Scalding tank

A few studies report the loosening of bacterial cells from animal skin by using chemical solutions as a tool for decontamination. Work by Humphrey et al. (Reference HUMPHREY, LANNING and BERESFORD1981) reported that adjusting the scalding water pH to 9.0 with sodium hydroxide led to a decrease in aerobic bacteria and coli-aerogene counts in chicken carcasses. Other research (Dickson and Maynard, 1992; Dickson, Reference DICKSON1988) reported that washing the lean and fat tissues of bovine species with a concentrated solution of sodium or potassium hydroxide decreased populations of Salmonella typhimurium and Listeria monocytogenes by two to three log cycles and one to two log cycles, respectively. Scalding by immersion removes bacteria from skin and feathers and, after initial immersion, the number of bacteria on scalding water reaches equilibrium (Mulder and Veerkamp, Reference MULDER and VEERKAMP1974). This is achieved when the number of bacteria leaving the scalding tank is equal to the number of bacteria entering with new carcasses (Cason et al., Reference CASON, HINTON and INGRAM2000). The scalding process is limited in its effectiveness because the majority of birds carries faecal material on their feathers. Attempts to minimise such problem include carcasses spraying and brushing simultaneously before scalding (Sànchez-Plata, Reference SÀNCHEZ-PLATA2007), which favours decreasing bleeding in the scalding tank and, consequently, reduced organic load, increasing the antimicrobial effect of this step (McKee, Reference McKEE2002).

Defeathering

The Canadian Food Inspection Agency, Meat Hygiene Directives 2007, Directive 07, chapter 19.4 ‘Dressing Procedures’, item 19.4.1.2 states that:

‘Defeathering and Washing’ describes that ‘In the dressing of poultry carcasses, all hair, feathers, dirt, scurf, etc., must be completely removed and the carcass thoroughly washed prior to any further incision being made.’

Besides this, it continues: ‘In order to reduce the attachment of Salmonella spp. and other bacteria to the skin, spray washing of carcasses must occur within 15 seconds after defeathering and after carcass transfer. Sprays at both washing stations shall be of sufficient volume and pressure, to completely remove visible foreign material from the surface of the carcass, including the hocks and any exposed surfaces as a result of bleeding or decapitation.’

Nde et al. (Reference NDE, McEVOY, SHERWOOD and LOGUE2007) studied Salmonella spp. cross contamination in turkey carcasses during defeathering, and demonstrated the relationship between presence of Salmonella spp. on living turkeys feathers and carcass skin after defeathering. The authors suggested that certain decontamination procedures applied to the external surface of living turkeys could reduce cross-contamination by Salmonella spp. during defeathering. Such a step has been already used in pork processing. Once contamination is present on any part of the bird's surface, it is suggested that feathers could be a significant source of carcass contamination, higher than contamination originated from faeces, which is generally internal. This fact was confirmed by Mulder et al. (Reference MULDER, DORRESTEIJN and VAN1978), who worked with carcasses that had been inoculated internal and externally with nalidixic acid resistant E. coli K12, and concluded that birds inoculated on their external surface before scalding were a potential source of cross contamination during processing.

Another argument for installing washing sprays after defeathering is based on the paper published by Allen et al. (Reference ALLEN, HINTON, TINKER, GIBSON, MEAD and WATHES2003). They identified air as a principal cross-contamination route during the defeathering step, rather than contact of carcass with defeathering equipment.

In work carried out by Burfoot et al. (Reference BURFOOT, WHYTE, TINKER, HAL and ALLEN2007) it was concluded that carcasses can be contaminated from preparation surfaces, leading to additional air contamination in other processing areas. White et al. (Reference WHITE, COLLINS, McGILL, MONAHAN and O'MAHONY2001) demonstrated a significant difference on aerobic counts between the defeathering room and evisceration room in three plants from Ireland. The defeathering room presented the highest numbers for total counts of aerobic mesophilic and psychrophilic e.g. Enterobacteriaceae, E. coli and thermophilic Campylobacter spp. Salmonella spp. were not identified. Such airborne contamination can be deposited on carcasses, leading to an increase of microbial populations on carcass skin and carrying this contamination to the whole processing line.

