Visible contamination on animals and carcasses and the microbiological condition of meat

It is generally assumed that preventing visible contamination of or removing visible contamination from carcasses will enhance the microbiological safety of meat. Visible contamination of carcasses can be reduced by washing or otherwise cleaning animals before slaughter, by dehairing hides before carcasses are skinned or dressed with the skin on, or by performing skinning and eviscerating operations in manners that avoid the transfer of filth from the hide to the meat or the spillage of gut contents. Visible contamination can be removed by washing, trimming, or vacuuming carcasses. The available data appear to indicate that, of the various actions that can be taken to obtain carcasses that are free of visible contamination, only minimizing the visible contamination of meat during skinning and eviscerating operations may also ensure a degree of control over the microbiological contamination of meat. It might be preferable for visible contamination to be controlled largely by superior skinning and eviscerating practices rather than by animal or carcass cleaning treatments, which may not prevent the depositing of bacteria on or the removal of substantial numbers of bacteria from carcasses.     

Microbial contamination occurring on lamb carcasses processed in the United States

Lamb carcasses (n = 5,042) were sampled from six major lamb packing facilities in the United States over 3 days during each of two visits (fall or winter, October through February; spring, March through June) in order to develop a microbiological baseline for the incidence (presence or absence) of Salmonella spp. and for populations of Escherichia coli after 24 h of chilling following slaughter. Samples also were analyzed for aerobic plate counts (APC) and total coliform counts (TCC). Additionally, incidence (presence or absence) of Campylobacter jejuni/coli on lamb carcasses (n = 2,226) was, determined during the slaughtering process and in the cooler. All samples were obtained by sponge-sampling the muscle-adipose tissue surface of the flank, breast, and leg of lamb carcasses (100 cm2 per site; 300 cm2 total). Incidence of Salmonella spp. in samples collected from chilled carcasses was 1.5% for both seasons combined, with 1.9% and 1.2% of fall or winter and spring samples being positive, respectively. Mean (log CFU/cm2) APC, TCC, and E. coli counts (ECC) on chilled lamb carcasses across both seasons were 4.42, 1.18, and 0.70, respectively. APC were lower (P < 0.05) in samples collected in the spring versus fall or winter, while TCC were higher in samples collected in the spring. There was no difference (P > 0.05) between ECC from samples collected in the spring versus winter. Only 7 out of 2,226 total samples (0.3%) tested positive for C. jejuni/coli, across all sampling sites. These results should be useful to the lamb industry and regulatory authorities as new regulatory requirements for meat inspection become effective.     

Importance of airborne contamination during dressing of beef and lamb carcasses

Carcasses along slaughter lines were exposed to normal slaughterhouse air or ultraclean air provided from a unit fitted with a HEPA filter. In cattle slaughterhouses, aerobic viable counts were measured by sponging the brisket at the end of the line to determine whether the slaughterhouse air had led to contamination of the carcasses. Furthermore, a replica cattle carcass with settle plates attached was exposed to similar conditions. The greatest contamination of the plates occurred at the hide puller (P < 0.01). The use of ultraclean air reduced the deposition of organisms onto settle plates (P < 0.01). The airborne route contributed to contamination in cattle slaughterhouses, but other vectors were more important. Further study of contamination of the brisket, at the time that it was first exposed, showed that knives transfer contamination from the hide. The use of ultraclean air at this position showed that the airborne route was a contributor to contamination (P < 0.1), but it was not the greatest vector. In lamb slaughterhouses, the highest counts on settle plates were found at the fleece puller (P < 0.05). The highest counts on the lamb carcasses were found on the brisket exposed from the start of the line to just after the fleece puller (P < 0.05). There was no clear relationship between the measured counts and the concentration of organisms in the air, indicating that the airborne route in lamb slaughterhouses contributes less to carcass contamination than do the surface contacts.     

