An evaluation of the effectiveness of FreshCase technology to extend the storage life of whole muscle beef and ground beef.

The objective of this study was to identify the maximum time of refrigerated storage before aerobic psychrotrophic bacteria (APB) grew to a level indicative of spoilage (7 log cfu/g) or other indicators of spoilage were observed for whole muscle beef and ground beef packaged using FreshCase technology. Storage life for beef steaks stored in FreshCase packages at 4°C was 36 d, with ground beef stored in FreshCase packages at 4°C lasting 10 d. Additionally, greater ( < 0.05) a* (redness) values were detected in FreshCase packaged samples of both beef steaks and ground beef over storage time. At the point of spoilage, off-odors were detected at very low levels in all samples along with low thiobarbituric acid values (< 2 mg malonaldehyde/kg). Therefore, use of FreshCase technology in whole muscle beef and ground beef is a viable option to extend storage life.

An evaluation of the effectiveness of FreshCase technology to extend the storage life of whole-muscle pork and ground pork sausage.

The objective of this study was to identify the maximum time of refrigerated storage before aerobic psychrotrophic bacteria grew to a level indicative of spoilage (7 log cfu/g) or other indicators of spoilage were observed for whole-muscle pork and ground pork sausage packaged using FreshCase technology. Pork chops and pork sausage were packaged using conventional vacuum packaging without nitrite in film (Control) or using FreshCase technology and were compared with respect to microbial counts, pH, instrumental color measurements, lipid oxidation level, and sensory properties. The storage life was 45 d for pork chops stored in FreshCase packages at 1°C and 19 d for ground pork sausage stored under the same condition. Results indicated that both pork chops and sausage stored in FreshCase packages retained redder color ( < 0.05) than those stored in Control packages. No differences ( > 0.05) existed between Control and FreshCase packaged samples for any off-odor detection for either pork chops or sausage. Moreover, levels of oxidative rancidity in all packages had low thiobarbituric acid reactive substances values. The results indicated that FreshCase technology can be used to extend storage life of pork products without having adverse effects on pork quality.

Effect of packaging during storage time on retail display microbial population of beef strip loins from two different production systems.

Two studies were conducted to evaluate the influence of packaging during storage of strip loins (to simulate export shipment) from steers fattened on intensive grazing systems (Uruguay; UR) or on a high-concentrate diet (United States; US) on retail display life microbial growth. Four or 3 different packaging treatments were applied to UR and US strip loin roasts or steaks during 35 d of storage; treatments were applied 7 d following slaughter. After 35 d of storage, the samples were evaluated during simulated retail display for up to 6 d. In Exp. 1, the treatments were vacuum packaging (VP), low-oxygen modified atmosphere packaging (MAP) with N and CO (MAP/CO), low-oxygen MAP with N plus CO and CO, and VP plus an application of peroxyacetic acid (VP/PAA). In Exp. 2, block 1, the treatments were VP, MAP/CO, and VP with ethyl--lauroyl--arginate HCl incorporated into the film as an antimicrobial agent (VP/AM). In Exp. 2, block 2, the treatments were VP, MAP/CO, MAP/CO, and VP/AM. For retail display, VP treatments were sliced and repackaged in PVC overwrap, and MAP treatments were actually PVC overwrap trays that were removed from a master bag with the prescribed gas treatment. Regardless of production system and packaging treatment, mesophilic and psychrotrophic counts of 6.9 to 7.8 and 6.7 to 7.7 log10 CFU/cm, respectively, were obtained at the end of retail display, except for US samples in Exp. 2 (5.5 to 6.3 log CFU/cm). No differences ( > 0.05) were detected for spp. counts among packaging treatments in US steaks at the end of the display time in Exp.1, whereas, for UR steaks, both MAP treatments had lower ( < 0.05) spp. counts than VP treatments. spp. counts were lower ( < 0.05) in the MAP/CO treatment than in the other 3 treatments in US samples on d 6 of retail display for Exp. 2. At the end of display time and for Exp. 1, US steaks under MAP/CO had greater ( < 0.05) lactic acid bacteria (LAB) counts than samples in both VP treatments; no differences ( > 0.05) among packaging were detected for UR steaks. Both MAP and VP/AM treatments in the US samples for Exp. 2 had lower ( < 0.05) LAB counts on d 6 of display than the VP treatment, but no differences ( > 0.05) were found among packaging treatments for the UR samples. To maximize shelf life (storage and display life) of exported fresh beef, it is critical to minimize bacterial populations during processing and storage.

