hydroxide) in a 1% solution has a pH of 11.0, which may reduce bacteria levels on carcasses. In this study, 600 broilers (Ross 708 straight run, 6 wk of age) with 300 broilers in each of 2 experimental trials were divided into 4 scald treatments (inoculated with ST) and 2 noninoculated groups. The treatment groups included 4 scald treatments (n = 50 per experimental group per trial): soft scald (SS; 50°C for 90 s), soft scald with 1.0% added RP scald (SSRP), hard scald (56.6°C for 45 s; HS), and hard scald with 1.0% added RP scald. The
noninoculated groups (n = 50 per group per trial) are represented by SS0 and HS0. After defeathering, carcass rinses were collected for ST detection. Results indicated that inoculated broilers from hard scald with 1.0% added RP scald had the lowest Salmonella recovery, whereas carcasses from the SS treatment with no RP additive had the highest ST recovery. In trial 1, the SSRP was more effective in reducing ST than HS alone; however, this trend was not consistent. In trial 2, HS alone was more effective in ST reduction than SSRP. Within each scald temperature, the addition of RP scald increased ST reduction; therefore, RP scald may be effective in reducing ST on broiler carcasses in poultry scalder applications, particularly when hard scald temperatures are used.
Key words: scald additive, Salmonella, hard scald, soft scald, antimicrobial treatment 2008 Poultry Science 87:1672–1677 doi:10.3382/ps.2008-00061
INTRODUCTION Salmonella continues to be one of the most common causes of foodborne illness in the United States, with Salmonella Typhimurium (ST) being one of the most common serotypes causing salmonellosis (CDC, 2006). Under the current HACCP system, all broiler processing plants are required to meet Salmonella performance standards that are based on the national baseline study conducted in 1994 and 1995. Under these standards, if 20% or more broiler carcasses test positive for Salmonella, then the processing plant fails to comply. A study in the United States found that 33.9% of retail broiler carcasses tested positive for Salmonella over a 20-wk sampling period (Simmons et al., 2003). Therefore, additional intervention strategies during various stages of poultry processing are needed to help plants reduce Salmonella on poultry. Adding alkaline scald additives to scald tanks may help reduce bacterial loads on carcasses. Humphrey et al. (1981) reported a reduction of fecal matter on feathers and a reduction in total bacterial counts when scald water
©2008 Poultry Science Association Inc. Received February 6, 2008. Accepted April 3, 2008. 1 Corresponding author:
[email protected]
pH was adjusted to 9.0 ± 0.2 by adding sodium hydroxide to scald water. The RP scald (Duchem Industries, Newnan, GA) is a commercial scald additive that has been used in commercial scald tanks to help reduce the appearance of bruising on broilers. The active ingredient in RP scald is sodium hydroxide, which creates a highly alkaline environment when mixed with water. It is thought that the alkaline environment created by RP scald may reduce microbial levels in scalding applications. Although the high pH may reduce bacteria, some potential negative effects of using high pH compounds could include the possibility of inactivating chlorine in the chiller if the chiller pH was raised as a result of residual sodium hydroxide on the carcasses. Monitoring and controlling the pH of the chiller would remedy this issue. In addition to adding a high pH compound to the scalder, temperature of the scald water can also influence the levels of bacteria. Generally, 2 types of scald applications are used in poultry processing. These scalding methods are referred to as soft scald and hard scald. Although scalding times, temperatures, and scalder configurations vary considerably among plants, a soft scald generally refers to scalding at 53.0°C for 120 s, and this scalding method is designed to leave the waxy stratum corneum layer (cuticle) of the skin on the carcasses where pigments may be deposited (Sams, 2001). Alternatively, hard scald applications are higher temperatures for a shorter time,
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USE OF A SCALD ADDITIVE TO REDUCE SALMONELLA
but this method removes the cuticle, resulting in a pale appearance of the carcass. Hard scald temperatures have a greater effect on reducing levels of bacteria compared with lower temperatures (Notermans and Kampelmacher, 1975). Because temperature alone may impact bacterial survival in the scalder, it is important to determine the isolated effect of scalding temperature as well as the combined effect of temperature with RP scald in terms of their ability to decrease Salmonella on inoculated carcasses. Therefore, the objective of this study was to validate the efficacy of RP scald to reduce Salmonella on inoculated carcasses when used in soft and hard scald applications.
MATERIALS AND METHODS Salmonella Inoculum Preparation Test tubes containing 10 mL of tryptic soy broth (Acumedia, Acumedia Manufacturers Inc., Lansing, MI) were inoculated with a frozen culture of a nalidixic acidresistant strain of ST. After incubation at 37°C for 24 h, a 10-L loopful of the ST culture was streaked onto xylose lysine tergitol 4 Agar (XLT4; Acumedia, Acumedia Manufacturers Inc., Lansing, MI) containing Tergitol 4 supplement and 0.1% nalidixic acid (Difco Laboratories, Detroit, MI). All XLT4 plates used in this experiment contained the supplement and nalidixic acid so that the media would be selective for recovering the nalidixic acid-resistant strain of ST. The plates were incubated at 37°C for 48 h. Black, isolated colonies were picked from the XLT4 plates, and fresh tryptic soy broth tubes containing 0.1% nalidixic acid were inoculated with one colony per test tube. Test tubes were incubated 20 to 24 h. A stock culture of 108 ST was prepared.
Fecal Slurry Preparation To mimic natural conditions, a fecal slurry was used as the vehicle for ST inoculation because fecal matter is generally positive for Salmonella in broiler flocks that are shedding the microorganism. Equal proportions of distilled water and fecal matter collected from the Auburn University Poultry Research Unit were used to make 500 mL of a fecal slurry. The fecal matter was autoclaved (121°C for 30 min at 30 psi, Getinge 522LS Steam Sterilizer, Rochester, NY) to kill any existing microorganisms and then cooled to room temperature. Microbial analyses of the autoclaved fecal matter were carried out to confirm that the autoclave cycle killed microorganisms. Approximately 180 mL of the autoclaved fecal matter was reserved for use as the sterile fecal slurry. A total of 300 mL of inoculated fecal slurry was prepared by adding 120 mL of the stock 108 ST inoculum to 180 mL of autoclaved fecal matter, giving a 1:1.5 ratio of ST to fecal matter. In other words, 1 mL of 108 ST was present in each 2.5 mL of the stock of inoculated fecal slurry.
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Broilers Broilers (Ross 708 straight run, 42 d of age, n = 600 total; Aviagen, Huntsville, AL) were used for the experiment. In trial 1, broilers (n = 300) were obtained from a commercial grower and transported to the Auburn University Poultry Research Unit (
