Cooked, chilled beef and cooked, chilled pork were inoculated with three strains of Clostridium perfringens (NCTC 8238 [Hobbs serotype 2], NCTC 8239 [Hobbs serotype 3], and NCTC 10240). Inoculated products were heated to 75°C, held for 10 min in a circulating water bath to heat activate the spores, and then chilled by circulating chilled brine through the water bath. Samples were chilled from 54.4 to 26.6°C in 2 h and from 26.6 to 4.4°C in 5 h. Differences in initial C. perfringens log counts and log counts after chilling were determined and compared with the U.S. Department of Agriculture (USDA) stabilization guidelines requiring that the chilling process allow no more than 1 log total growth of C. perfringens in the finished product. This chilling method resulted in average C. perfringens increases of 0.52 and 0.68 log units in cooked beef and cooked pork, respectively. These log increases were well within the maximum 1-log increase permitted by the USDA, thus meeting the USDA compliance guidelines for the cooling of heat-treated meat and poultry products.

Nisin (NS), microwave (MW), and nisin plus microwave (NS + MW) treatments were applied to precooked beef semitendinosus muscles inoculated with spores of Clostridium sporogenes . Samples were then vacuum packaged and stored at 4°C or 10°C for 21 or 70 days. After 21 days of storage at 10°C, NS and NS + MW reduced viable vegetative cell (VVC) counts by approximately 3 log cycles compared to the control. After 70 days storage, VVC counts were higher ( P < 0.05) at 10°C than 4°C only for the control. However, at 4°C, VVC counts for each treatment were not different ( P > 0.05) from those of the control. After 70 days of storage at 10°C, VVC counts were lower ( P < 0.05) for NS and NS + MW treatments than for the control.

The effects of extrusion cooking alone or in combination with electron beam radiation (3.5 kGy) on vacuum-packaged beef-based snack sticks containing beef cardiac muscle were investigated. During formulation, Clostridium sporogenes PA 3679 spores were added to achieve a concentration of 4 log CFU/g. Twin-screw extrusion cooking at 72°C reduced aerobic plate counts (APCs) by 3.63 log cycles and C. sporogenes viable cell counts by 2.02 log cycles for the inoculated product. After irradiation (3.5 kGy), APCs were decreased to 1 log CFU/g when compared to 0 kGy counterparts receiving 0 kGy. Spores were not detected in irradiated inoculated samples, which contained C. sporogenes PA 3679 at levels of 3.17 to 3.50 log CFU/g after extrusion cooking.

The effectiveness of a steam pasteurization process for reducing naturally occurring bacterial populations on freshly slaughtered beef sides was evaluated in a large commercial facility. Over a period of 10 days, 140 randomly chosen beef sides were microbiologically analyzed. Each side was sampled immediately before, immediately after, and 24 h after steam pasteurization treatment. Total aerobic bacteria (APC), Escherichia coli (generic), coliform, and Enterobacteriaceae populations were enumerated. The process significantly ( P ≤ 0.01) reduced mean APCs from 2.19 log CFU/cm 2 before treatment to 0.84 log CFU/cm 2 immediately after and 0.94 log CFU/cm 2 24 h after treatment. Before pasteurization (8 s steam exposure), 16.4% of carcasses were positive for generic E. coli (level of 0.60 to 1.53 log CFU/cm 2 ), 37.9% were positive for coliforms (level of 0.60 to 2.26 log CFU/cm 2 ), and 46.4% were positive for Enterobacteriaceae (level of 0.60 to 2.25 log CFU/cm 2 ). After pasteurization, 0% of carcasses were positive for E. coli , 1.4% were positive for coliforms (level of 0.60 to 1.53 log CFU/cm 2 ), and 2.9% were positive for Enterobacteriaceae (level of 0.60 to 1.99 log CFU/cm 2 ). Of the 140 carcasses evaluated, one carcass was positive for Salmonella spp. before treatment (0.7% incidence rate); all carcasses were negative after steam treatment. This study indicates that steam pasteurization is very effective in a commercial setting for reducing overall bacterial populations on freshly slaughtered beef carcasses. The system may effectively serve as an important critical control point for HACCP systems at the slaughter phase of beef processing. In conjunction with other antimicrobial interventions (mandated by USDA to achieve zero tolerance standards for visible contamination) and good manufacturing practices, this process can play an important role in reducing the risk of pathogenic bacteria in raw meat and meat products.