Effect of packaging during storage time on retail display shelf life of longissimus muscle from two different beef production systems.

Two studies were conducted to evaluate the influence of packaging and production system (PS) on retail display life color (L*, a*, and b*), fatty acid profile (% of total fatty acids), lipid oxidation (thiobarbituric acid reactive substances; mg malondialdehyde/kg of muscle), vitamin E content (µg/g of muscle), and odor (trained panelists) during storage of LM. Four (or 3) different packaging treatments were applied to LM from steers fattened on grazing systems (Uruguayan) or on high-concentrate diets (U.S.). From fabrication to application of treatments, Uruguayan LM were vacuum packaged for air shipment and U.S. LM were also vacuum packaged and kept in a cooler until Uruguayan samples arrived. Treatments were applied 7 d after slaughter. In Exp. 1, treatments were vacuum packaging (VP), low-oxygen (O) modified atmosphere packaging (MAP) with nitrogen (N2) and carbon dioxide (MAP/CO), low-O MAP with N2 plus CO and carbon monoxide (MAP/CO), and VP plus an application of peroxyacetic acid (VP/PAA). In Exp. 2 block 1, treatments were VP, MAP/CO, and VP with ethyl-arginate HCl incorporated into the film as an antimicrobial agent (VP/AM). In Exp. 2 block 2, treatments were VP, MAP/CO, MAP/CO, and VP/AM. After 35 d storage, steaks were evaluated during simulated retail display for up to 6 d. In Exp. 1, Uruguayan steaks under MAP/CO had greater ( < 0.05) a* values than VP/PAA and MAP/CO on d 6 of display. For U.S. beef, the MAP/CO had the reddest lean color ( < 0.05) compared with the other 3 packaging treatments on d 6 of display in Exp. 1. Packaging × PS × time interaction was significant ( < 0.05) in Exp. 1. In Exp. 2, MAP/CO in Uruguayan steaks also had the greatest a* values on d 6 of display, but no differences ( > 0.05) were detected among both VP and MAP/CO in U.S. steaks at this time. No significant ( > 0.05) packaging × PS × time interaction was observed in Exp. 2. Only PS (both experiments) and time (Exp. 1) affected ( < 0.05) L* values. In both experiments, U.S. steaks had greater ( < 0.05) L* values than Uruguayan steaks. Vitamin E content in Uruguayan steaks was greater ( < 0.05) than in U.S. steaks. Packaging × PS, PS × time, and packaging × PS × time interactions were not significant ( > 0.05) for any of the fatty acids. Beef from Uruguayan had lower ( < 0.05) SFA and MUFA and greater ( < 0.05) PUFA and n-6 and n-3 fatty acid percentages than U.S. beef. Complexity of fresh meat postmortem chemistry warrants a more comprehensive approach to maximize shelf life.

Evaluation of lactic acid as an initial and secondary subprimal intervention for Escherichia coli O157:H7, non-O157 Shiga toxin-producing E. coli, and a nonpathogenic E. coli surrogate for E. coli O157:H7.

