Shelf-Life Characteristics and Aerobic Plate Counts of Ground Beef As Influenced by Fat Level and Fat Source.

Shelflife characteristics were scored in ground beef manufactured to certain levels of fat (16 ± 1%, 20 ± 1%, 24 ± 1%, 28 ± 1%) from various sources of fat trimmings (Choice flanks, plates, trimmings, brisket and kidney fat). Aerobic Plate Counts (APCs) were determined on the various lean and fat trimmings and the final ground beef (24 and 28% fat levels only). The characteristics were assessed over a 3-day retail display period. Off-odor was rated as stronger in ground beef formulated to 28% fat than to 16% fat. Increases in the duration of retail display were associated with greater darkening and surface discoloration of ground beef. Formulations with kidney and brisket fat had high (107/g) APCs at the start of the shelflife study in one batch. However, the increase in APCs over the 3-day display was less for ground beef containing these two materials than for ground beef with fat from other sources. It would appear that APCs can be as high as 107/g in 4- to 5-day postmortem trimmings under industrial conditions. Surface discoloration was strongly related with APCs (r = 0.82). The presence of 50-75% surface discoloration in ground beef was a good indication of APCs in excess of 108/g.

Effect of sample transport systems on survival of bacteria in ground beef.

The effects of two transport systems and cryoprotective agents on the survival of bacteria in ground beef samples were evaluated. Survival of Clostridium perfringens in ground beef samples after simulated transport (72 h) was higher (about 99%) in Dry Ice than in Trans Temp shipping units (-3 degrees C). There were no significant differences between the two transport systems in survival of coliforms, Escherichia coli, Staphylococcus aureus, or aerobic bacteria. Mixing ground beef samples at a ratio of 1:1 (wt/vol) with 10, 20, or 30% buffered solutions of dimethyl sulfoxide or glycerol before freezing improved the survival of C. perfringens and coliforms in both transport systems. Recovery of E. coli was significantly higher with the addition of 10% dimethyl sulfoxide before Dry Ice transport. Addition of 10% dimethyl sulfoxide resulted in a 100% recovery of both S. aureus and aerobic bacteria from ground beef after simulated transport in Trans Temp shipping units. The use of cryoprotective agents can improve the survival of bacteria during transport of ground beef samples.

Bacteriological Quality of Ground Beef Prepared from Hot and Chilled Beef Carcasses.

The bacteriological quality of ground beef chub packs prepared from beef sides at 2 h postmortem (hot-boned) and opposite sides conventionally chilled for 24 h at 3 C (cold-boned) were compared at the time of preparation and at 3-day intervals up to 45 days of storage at 0 C. Aerobic plate counts (APCs) in ground beef from hot-boned beef were either significantly lower or not significantly different from APCs in ground beef from cold-boned carcasses. There were no significant differences of any practical importance in Most Probable Numbers (MPNs) of coliforms and Escherichia coli between hot-boned and cold-boned ground beef stored at 0 C. Ground beef prepared from hot-boned beef offers great potential to the meat industry for energy conservation. The bacteriological quality of ground beef from hot-boned carcasses does not limit and might enhance the feasibility of boning carcasses before chilling.

Differentiation of Salmonella Serotypes by pyrolysis-gas-liquid chromatography of cell fragments.

Pyrolysis-gas-liquid chromatography (PGLC) of whole cells and cell fragments was used to differentiate 10 Salmonella serotypes. Lyophilized samples (200 microgram) of whole cells, cell walls, flagella, and deoxyribonucleic acid from each serotype were analyzed in duplicate by PGLC. Pyrochromatograms recorded as pyrolytic elution patterns represented thermal fragmentation products of the samples. Mathematical expressions of percent similarity and percent conformity were calculated for all possible pair combinations of the 10 serotypes. Stepwise discriminant analysis of the PGLC data showed that 100 percent correct classification of the 10 serotypes was possible from the flagella or deoxyribonucleic acid pyrochromatograms. The classification matrix of the whole-cell data showed a 90 percent correct classification. PGLC of cell fragments may provide useful information for taxonomic studies of Salmonella and other microorganisms.

Comparison of Methods for Estimation of Coliforms, Fecal Coliforms and Enterococci in Retail Ground Beef.

Seven recommended methods for estimation of coliforms, three for fecal coliforms and four for enterococci were tested on 30 retail ground beef samples. Lauryl sulfate tryptose broth gave higher coliform counts than did MacConkey's broth or brilliant green lactose bile broth 2% in 3-tube Most Probable Number (MPN) methods. With all MPN broths, coliforms counts were significantly (P ⩽0.05) higher after 48 than after 24 h of incubation. Presumptive coliform counts were higher with surface-overlay plating on violet red bile agar than with pour plating on the same agar or with the MPN broths. However, presence of Escherichia coli Type I was not confirmed as often from the agar medium as the broths. For estimation of fecal coliforms, counts did not differ significantly (P ⩽0.05) between EC broth (45.5 C) and brilliant green lactose bile broth 2% (44 C). Enterococci counts varied significantly (P ⩽0.05) among the four methods.

Device for Microbiological Sampling of Meat Surfaces.

A coring device for sampling meat surfaces was developed. Aerobic plate counts of beef and pork carcasses were significantly higher when determined by the coring method than by the cotton or alginate swab technique.