Evisceration

The Canadian Food Inspection Agency, Meat Hygiene Directives 2007, Directive 07, chapter 19.4 ‘Dressing Procedures’ item 19.4.1.5 states that; ‘Application of a water film during evisceration procedures’ states that evisceration equipment designed to completely detach the viscera, may also spray the cavity and the viscera provided that:

‘…venting, opening and evisceration operations are controlled as part of a HACCP system; consistent and adequate water pressure and volume is supplied to all the spray nozzles applied to the carcass and/or viscera during venting, opening and evisceration operations; post mortem examination is not compromised (e.g.: excessive water in the cavity)…’

Also in chapter 19.5, ‘Additional Evisceration Floor Procedures’, item 19.5.2: ‘Off-line Reprocessing/Reconditioning’ and 19.5.3: ‘On-line Reprocessing and Reconditioning’, suggests the following:

‘Off-line Reprocessing: Removal of contamination (faecal, bile, ingesta, and extraneous material) from within the abdominal cavity of carcasses by washing, vacuuming, trimming or combinations thereof at a designated off-line work station according to the operator's approved written protocol.

On-line Reprocessing: Removal on-line of contamination (faecal, bile, ingesta and extraneous material) from within the abdominal cavity of carcasses according to the applicable policy and an approved operator-specific written protocol.’

According to regulations from U.S. Department of Agriculture Food Safety Inspection Service (FSIS), visible faecal contamination must be removed before the carcass enters the cooling tank. Carcasses with faecal residues which have been washed are considered microbiologically indistinguishable from those not contaminated with visible faeces (Blankenship et al., Reference BLANKENSHIP, BAILEY, COX, MUSGROVE, BERRANG, WILSON, ROSE and DUA1993). Thus, when correctly done, this washing step, commonly denominated as ‘reprocessing’, is successful in cleaning carcasses and results in a safe meat product (Berrang et al., Reference BERRANG, BAILEY, ALTEKRUSE, PATEL, SHAW, MEINERSMANN and FEDORKA-CRAY2007).

Although visible contamination can indicate evidence for microbiological infection, lack of visible contaminants does not indicate that contamination is absent or limited (Brown et al., Reference BROWN, HOLLINGSWORTH, NICKELSON II, SHERIDAN, STEVENSON, SUMNER, THENO, USBORNE and ZINK2000), nor does it confirm absence of pathogenic microorganisms (Jiménez et al., Reference JIMÉNEZ, SALSI, TIBURZI and PIROVANI2002).

Kemp et al. (Reference KEMP, ALDRICH, GUERRA and SCHEIDER2001) concluded that a significant difference was found between carcasses washed on-line in IOBW (Inside-Outside Bird Washer) systems and carcasses washed off-line using E. coli as an indicator organism of contamination. Significant differences were not found for Salmonella spp. or Campylobacter spp.. Authors also affirm that: ‘Additional handling required for off-line processing increases the possibility of cross contamination and the continuous on-line tested system did not only decrease the need of additional handling but also the incidence of Salmonella spp. in tested carcasses’.

Franchin et al. (Reference FRANCHIN, STEINMULLER, DEGENHARDT, STOFELS, J.G., DAVILA, OGLIARI, NALIN and GARZIEIRA2007b) tested the efficiency of cutting and washing contaminated body parts and observed that:

‘Procedure of cutting skin parts with apparent faecal contamination is not a uniquely adequate procedure for eliminating this kind of contamination, as carcasses washing is equally successful. This procedure does not involve the work force and decreases the possibility of cross contamination due to handling’.

In reprocessed carcasses sampled by rinsing pre-chiller, significant differences were not observed between incidence of pathogen contamination and number of inspected carcasses, or between incidence of pathogens and number of contaminated carcasses reprocessed before pre-chilling stages. Hence, pathogens present on carcasses could have another origin, not only from visible faecal contamination occurring during processing (Cason and Berrang, Reference CASON and BERRANG2002).

