Minimum leak size determination, under laboratory and commercial conditions, for bacterial entry into polymeric trays used for shelf-stable food packaging.

This study sought to determine the minimum leak size for entry of Enterobacter aerogenes under laboratory conditions, and normal flora under commercial conditions, into tryptic soy broth with yeast extract (TSBYE), homestyle chicken, and beef enchilada packaged in 355-ml polyethylene terephthalate/ethylene vinyl alcohol/polypropylene trays. Channel leaks (diameters of 50 to 200 microm) were made across the sealing area of the trays. Pinholes (diameters of 5 to 50 microm) were made by imbedding laser-drilled metal and plastic disks into the tray lids. For the laboratory simulation, all trays were submerged and agitated for 30 min at 25 degrees C in phosphate-buffered saline that contained 10(7) CFU/ml of E. aerogenes. Under commercial conditions, trays with channel leaks were processed in retorts to achieve commercial sterility. All trays were subsequently incubated at 37 degrees C for 2 weeks, and their contents plated onto eosin-methylene blue agar (for laboratory simulation) to enumerate E. aerogenes and brain heart infusion agar (for commercial conditions) to determine the presence of any bacteria. Under laboratory conditions, minimum pinhole sizes for E. aerogenes entry approximated 5 microm (TSBYE, metal disks; homestyle chicken, plastic disks), 20 microm (beef, plastic disks), and 30 microm (beef, metal disks). The minimum channel leak sizes for entry of E. aerogenes approximated 10 microm (TSBYE), 70 microm (chicken), and 200 microm (beef enchilada). Under commercial conditions, the minimum channel leak size for bacterial entry approximated 40 microm (TSBYE), 50 microm (homestyle chicken), and more than 200 microm (beef). Results showed that E. aerogenes can enter pinholes as small as 5 microm under a worst-case scenario. This information can be used to set pass and fail parameters for leak detection devices.

Control of Listeria monocytogenes with combined antimicrobials on beef franks stored at 4 degrees C.

Contamination of ready-to-eat meat products such as beef franks with Listeria monocytogenes has become a major concern for the meat processing industry and an important food safety issue. The objective of this study was to determine the effectiveness of combinations of antimicrobials as aqueous dipping solutions to control L. monocytogenes on vacuum-packaged beef franks stored at 4 degrees C for 3 weeks. Commercial beef franks were dipped for 5 min in three antimicrobial solutions: pediocin (6,000 AU), 3% sodium diacetate and 6% sodium lactate combined, and a combination of the three antimicrobials. Samples were then inoculated with 10(7) CFU/g of either four L. monocytogenes strains individually or a cocktail of the four strains, vacuum packaged, and stored at 4 degrees C for 3 weeks. Sampling was carried out at day 0 and after 2 and 3 weeks of storage. Individual strains, as well as the cocktail, exhibited different responses to the antimicrobial treatments. After 2 and 3 weeks of storage at 4 degrees C, pediocin-treated beef franks showed a less than 1-log reduction for all bacterial strains. Samples treated with the sodium diacetate-sodium lactate combination showed about a 1-log reduction after 2 weeks of storage for all strains and between a 1- and 2-log reduction after 3 weeks of storage, depending on the bacterial strain. When the three antimicrobials were combined, reductions ranged between 1 and 1.5 log units and 1.5 to 2.5 log units after 2 and 3 weeks of storage, respectively, at 4 degrees C. These results indicate that the use of combined antimicrobial solutions for dipping treatments is more effective at inhibiting L. monocytogenes than treatments using antimicrobials such as pediocin separately.

Regulation of neurotoxin complex expression in Clostridium botulinum strains 62A, Hall A-hyper, and NCTC 2916.

The kinetics of botulinum toxin gene expression have been investigated in Clostridium botulinum type A strains 62A, Hall A-hyper, and type A(B) strain NCTC 2916 during the growth cycle. The analyses were performed in TPGY and type A Toxin Production Media (TPM). The mRNA transcript levels encoding the proteins of the neurotoxin complex were determined using Northern analyses. Neurotoxin concentrations in culture supernatants and lysed cell pellets were assayed using ELISA, Western blots, and mouse bioassay. Proteolytic activation of botulinum neurotoxin during the growth cycle was evaluated by Western blots. For all three strains, mRNA transcripts for the toxin complex genes were initially detected in early log phase, reached peak levels in early stationary phase, and rapidly decreased in mid-to-late stationary phase and during lysis. Toxin expression varied depending on the strain and growth medium. Toxin production was highest in strain Hall A-hyper, followed by NCTC 2916 and 62A. For C. botulinum strain Hall A-hyper, cell lysis and toxin release into the supernatant occurred rapidly for cells grown in TPM, while cells grown in TPGY remained in stationary phase with minimal lysis and toxin release through 96 h of growth. In contrast, strains 62A and NCTC 2916 lysed more extensively than Hall A-hyper in TPGY. TPM supported higher toxin production and activation than TPGY in strains 62A and Hall A-hyper. These data support that the genes of the botulinum neurotoxin complex are temporally expressed during late-log and early stationary phase and that toxin complex formation depends on the strain and growth medium. Botulinum toxin synthesis and activation appears to be a complex process that is highly regulated by nutritional and environmental conditions. Further research is needed to elucidate the sensing mechanisms and genetic regulatory factors controlling these processes.