Comparison of Single and Multiple Stage Sieve Samplers for Airborne Microorganisms 1, 3.

Single and multiple stage air samplers were evaluated under commercial conditions for enumerating airborne microbial particles in a plant in which swine were slaughtered and pork was further processed. Three volumes of air, 0.014, 0.028, (1 ft3), and 0.057 cu M were sampled in duplicate on each of 2 days (for airborne molds, yeasts, coliforms, and aerobic bacteria) in eight rooms where pork carcasses were handled and further processed. Unexpectedly, the microbial counts were low during this winter sampling. The single and multiple samplers yielded mean (log10) counts (n = 94) of 0.15 and 0.42; -0.23 and -0.36; 1.18 and 1.29; and -0.63 and -0.91 per 0.028 cm M; for molds, yeasts, aerobes and coliforms, respectively. The multiple sampler detected slightly greater numbers of molds and aerobic bacteria, but did not define the differences in aerobic bacterial numbers from among the various processing rooms as readily as the single stage sampler. Counts of coliforms were higher from the single than from the multiple stage sampler. The single stage sampler required only one petri dish per sample, as compared with six for the multiple stage sampler, so it required less medium and time for evaluating air for microorganisms.

Comparative Study of Two Methods for Detection of Clostridium perfringens in Ground Beef.

The tryptose-sulfite-cycloserine agar pour plate method was superior to selective enrichment in liquid sulfite medium for isolation of small numbers of Clostridium perfringens from frozen ground beef.

Survival of Vibrio parahaemolyticus in Various Diluents.

Survival of Vibrio parahaemolyticus in various diluents was investigated. 100 mM potassium phosphate buffers (pH 6, 7, and 8) without added NaCl were extremely deleterious to V. parahaemolyticus 04:Kll in comparison to the same diluent with either 0.5, 3, or 6% NaCl. Maximum counts were obtained when phosphate buffers containing 3% NaCl were used as diluents. There were no significant differences among survivor counts of cells exposed for 20 min to 100 mM potassium phosphate 3% NaCl buffer at either pH 6, 7, or 8. Greater than 99.9% of the cell population was destroyed within 20 min in 0.1% peptone diluent without NaCl when compared to 0.1% peptone with either 0, 5, 3, or 6% NaCl. Cell counts using 0.1% peptone diluents containing 3 and 6% NaCl were not significantly different; however, both were superior to 0.1% peptone containing 0.5% NaCl. Survival data for V. parahaemolyticus 04: Kll in distilled water containing 0, 0.5, 3. and 6% added salt were similar to data for the 0.1% peptone diluents. Culture age (4, 10, and 24 h) and time of exposure to the diluents also significantly affected survival of V. parahaemolyticus 04:Kll and 17802.

Sublethal heat stress of Vibrio parahaemolyticus.

When Vibrio parahaemolyticsu ATCC 17802 was heated at 41 degrees C for 30 min in 100 mM phosphate-3% NaCl buffer (pH 7.0), the plate counts obtained when using Trypticase soy agar containing 0.25% added NaCl (0.25 TSAS) were nearly 99.9% higher than plate counts using Trypticase soy agar containing 5.5% added NaCl (5.5 TSAS). A similar result was obtained when cells of V. parahaemolyticus were grown in a glucose salts medium (GSM) and heated at 45 degrees C. The injured cells recovered salt tolerance within 3 h when placed in either 2.5 TSBS or GSM at 30 degrees C. The addition of chloramphenicol, actinomycin D, or nalidixic acid to 2.5 TSBS during recovery of cells grown in 2.5 TSBS indicated that recovery was dependent upon protein, ribonucleic acid (RNA, and deoxyribonucleic acid (DNA) synthesis. Penicillin did not inhibit the recovery process. Heat-injured, GSM-grown cells required RNA synthesis but not DNA synthesis during recovery in GSM. Chemical analyses showed that total cellular RNA decreased and total cellular DNA remained constant during heat injury. The addition of [6-3H]uracil, L-[U-14C]leucine, and [methyl-3H]thymidine to the recovery media confirmed the results of the antibiotic experiments.

Bacteriological quality and shelf life of ground beef.

The bacteriological quality of unfrozen raw ground beef was evaluated after 0, 3, 6, 9, 12, 15, and 18 days of storage at 29 +/- 1 F (-1.7 +/- 0.6 C). At the time of fabrication, all of the ground beef samples contained 10(6) or fewer total aerobic and psychrotrophic bacteria/g; 81% contained 100 or fewer coliforms/g; 94% contained 100 or fewer Escherichia coli/g; and all of the samples contained 100 or fewer coagulase-positive Staphylococcus aureus and Clostridium perfringens/g. Total aerobic and psychrotrophic bacteria increased by 1 log between 3 and 18 days of storage. Coliform and E. coli counts decreased during storage, whereas coagulase-positive S. aureus and C. perfringens counts did not change significantly. These data indicate that meat processors, wholesalers, and retailers could improve the bacteriological quality and prolong the shelf life of ground beef packaged in oxygen-impermeable film if the temperature of product never exceeded 29 +/- 1 F (-1.7 +/- 0.6 C).

Dye reduction method for estimating bacterial counts in ground beef.

A dye reduction method was developed for estimating total aerobic and/or psychrotrophic bacterial counts in ground beef. The method is based on color changes in indicator disks placed on the meat surface.