Enhanced control of microbiological contamination of product at a large beef packing plant

Swab samples were obtained from groups of 25 carcasses at various stages of processing at a large beef packing plant. The log mean number of aerobes recovered from carcasses after skinning was 2.2 log CFU/cm(2). Spraying the uneviscerated carcasses with 5% lactic acid reduced the numbers of aerobes by about 1 log unit; but subsequent carcass dressing operations, a second treatment with 5% lactic acid, pasteurizing, and carcass cooling had no substantial effect upon the number of aerobes on carcasses. The total numbers of coliforms or Escherichia coli cells recovered from skinned carcasses were <2 log CFU/2,500 cm(2). The numbers were reduced by the washing of uneviscerated carcasses but increased after evisceration operations. The numbers were reduced by spraying with lactic acid and pasteurizing, with no coliforms or E. coli being recovered from pasteurized carcass sides. No coliforms or E. coli cells were recovered from the forequarters of cooled carcass sides, but E. coli cells were recovered from the hindquarters of 1 of 50 cooled carcass sides, at 1.4 log CFU/1,000 cm(2). The numbers of aerobes on conveyor belts in the carcass breaking facility were similar to the numbers on cooled carcass, but the numbers of aerobes on cuts and trimmings and the number of coliforms and E. coli cells on the products and belts were higher than the numbers on carcasses. The findings indicate that most cooled carcasses produced at the plant carry E. coli at numbers <1 CFU/10,000 cm(2) but that product can be contaminated with small numbers of E. coli (<1 CFU/100 cm(2)) during carcass breaking.     

The microbiological conditions of the carcasses of six species after dressing at a small abattoir

At a small abattoir, samples were collected from carcasses of cattle, pigs, deer, bison, ostriches and emus at the ends of the dressing processes. A single sample was collected from each of 50 or 25 carcasses of each species, by swabbing a randomly selected area of 100 cm². Total aerobes, coliforms and Escherichia coli were enumerated in each sample. The microbiological conditions of the carcasses were assessed by reference to the log mean numbers of total aerobes, coliforms and E. coli estimated from sets of counts recovered from 25 samples, or to the log total numbers of coliforms and E. coli recovered from each set of 25 samples. The log mean numbers of total aerobes on beef carcasses were about 2·5 log cfu cm⁻². The log mean numbers of aerobes on deer carcasses were similar, but the log mean numbers on other types of carcass were 0·5–1 log unit more. The coliforms recovered from carcasses were largely E. coli, except for pig carcasses where E. coli were only about 10% of the coliforms recovered. Escherichia coli were recovered from the majority of samples from beef and pig carcasses, at log mean numbers about 1·5 and 2·5 log cfu 100 cm⁻², respectively, and log total numbers recovered >3 log cfu 2500 cm⁻². Escherichia coli were recovered from minorities of samples from deer, buffalo, ostrich and emu carcasses at log total numbers about 2 log cfu 2500 cm⁻². The findings indicate that when carcasses of different species are dressed at an abattoir, similar microbiological contamination of the various types of carcass cannot be assumed.     

The effects on product of a hot water pasteurizing treatment applied routinely in a commercial beef carcass dressing process