Lactic acid can reduce microbial contamination on beef carcass surfaces when used as a food safety intervention, but effectiveness when applied to the surface of chilled beef subprimal sections is not well documented. Studies characterizing bacterial reduction on subprimals after lactic acid treatment would be useful for validations of hazard analysis critical control point (HACCP) systems. The objective of this study was to validate initial use of lactic acid as a subprimal intervention during beef fabrication followed by a secondary application to vacuum-packaged product that was applied at industry operating parameters. Chilled beef subprimal sections (100 cm(2)) were either left uninoculated or were inoculated with 6 log CFU/cm(2) of a 5-strain mixture of Escherichia coli O157:H7, a 12-strain mixture of non-O157 Shiga toxin-producing E. coli (STEC), or a 5-strain mixture of nonpathogenic (biotype I) E. coli that are considered surrogates for E. coli O157:H7. Uninoculated and inoculated subprimal sections received only an initial or an initial and a second "rework" application of lactic acid in a custombuilt spray cabinet at 1 of 16 application parameters. After the initial spray, total inoculum counts were reduced from 6.0 log CFU/cm(2) to 3.6, 4.4, and 4.4 log CFU/cm(2) for the E. coli surrogates, E. coli O157:H7, and non-O157 STEC inoculation groups, respectively. After the second (rework) application, total inoculum counts were 2.6, 3.2, and 3.6 log CFU/cm(2) for the E. coli surrogates, E. coli O157:H7, and non-O157 STEC inoculation groups, respectively. Both the initial and secondary lactic acid treatments effectively reduced counts of pathogenic and nonpathogenic strains of E. coli and natural microflora on beef subprimals. These data will be useful to the meat industry as part of the HACCP validation process.

Fate of Listeria monocytogenes during freezing, thawing and home storage of frankfurters.

Little information is available regarding the fate of Listeria monocytogenes during freezing, thawing and home storage of frankfurters even though recent surveys show that consumers regularly store unopened packages in home freezers. This study examined the effects of antimicrobials, refrigerated storage, freezing, thawing method, and post-thawing storage (7 degrees C) on L. monocytogenes on frankfurters. Inoculated (2.1 log CFU/cm(2)) frankfurters formulated without (control) or with antimicrobials (1.5% potassium lactate plus 0.1% sodium diacetate) were vacuum-packaged, stored at 4 degrees C for 6 or 30 d and then frozen (-15 degrees C) for 10, 30, or 50 d. Packages were thawed under refrigeration (7 degrees C, 24 h), on a countertop (23 +/- 2 degrees C, 8 h), or in a microwave oven (2450 MHz, 1100 watts, 220 s followed by 120 s holding), and then stored aerobically (7 degrees C) for 14 d. Bacterial populations were enumerated on PALCAM agar and tryptic soy agar plus 0.6% yeast extract. Antimicrobials completely inhibited (p < 0.05) growth of L. monocytogenes at 4 degrees C for 30 d under vacuum-packaged conditions, and during post-thawing aerobic storage at 7 degrees C for 14 d. Different intervals between inoculation and freezing (6 or 30 d) resulted in different pathogen levels on control frankfurters (2.1 or 3.9 log CFU/cm(2), respectively), while freezing reduced counts by <1.0 log CFU/cm(2). Thawing treatments had little effect on L. monocytogenes populations (<0.5 log CFU/cm(2)), and post-thawing fate of L. monocytogenes was not influenced by freezing or by thawing method. Pathogen counts on control samples increased by 1.5 log CFU/cm(2) at d-7 of aerobic storage, and reached 5.6 log CFU/cm(2) at d-14. As indicated by these results, consumers should freeze frankfurters immediately after purchase, and discard frankfurters formulated without antimicrobials within 3 d of thawing and/or opening.

Effect of meat binding formulations on thermal inactivation of Escherichia coli O157:H7 internalized in beef.