The effectiveness of a recently invented “steam pasteurization” (S) process in reducing pathogenic bacterial populations on surfaces of freshly slaughtered beef was determined and compared with that of other standard commercial methods including knife trimming (T), water washing (35°C; W), hot water/steam vacuum spot cleaning (V), and spraying with 2% vol/vol lactic acid (54°C, pH 2.25; L). These decontamination treatments were tested individually and in combinations. Cutaneus trunci muscles from freshly slaughtered steers were inoculated with feces containing Listeria monocytogenes Scott A, Escherichia coli OI57:H7, and Salmonella typhimurium over a predesignated meat surface area, resulting in initial populations of ca. 5 log CFU/cm 2 of each pathogen. Tissue samples were excised from each portion before and after decontamination treatments, and mean population reductions were determined. Treatment combinations evaluated were the following (treatment designations within the abbreviations indicate the order of application): TW, TWS, WS, VW, VWS, TWLS, and VWLS. These combinations resulted in reductions ranging from 3.5 to 5.3 log CFU/cm 2 in all three pathogen populations. The TW, TWS, WS, TWLS, and VWLS combinations were equally effective ( P > 0.05), resulting in reductions ranging from 4.2 to 5.3 log CFU/cm 2 . When used individually, T, V, and S resulted in pathogen reductions ranging from 2.5 to 3.7 log CFU/cm 2 Steam pasteurization consistently provided numerically greater pathogen reductions than T or V. Treatments T, V, and S were all more effective than W (which gave a reduction on the order of 1.0 log CFU/cm 2 ). Steam pasteurization is an effective method for reducing pathogenic bacterial populations on surfaces of freshly slaughtered beef, with multiple decontamination procedures providing greatest overall reductions.

Standardized microbiological sampling and testing procedures were developed that can be used throughout the beef slaughter and processing industry to facilitate the collection and any desired compilation of comparative data. Twenty samples each from carcasses (brisket, flank, and rump areas combined); subprimal cuts (clods); lean trim; and cutting and/or conveyor surfaces were collected in three slaughter and processing operations, with the first operation being a preliminary trial and resulting in no reported data. Microbiological analyses for Clostridium perfringens , Escherichia coli O157:H7, Listeria monocytogenes , Salmonella spp., Staphylococcus aureus , Campylobacter jejuni/coli , total coliforms, E. coli Biotype I, and aerobic mesophilic bacteria (aerobic plate count, APC) were performed on all samples by an outside laboratory. The procedures developed were effective in allowing samples to be collected, shipped, and analyzed in the same manner for all operations. From a logistical standpoint, approximately 20 samples each of carcasses, clods, lean trim, and surfaces could be taken within 4 to 6 h by five people. Forty samples each of carcass, clod, lean trim, and conveyor surfaces from two plants tested negative for E. coli O157:H7, Salmonella spp., and Listeria spp., with the exception of L. monocytogenes being isolated from one carcass and one clod sample. APCs and total coliform counts were between 10 3 to 10 5 and 10 2 to 10 3 CFU/cm 2 or CFU/g, respectively, for the 40 samples each of carcasses, clods, and lean trim. APCs for surface swab counts ranged from ≤ 10 to 10 3 CFU/cm 2 .

A study to compare procedures and interventions for removing physical and bacterial contamination from beef carcasses was conducted in six carcass conversion operations that were representative of modern, high-volume plants and located in five different states. Treatment procedures included trimming, washing, and the current industry practice of trimming followed by washing. In addition, hot (74 to 87.8°C at the pipe) water washing and rinsing with ozone (0.3 to 2.3 ppm) or hydrogen peroxide (5%) were applied as intervention treatments. Beef carcasses were deliberately contaminated with bovine fecal material at >4.0 log colony-forming units (CFU)/cm 2 in order to be better able to observe the decontaminating effects of the treatments. Carcasses were visually scored by 2 to 3 trained personnel for the level of gross contamination before and after treatment. Samples (10 by 15 cm, 0.3 to 0.5 cm thick) for microbiological testing were excised as controls or after application of each procedure or intervention and analyzed for aerobic mesophilic plate counts, Escherichia coli Biotype I counts, and presence or absence of Listeria spp., Salmonella spp., and Escherichia coli O157:H7. Average reductions in aerobic plate counts were 1.85 and 2.00 log CFU/cm 2 for the treatments of trimming-washing and hot-water washing, respectively. Hydrogen peroxide and ozone reduced aerobic plate counts by 1.14 and 1.30 log CFU/cm 2 , respectively. In general, trimming and washing of beef carcasses consistently resulted in low bacterial populations and scores for visible contamination. However, the data also indicated that hot- (74 to 87.8°C at the pipe) water washing was an effective intervention that reduced bacterial and fecal contamination in a consistent manner.

