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Salmonella contaminatron is of major concern in the production of pork As part of a UK Food Standards Agency project looking at reducing salmonella contamrnation, a survey of current processing conditions in UK pig slaughterhouses and a review of published data identified pork scalding and dehairing systems as a likely major source of salmonella contamination during pork processing. The arm of this study was to evaluate the factors that may have an influence on the levels of Salmonella spp. on the surface of pigs during the scalding and deharring process. The scald tank temperature, scalding time and changes in the conditron of the scald tank water were analysed during the processing of two batches of prgs in a small EU licensed abattorr. In each trial the levels of Enterobacteriaceae (indicative of faecal and hence possible Salmonella contamrnation) at 8 different sites on three carcasses, both before and after the scalding and deharring process, were determined. Introduction The treatment of prgs differs from that of sheep and cattle in that the skrn is not usually removed during slaughter. The ha1r 1s removed by scalding and deha1ring, usually followed by s1ngeing and polishrng. Traditionally carcasses are passed through a trough of hot water the scalding tank. The water IS kept at approximately 60-6S"C and the period of immersion can last for up to 10 minutes . This softens the attachment of the hair roots to the skin facilitatrng the removal of the bnstles with the minimum of force. Following scalding the carcass passes to a dehainng machine, where it is rapidly rotated horizontally while berng scraped by metal tipped rubber fingers or protrus1ons that run at h1gh speed and have the act1on of nails. There are some systems that combine scalding and deha1ring in a single piece of equ1pment. Dehairing systems are not always completely effective, and 1n many abatto1rs there may be a manual scrap1ng stage after deha1ring (and before singe1ng) to remove any stubborn hairs. Very few stud1es have 1nvest1gated the effect of scalding temperatures on carcass temperatures VanderWal et al. {1993) found that scalding at 60"C for as long as 12 min results in an increase in temperature just below the skin of more than 1 o•c and in the muscle temperature of 1 •c. Scalding (in a comb1ned scalder/deha1rer) for S.S to 7.S mrn gave satisfactory results (though "autumn ha1r" required 9 min). Maribo et al. {1998) measured a 1.0 and 0.4"C rise in the temperature of them longissimus dorsi (at 40 mm depth between the 2nd and 4th lumber vertebra) and m. biceps femoris after scald1ng (60"C, 7 min). S1nce the sk1n of p1gs IS frequently dirty, the water rn the tanks can become contaminated with protein, blood, urine and faeces building up 1n the tank. Studies have shown that large numbers of thermophilic bacilli capable of growrng at h1gh temperature can be found 1n tank scalding water (Sorqv1st & Dan1elsson-Tham, 1987). However, they conclude that although the exterior surfaces of carcasses may become contaminated with Bacillus spp. they are not a problem regarding health or sporlage Adjustment of the pH by adding lime has been reported to reduce counts 1n the scald water but fail to reduce contamination on the skrn (Mackey & Roberts, 1991) A study on the surv1val of Salmonella spp. in samples of commerc1al scald tank water at 50, 55 and 60"C showed that a lime-temperature combination of 1.4 m1n at 60"C is required to achieve a 1 log reduction in salmonella in scald tank water (Bolton et al. , 2003). S ss1on 4 Control strategies Safe pork 2007 -Verona (Italy 257 Materials and methods Batches (n=23 and n=15) of pigs were slaughtered and bled in the normal manner 1n the EU licensed abattoir at Langford on separate days. Physical analysis: For each pig processed the res1dence time in the scalding tank and the deha1rer was measured, as well as the surface temperature of each carcass before and after scalding/dehairing using infrared thermometry (trial 1: Minolta Land Cyclops Compac 3; tnal 2: D1gitron D202AFCF). The water temperature in the scald tank, at a he1ght of 1 and 33 em from the base, was logged throughout the process (Comark Diligence EV N2014) and water samples removed at the start and after pigs 6, 10, 17 and 23 in the first batch and at the start and after each pig in the second batch. The Redox potential, pH, conductivity, turbidity, free chlorine and total chlorine in each sample were determined (Hanna 4 in 1 water tester; Hanna C114 meter). Microbiological analysis: Before scalding seven 50 cm2 sites (randomising between left and nght) of 3 animals (first, last and one in the middle of the batch) were sampled usmg a wetted sponge swab and the inside of the mouth was swabbed using jumbo swabs. The pigs were then scalded and dehaired using the normal practice at the abattoir. After this process the pigs were sampled at positions adjacent to those previously sampled. Swabs were also taken on surfaces in the dehairer and gambrelling table at the beginning and end of each trial. All samples were enumerated for Enterobacteriaceae. Results and discussion Manually controlled processing times were found to be very variable (Figure 1) with extremes from 3.6 to 7.5 minutes for scalding and 0.48 to 1.67 m1nutes for dehairing in tnal 1 and 2. 77 to 6 47 minutes for scalding and 0.87 to 2.13 minutes for dehairing in trial 2. Overall, carcasses were on average scalded for 4.93 (SO 1.32) minutes and dehaired for 0.97 (SO 0.40) minutes. 23 22 21 20 19 18 17 16 15 14 Cl 13 0.. 11 10 9 8 7 6 5 4 3 2 1 0 1 2 0 Scald time (min) • Dehair time (min)

Changes in carcass microbial distribution and water conditions during the scalding and dehairing of pig carcasses