This study evaluated the effects of meat binding or restructuring formulations, including salt/phosphate, algin/calcium, ActivaRM, and Fibrimex, with or without 0.27% (wt/wt) lactic acid, on thermal inactivation of internalized Escherichia coli O157:H7 in ground beef, serving as a model system for restructured products. Ground beef batches (700 g; approximately 5% fat) were mechanically mixed with a 5-strain composite of E. coli O157:H7 (7 log CFU/g) and then with the restructuring formulations. Product portions (30 g) were extruded into plastic test tubes (2.5 x 10 cm) and stored at 4 degrees C (18 h), before heating to 60 or 65 degrees C in a circulating water bath to simulate rare or medium-rare doneness of beef, respectively. Cooking to 60 or 65 degrees C reduced (P < 0.05) bacterial counts of control samples by 1.8 and 3.2 log CFU/g, respectively. Thermal destruction at 60 degrees C was not different (P > 0.05) among all treatments and the control. At 65 degrees C, greater (P < 0.05) thermal inactivation of E. coli O157:H7, as compared to the control, was obtained in samples treated with lactic acid alone (reductions of 4.9 log CFU/g), whereas for all other treatments, microbial destruction (reductions of 2.2 to 4.5 log CFU/g) was comparable (P > 0.05) to that of the control. Cooking weight losses were lower (P < 0.05) in salt/phosphate samples (<1%) compared to other formulations and the control (7.4% to 15.9%). Findings indicated that, under the conditions examined, restructuring of beef with salt/phosphate, algin/calcium, ActivaRM, or Fibrimex did not affect inactivation of internalized E. coli O157:H7 in undercooked (60 or 65 degrees C) samples, whereas inclusion of lactic acid (0.27%) in nonintact beef products enhanced pathogen destruction at 65 degrees C.

Evaluation of changes in Listeria monocytogenes populations on frankfurters at different stages from manufacturing to consumption.

This study evaluated the fate of inoculated Listeria monocytogenes on frankfurters stored under conditions simulating those that may be encountered between manufacturing and consumption. Frankfurters with or without 1.5% potassium lactate and 0.1% sodium diacetate (PL/SD) were inoculated (1.8 +/- 0.1 log CFU/cm(2)) with a 10-strain composite of L. monocytogenes, vacuum-packaged, and stored under conditions simulating predistribution storage (24 h, 4 degrees C), temperature abuse during transportation (7 h, 7 degrees C followed by 7 h, 12 degrees C), and storage before purchase (60 d, 4 degrees C; SBP). At 0, 20, 40, and 60 d of SBP, samples were exposed to conditions simulating delivery from stores to homes or food establishments (3 h, 23 degrees C), and then opened or held vacuum-packaged at 4 or 7 degrees C for 14 d (SHF). Pathogen counts remained relatively constant on frankfurters with PL/SD regardless of product age and storage conditions; however, they increased on product without antimicrobials. In vacuum-packaged samples, during SHF at 4 degrees C, the pathogen grew faster (P < 0.05) on older product (20 d of SBP) compared to product that was fresh (0 d of SBP); a similar trend was observed in opened packages. At 7 degrees C, the fastest growth (0.35 +/- 0.02 log CFU/cm(2)/d) was observed on fresh product in opened packages; in vacuum-packages, growth rates on fresh and aged products were similar. By day 40 of SBP the pathogen reached high numbers and increased slowly or remained unchanged during SHF. This information may be valuable in L. monocytogenes risk assessments and in development of guidelines for storage of frankfurters between package opening and product consumption.

Antimicrobial activity of epsilon-polylysine against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in various food extracts.

