Log CFU Cm-2 Research Articles

Sensorial and microbial effects of gaseous ozone on fresh scad (Trachurus trachurus).

The bactericidal activity of gaseous ozone was investigated using a commercial ozone generator. Five species of fish bacteria, Pseudomonas putida, Shewanella putrefaciens, Brochothrix thermosphacta, Enterobacter sp. and Lactobacillus plantarum, were inoculated on agar surfaces and exposed to different ozonation times in a gas chamber. Results showed ozone in relatively low concentrations (< 0.27 x 10(-3) g l-1) was an effective bactericide of vegetative cells of the five fish bacteria. The age of the cell culture was shown to influence the cell response following exposure. Survival rate was not linearly related to ozonation time, but exhibited biphasic death over an extended period. Similar bactericidal effects were observed on fish skin treated with ozone daily in the laboratory, with decreases of 1.0 log cfu cm-2 for the micro-organisms studied. Whole fish treated daily in the laboratory using a commercial ozone generator showed improved scores for sensory analyses compared with the controls. The results were statistically significant. Fish treated on board ships were also analysed for microbiological and sensory changes. Controls were obtained from a similar vessel without the ozone facility in the hold. Similar trends to those recorded in the laboratory for the microbiological and sensory results on ozonated fish were observed.

The survival and growth of acid-adapted mesophilic pathogens that contaminate meat after lactic acid decontamination.

Lactic acid decontamination (LAD) may adapt pathogens to lactic acid. Such organisms may have an increased resistance to acid and can contaminate meat after LAD. The survival and growth of acid adapted Campylobacter jejuni, Salmonella typhimurium. Escherichia coli O157:H7 and Staphylococcus aureus inoculated on skin surface of still warm pork belly cuts 2 h after LAD was examined during chilled (4 degrees C) storage and refrigeration abuse equivalent to 12.5 degrees C. Lactic acid decontamination included dipping in 1, 2 or 5% lactic acid solutions at 55 degrees C for 120 s. Lactic acid decontamination brought sharp reductions in meat surface pH, but these recovered with time after LAD at approximately 1-1.5 pH units below that of water-treated controls. A sharp decrease in the number of cfu of pathogens occurred on chilled 2-5% lactic acid treated pork belly cuts when the skin surface was less than pH 4.8-5.2. The reductions ranged from 0.1-0.3 log10 cfu cm-2 for E. coli O157:H7 to over 1.7-2.4 log10 cfu cm-2 for Camp. jejuni, respectively. Increase in storage temperature from 4 to 12.5 degrees C reduced delayed decrease in numbers of all pathogens except Camp. jejuni by a factor of two. Deaths in Camp. jejuni at 12.5 degrees C slightly exceeded those at 4 degrees C. After the initial sharp decline, the number of cfu of mesophilic pathogens decreased gradually at a rate similar to that on water-treated controls. Growth of all mesophilic pathogens except Camp. jejuni on 2-5% LAD meat occurred during storage at 12.5 degrees C when the meat surface pH exceeded 4.8-5.2, and was slower than on water-treated controls. Low temperature and acid-adapted E. coli O157:H7, Salm. typhimurium and Staph. aureus, and acid adapted Camp. jejuni that contaminate skin surface after hot 2-5% LAD, did not cause an increased health hazard, although microbiota and intrinsic parameters (lactic acid content, pH) were created that could advantage their survival and growth.

Effectiveness of a steam-vacuum sanitizer for reducing Escherichia coli O157:H7 inoculated to beef carcass surface tissue.

A steam-vacuum sanitizer reduced aerobic plate counts associated with bovine faecal contamination from 5.5 log10 cfu cm-2 to 3.0 +/- 0.21 log10 cfu cm-2 on beef carcass short plates. The same beef carcass short plates inoculated with 7.6 +/- 0.09 log10 cfu cm-2 Escherichia coli O157:H7 in faeces, yielded an average residual level of E. coli O157:H7 of 2.1 +/- 0.21 log10 cfu cm-2, after steam-vacuum treatments. This study demonstrates the effectiveness of a steam-vacuum sanitizer for removing E. coli O157:H7 from beef carcasses.

Reduction of Brochothrix thermosphacta on beef surfaces following immobilization of nisin in calcium alginate gels.

Lean and adipose beef carcass tissues inoculated with Brochothrix thermosphacta (BT) (approx. 4.50 log10 cfu cm-2) were left untreated (U) or treated with 100 micrograms ml-1 nisin (N), calcium alginate (A) or 100 micrograms ml-1 nisin immobilized in a calcium alginate gel (AN). Tissue samples were refrigerated after treatments and bacterial populations and nisin activity were determined at 0, 1, 2 and 7 d. U, A and N treatments of lean and adipose tissues did not suppress bacterial growth ( > 6 log10 cfu cm-2 by day 7) while treatments of lean and adipose tissues with AN suppressed bacteria ( > 2.42 log10 cfu cm-2 by day 7). Bacteriocin titres from both tissues were higher in AN vs N samples after the 7 d incubation. This study demonstrates that immobilization of nisin in a gel may be a more effective delivery system of a bacteriocin to the carcass surface than direct application.