Evaluation of control over the microbiological contamination of carcasses in a lamb carcass dressing process operated with or without pasteurizing treatment

The aim of this study was to quantify the hygienic status of a lamb slaughterhouse by means of multivariate statistical analysis, to demonstrate how the microbiological data could be exploited to improve the lamb slaughter process by constructing control charts and to evaluate the potential effect of an intervention step such as steam application on the microbiological quality of lamb carcasses. Results showed that pelt removal and evisceration were hygienically uncontrolled. TVC and Enterobacteriaceae progressively increased from the stage ‘after pelt removal of hind and forelegs/before final pulling’ to the stage ‘after evisceration/before pluck removal’ thus indicating possible deposition of microorganisms during these operations. It seems that the processing stages of freshly produced carcasses were better distinguished by Enterobacteriaceae, with evisceration contributing mostly to the final Enterobacteriaceae counts. Application of steam during the lamb slaughter process reduced microbial counts without adverse effects on the organoleptic characteristics of the carcasses. Moreover, the construction of control charts showed that decontamination with steam contributed to the maintenance of an in control process compared to that before the application of steam, suggesting the potential use of steam as an intervention step during the lamb slaughter process.     

Hot water and organic acid interventions to control microbiological contamination on hog carcasses during processing

Pork skin and muscle tissue were washed with water at temperatures from 25 to 80 degrees C. Water temperatures of 65 and 80 degrees C resulted in greater population reductions of Enterobacteriaceae on pork muscle tissue than lower water temperatures. There was no observable effect of water temperature on population reductions of Enterobacteriaceae on pork skin. Water temperatures of 55, 65, and 80 degrees C reduced the populations of Enterobacteriaceae on inoculated scalded carcasses processed in a university abattoir by 1 to 1.5 log/cm2. Following the water wash with an organic acid rinse resulted in further numerical reductions in populations, although these were not statistically different from the water wash alone. The jowls of both scalded and skinned carcasses processed in a commercial establishment were directly inoculated with a fecal material slurry and then processed with organic acid rinsing only, hot water washing only, or a combination of hot water washing followed by organic acid rinsing. The hot water and acid treatment reduced the populations of mesophilic aerobic bacteria and Escherichia coli by approximately 2 log cycles on both scalded and skinned hog carcasses. The combined treatment resulted in 60% of the scalded carcasses and 40% of the skinned carcasses with undetectable levels of E. coli after direct fecal inoculation of the carcasses. Hot water washing followed by organic acid rinsing can significantly improve the microbiological quality of pork carcasses.     

Spray chilling of lamb carcasses

Two spray-chilling treatments were developed to improve appearance and reduce weight loss during lamb chilling. Rates of cooling and weight loss and meat quality were compared to conventionally chilled carcasses.

The first treatment was an intermittent spray during the first 3 h of chilling. The second consisted of only two sprays at 2 h and 10 h post mortem. The conventional control was a two-stage process, with air at 10°C and 1 m/s up to 10 h post mortem, followed by air at 0°C and 1 m/s for a further 14 h.

Both treatments significantly reduced weight loss at 24 h post mortem compared to conventional, from 2·20% to 0·86% and 1·20%, respectively. During a further 4 days storage, the savings were maintained, with weight losses being 3·97%, 2·97% and 3·19%, respectively.

There were small (<1 h) but significantly reductions in the cooling times of spray-chilled loins and legs, attributed to sustained evaporative cooling of the continually wetted surfaces.

No effects on texture or drip loss and only slight effects on surface lean and fat colour were found. Variation in texture between animals within treatments was far greater than between treatments and could not be accounted for by variations in cooling rates.     

Sources and extent of microbiological contamination of beef carcasses in seven United States slaughtering plants