This study compared the antimicrobial effects of epsilon-polylysine (epsilon-PL) against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in 6 food extracts and in broth. The food extracts (10% (w/w) in distilled water) evaluated were fat-free and whole fat milk, beef, bologna, rice, and vegetables (50:50 ratio of broccoli and cauliflower). epsilon-PL was tested at 0.005% and 0.02% (w/v) against E. coli O157:H7 and L. monocytogenes, and 0.02% and 0.04% (w/v) against S. Typhimurium. The substrates were inoculated (5 log CFU/mL) and periodically analyzed for surviving populations during storage at 12 degrees C for 6 d. In general, all 3 pathogens reached 7 to 9 log CFU/mL within 2 d in control substrates (no epsilon-PL). Immediate bactericidal effects (P < 0.05) following exposure to epsilon-PL were obtained in the rice (all pathogens) and vegetable (E. coli O157:H7 and S. Typhimurium) extracts. During storage, antimicrobial effects of epsilon-PL were more pronounced in the food extracts than in the broth medium. The greatest antimicrobial activity for all 3 pathogens was obtained in the rice and vegetable extracts, where counts were reduced (P < 0.05) to below the detection limit (0.0 log CFU/mL) by one or both epsilon-PL concentrations tested. In the other food extracts (fat-free milk, whole fat milk, beef, and bologna), both epsilon-PL concentrations tested generally resulted in lower (P < 0.05) pathogen levels at the end of storage compared to initial counts, with better bactericidal effects exerted by the higher of the 2 epsilon-PL concentrations. Additional research is needed to explore the potential antimicrobial effects of epsilon-PL in real food systems.

Control of Listeria monocytogenes on frankfurters with antimicrobials in the formulation and by dipping in organic acid solutions.

The antilisterial activity of sodium lactate (SL) and sodium diacetate (SD) was evaluated in a frankfurter formulation and in combination with a dipping treatment into solutions of lactic acid or acetic acid after processing and inoculation. Pork frankfurters were formulated with 1.8% SL or 0.25% SD or combinations of 1.8% SL with 0.25 or 0.125% SD. After processing, frankfurters were inoculated (2 to 3 log CFU/cm2) with a 10-strain composite of Listeria monocytogenes and left undipped or were dipped (2 min) in 2.5% solutions of lactic acid or acetic acid (23 +/- 2 degrees C) before vacuum packaging and storage at 10 degrees C for 40 days. Total microbial populations and L. monocytogenes, lactic acid bacteria, and yeasts and molds were enumerated during storage. Sensory evaluations also were carried out on frankfurters treated and/or formulated with effective antimicrobials. The combination of 1.8% SL with 0.25% SD provided complete inhibition of L. monocytogenes growth throughout storage. Dipping in lactic acid or acetic acid reduced initial populations by 0.7 to 2.1 log CFU/cm2, but during storage (12 to 20 days), populations on dipped samples without antimicrobials in the formulation reached 5.5 to 7.9 log CFU/cm2. For samples containing single antimicrobials and dipped in lactic acid or acetic acid, L. monocytogenes growth was completely inhibited or reduced over 12 and 28 days, respectively, whereas final populations were lower (P < 0.05) than those in undipped samples of the same formulations. Bactericidal effects during storage (reductions of 0.6 to 1.0 log CFU/ cm2 over 28 to 40 days) were observed in frankfurters containing combinations of SL and SD that were dipped in organic acid solutions. Inclusion of antimicrobials in the formulation and/or dipping the product into organic acid solutions did not affect (P > 0.05) the flavor and overall acceptability of products compared with controls. The results of this study may be valuable to meat processors as they seek approaches for meeting new regulatory requirements in the United States.

Genotypic analysis of Escherichia coli strains from poultry carcasses and their susceptibilities to antimicrobial agents.

Plasmid profiling and amplified fragment length polymorphism (AFLP) analysis were used to genotype 50 Escherichia coli strains from poultry carcasses. Thirty different plasmid profiles were evident, and clustering of the AFLP data showed that they were a distinctly heterogeneous group of strains. Susceptibility testing against five antimicrobial agents used in the South African poultry industry showed all strains to be susceptible to danofloxacin and colistin, while the majority (96%) were resistant to two tetracyclines.

Antimicrobial susceptibilities of isolates of Staphylococcus aureus, Listeria species and Salmonella serotypes associated with poultry processing.