The effects of a pasteurizing treatment on the microbiological condition and the appearance of carcasses, routine in a commercial carcass dressing process, were examined. Beef carcass sides were pasteurized with water at 85°C. During 2-h periods, all sides from the dressing process were treated for 8, 9, 10, 11 or 12 s. During each period, microbiological samples were obtained by swabbing five randomly selected sides before and five others after the treatment, with a single sample being obtained from 25 treated and 25 untreated sides from each treatment time. All treatments similarly reduced the log mean numbers of total aerobic counts by about 1 log unit, but the reductions in the log total numbers of coliforms orEscherichia coli recovered from 25 samples increased with increasing treatment time, to >2 log units with treatment times of 11 or 12 s. Cooling of the sides did not obviously reduce the numbers of total aerobic bacteria on beef sides, but there were small reductions in the numbers of coliforms and E. coli on both treated and untreated sides. After cooling, sides treated routinely for 10 s yielded total aerobic counts at log mean numbers of about 2 log cfu cm⁻², and coliforms and E. coli at log total numbers of <2 and <1 log cfu 2500 cm⁻², respectively. After the carcass breaking process, loin primal cuts and manufacturing beef from such sides yielded total aerobic counts at log mean numbers of about 3 and about 4 log cfu cm⁻², respectively; coliform counts at log total numbers of about 3 and about 4 log cfu 2500 cm⁻², respectively; and E. coli counts at log total numbers >2 log cfu 2500 cm⁻²; which indicated that product was contaminated from improperly cleaned equipment during the carcass breaking process. When sides treated for 10 s with water that had previously been used to treat 120 or more sides were compared after cooling with untreated sides from the same carcasses, the appearances of treated sides were judged to be less desirable than those of the untreated sides because of the less desirable appearance of the fat tissue on the treated sides. However, the mean differences between untreated and treated sides for overall appearance and the appearance of fat tissue were only 0·45 and 0·46 assessment units, respectively, for assessments on a seven-point scale. The small adverse effect of the pasteurizing treatment on the appearance of beef carcass sides apparently did not affect the value of the meat. Thus, the data indicated that, in commercial practice, pasteurizing treatment times should be set by reference to reductions in numbers of E. coli rather than of total aerobic counts, to assure the maximum possible reduction in the number of enteric pathogens; that protein suspended in the circulating water of pasteurizing equipment will accumulate to levels that affect the appearance of carcass fat, unless the water is changed at appropriate intervals or actions are taken to remove the protein from the water or carcass surfaces; and that pasteurizing of carcasses alone is inadequate for assuring the safety of meat when recontamination of product with enteric organisms occurs during the carcass-breaking process.     

Contamination of beef trimmings with Escherichia coli during a carcass breaking process

Log numbers of total aerobic counts, coliforms and Escherichia coli recovered from beef trimmings collected after a carcass breaking process were, respectively, about 1, >3, and >3 log units greater than the numbers recovered from carcasses entering the breaking process. The numbers of those three types of bacteria recovered from trimmings tended to increase at successive stages of trimmings collection. Aerobes were recovered from pooled water on cleaned equipment at log numbers up to 5 per sample, from steel mesh gloves after cleaning at log numbers up to 8 per glove, and from detritus persisting in equipment after cleaning at log numbers up to 8 per sample. Coliforms were recovered from most mesh gloves and samples. E. coli were recovered from minorities of mesh gloves and samples of detritus, but were not recovered from samples of water. E. coli generally formed <10% of the coliforms recovered from any glove or sample. However, E. coli were generally predominant in the coliforms recovered from meat. That difference in the coliform populations recovered from trimmings and cleaned equipment appears incompatable with a conclusion that the trimmings are contaminated during carcass breaking from only the bacterial populations that evidently persist in equipment after cleaning. The data, therefore, suggest that carcasses entering the breaking process may be sporadically contaminated at localized sites with large numbers of E. coli which are distributed over the product during the breaking process in addition to the product being contaminated de novo from improperly cleaned equipment.     

Microbiological conditions of air knives before and after maintenance at a beef packing plant

Microbiological samples were obtained from air knives i.e., hand-held tools powered by compressed air, which were used during beef carcass skinning, and from equipment used for their maintenance. Bacteria from samples were enumerated by hydrophobic grid membrane filtration procedures. Knives presented for maintenance yielded aerobes at log mean numbers about 6 log cfu/knife, and coliforms, Escherichia coli and aeromonads at log total numbers about 4 log cfu/25 knives. After degreasing and at all subsequent stages of maintenance, the numbers of each group of bacteria were about 2 log units less. The numbers of bacteria recovered from the blade polishing machine were similar to the numbers recovered from knives presented for maintenance, but fewer bacteria were recovered from the blade sharpening machine. The findings suggest that it is possible for meat to be contaminated with hazardous bacteria derived from populations that persist on powered tools used for carcass dressing and on maintenance equipment.     