This study determined microbiological loads of beef carcasses at different stages during the slaughtering to chilling process in seven (four steer/heifer and three cow/bull) plants. Potential sources of contamination (feces, air, lymph nodes) were also tested. Each facility was visited twice, once in November through January (wet season) and again in May through June (dry season). Carcasses were sampled by aseptic excision of surface tissue (100 cm2) from the brisket, flank, and rump (30 samples each) after hide removal (pre-evisceration), after final carcass washing, and after 24-h carcass chilling. The samples were analyzed individually by standard procedures for aerobic plate counts (APC), total coliform counts (TCC), Escherichia coli biotype I counts (ECC), and presence of Salmonella. Incidence of Salmonella was higher on dry feces of older compared to younger animals, fresh feces of younger compared to older animals, and on cow/bull carcasses compared to steer/heifer carcasses. Most factors and their interactions had significant (P < or = 0.05) effects on the bacterial counts obtained. Depending on plant and season, APC, TCC, and ECC were < or =10(4), < or =10(2), and < or =10(1) CFU/cm2 in 46.7 to 93.3, 50.0 to 100.0, and 74.7 to 100.0% of the samples, respectively. TCC exceeded 10(3) CFU/cm2 in 2.5% (wet season) and 1.5% (dry season) of the samples. ECC exceeded 10(2) CFU/cm2 in 8.7%, 0.3%, and 1.5% of the pre-evisceration, final carcass-washing, and 24-h carcass-chilling samples, respectively, during the wet season; the corresponding numbers during the dry season were 3.5%, 2.2%, and 3.0%, respectively. These data should serve as a baseline for future comparisons in measuring the microbiological status of beef carcasses, as the new inspection requirements are implemented.     

The ultra-rapid chilling of lamb carcasses

Experiments were carried out on the effects of chilling lamb carcasses very rapidly in a pre-rigor condition. The chilling regime which was finally used was to cool the carcasses at an ambient temperature of -20°C and an air speed of 1·5 m/s for 3·5 h. Examination of striploins from carcasses subjected to this chilling regime showed that, after 7 day's storage, the meat was as tender as that from carcasses which had been conventionally chilled at 4°C for 24 h There were significant reductions in weight loss as a result of ultra rapid chilling, compared to conventionally chilled carcasses. The reductions obtained after 24 h varied between 0·8 and 0·9%, depending on whether the carcasses were washed or unwashed.     

Effects of spray-cooling processes on the microbiological conditions of decontaminated beef carcasses

Spray processes for cooling decontaminated carcasses were examined at four beef packing plants. Temperature histories were collected from deep leg sites on 25 carcasses and from randomly selected sites on the surfaces of a further 25 carcasses selected at random from carcasses undergoing cooling at each plant. Carcass cooling rates were similar at all four plants. Proliferation values calculated from surface temperature histories indicated similar increases of < or = 2 log units in the numbers of pseudomonads on carcasses at all plants and increases of <0.5 and >0.5 log units in the numbers of Escherichia coli on carcasses at plants A and B and plants C and D, respectively. The numbers of aerobes recovered from carcasses after cooling were about 1 log unit larger than the numbers recovered from carcasses before cooling at plants A, B, and C but >1.5 log units larger at plant D. These increases in numbers of aerobes were in agreement with the estimated proliferations of pseudomonads. The larger increase in the number of aerobes on carcasses at plant D may be attributable to carcasses not being pasteurized at that plant, while carcasses were pasteurized at all of the other plants. The numbers of E. coli recovered from carcasses after cooling at plants B, C, and D were also in agreement with the increases calculated from surface temperature histories. However, numbers of E. coli declined by about 1 log unit during carcass cooling at plant A. This decline may have been due to death occurring during chilling for some E. coli cells that were injured rather than killed by pasteurization with sprayed hot water at plant A, whereas pasteurization with steam at plants B and C seemingly left few injured E. coli cells. The growth of bacteria on decontaminated carcasses during spray cooling at the four plants was apparently constrained by temperature alone.     

Electrical stimulation of rabbit and lamb carcasses.

Electrical stimulation of rabbit and lamb carcasses at voltages of 250 V, pulsed at 15 Hz, resulted in a rapid immediate fall of pH and a sustained rate of fall 2–3 times greater than normal. The ATP level falls in step with the pH; at about pH 6.2, 50% of it has disappeared and at pH 5.7, more than 90%. In lamb carcasses rigor onset in the major muscles of fore-, hind-limbs and back occurs 4–5 h earlier than the normal 5–7 h and rigor is complete at least 4 h earlier. As a result, it is safe to cool or freeze stimulated lamb carcasses within 3 h of slaughter, compared with the need to delay at least 10 h with normal carcasses to ensure that cold- or thaw-contracture will not occur with subsequent toughening of the meat.     