The broth microdilution method was used to determine the activities of selected antimicrobial agents used in the South African poultry industry (danofloxacin, neomycin, chlortetracycline, oxytetracycline, tylosin and colistin) and vancomycin against bacterial isolates previously obtained from carcasses and selected equipment surfaces and environmental sources associated with poultry processing. The antimicrobial susceptibilities of 38 isolates of Staphylococcus (S.) aureus, 25 Listeria (L.) innocua, 18 L. monocytogenes, and 62 isolates belonging to six Salmonella (Salm.) serotypes (Salm. agona, Salm. blockley, Salm. enteritidis, Salm. isangi, Salm. reading and Salm. typhimurium) were determined. The most active antimicrobial agent against all the isolates tested was danofloxacin with minimum inhibitory concentrations (MICs) for 90% of the isolates (MIC90) not exceeding 0.25 and 2 microg/ml for gram-negative and gram-positive isolates, respectively. Conversely, high MICs were recorded for all the isolates tested against chlortetracycline and oxytetracycline (MIC90 range of 32 to > 512 microg/ml), except for the L. monocytogenes and Salm. enteritidis isolates (MIC range of < or = 0.5-4 microg/ml). Neomycin was found to be active against S. aureus, L. innocua, L. monocytogenes, Salm. enteritidis and Salm. isangi isolates, with MICs not exceeding 8 microg/ml. MIC ranges for tylosin and vancomycin, which were only tested against the gram-positive isolates, were from 1 to > 512 microg/ml and from 1 to 4 microg/ml, respectively. The MIC range for the remaining antimicrobial agent, colistin, which was only tested against the Salmonella isolates, was 0.5-16 microg/ml. The lack of MIC breakpoints for the antimicrobial agents used in the poultry industry did not allow for definite conclusions as to the level of resistant bacteria associated with poultry carcasses and the processing environment in this study.

Characterization and determination of origin of lactic acid bacteria from a sorghum-based fermented weaning food by analysis of soluble proteins and amplified fragment length polymorphism fingerprinting.

The group that includes the lactic acid bacteria is one of the most diverse groups of bacteria known, and these organisms have been characterized extensively by using different techniques. In this study, 180 lactic acid bacterial strains isolated from sorghum powder (44 strains) and from corresponding fermented (93 strains) and cooked fermented (43 strains) porridge samples that were prepared in 15 households were characterized by using biochemical and physiological methods, as well as by analyzing the electrophoretic profiles of total soluble proteins. A total of 58 of the 180 strains were Lactobacillus plantarum strains, 47 were Leuconostoc mesenteroides strains, 25 were Lactobacillus sake-Lactobacillus curvatus strains, 17 were Pediococcus pentosaceus strains, 13 were Pediococcus acidilactici strains, and 7 were Lactococcus lactis strains. L. plantarum and L. mesenteroides strains were the dominant strains during the fermentation process and were recovered from 87 and 73% of the households, respectively. The potential origins of these groups of lactic acid bacteria were assessed by amplified fragment length polymorphism fingerprint analysis.

Bacterial counts associated with poultry processing at different sampling times.

Aerobic plate counts, Enterobacteriaceae counts and Pseudomonas counts were performed on neck skin samples from six processing steps in a poultry abattoir at three different sampling times. Sampling time 1 was shortly after start-up of processing operations, time 2 after a tea break which was preceded by a cold water rinse-down of equipment surfaces, and time 3 before shut-down. No significant differences (P > 0.05) in microbial numbers of neck skin samples were observed between the three sampling times at the six sampling sites. At this particular processing plant, therefore, sampling at any time of the processing shift would thus not lead to significantly different bacterial counts of neck skins. The lowest aerobic plate counts, over all three sampling times, were obtained for neck skins sampled after spray washing, and the highest for neck skins sampled after packaging. This indicated the efficacy of the washing step in reducing microbial contamination but subsequent re-contamination of carcasses. Despite the Pseudomonas counts of neck skins being lower than the Enterobacteriaceae counts at the beginning of processing, packaging of carcasses resulted in Pseudomonas counts that were higher than the Enterobacteriaceae counts.