The effects of hot water pasteurizing treatments on the appearances and microbiological conditions of beef carcass sides

Beef carcasses from a commercial carcass dressing process were selected at random. One side of each selected carcass was deluged with water at 85°C, with 10, 25 and 25 sides being treated for 20, 15 and 10 s, respectively. After cooling, the treated and untreated sides of each carcass were assessed for the appearances of the fat, membrane-covered, cut bone and cut muscle surfaces and for the overall appearance of each side. For all treatments, the differences between the mean scores, on a seven-point scale, for treated and untreated sides were greatest for the appearances of cut muscle surfaces, the differences for that tissue being 1·04, 0·85 and 0·56 assessment units less for treated than for untreated sides from the 20, 15 and 10 s treatments, respectively. Microbiological samples were collected by swabbing both sides of each of the carcasses used in the 15 and 10 s treatments, both after the treatments and after cooling of the sides. Both treatments reduced the log total numbers of the total aerobic counts recovered from 25 sides by about 1·5 and the log total numbers of coliforms and Escherichia coli recovered from 25 sides by about 2. Cooling of the sides resulted in small reductions in the numbers of all three of those groups of bacteria on untreated sides, but similar reductions in only the numbers of coliforms and E. coli on treated sides. One side from each of 25 carcasses which had been heavily contaminated with visible filth during dressing was treated for 10 s. Microbiological samples were collected from both sides of each carcass before and after treatment. The numbers of bacteria recovered from untreated sides were similar to the numbers recovered from the untreated sides from carcasses selected at random, but the treatment reduced the log total numbers of total aerobic counts, coliforms and E. coli recovered from 25 carcasses by only 1, 1·5 and 1·5, respectively. The data indicate that treatment of beef carcass sides with water of 85°C for 10 s will substantially reduce the numbers of bacteria on the meat without unacceptable damage to the appearance of the product.     

An evaluation of street-vended sliced papaya (Carica papaya) for bacteria and indicator micro-organisms of public health significance

Thirty samples of ripe papaya (Carica papaya) slices, collected in Calcutta from the itinerant roadside vendors were collected over a 3-month period. The papaya were tested for total aerobic plate count (TPC), coliform and fecal coliform counts, and various foodborne pathogens. TPCs ranged from 3·3 to 6·52 log cfu g⁻¹ (average=5·96 log cfu g⁻¹). Eleven samples had counts >6 log cfu g⁻¹. Coliforms were detected in 70% of the samples with the average concentration being 13·5 g⁻¹. The presence ofEscherichia coli was confirmed in 48% of the samples positive for coliforms. Salmonella and Vibrio cholerae were detected in one sample each, and low levels of coagulase-positive Staphylococcus aureus were detected in 17% of the samples. An apparent relationship between high aerobic plate counts, detection of coliforms and the presence of enteric pathogens was observed.     

Improvement of the hygienic performance of the hindquarters skinning operations at a beef packing plant

The hindquarters skinning operations in a commercial beef carcasses dressing process were modified, and for short trial periods reorganized for the purpose of reducing the numbers of bacteria deposited on the carcasses. During performance of modified or reorganized operations, samples were obtained from randomly selected carcasses, by swabbing specified sites related to opening cuts, rump skinning or flank skinning operations, randomly selected sites along the lines of the opening cuts, randomly selected sites on the skinned hindquarters of carcasses, or randomly selected sites on carcass sides leaving the dressing process. For each form of the hindquarters skinning operations, a set of 25 samples of each type was collected, with a single sample being obtained from each selected carcass or side. Aerobic counts, coliforms and Escherichia coli were enumerated in each sample, and a log mean value was estimated for each set of 25 counts on the assumption of a log normal distribution of the counts. The data indicated that the log numbers of total aerobes, coliforms and E. coli that were deposited on carcasses during the modified hindquarters skinning operations were generally about 0.5, 1.0 and 1.0 log unit less, respectively, than the log numbers that had been deposited on the carcasses during the unmodified operations. Reorganization of the modified operations gave further small but consistent reductions in the numbers of bacteria. It, therefore, appears that changes to dressing procedures which are guided by appropriate microbiological data can produce consistent reductions in the microbiological contamination of carcasses.     

Decontamination of carcasses by vacuum-hot water cleaning and steam pasteurizing during routine operations at a beef packing plant

The microbiological effects of three operations for cleaning areas on dressed beef carcasses with vacuuming equipment which also applies hot water to the carcass, and of an operation for pasteurizing beef carcass sides with steam, were assessed. All four operations were routine in a commercial carcass dressing process. For each operation, swab samples were obtained from randomly selected carcasses, with a single sample being collected from each carcass, from a site selected at random from those affected by the operation. For the cleaning operations, 25 samples were obtained before and 25 after each operation. For the pasteurizing operation, 50 samples were obtained before and 50 after the operation. In addition, 50 samples were obtained from beef sides after the carcass cooling process which followed the pasteurizing operation. Total aerobic counts, coliforms and Escherichia coli from each sample were enumerated. The cleaning operations generally reduced the log mean numbers of bacteria on treated areas by ≤ 0.5 and had no discernible effect on the overall microbiological condition of the carcasses emerging from the process. The pasteurizing operation reduced the log mean numbers of total aerobic bacteria on carcasses by about 1, and the log mean numbers of coliforms and E. coli by > 2. The cooling process had no affect on the total counts, but further reduced the log mean numbers of coliforms and E. coli, apparently by about 1, to give beef sides from which E. coli were not recovered.     