It has been reported that bacteria adhere quickly to carcass surfaces which makes removal more difficult (Cason and Berrang, Reference CASON and BERRANG2002; Notermans et al., Reference NOTERMANS, TERBIJHE and SCHOTHORST1980). However, studies in re-processing have clearly demonstrated decreased bacterial counts in samples from carcasses washed immediately after contamination (Fletcher et al., 1997; Powell et al., Reference POWELL, BLANK, HYDAMAKA and DZOGEN1995; Blankenship et al., Reference BLANKENSHIP, BAILEY, COX, MUSGROVE, BERRANG, WILSON, ROSE and DUA1993; Waldroup et al., Reference WALDROUP, RATHGEBER, HIERHOLZER, SMOOT, MARTIN, BILGILI, FLETCHER, CHEN and WABECK1993 Blankenship et al., Reference BLANKENSHIP, COX, CRAVEN, MERCURI and WILSON1975).

Handlers and manipulators have incorporated internal and external washing sprays (IOWB) into processing systems in an attempt to reduce visible bacterial contaminations (Smith et al., Reference SMITH, NORTHCUTT, CASON, HINTON, BUHR and INGRAM2007). Smith et al. (Reference SMITH, NORTHCUTT and MUSGROVE2005) noticed that IOWB systems decrease the incidence of Campylobacter spp. and Salmonella spp. in visible contaminated carcasses and did not find evidence that carcasses with visible faecal contamination had contaminated other carcasses when using the IOWB system. This system is used commercially as the final step for reducing visible contamination and bacterial loads pre-refrigeration. However, other studies reported only a small effect of washing on reducing incidence of bacteria in carcasses (Smith et al., Reference SMITH, NORTHCUTT, CASON, HINTON, BUHR and INGRAM2007). Smith et al. (Reference SMITH, NORTHCUTT, CASON, HINTON, BUHR and INGRAM2007) showed that carcasses with external faecal contamination were observed only occasionally after internal and external washing. No contamination from internal residues in carcasses was observed after using the IOWB system. Depending on exposure time, bacterial adherence depends on type of tissue, i.e. the thoracic cavity has a smooth texture which presents less affinity for adherence.

Studies in reprocessing have demonstrated that carcasses with faecal contamination can be cleaned by washing to reach the same bacterial status as non-infected carcasses (Powell et al., Reference POWELL, BLANK, HYDAMAKA and DZOGEN1995; Blankenship et al., Reference BLANKENSHIP, BAILEY, COX, MUSGROVE, BERRANG, WILSON, ROSE and DUA1993; Waldroup et al., Reference WALDROUP, RATHGEBER, HIERHOLZER, SMOOT, MARTIN, BILGILI, FLETCHER, CHEN and WABECK1993; Blankenship et al., Reference BLANKENSHIP, COX, CRAVEN, MERCURI and WILSON1975; Fletcher et al., 1997). In four out of five plants tested by Powell et al. (Reference POWELL, BLANK, HYDAMAKA and DZOGEN1995) and Waldroup et al. (Reference WALDROUP, RATHGEBER, HIERHOLZER, SMOOT, MARTIN, BILGILI, FLETCHER, CHEN and WABECK1993), reprocessed carcasses presented significantly lower counts of E. coli than those tested immediately after first inspection. Nowadays a higher water volume is used compared to earlier years, with more emphasis on carcass washing for preventing visible contamination.

A document released on May 16, 2002 by the Veterinary Department of the Russian Federation concerning Veterinary-Sanitary Requirements for Inspection Control of Poultry Slaughtering Companies (Kravtchuk, Reference KRAVTCHUK2002) requires that, after disembowelling, the internal and external carcass surfaces and carcasses must be washed in potable running water. After washing, no dirt must be seen on carcass surface.

Technical Regulation of Technological and Hygienic-Sanitary Inspection of Poultry Meat, regulation 210, October 10, 1998 describes (Brasil, Reference BRASIL1998):

‘4.4.1 Evisceration must be carried out in appropriate installations, isolated from scalding and defeathering rooms by walls, including steps from neck skinning operation until the carcass final toilette.