A novel method for assessing the role of air in the microbiological contamination of poultry carcasses

This paper describes a novel method of measuring the contamination of raw foods with airborne bacteria during primary processing. To demonstrate the approach, this study aimed to quantify the role of airborne bacteria in the contamination of broiler chicken carcasses undergoing processing in an evisceration room. Settle plates and broiler carcasses were exposed to the evisceration room air or to ultra-clean air provided by a high efficiency particulate air (HEPA) unit located within the room. The use of ultra-clean air reduced the total aerobic counts on horizontal settle plates by 68-fold, and on vertical settle plates by 14-fold. The use of ultra-clean air had no significant effect on the total aerobic counts on carcasses as measured by sponging (3.5 log(10) CFU cm(-2)) or skin excision (4.0 log(10) CFU cm(-2)). The novel approach was able to show that the carcasses entering the room were so heavily contaminated that the airborne bacteria in the evisceration room contributed less than 1% of the total numbers of bacteria on the carcasses.     

Combined effects of lactic acid and nisin solution in reducing levels of microbiological contamination in red meat carcasses

Changes in bacterial counts on beef carcasses at specific points during slaughter and fabrication were determined, and the effectiveness of nisin, lactic acid, and a combination of the lactic acid and nisin in reducing levels of microbiological contamination was assessed. Swab samples were obtained from the surfaces of randomly selected beef carcasses. Carcasses were swabbed from the neck, brisket, and renal site after skinning, splitting, and washing. Treatments involving lactic acid (1.5%), nisin (500 IU/ml), or a mixture of nisin and lactic acid were applied after the neck area was washed. A control group was not sprayed. Results indicated that the highest prevalence of aerobic plate counts (APCs), total coliforms, and Escherichia coli was found in the neck site after splitting, and the lowest level of microbial contamination was found after skinning. Washing with water did not significantly reduce the bacterial load. The largest reduction in APCs, total coliforms, and E. coli occurred on carcasses treated with a mixture of nisin and lactic acid. A mixture of nisin and lactic acid can be applied to beef carcasses through spray washing and can reduce bacterial populations by 2 log units.     

Use of electronic probes for classifying lamb carcasses

Three commercially available electronic lamb carcass grading probes (Hennessy Grading Probe, AUS-Meat Sheep Probe, Swedish FTC Lamb Probe) and one developmental probe (Ruakura GR lamb probe) were assessed for accuracy and suitability for use on-line on the lamb dressing chain for objectively classifying lamb carcasses. GR is the total tissue thickness over the 12th rib taken at a distance 11 cm from the mid-line, used to define fatness in lamb carcass grading in New Zealand. Probe measurements were compared with manually measured GR (sometimes used at present) and Toland probe measurements (total tissue depth between the ribs) for accuracy of predicting both GR on the right side of the carcass and also carcass water (indicating muscle) and fat content. Probes were tested on six occasions, each having approximately 50 lambs. All probes combined with carcass weight accounted for over 70% of the variation (R(2)) of GR right, with GR left accounting for 92% of the variation of GR right. Inclusion of a quadratic probe term was not quite as useful as inclusion of carcass weight for predicting GR right. The three commercial electronic probes individually when combined with carcass weight could account for 36-49% of the variation in the percentage of water and fat in the carcass, with the manual GR probe (right) on the chilled carcass accounting for 55% of the variation in water and 58% of the variation in fat percentages. Chilled carcass measurements are expected to give better results than readings on hot carcasses. The use of a quadratic probe coefficient instead of carcass weight with the probe readings gave similar accuracy of prediction of carcass composition. There was little difference between the two sides in the accuracy of prediction. Small differences were found between regressions relating probe readings to GR and composition for the different probing occasions. The electronic probe results from this trial are consistent with overseas results where probes are in use for objectively grading the carcasses of meat animals.     