Microbiological condition of beef mechanically tenderized at a packing plant

When striploins were mechanically tenderized at a beef packing plant, the log total numbers of aerobes, coliforms, staphylococci/listerias and Escherichia coli recovered from surfaces before or after tenderizing were about 2.8, 2.0, 0.6 and 0.3 log cfu 25 cm⁻², respectively. The numbers of those organisms recovered from the deep tissues of the tenderized meat were about 2.0, 1.5 and 1.2 log cfu 25 g⁻¹ and none, respectively. The aerobes recovered from the deep tissues were unexpectedly numerous in view of the small numbers of bacteria on meat surfaces. That suggests deep tissue contamination was affected by factors other than the numbers on meat surfaces. After cooking tenderized beef to medium rare or well done conditions, with maximum temperatures at steak centres of 65.4 or 73.4 °C, respectively, aerobes were recovered from only 2 of 25 samples cooked to each condition, at numbers of one or two per sample. This indicates that such cooking can ensure the microbiological safety of mechanically tenderized beef prepared under controlled conditions.     

Contamination of beef chucks with Escherichia coli during carcass breaking.

Samples were obtained by swabbing the whole of the chuck portion on each of the first 500 sides that entered a beef carcass breaking process and the whole of the outer surface of each of the chuck primal cuts that were prepared from those portions. Swabs obtained from groups of 10 sides or cuts that entered or emerged from the process consecutively were combined, and the coliforms and Escherichia coli recovered from each group were enumerated. Coliforms and E. coli were recovered only sporadically from groups of sides at log total numbers of 4.0 and 3.5 log CFU/500 sides, respectively. Coliforms were recovered from three and E. coli from none of the first six groups of cuts. Coliforms and E. coli were recovered from all subsequent groups of cuts, initially at log numbers mostly <3 log CFU/10 cuts, but ultimately at log numbers mostly >3 log CFU/10 cuts. The log total numbers of coliforms and E. coli recovered from cuts were >6.0 and 5.5 log CFU/500 cuts, respectively. After the breaking of about 600 sides, samples were obtained by swabbing a table onto which the part of the side that included the chuck portion was deposited after it was cut from the hanging side, and the belt that was used for conveying chucks. The numbers of coliforms and E. coli recovered from the table and conveyor belt were comparable with the numbers recovered from sides and cuts, respectively. Those findings show that most of the coliforms and E. coli recovered from the cuts were not present on carcass sides but that they originated largely from the cut conveying equipment.     

Comparison of Decontamination Efficacy of Antimicrobial Treatments for Beef Trimmings against Escherichia coli O157:H7 and 6 Non-O157 Shiga Toxin-Producing E. coli Serogroups

Abstract: The decontamination efficacy of 6 chemical treatments for beef trimmings were evaluated against Escherichia coli O157:H7 and 6 non‐O157 Shiga toxin‐producing E. coli (nSTEC) serogroups. Rifampicin‐resistant 4‐strain mixtures of E. coli O157:H7 and nSTEC serogroups O26, O45, O103, O111, O121, and O145 were separately inoculated (3 to 4 log CFU/cm²) onto trimmings (10 × 5 × 1 cm; approximately 100 g) fabricated from beef chuck rolls, and were immersed for 30 s in solutions of acidified sodium chlorite (0.1%, pH 2.5), peroxyacetic acid (0.02%, pH 3.8), sodium metasilicate (4%, pH 12.5), Bromitize^® Plus (0.0225% active bromine, pH 6.6), or AFTEC 3000 (pH 1.2), or for 5 s in SYNTRx 3300 (pH 1.0). Each antimicrobial was tested independently together with an untreated control. Results showed that all tested decontamination treatments were similarly effective against the 6 nSTEC serogroups as they were against E. coli O157:H7. Irrespective of pathogen inoculum, treatment of beef trimmings with acidified sodium chlorite, peroxyacetic acid, or sodium metasilicate effectively (P < 0.05) reduced initial pathogen counts (3.4 to 3.9 log CFU/cm²) by 0.7 to 1.0, 0.6 to 1.0, and 1.3 to 1.5 log CFU/cm², respectively. Reductions of pathogen counts (3.1 to 3.2 log CFU/cm²) by Bromitize Plus, AFTEC 3000, and SYNTRx 3300 were 0.1 to 0.4 log CFU/cm², depending on treatment. Findings of this study should be useful to regulatory authorities and the meat industry as they consider nSTEC contamination in beef trimmings. Practical Applications: Findings of this study should be useful to: (i) meat processors as they design and conduct studies to validate the efficacy of antimicrobial treatments to control pathogen contamination on fresh beef products; and (ii) regulatory agencies as they consider approaches for better control of the studied pathogens.     

