Treatments with Nisin and Chelators to Reduce Salmonella and Escherichia coli on Beef †

Salmonella typhimurium ATCC 14028 or Escherichia coli O157:H7 attached to lean beef tissue were treated with citrate, lactate, sodium hexametaphosphate, or EDTA, alone or in combination with nisin in simple buffers, and incubated at 4°C for up to 3 days. Lactate with nisin reduced S. typhimurium attached to beef by 040 log₁₀ CFU/cm², while EDTA and nisin reduced E. coli O157:H7 by 0.42 log₁₀ CFU/cm². Unlike earlier in vitro studies in which treatments with nisin and chelating agents resulted in reductions of > 4 log₁₀ CFU/cm², such reductions were not observed in situ.

Resistance of Acid-Adapted Salmonellae to Organic Acid Rinses on Beef †

Four strains of salmonellae, including three bovine isolates and an ATCC strain, were adapted to growth in acidic conditions by sequential transfer in tryptic soy broth with reduced pH values. The cultures were transferred until good growth (approximately log₁₀7 CFU/ml) was obtained within 24 h at 37°C at pH 5.0. Lean beef tissue was inoculated by immersion into either the acid-adapted or the homologous parent strain of each bacterium. The inoculated tissue was rinsed for 10s in 1.5% or 3.0% lactic acid solutions at 23°C or 55°C. Reductions in bacterial populations were compared between the parent and acid-adapted strains to determine if the acid-adapted strains were more resistant to the organic acid rinses. Acid-adapted strains had either equal or greater sensitivity to organic acid rinses than their homologous parent strains, indicating that acid adaptation did not result in bacteria which were resistant to organic acid rinses. Acid-adapted strains had significantly lower D_55°C^- values than their homologous parent strains.

Microbiological Quality of Beef Carcasses and Vacuum-Packaged Subprimals: Process Intervention during Slaughter and Fabrication

Beef carcass sides (n = 9 per replicate) were sprayed with water (W), 200 ppm chlorine ©, or 3% (vol/vol) lactic acid (L) immediately after rail inspection and at the end of an 8-h spray-chill cycle, resulting in a total of nine different spray combinations. All treatment combinations involving chlorine and/or lactic acid reduced carcass contamination. The reductions in mean log₁₀ CFU/cm² for carcass aerobic plate count (APC) data ranged from 0.4 to 1.8. The treatment combination using lactic acid at both spray times (L+L) resulted in the greatest reduction. Additionally, treatment combinations involving lactic acid at either time and in combination with water or chlorine tended to reduce APCs more than those treatment combinations without acid. Browning of blood splashes was observed on carcasses sprayed with lactic acid and persisted until fabrication at 72 h postmortem. A companion study was designed, in conjunction with the carcass decontamination study, to evaluate effect of carcass treatment on the microbiological quality of subprimal subdivisions derived from treated carcasses. A facet of the subprimal study evaluated chlorine spray (200 ppm) and microwave radiation as approaches to improving subprimal shelf life and safety. Cuts taken from sprayed carcasses were vacuum packaged with or without intervention treatments, stored at 1 to 2°C and evaluated for both APC and pathogen populations at specified intervals of up to 120 days. These results demonstrated that neither carcass nor intervention treatment had any significant (P > 0.05), beneficial effect on the microbiological quality of subprimal cuts.

Growth Potential of Individual Strains of Listeria monocytogenes in Fresh Vacuum-Packaged Refrigerated Ground Top Rounds of Beef

Separate inocula of four strains of Listeria monocytogenes were prepared at 4°C and inoculated (3.58 to 4.67 log₁₀ colony forming units [CFU]/g) in top round ground beef (< 4.0% fat) patties (78.8 ± 6.7 g) of normal (5.47 ± 0.03) or high (6.14 ± 0.08) pH, which were stored (4°C) vacuum-packaged for 56 days and analyzed for L. monocytogenes , total aerobic plate counts (APC) and pH. In normal-pH ground beef, strain N-7143 (serotype 3a), multiplied from 4.25 ± 0.71 log₁₀ CFU/g at day of inoculation to 6.53 ± 0.34 log₁₀ CFU/g at 35 days of storage (P < 0.05); a 2.3 log₁₀ CFU/g increase. Populations of strain Na-19 (serotype 3b) increased 1.8 log₁₀ CFU/g in 35 days of storage, while numbers of strain Na-16 (serotype 1/2a) did not change (P > 0.05) during the 56 days of storage. Strain Scott A (serotype 4b) decreased in numbers from 4.00 ± 1.21 log₁₀ CFU/g at day-0 to 2.72 ± 0.98 log₁₀ CFU/g at 56 days. Populations of strain Scott A were lower (P < 0.05) than other strains after 21 days of storage. In high-pH ground beef, populations of strains Na-19, N-7143 and Na-16 increased (P < 0.05) by 2.87, 2.64 and 2.24 log₁₀ CFU/g, respectively, in 28 days. Populations of strain Scott A did not change significantly (P > 0.05), and they were lower (P< 0.05) than populations of other strains at 28 days. The results indicated that although growth of L. monocytogenes in vacuum-packaged, refrigerated ground beef was slow, it proceeded more rapidly in product of pH values above 6.0, and depended on strain of the pathogen tested.