Assessment and development of procedures and apparatus to reduce contamination of lamb carcasses during pelt removal in low-throughput abattoirs.

Two series of experiments were carried out to investigate methods of reducing contamination of lamb carcasses in low-throughput abattoirs, where cradle dressing is normally employed. In the first series, cradle design and pelt removal procedure were investigated, and a method was developed for assessing gross visible contamination. Significant improvements in microbiological and gross visible contamination (P < 0.01) were achieved by procedural changes only; modifications to the cradle design had no effect. In the second series of experiments, two improved methods of pelt removal and the effect of hand washing prior to carcass contact during the pelt removal procedure were investigated. The improved methods comprised a Frame system, in which the pelt was removed in a manner similar to that in a high-throughput inverted line, and a Hybrid system, in which the pelt was removed from the forequarters on a conventional cradle before the carcass was suspended in an "inverted" vertical position for removal of the pelt from the abdomen and hindquarters. The results of microbiological and gross visible contamination from these methods, with and without hand washing, were compared with the conventional Cradle method of pelt removal. Both the Hybrid and Frame systems had significantly less microbiological and gross visible contamination (P < 0.01). However, hand washing had no significant effect on the level of carcass contamination for all three methods of pelt removal. Greatest reductions in microbiological and gross visible contamination were achieved using techniques that minimized hand contact with the carcass during pelt removal by adoption of inverted dressing procedures. Equipment redesign did not reduce carcass contamination.     

Characteristics of lamb carcasses of contrasting subjective muscularity

In order to compare characteristics of lamb carcasses with superior muscularity (the European E class) with carcasses that did not fit the E specification, 114 E carcasses were individually matched for weight and fatness class with 114 Non-E carcasses. The carcasses (mean WEIGHT = 17 kg) were processed under commercial conditions into six trimmed, boneless cuts of the leg and saddle (inside, outside, knuckle, rump, striploin and tenderloin) and two bone-in cuts (hind-shank and 7-rib rack). After adjustment for carcass weight, fatness (as assessed by fat depth C and tissue depth GR) and sex, the E-class group, relative to the Non-E group, had a 4.3% higher yield of leg and saddle cuts, a 14.2% higher leg muscularity index calculated from the weights of trimmed boneless cuts around the femur and femur length, a 13.6% higher muscle to bone ratio in the femur region, an 8.2% greater ‘eye’-muscle depth (B), and a 3.7% greater ‘eye’-muscle width (A) (all P < 0.001). All boneless cuts except the knuckle were heavier for the E group. Carcasses of female lambs had legs with higher muscle to bone ratios and a higher yield from the leg plus saddle (both P < 0.01), but the muscularity index was similar between sexes. It is concluded that although lamb carcasses subjectively selected as having higher muscularity will yield slightly more meat, this difference will be small compared with the greater muscle depth relative to bone length. The importance consumers attach to carcass or cut shape over and above any association with meat yield needs to be assessed.     

The production and microbiological status of skin-on sheep carcasses

There is a demand by certain ethnic consumer groups in the United Kingdom for skin-on, singed carcasses, primarily from older sheep, but their production is illegal under current EU legislation. The aim of this study was to devise a protocol to produce carcasses having the desired ‘smoked’ colour and odour and an acceptable microbiology. A successful result could form the basis of a case to revise the legislation. Three key steps in the selected procedure were carcass singeing using specially designed gas burner equipment, pressure washing to clean the carcass and then evisceration. It was shown that a second heat application, termed ‘toasting’, if applied after evisceration, significantly (P < 0.001) reduced Enterobacteriaceae and TVC counts on carcasses before chilling. Microbiological quality was also improved when toasting was the final step, following carcass splitting and inspection. Carcasses produced in this way had significantly (P < 0.001) lower Enterobacteriaceae and TVC counts before chilling than conventionally dressed sheep carcasses produced in the same abattoir.     

