Recontamination Of Product Research Articles

The effects on product of a hot water pasteurizing treatment applied routinely in a commercial beef carcass dressing process

The effects of a pasteurizing treatment on the microbiological condition and the appearance of carcasses, routine in a commercial carcass dressing process, were examined. Beef carcass sides were pasteurized with water at 85°C. During 2-h periods, all sides from the dressing process were treated for 8, 9, 10, 11 or 12 s. During each period, microbiological samples were obtained by swabbing five randomly selected sides before and five others after the treatment, with a single sample being obtained from 25 treated and 25 untreated sides from each treatment time. All treatments similarly reduced the log mean numbers of total aerobic counts by about 1 log unit, but the reductions in the log total numbers of coliforms orEscherichia coli recovered from 25 samples increased with increasing treatment time, to >2 log units with treatment times of 11 or 12 s. Cooling of the sides did not obviously reduce the numbers of total aerobic bacteria on beef sides, but there were small reductions in the numbers of coliforms and E. coli on both treated and untreated sides. After cooling, sides treated routinely for 10 s yielded total aerobic counts at log mean numbers of about 2 log cfu cm−2, and coliforms and E. coli at log total numbers of <2 and <1 log cfu 2500 cm−2, respectively. After the carcass breaking process, loin primal cuts and manufacturing beef from such sides yielded total aerobic counts at log mean numbers of about 3 and about 4 log cfu cm−2, respectively; coliform counts at log total numbers of about 3 and about 4 log cfu 2500 cm−2, respectively; and E. coli counts at log total numbers >2 log cfu 2500 cm−2; which indicated that product was contaminated from improperly cleaned equipment during the carcass breaking process. When sides treated for 10 s with water that had previously been used to treat 120 or more sides were compared after cooling with untreated sides from the same carcasses, the appearances of treated sides were judged to be less desirable than those of the untreated sides because of the less desirable appearance of the fat tissue on the treated sides. However, the mean differences between untreated and treated sides for overall appearance and the appearance of fat tissue were only 0·45 and 0·46 assessment units, respectively, for assessments on a seven-point scale. The small adverse effect of the pasteurizing treatment on the appearance of beef carcass sides apparently did not affect the value of the meat. Thus, the data indicated that, in commercial practice, pasteurizing treatment times should be set by reference to reductions in numbers of E. coli rather than of total aerobic counts, to assure the maximum possible reduction in the number of enteric pathogens; that protein suspended in the circulating water of pasteurizing equipment will accumulate to levels that affect the appearance of carcass fat, unless the water is changed at appropriate intervals or actions are taken to remove the protein from the water or carcass surfaces; and that pasteurizing of carcasses alone is inadequate for assuring the safety of meat when recontamination of product with enteric organisms occurs during the carcass-breaking process.

Changes in the strength of attachment of micro-organisms to surfaces following treatment with disinfectants and cleansing agents.

Suspensions of Pseudomonas aeruginosa and Staphylococcus epidermidis, and biofilms established (16 h) on submerged glass and stainless steel (216 2B) coupons, were exposed to sodium hypochlorite (0.02% or 0.015% w/v), Dodigen (0.0015% w/v or 0.0006% w/v), sodium dodecylsulphate (6% w/v or 0.1% w/v) and Tween-80 (6% w/v) for 5 min at 20 degrees C. Survival was assessed by viable counts and blot succession. Biofilm bacteria were significantly less susceptible to these biocides than were planktonic cells, but their attachment to the surfaces was loosened by such treatments. Treatment with the non-ionic surfactant, Tween-80, however, strengthened the attachment of Staph. epidermidis to stainless steel. Such effects on attachment strength, which are species and surface dependent, have profound implications on post-treatment cleansing and possible re-contamination of product in clean-in-place (CIP) systems.