Biogenic Amine Formation in Fresh Vacuum-Packaged Beef Stored at -2°C and 2°C for 100 Days

When fresh, vacuum-packaged, meat products are stored for extended periods of time, undesirable changes, due to naturally occurring microbial flora present during packaging occur. Lactobacillus spp. are known to form amines through the decarboxylation of free amino acids. Tyramine and histamine can cause intoxication in individuals taking monoamine oxidase-inhibiting drugs. This study determined 1) the effect of storage temperature on bacterial growth and biogenic amine production in vacuum-packaged beef subprimals, 2) the effect of washing subprimals with water to remove tyramine contamination, and 3) the penetration of tyramine from the surface of the subprimal. Inside rounds were vacuum packaged and stored at -2°C or 2°C. Samples were evaluated over 100 days for amine concentrations, total psychrotrophic counts and lactic acid bacteria. Tyramine, putrescine and cadaverine were detected in this study. Significant levels (15 μg/g) of tyramine were detected at 20 days of storage at 2°C and 40 days of storage at -2°C. Putrescine and cadaverine were detected first at 40 days of storage at 2°C and 60 days of storage at -2°C. Both treatment groups contained about 130 μg/g of tyramine at 100 days of storage. Psychrotrophic plate counts and lactic acid bacteria counts were initially 10³ colony forming units (CFU)/cm² and ranged from 10⁶-10⁷ CFU/cm² at 100 days of storage. Even though tyramine was evident at a depth of 6 mm from the surface of the cut, one-third of the amine was removed by washing the subprimal with tap water.

Influence of Cooling Rate on Outgrowth of Clostridium perfringens Spores in Cooked Ground Beef

The ability of Clostridium perfringens spores to germinate and grow was studied to determine a safe cooling rate for cooked beef. Beef samples were inoculated with a cocktail of three strains of heat-shocked C. perfringens spores (NCTC 8238, NCTC 8239 and ATCC 10288), vacuum-packaged, and cooked in a stirred water bath to an internal temperature of 60°C in 1 h. Then, samples were cooled through the temperature range of 54.4°C to 7.2°C at rates varying from 6 to 18 h. Samples were removed at various times during cooling to determine if the spores had germinated and multiplied. The samples were plated on tryptose-sulfite-cycloserine agar and incubated anaerobically at 37°C for 48 h. Minimal growth was observed with cooling periods of up to 15 h. However, with the time to achieve 7.2°C extended to 18 h, C. perfringens spores germinated and grew from an inoculum of approximately 1.5 log₁₀ to about 6.0 log₁₀ CFU/g. This study indicated that pasteurized cooked beef must be cooled to 72°C in 15 h or less to prevent C. perfringens foodborne disease outbreaks.

Growth of Listeria monocytogenes on Different Muscle Tissues

Growth of Listeria monocytogenes on raw and cooked beef, chicken, catfish, and shrimp was compared. Samples were inoculated with L. monocytogenes and stored at 4°C for 11 days. Listeria monocytogenes and psychrotrophic populations were monitored. Growth of L. monocytogenes was faster and reached a higher population on raw and cooked catfish and shrimp than on beef or chicken. Psychrotrophic populations were greater on beef and chicken than on catfish and shrimp after 11 days regardless of whether the muscle was raw or cooked. To determine what factor or factors inherent in the tissues may contribute to this growth-rate difference, beef and shrimp tissues were used. The pH of each tissue type was adjusted to yield portions of beef and shrimp at pH 5.7 (pH of fresh beet) and 7.6 (pH of fresh shrimp). Portions were inoculated with L. monocytogenes and stored at 4°C for 11 days. Listeria monocytogenes grew significantly faster on beef adjusted to 7.6 than on beef at the normal pH and on shrimp at pH 7.6 than on shrimp adjusted to pH 5.6. Thus, some difference in growth rate is due to inherent pH differences of fresh tissues. However, on cooked tissues the growth rate on acidified shrimp was the same as that on shrimp with the normal pH of 7.6. Growth rates of Listeria on cooked beef at either pH were similar to those noted on the uncooked tissue. This indicates additional factors in shrimp exert inhibitory effects at reduced pH levels that may be heat related.