Assessment of the hygienic performances of two beef carcass cooling processes from product temperature history data or enumeration of bacteria on carcass surfaces

The carcass cooling processes at two beef slaughtering plants were examined. Temperature histories were collected from the deep leg, the aitch bone pocket surface and randomly selected surface sites of carcasses passing through each process. For each process, sets of25temperature histories were collected for each type of site, with a single history being collected from each of75randomly selected carcases. A swab sample was obtained from a randomly selected site on each of25randomly selected carcasses entering and25leaving each process. Total aerobic counts, coliforms andEscherichia coliwere enumerated in each sample. Carcasses resided in the chiller at plant A for between 15.8 and 28.0h, but for between 20.0 and 24.0h at plant B. The ranges of minimum temperature attained at all three types of site were generally lower at plant B than at plant A. However, 1/25 carcasses at both plants had high minimum temperatures indicative of ineffective cooling. AnE. coliproliferation value was calculated for each temperature history from a surface site. The sets of proliferation values for aitch bone pocket sites on carcasses passing through either process complied with three points of a four point criteria for acceptable carcass cooling, but one value in each exceeded the stipulated maximum value. Proliferation values for randomly selected sites indicated that if temperature alone controlled bacterial growth during cooling, then numbers ofE. colion cooling carcasses would on average increase by about 1 log unit at plant A but by only about 0.3 log units at plant B. However, enumeration of bacteria showed that cooling reduced the mean numbers of total counts, coliforms andE. colion carcasses at plant A by <0.5 log units, while at plant B, cooling reduced the mean numbers of total counts by about 0.5 log units, and mean numbers of coliforms andE. coliby 2 log units. The findings indicate that microbiological data are required to properly assess the hygienic effects of carcass cooling processes, but that temperature history data may be conveniently used for monitoring the maintenance of standard operating procedures in such processes.     

Comparison of excision and swabbing sampling methods to determine the microbiological quality of swine carcass surfaces

Although different sampling methods are available to determine the microbiological quality of animal carcass surfaces, these vary in their ability to recover bacteria quantitatively. In this study, excision and swabbing (one-site vs three-site) sampling methods were compared for their recovery (both numbers and incidence) of total aerobic bacteria (APC), total coliforms, and Escherichia coli biotype I from swine carcass surfaces. In addition, the effect of refrigerated storage (to simulate shipment to an off-site laboratory) was investigated, as well as the effectiveness of the one vs three anatomical site swabbing methods. Based on samples from 120 market swine carcasses, the excision method recovered the highest levels (P>0·05) of all three groups of bacteria (APCs, coliforms, and E.coli), followed by the three-site method and finally the one-site method. For the APCs, the recovery, given as log cfu cm⁻², were 4·7, 4·0 and 3·3 respectively for excision, three-site swab, and one-site swab methods; for coliforms, the recovery was 2·1, 0·3 and −0·1 respectively; and for E.coli it was 2·4, 0·3, and −0·3 respectively. Comparing the swabbing methods, the three-site swab method recovered higher levels (P>0·05) of the three groups of bacteria than the one-site swab method, with the ham being responsible for this increased recovery. Excision and the three-site swab method gave a higher incidence of E. coli (45 and 58 positive (one colony on one of the duplicate plates) out of 120 carcasses respectively) than the one-site swab method (23 positive out of 120 carcasses). Storage of the swabs overnight in the cold did not cause a decrease (P>0·05) in either the number or incidence of bacteria recovered. These data indicate that while the excision method will recover the highest number and incidence of bacteria, swabbing methods can provide an alternative to this more labor intensive and destructive method.     