4.4.2 Before evisceration, carcasses must be washed by spraying with appropriate water pressure, with gushes oriented in a way that the whole carcass is washed, including feet. In non automated evisceration systems, these sprays can be located at the beginning of evisceration spout or at the entrance of evisceration room.

4.4.19 Final spray washing of carcasses after evisceration must be carried out by adequate equipment used for efficient washing of internal and external surfaces. Carcasses can also be washed ‘internally’ with a pistol-like equipment, with appropriate water pressure.

4.4.19.2 Washing equipment, when using spray washing and spray pre-chilling, must be located after evisceration and immediately before pre-chilling system, being not allowed any carcass manipulation after washing procedure.’

In annex VI, ‘Workflow of Federal Inspection Service in Poultry Slaughter Houses’ at item 2, during slaughtering, sub item 2.6.1 describes the:

‘Appropriate working of carcass external washing spray, when entering clean zone, for proceeding to evisceration’; and at sub item 2.13 describes ‘Efficiency evaluation of carcass external washing at the exit of evisceration spout. Carcass must enter the pre-chilling system free of dirt or strange materials’.

Analysing the above regulation, it is clear that a spray can be installed on the exit of the evisceration spout for external washing and another spray immediately before the chiller for internal and external washing of carcasses.

Chilling

Cason et al. (Reference CASON, M.E. BERRANG, R.J., BUHR and COX2004) observed that bacterial counting of carcasses with apparent faecal contamination did not present significantly different results from those obtained after the chiller for samples acquired either from rinsing or removing skin portions.

Carcass washing carried out in poultry plants is more vigorous and uses higher water volumes nowadays compared to some years ago. It can be said that the effectiveness of removing bacteria from carcasses by washing is influenced by the vigorous nature of the washing system applied. Voidarou et al. (Reference VOIDAROU, VASSOS, T., KOUTSOTOLI, TSIOTSIAS, SKOUFOS, TZORA, MAIPA, ALEXOPOULOS and BEZIRTZOGLOUS2007) reported that contamination of carcasses is decreased when it undergoes a washing step in the immersion chiller. They suggested that Clostridium perfringens, especially its spores which are more tolerant to several physicochemical effects than faecal indicator bacteria, can be used as contamination indicators in contaminated chiller water.

Northcutt et al. (Reference NORTHCUTT, CASON, SMITH, BUHR and FLETCHER2006), evaluated the amount of water used on chicken carcasses which were subject to cooling by immersion, and concluded that ‘increasing the water volume without controlling other aspects of immersion in the chiller (water temperature, carcass retention time, initial bacterial loads and amount of chloride) will allow only a little improvement in carcasses microbiological status, but increasing water volume during immersion in chiller results in removing of additional bacteria in carcasses.

Bilgili et al. (Reference BILGILI, WALDROUP, ZELENKA and MARIONS2002) studied the influence of visible ingesta in pre-chilled carcasses, and concluded that microbial loads in carcasses collected before and after immersion chilling were significantly different among sampled plants, but did not present significant differences (p>0.05) for counts among carcasses, with or without visible contamination in both sampled chillers. Modern systems of immersion chilling represent an efficient intervention step. The authors concluded that there was no scientific basis to consider ingesta as a contaminant of carcasses during processing as per the Food Safety Performance Standard.

Lillard (Reference LILLARD1989) confirmed that Salmonella spp. was more easily isolated from samples collected after the chiller than before due to the fact that the mechanical action of water reduces cell adherence. Jiménez et al. (Reference JIMÉNEZ, SALSI, TIBURZI and PIROVANI2002) concluded that the increases in Salmonella spp. due to visible faecal contamination after washing is due to the low adherence of the microorganism. Indeed, apparently clean carcasses (carcasses presenting non visible faecal contamination) can carry Salmonella spp. with the same frequency of carcasses with visible faecal contamination.