Antimicrobial Effects of Trisodium Phosphate Against Bacteria Attached to Beef Tissue

Sliced beef tissue was artificially contaminated with Salmonella typhimurium , Listeria monocytogenes and Escherichia coli O157:H7. The contaminated tissue was immersed in 8, 10 and 12% solutions of trisodium phosphate at 25, 40 and 55°C with contact times of up to 3 min. The concentration of the trisodium phosphate solution was not a significant factor in reducing the populations of the bacteria on either lean or adipose tissue. Reductions in bacterial populations of 1 to 1.5 log₁₀ cycles were obtained on lean tissue contaminated with the gram-negative pathogens, although less reduction in population was seen with L. monocytogenes . Greater reductions in bacterial populations were observed on adipose tissue, with maximum reductions of 2 to 2.5 log₁₀ cycles and 1 to 1.5 log₁₀ cycles for the gram-negative and the gram-positive pathogens, respectively. Typically greater reductions in bacterial populations were seen as the temperature of the trisodium phosphate solution increased. Surface beef carcass tissue was inoculated with E. coli ATCC 25922 and sanitized with 8% trisodium phosphate using a model carcass washing system. Population reductions with the carcass washer and lean tissue were comparable to those observed in the laboratory with E. coli O157:H7. However, greater reductions were observed on adipose tissue from the model system, suggesting that the physical washing procedure may have contributed to the reduction in the bacterial population.

Growth of Selected Cross-Contaminating Bacterial Pathogens on Beef and Fish at 15 and 35°C. J Food Prot 1994;57:337-340. [PMID: 31113126 DOI: 10.4315/0362-028x-57.4.337]

Isolates of Escherichia coli and Clostridium perfringens from beef and Aeromonas hydrophila from fish were examined for their ability to survive and grow as cross-contaminates on nonnative tissues at simulated ambient (35°C) and aging/conditioning (15°C) temperatures of handling and retailing found in the tropics. Growth of all isolates over a 10-h period was greater (P < 0.05) on their native tissues at both temperatures. The aging/conditioning temperature effectively limited growth of E. coli and A. hydrophila to less than l-log_l0 CFU/g and prevented growth of C. perfringens on beef and fish samples. All three isolates demonstrated characteristic mesophilic growth response on both tissues at 35°C during the 10-h retail period. The study suggests that two muscle food products could be jointly handled to efficiently use available storage/haulage capacity in tropical countries. Potential savings in space, labor and energy would be made if cross-contamination between the two products is minimized by available packaging and sanitizing technologies.

The effect of the pH of meat on the boiling test

The effect of the pH on the boiling test was studied in 68 beef and 108 pork muscles. The pH had a significant effect on the sensory scores obtained from the boiling test. The effect was particularly pronounced in the odour of meat. In beef the odour scores remain steady for samples with a pH value under about 6.2 and start to increase rapidly in higher pH values. In pork the increase in scores appears to be linear. The odour observed in high pH meat was described by the judges as abnormal and ammonialike. In the case of meat with a high pH, the results of the boiling test at meat inspection should be interpreted with extreme caution.

A survey of the hygienic quality of beef and pork carcasses in Norway

The bacteriological quality of beef and pig carcasses was assessed at 9 Norwegian abattoirs by sampling 10 carcasses at multiple sites on each of several visits. On beef carcasses the following sites consistently carried higher numbers of bacteria: the Brisket, the Fore-ribs, the Flank groin, and the Round medial. There was no evidence that beef slaughter and dressing in the hanging position was superior to methods where the carcass was lying until the hide puller. On pork carcasses the Cheek, and the Abdomen lateral surface (belly) were most heavily contaminated. The hygienic quality of pork carcasses in abattoirs where singeing was a separate step tended to be better than where a combined singeing and dehairing machine was used.

This survey suggests that bacteriological monitoring of slaughter at this level of sampling and visiting is able to detect consistently poor hygienic practices.

Where direct comparisons with data from other countries could be made, the present investigation indicates that the bacterial counts on Norwegian beef and pork carcasses are of the same order or better.