Effectiveness of 0, 1.5 and 3.0% gluconic acid (G) and/or 0 and 1.5% lactic acid (L) solutions in reducing aerobic psychrotrophic bacteria plate counts (PPCs) and lactic acid bacteria counts (LACs) on vacuum-packaged beef was investigated at 0, 14, 28 and 56 days of storage. Instrumental and visual color changes were evaluated up to 28 days. Steaks treated with 1.5% L, plus 1.5% G or 3.0% G, solutions showed 2.0 and 2.5 log reductions ( P <0.05) in PPCs compared to nontreated samples, respectively, at days 28 and 56. At 1.5%, G or L intervention for 0 and 14 days PPCs did not differ ( P >0.05). However, PPCs were lower ( P <O.05) for samples treated with 1.5% L than with 1.5% G at 28 and 56 days of storage. The effect of G plus L in reducing ( P <0.05) LACs was evident at all storage periods. Inoculation with Lactobacillus fermentum (10 4 colony forming units [CFU]/ml) resulted in higher ( P <0.05) PPCs and LACs at 28 and 56 days compared to noninoculated counterparts. Increasing G from 1.5 to 3.0% decreased ( P <0.05) redness and increased ( P <0.05) yellowness at day 0. Samples treated with 1.5% L solution had numerically the lowest a* values at days 0 and 14. This detrimental effect was reduced ( P <0.05) when 1.5% G was added in combination with L, because redness increased ( P <0.05) at day 14. At 0 day, 1.5% L steaks showed the fastest ( P <0.05) rate of color deterioration. At 14 days, the presence of L alone or in combination with 1.5 or 3% G resulted in steaks with slightly faster ( P <0.05) color deterioration compared to steaks treated with G or not treated. At day 28, 3.0% G samples revealed the fastest ( P <0.05) color deterioration. This detrimental effect on color was reduced ( P <O.05) when G plus L was applied at 1.5%.

Aroma notes of chuck rolls from decontaminated beef carcasses were evaluated. Carcasses were spray-treated with either water, 200 ppm chlorine or 3% lactic acid immediately after inspection and again after spray chilling. Following fabrication, each chuck roll was divided into four pieces; vacuum-packaged; and stored for 10, 40, 80 or 120 days at 4°C. At different storage times, a six-member, professional, sensory panel evaluated beefy, bloody, sour, grassy, spoiled and metallic aromatic impressions on cooked patties made from ground chuck roll pieces using a 15-point attribute scale. Psychrotrophic bacterial counts were conducted on raw, ground samples. Principal component statistical analysis showed that the first principal component described 96% of the data and, therefore, it was used as an average acceptability score that explained all aroma descriptors. Chucks from chlorine-treated carcasses tended to have higher (P = 0.08) acceptability scores, followed by lactic acid – and water-treated counterparts. The rate of change in aroma occurred faster between 10 and 40 days for lactic acid – and water-treated samples and between 40 and 80 days for chlorine-treated samples. Bacterial counts increased during storage up to 80 days; however, treatments were not different (P >0.05).

Undesirable changes in vacuum-packaged beef products during prolonged storage can present a problem to some consumers. Bacterial proteolysis and decarboxylation can release pressor amines, such as tyramine and histamine, that can be toxic when ingested by individuals taking monoamine oxidase-inhibiting drugs. This study determined the effect of carcass decontamination on bacterial growth and biogenic amine production in vacuum-packaged subprimals. Beef carcasses were treated with 200 ppm chlorine or 3% lactic acid sprays, fabricated, vacuum packaged, and stored at 1°C. Samples were evaluated up to 120 d for amine concentrations, total aerobic counts, and lactic acid bacteria. Of all the amines monitored, only tyramine was consistently detected over the course of the study. Significant levels of tyramine were detected starting at day 20 of storage in all treatments and controls. By day 60, the levels had increased to about 50 μg/g and continued to increase to about 180 μg/g by 120 d of storage. Tryptamine was detected in some samples by 60 d of storage, but the levels were variable and did not follow any trend. Initial aerobic plate counts ranged from 10-200 CFU/cm 2 , whereas lactic acid bacteria counts were from 6-46 CFU/cm 2 . Bacterial numbers increased exponentially until about day 60, when they leveled off at between 10 6 -10 7 CFU/cm 2 , with no differences between any of the treatments and/or controls. Although the vacuum-packaged beef was organoleptically acceptable up to day 60 (day 90 for some samples), it could pose some risk to individuals sensitive to biogenic amines if the product is stored at 1°C or higher for 60 d or more.