HACCP concept

Under HACCP (Hazard Analysis Critical Control Point) generic proposals, published in 1997 (Generic HACCP Application in Broiler Slaughter and Processing) by the National Advisory Committee on Microbiological Criteria for Foods (McNamara, Reference McNAMARA1997), it was reported that:

‘Spray washing or other forms of rinsing are used to remove organic material and some of the microorganisms that may have been acquired during defeathering and evisceration. This step helps to reduce bacterial levels on carcasses, including Enterobacteriaceae and Salmonella spp. Frequent, multiple sprays, from bleeding to chilling, are more effective in reducing bacterial levels than a single final wash. Immediate spray washing has been demonstrated to be as effective as trimming for removing faecal contamination acquired during evisceration.

In such context, CCP 2 referrers to ‘final washing’ reports: ‘monitoring of this CCP involves ensuring that water flow, way of washing and residual levels of chloride, are kept in specific levels and visible defects are suitably removed from carcasses during washing’.

Critical limits for this CCP do not require zero tolerance for faecal contamination, but ‘less than or equal to’ 0.5% of carcasses should have gastrointestinal tract-sourced visible contamination.

The FSIS (1997) have zero tolerance for visible faecal contamination, as this contamination is the main vehicle for spreading diseases caused by microorganisms such as Salmonella spp. in the human population. In order to attain zero tolerance status for visible faecal contamination in carcasses and to fulfil the microbiological requirements under HACCP, several Brazilian industries which export chicken carcass and sub-products, have faced difficulties in achieving this status, as in Brazil, only the removing of visibly contaminated portions is allowed. Several intervention strategies for decontamination involve the use of antimicrobial baths and washings. However, there is no intervention that is entirely adequate for minimising microbiological contamination in carcasses during processing. Reducing microbial hazards in final meat product requires implementation of multi-sequential interventions working as multiple obstacles (Bacon et al., Reference BACON, BELK, SOFOS, CLAYTON, REAGAN and SMITH2000) including:

1. a) Scalding tank - where birds are immersed at temperatures ranging from 42° to 60°C;

2. b) Rinse or spray washes - applications of antimicrobial substances in several stages of processing line (after defeathering and evisceration, before and after chiller);

3. c) On-line reprocessing - where automated systems wash the carcass with antimicrobial substances in order to assure removal of visible faecal contamination;

4. d) Chilling of carcasses by immersion in a tank containing an antimicrobial solution such as chloride (Stopforth et al., Reference STOPFORTH, O'CONNOR, LOPES, KOTTAPALLI, HILL and SAMADPOUR2007).

Washing contaminated portions is cited in HACCP's Microbiological Safety and Quality section, edited by International Commission on Microbiological Specifications for Foods (ICMSF) and produced in 1997. It states that:

‘Gush washing of carcasses after defeathering and during other processing steps removes contaminant material that is weakly adhered with microbiota (…). After evisceration and inspection, carcasses are generally washed in order to reduce contamination during these operations. Once microbial contamination becomes more tightly adhered to skin, washing must be performed as fast as possible including the abdominal cavity and external surface of carcass. Monitoring by observation is the way to evaluate that the carcass surface and abdominal cavity are completely washed’.

Conclusions presented by Gill et al. (Reference GILL, BRYANT and MCGINNIS2000) confirmed these findings, as statistical differences, found after carcass washing, were associated with faecal particles, which are more easily removed from carcasses than bacteria. For bovine carcasses, Prasai et al. (Reference PRASAI, PHEBUS, ZEPEDA, KASTNER, BOYLE and FUNGO1995) concluded that, besides contamination spreading after washing due to water sprayers, there was a reduction in bacterial contamination on the carcass surface. Such observations demonstrate that the process of washing could spread or dilute bacterial contamination from one area of carcass to another, however the impact of washing on reducing bacterial contamination is known to be more efficient than not washing.

Notermans and Kampelmacher (Reference NOTERMANS and KAMPELMACHER1975) suggested that frequent washing carried out to keep the carcass wet during processing, prevents adherence of bacteria to the skins surface and reduces the number of bacteria tightly adhered to the skin. In later research, Notermans et al. (Reference NOTERMANS, TERBIJHE and SCHOTHORST1980) reported that delaying washing after faecal contamination is less efficient than immediate washing. Sprays must therefore be located where faecal contamination is most likely to occur, such as after carcass opening or evisceration.