Proximate sources of bacteria on boneless loins prepared from routinely processed and detained carcasses at a pork packing plant

Microbiological samples were obtained by swabbing detained and routinely processed pig carcasses before and after cooling, and sides, loin portions and loin cuts at various stages of the carcass breaking process. Aerobes, coliforms and Escherichia coli were enumerated in each sample. All three groups of bacteria were more numerous on detained than on routinely processed carcasses. Both trimming and cooling reduced the numbers of E. coli but not the numbers of aerobes on detained carcasses. After cooling, the log mean number of aerobes and E. coli on detained carcasses were each about 0.5 log unit more than the log mean numbers on routinely processed carcasses, but numbers of coliforms on the two types of carcass were similar. There were small increases in the numbers of coliforms and E. coli on carcasses during their movement from the cooler to the breaking facility. The numbers of bacteria on the meat apparently did not increase during the carcass-breaking process, although bacteria were redistributed on the product. Despite that, substantial numbers of bacteria were recovered from parts that do not contact food in cleaned conveying equipment used for carcass breaking. However, those bacteria included few coliforms and no E. coli. These findings suggest that the contamination of meat with E. coli from persistent detritus in carcass breaking equipment, such as has been found to occur at beef packing plants, may be prevented when carcass-breaking equipment and facilities are dried after cleaning, and wetting of equipment during processing is avoided.     

Recovery of bacteria from poultry carcasses by rinsing,swabbing or excision of skin

Groups of 25 uneviscerated or eviscerated carcasses were obtained at four points in a commercial broiler chicken carcass dressing process. Carcasses from each point in the process were sampled by excision of skin from randomly selected sites, excision of skin from necks, swabbing carcasses with cellulose acetate sponges, or by rinsing whole carcasses. Total aerobic counts, coliforms and Escherichia coli recovered from each sample were enumerated. Values for the log mean number cm⁻² (log A) and the log of the total numbers recovered 25 cm⁻² (N) were calculated for each set of 25 counts. For sets of counts for the same group of bacteria obtained from carcasses at the same stage of processing, the three values for log A or three values for N for sets of counts obtained by excision of skin from randomly selected sites or necks, or by rinsing differed by < 0.5 log unit. However, about half the values for log A or N for sets of counts obtained by swabbing differed by >0.5 log unit from the corresponding values for sets of counts obtained by the other methods. Those data indicate that sampling of poultry carcasses by excision of skin from randomly selected sites or necks, or by rinsing will recover similar numbers of bacteria per unit area of carcass surface.     

Comparison of methods for sampling and enumeratingEscherichia colion pig carcasses

On each of 55 days, split pig carcasses leaving a carcass cooling process were selected at random for sampling and enumeration of genericEscherichia coliby three methods. Method A involved swab sampling with a single, cellulose acetate sponge, of three specified sites on one side of each selected carcass, with each swabbed area of 100 cm²being delimited by a template, and enumeration ofE. coliby a plating technique with a level of detection of 1 cfu 24 cm⁻², as specified by the US Department of Agriculture (USDA). Method B involved swabbing the same three sites as in method A, but each site was swabbed with a separate gauze swab over an undelimited area of approximately 100 cm². The three swabs from each carcass were combined for the enumeration ofE. colias in method A. Method C involved swabbing a single, randomly selected site on each selected carcass with a gauze swab as in method B, and enumeration ofE. coliby a hydrophobic grid membrane filtration technique with a level of detection of 1 cfu 100 cm⁻². All three methods yieldedE. coliwith similar frequency and with the recovery of similar numbers of cfu. Therefore, method B can be regarded as equivalent to method A for demonstration of compliance with the USDA criterion for acceptableE. colicontamination of cooled pig carcasses. However, because of the difference in the sites that are sampled method C could be regarded as equivalent to method A only if anE. colicriterion appropriate to method C but equivalent to the USDA criterion can be recognized by regulatory authorities.     