We studied the chilling rate of hot-boned beef required to control bacterial growth during storage and display. Hot-boned cuts were chilled to 21 C by 3, 5, 9, and 12 h after their removal from the carcass. Cuts were vacuum-stored at 2.2 C for 14 or 21 d, then displayed at 2.2 C for 3 days under natural fluorescent lighting. Initial bacterial loads of hot-boned cuts were low (Log 0–3 CFU/cm 2 ). Conventionally chilled beef (48 h at 2.2 C) and hot-boned cuts chilled to 21 C by 3, 5, and 9 h had lower bacterial counts and more desirable color and odor than hot-boned cuts chilled slower (12 h to 21 C). In general, indicator organisms and potential pathogens (coliforms, fecal coliforms, coagulase-positive Staphylococcus aureus , Clostridium perfringens , and fecal streptococci) were more numerous for cuts with slower chilling rates (9 and 12 h to 21 C) than for cuts chilled faster (3 and 5 h to 21 C and conventionally chilled beet). No Salmonella were detected. Hot-boned beef cuts are in good bacteriological condition (no potential health hazards) for storage if chilled to 21 C in 3 to 9 h.

Mesophilic and psychrotrophic bacterial counts of hot-boned and conventionally treated cuts from 15 steers were low [Log 0–2 colony forming units (CFU)/cm 2 ] at 0 time; and after 14 days of vacuum-packaged storage (2.2 C), hot-boned cuts had higher counts than conventionally-treated cuts. In the first experiment involving 10 steers, the mesophilic and psychrotrophic counts for hot-boned cuts were Log 5.26 CFU/cm 2 and Log 5.15 CFU/cm 2 , respectively, and for conventionally treated cuts, log 4.64 CFU/cm 2 and Log 4.43 CFU/cm 2 , respectively. In the second experiment involving 5 steers, the mesophilic and psychrotrophic counts were Log 6.62 CFU/cm 2 and Log 6.61 CFU/cm 2, respectively, for hot-boned cuts; and Log 5.93 CFU/cm 2 and Log 4.91 CFU/cm 2 , respectively, for conventionally treated cuts. Some hot-boned cuts had low levels (Log 0–3 CFU/cm 2) of coliforms, fecal coliforms, Clostridium perfringens , coagulase-positive Staphylococcus aureus and fecal streptococci. No Salmonella were recovered from any cuts. Temperature-decline data indicated that hot-boned cuts had longer (several hours) periods of rapid bacterial growth (above 21 C) than conventionally-treated cuts. The longer rapid growth period for hot-boned cuts may have contributed to higher microbial loads and subsequently to more growth of bacteria in cold storage. Slower chilling of hot-boned samples stemmed from vacuum-packaging and boxing soon after cutting. Temperature control of hot-boned meat during the first several hours of chilling is critical, particularly if hot cuts are vacuum-packaged and boxed before chilling. Some temperature decline guidelines, based on bacterial counts, are presented for hot-boned, vacuum-packaged boxed cuts. Most hot-boned cuts processed and stored under our experimental conditions were bacteriologically acceptable.

Acetate and mylar adhesive tapes were used to estimate microbial loads on surfaces of 60 red meat samples. The conventional method of excision, rinsing and blending of meat was used as a comparison. The mylar tape method was found to provide statistically significant correlation compared with the conventional method. We suggest that when the tape count is > log 2 CFU/cm 2 , bacterial counts are high on meat surfaces (ca. log 5–7 CFU/cm 2 ); between log 1–2 CFU/cm 2 , counts are intermediate (ca. log 3–4 CFU/cm 2 ) and < log 1 CFU/cm 2 , counts are low (ca. log 3 CFU/cm 2 ). The tape method is easy to perform and requires little time and material. With multiple transfers, it may be used to evaluate counts at different incubation temperatures and on different types of agar media.