Amplified fragment length polymorphism fingerprinting of Pseudomonas strains from a poultry processing plant.

Molecular typing has been used previously to identify and trace dissemination of pathogenic and spoilage bacteria associated with food processing. Amplified fragment length polymorphism (AFLP) is a novel DNA fingerprinting technique which is considered highly reproducible and has high discriminatory power. This technique was used to fingerprint 88 Pseudomonas fluorescens and Pseudomonas putida strains that were previously isolated from plate counts of carcasses at six processing stages and various equipment surfaces and environmental sources of a poultry abattoir. Clustering of the AFLP patterns revealed a high level of diversity among the strains. Six clusters (clusters I through VI) were delineated at an arbitrary Dice coefficient level of 0.65; clusters III (31 strains) and IV (28 strains) were the largest clusters. More than one-half (52.3%) of the strains obtained from carcass samples, which may have represented the resident carcass population, grouped together in cluster III. By contrast, 43.2% of the strains from most of the equipment surfaces and environmental sources grouped together in cluster IV. In most cases, the clusters in which carcass strains from processing stages grouped corresponded to the clusters in which strains from the associated equipment surfaces and/or environmental sources were found. This provided evidence that there was cross-contamination between carcasses and the abattoir environment at the DNA level. The AFLP data also showed that strains were being disseminated from the beginning to the end of the poultry processing operation, since many strains associated with carcasses at the packaging stage were members of the same clusters as strains obtained from carcasses after the defeathering stage.

Microbial populations associated with commercially produced South African sorghum beer as determined by conventional and Petrifilm plating.

Microbial populations of 46 commercially produced sorghum beer samples from retail outlets in Johannesburg, South Africa, were enumerated and characterized. Aerobic plate counts, lactic acid bacteria counts and yeast counts were performed by conventional and Petrifilm plating. Conventional methods yielded yeast counts of 7.84 log CFU/ml, lactic acid bacteria counts of 6.44 log CFU/ml and aerobic plate counts of 5.96 log CFU/ml. In comparison, Petrifilm counts were 7.85 log CFU/ml for yeasts, 5.31 log CFU/ml for lactic acid bacteria and 5.34 log CFU/ml for aerobic bacteria. Characterization of 419 predominant bacterial isolates from Standard One Nutrient Agar, MRS Agar and corresponding Petrifilm plates yielded 88.0% lactic acid bacteria, 8.4% Bacillus species, 2.9% Micrococcus species and 0.7% Gram negative bacteria. Composition of predominant lactic acid bacteria populations from Standard One Nutrient Agar and both types of Petrifilm plates showed marginal differences. Increased proportions of heterofermentative lactic acid bacteria were, however, isolated from conventional MRS Agar compared to the modified Petrifilm product which represented the equivalent to MRS Agar.

Bacterial populations associated with the dirty area of a South African poultry abattoir.

Bacterial populations associated with three sample types from the neck region of poultry carcasses in the dirty area of an abattoir were characterized. Sample types before and after scalding were skin only, feathers only, and a skin and feather combination. The neck skin of carcasses after the defeathering processing stage was also sampled. Bacterial populations associated with water from the scald tank, rubber fingers at the exit of the defeathering machine, and air in the dirty area were also characterized. Bacterial colonies (751) were randomly isolated from yeast extract-supplemented tryptone soya agar plates exhibiting 30 to 300 colonies. Micrococcus spp. were isolated in the highest proportion from pre-and postscalded carcass samples (63.5 to 86.1% of isolates), regardless of the sample type. Conversely, Enterobacteriaceae (40.3%), Acinetobacter (19.4%), and Aeromonas/Vibrio (12.5%) species predominated on neck skin samples taken from mechanically defeathered carcasses. Isolates from the rubber fingers were, however, predominantly Micrococcus spp. (94.4%). Bacterial groups isolated in the highest proportion from scald tank water samples were Micrococcus spp. (38.3%), species of Enterobacteriaceae (29.1%), and lactic acid bacteria (17.0%). Corynebacterium spp., species of Enterobacteriaceae, and Micrococcus spp. were dominant on air settle plates.