Influence of organic acid concentration on survival of Listeria monocytogenes and Escherichia coli 0157:H7 in beef carcass wash water and on model equipment surfaces

Acid-adapted cultures of Escherichia coli O157:H7 and Listeria monocytogenes were inoculated in meat decontamination spray-washing runoff fluids in order to evaluate their survival and potential to form biofilms on stainless steel coupons. The cultures (10⁷ cfu ml⁻¹) and stainless steel coupons were exposed to mixtures of water and organic acid washings (composites of each of 2% acetic acid or lactic acid washings with water washings from meat decontamination in proportions of 1/9, 1/49, 1/99 [vol/vol]) or to water washings for up to 14 days at 15°C. E. coli O157:H7 formed biofilms and remained detectable (1.3 log cfu cm⁻²) on stainless steel for up to 4 d in the 1/9 dilution (pH 3.17–3.77) of the organic acid washings, and persisted throughout storage (14 d) in the 1/49 (pH 3.96–4.33) and 1/99 (pH 4.34–6.86) dilution of the organic acid washings. L. monocytogenes populations were unable to form detectable (<1.3 log cfu cm⁻²) biofilms in the 1/9 and 1/49 dilutions of both organic acid washings for up to 14 d; however, by day-14 in the 1/99 dilution of the washings, the pathogen was able to attach at detectable levels (2.7 to 3.4 logs). The pH effects of lower concentrations (1/49 or 1/99) of acidic washings decreased over time due to the formation of amine compounds produced by the natural meat flora, allowing resuscitation of the acid-stressed pathogen survivors. The resuscitation of acid-stressed pathogens may potentially enhance their survival and prevalence in biofilms and thus more attention should be focused on avoiding or minimizing the collection of decontamination runoff fluids on food contact equipment surfaces.     

The microbiological effects of breaking operations on hanging beef carcass sides

The microbiological effects of six of 16, sequential breaking operations on hanging beef carcasses were examined by swabbing a site selected for each operation, before and after the operation, on carcasses selected at random from those passing through a commercial carcass breaking process. In addition, samples were collected by rinsing or swabbing gloves worn by workers involved in the breaking of hanging carcasses. The data indicated that total aerobic counts at the selected sites increased as a result of operation 4, injecting nitrogen between the shoulder muscles; operation 5, sawing through the back bone; and operation 12, removing the last portions of the ribs and sternum. Total aerobic counts were little affected by operation 1, cutting between the ribs; operation 7, trimming the rump; and operation 8, cutting between the sternum and the rib cage. At five of the six sites the operation related to each did not increase the numbers of the few coliforms or Escherichia coli at the site, but operation 7, trimming the rump, decreased the numbers of coliforms and E. coli at a site in the anal area. E. coli were recovered in relatively large numbers from rinse samples of cotton gloves, but in only small numbers from swabs of those gloves. E. coli were recovered by rinse sampling from only two of the 25 steel mesh gloves that are worn beneath the cotton gloves. The findings show that carcasses entering the breaking facility are largely free of E. coli, except at the anal site, where about 5% of carcasses carry E. coli at log numbers >2 100 cm⁻². These numbers are reduced during the rump trimming operation, but small numbers of E. coli are deposited on the carcasses at various sites contacted by the gloved hands of workers. The gloves must be contaminated with E. coli from surfaces within the breaking facility, as the numbers on them are too large to be derived from the carcasses.     

Bacterial mediated off-flavours in retail-ready beef after storage in controlled atmospheres

The effects of anoxic storage under CO₂ at 2°C for up to 10 weeks followed by 28 h aerobic display in a retail case on flavour attributes and bacteriology of beef were examined. Pseudomonads reached 2.5 log cfu/cm² in one replication only and their numbers decreased with increasing storage time. Enterobacteriaceae and Brochothrix thermosphacta were not above levels of 1.0 and 2.0 log cfu/cm², respectively. Presumptive lactic acid bacteria increased to maximum numbers of 5.5 log cfu/cm² after 8 weeks. A subpopulation of lactic acid bacteria, able to grow in the presence of 12 g/l acetate, developed later in storage reaching a maximum population of 4.3 log cfu/cm². Flavour amplitude dropped to an inappropriate level after 6 weeks. Between 6 and 8 weeks, the numbers of lactic acid bacteria able to grow in the presence of 12 g/l acetate increased in the absence of an increase in presumptive lactic acid bacteria. This time coincided with the development of “off barny” aromatic, “off barny” aftertaste and unidentified “off” aromatic and a reduction in flavour amplitude suggesting a relationship between the growth of these organisms and changes in organoleptic properties.