Effect of dehairing operations on microbiological quality of swine carcasses

To develop a hazard analysis and critical control point plan for food processing operations, critical control points must be determined. Swine slaughtering and dressing operations were investigated to establish their critical control points. We monitored the microbiology of swine carcasses by surface swabbing carcass bellies at various steps during the process and by quantitating total aerobic plate count (APC) and coliforms. Starting with a dehaired carcass, the sequential steps monitored included presingeing, postsingeing, polishing, and chilling. Initial results indicate that singeing and chilling substantially reduced the levels of APC and coliforms, whereas polishing increased their levels. The hygienic characteristics of individual operations involved in dressing swine carcasses were then evaluated in the second experiment. A set of 40 randomly selected carcasses leaving singeer, polisher, shaver, and washer were sampled. Carcasses were heavily contaminated during the final polishing procedure, and the APC increased threefold compared with prepolishing levels. Washing reduced the bacterial numbers by 69%. To reduce the microbial load on swine carcasses, final polishing and manual shaving steps were not used during the dressing operation on a set of 90 carcasses. APCs on singed carcasses were reduced from 1.34 to -0.15 log10 CFU/cm2 when the final polisher and manual shavers were not used. However, carcasses were subsequently recontaminated with bacteria after evisceration, and the APCs were similar (P > 0.05) regardless of whether the final polishing and manual shaving steps were used, averaging 1.30 and 1.46 log10 CFU/cm2. These results indicated that individual operations can be identified as critical control points, appropriate limits can be set and monitored in a hazard analysis and critical control point system, and steps where further changes to reduce bacterial levels may be needed for swine slaughtering plants.     

The production and microbiological status of skin-on sheep carcasses

There is a demand by certain ethnic consumer groups in the United Kingdom for skin-on, singed carcasses, primarily from older sheep, but their production is illegal under current EU legislation. The aim of this study was to devise a protocol to produce carcasses having the desired ‘smoked’ colour and odour and an acceptable microbiology. A successful result could form the basis of a case to revise the legislation. Three key steps in the selected procedure were carcass singeing using specially designed gas burner equipment, pressure washing to clean the carcass and then evisceration. It was shown that a second heat application, termed ‘toasting’, if applied after evisceration, significantly (P < 0.001) reduced Enterobacteriaceae and TVC counts on carcasses before chilling. Microbiological quality was also improved when toasting was the final step, following carcass splitting and inspection. Carcasses produced in this way had significantly (P < 0.001) lower Enterobacteriaceae and TVC counts before chilling than conventionally dressed sheep carcasses produced in the same abattoir.     

Development of a quality classification system for lamb carcasses

A total of 1660 commercial lambs, with slaughter weights ≥ 32kg and having no more than two permanent incisors, were selected on the basis of age, weight, gender, and fatness to be representative of the Canadian market lamb population and utilized to develop a quality classification system for lamb carcasses. Based upon the findings obtained, lamb should be defined as carcasses from ovines weighing 32 kg live or more and with no more than two permanent incisors. Mutton should be defined as carcasses from ovines with more than two permanent incisors or carcasses from ovines that have lost their third temporary incisor. Milk-fed lamb should be defined as carcasses from ovines weighing less than 32kg live. Consequently, classification recommendations arising from the present study apply only to carcasses from ovines defined as lamb, according to the previous definitions. Thus, lamb carcasses so defined can be effectively segregated into three quality groups based upon expected consumer acceptance, utilizing simple, subjective evaluations of the breakjoints and ribs, as follows: Group 1 possessing very red and moist breakjoints and round, red ribs, Group 2 possessing slightly red to red breakjoints and oval shaped ribs, which are either slightly red or have traces of red colour, and Group 3 possessing white, dry breakjoints and flat, white ribs. Classification of lamb carcasses on this basis will allow compensation to producers based upon carcass merit, reflecting consumer acceptance. Although availability and consumer demand will ultimately determine price premiums and/or discounts, based upon present findings, Group 1 should contain 9% or less of the lamb carcasses being marketed and should receive a premium to compensate for a higher degree of consumer acceptance. Group 2 should contain 75% or more of the lamb carcasses being marketed and should receive prevailing market value. Group 3 should contain 15% or less of the lamb carcasses being marketed and should receive a discount to compensate for a lower degree of consumer acceptance.