Biofilms associated with poultry processing equipment.

Aerobic and Gram-negative bacteria were enumerated on non-metallic surfaces and stainless steel test pieces attached to equipment surfaces by swabbing and a mechanical dislodging procedure, respectively, in a South African grade B poultry processing plant. Changes in bacterial numbers were also monitored over time on metal test pieces. The highest bacterial counts were obtained from non-metallic surfaces such as rubber fingered pluckers and plastic defeathering curtains which exceeded the highest counts found on the metal surfaces by at least 1 log CFU cm-2. Gram-negative bacterial counts on all non-metallic surface types were at least 2 log CFU cm-2 lower than corresponding aerobic plate counts. On metal surfaces, the highest microbial numbers were obtained after 14 days exposure, with aerobic plate counts ranging from 3.57 log CFU cm-2 to 5.13 log CFU cm-2, and Gram-negative counts from 0.70 log CFU cm-2 to 3.31 log CFU cm-2. Scanning electron microscopy confirmed the presence of bacterial cells on non-metallic and metallic surfaces associated with poultry processing. Rubber 'fingers', plastic curtains, conveyor belt material and stainless steel test surfaces placed on the scald tank overflow and several chutes revealed extensive and often confluent bacterial biofilms. Extracellular polymeric substances, but few bacterial cells were visible on test pieces placed on evisceration equipment, spinchiller blades and the spinchiller outlet.

Biogenic amine formation by poultry-associated spoilage and pathogenic bacteria.

The production of biogenic amines by 50 poultry-associated bacterial strains (25 Pseudomonas, 13 Salmonella and 12 Listeria) was investigated on amine agar plates containing lysine, histidine, ornithine, phenylalanine, tryptophan and tyrosine. Seventy-four per cent of all the strains produced cadaverine and putrescine, while phenylethylamine, histamine, tyramine and tryptamine were produced by 72, 56, 34 and 24% of strains, respectively. Different patterns of biogenic amine production amongst the three bacterial genera tested were apparent as well as amongst strains of the same genus. This study highlighted a high incidence of biogenic amine-producing bacterial strains associated with poultry.

Microbiological survey of a South African poultry processing plant.

Bacterial populations associated with poultry processing were determined on neck skin samples, equipment surfaces and environmental samples by replicate surveys. Aerobic plate counts, Enterobacteriaceae counts, Enterobacteriaceae counts and Pseudomonas counts were performed by standard procedures and the prevalence of Listeria, presumptive Salmonella and Staphylococcus aureus determined. Statistically significant (P < 0.05) increases in counts of all types of bacteria were obtained on product samples as a result of processing. Although bacterial counts on neck skin samples decreased by 0.3 to 0.4 log CFU g-1 after spray washing of carcasses, subsequent spinchilling and packaging of whole carcasses resulted in 0.7 to 1.2 log CFU g-1 increases. Bacterial numbers on equipment surfaces, however, decreased significantly from the "dirty" to the "clean" areas of the abattoir. Transport cages, "rubber fingers", defeathering curtains, shackles and conveyor belts repeatedly showed aerobic plate counts in excess of 5.0 log CFU 25 cm-2. Aerobic plate counts of scald tank and spinchiller water were 2 log CFU ml-1 higher than those of potable water samples. Bacterial numbers of the air in the "dirty" area were higher than those of the "clean" area. Listeria, presumptive Salmonella and Staphylococcus aureus were isolated from 27.6, 51.7 and 24.1% of all product samples, respectively, and Listeria and Staphylococcus aureus were also isolated from selected equipment surfaces.