According to Bilgili (Reference BILGILI2001), bacteria are initially suspended in a superficial film of water and can be easily removed by an immediate and effective water spray. If there is continued bacterial contact with meat and skin for relative short periods, the adherence capacity of bacteria increases, reducing washing efficiency. Accidental contact with the digestive tract or its contents is undesirable, but frequently inevitable due to mechanical operations applied to carcasses during processing. Installation of sprays in places of possible faecal contamination may remove bacteria, diluting the number of viable cells and, more importantly, reconstituting a superficial water film in order to reduce the adherence capacity of bacteria on the carcass surface. Water chlorination can be used to promote additional reduction of bacterial load in eviscerated carcasses before refrigeration.

According to Nunes (Reference NUNES2008), hygiene quality depends on an efficient digesta removal, intestine rupture prevention, efficient sprinkling and availability of sprays for washing carcasses at the end of procedure. The correlation between fasting time and faecal contamination incidence seems to be localised, and the presence of faecal matter influences microbiological counts for E. coli, Salmonella spp. and Campylobacter before refrigeration. This correlation is not found with microbiological counts post-refrigeration. Evaluations carried out in different slaughtering houses showed that microbial loads from contaminated and non-contaminated carcasses, caused by incorrect fasting procedures, were not statistically different before and after refrigeration, allowing no correlation to be reported between the presence of visible ingesta and microbial contamination of carcasses.

Li et al. (Reference LI, SLAVIK, WALKER and XIONG1997) studied the effect of sprinkling trisodium phosphate, sodium bisulfate, cethylperidinium chloride and lactic acid at two spraying pressure levels (207 and 345 Kpa) during 30 or 90 seconds and at 30 cm distance from chicken carcasses on contamination. They reported only half the contamination by Salmonella typhimurium when using 90 second sprays, in comparison to carcasses sprayed with water containing 0.85% NaCl. The authors concluded that the poultry processing industry needs a spraying system that can be attached to an existing line and does not require a large space. Thus system optimization, by studying chemical, physical and mechanical parameters, is needed to minimise spraying time to attain the desired bacterial reduction level.

Rasschaert et al. (Reference RASSCHAERT, HOUF, GODARD, WILDEMAUWE, PASTUSACZAK-FRAK and DE ZUTTER2008) researched the relationship between Salmonella spp. species isolated from the gastrointestinal tract and from carcasses after slaughtering in order to determine potential sources of contamination in successively slaughtered flocks. They concluded that, “besides the status of the individual flock, it was essential to maintain the benefits of slaughter logistics, this not always being the case. Carcasses become contaminated mainly due to cross contamination from slaughter equipment, while the contribution of gastrointestinal colonisation for carcasses contamination seemed to remain low’.

Sanchez et al. (Reference SANCHEZ, FLUCKEY, BRASHEARS and McKEE2002) observed that “levels of bacterial loads for chickens after immersion chilling present an equilibrated distribution, while after air chilling it presents a wider variation”.

According to Fluckey et al. (Reference FLUCKEY, SANCHEZ, McKEE, SMITH, PENDLETON and BRASHEARS2003), the lack of a water immersion step in the air chilling process can result in higher variability in and levels of E. coli and coliforms.

According to Berrang and Bailey (Reference BERRANG and BAILEY2009), the efficiency of sprays installed in different areas is not evident for decreasing of counts of pathogenic bacteria when evaluated separately. Individual and combined effects of 5 washing on line locals were tested in Berrang and Bailey (Reference BERRANG and BAILEY2009) work. Carcasses were sampled before and after each washing step and evaluated for presence of Campylobacter spp., E. coli and Salmonella spp. It was observed that Campylobacter spp. counts decreased from 2.58 log to 1.15 log cfu/ml. Regarding Salmonella spp., the prevalence decreased from 80% to 24%, however, no single step in isolation was found to be responsible for this reduction. Applying five washing locations in series decreased the incidence of E. coli from 4.6 to 2.69 log cfu/mL. When evaluated separately, the advantage of each washing step was not evident. However, combined washing areas were effective on decreasing bacterial contamination on carcasses and were hence considered effective for pathogen control.