Bacteria were separated from raw meat homogenate by a simple three-stage process. Centrifugation (10 s at 2000 g) removed coarse particles; stirring with the cation exchange resin Bio-Rex 70 removed smaller particles and filtration through 0.22 micron membranes removed soluble materials. By this process 70-80% of the microbial populations of meat homogenates were consistently isolated on the filters. A linear relationship was found between log10 microbial ATP and log10 colony count of meat over the range 10(5)-10(9) cfu/g. The value of ATP/cfu for meat samples was within the range previously reported for pure cultures. These data indicated that ATP extracted from the filters originated from bacteria in the meat samples. Several samples can be analysed simultaneously in an elapsed time of 20-25 min. The variability associated with estimates of both colony counts and ATP levels has been determined.
The bioluminescent assay of ATP is rapid and simple and may be used as an estimate of microbial numbers. It therefore shows great potential as a technique to provide information on the microbiological quality of a food within a few minutes, in comparison with conventional techniques, which provide results retrospectively. However, despite the advantages of speed and sensitivity, no food microbiologists are using the technique for routine quality control and hygiene monitoring. This review seeks to highlight the reasons for this, and to offer some ideas for future research to increase the acceptance of ATP assays within the food industry.
A treatment combining hydrogen peroxide and ultra-violet (UV-C) irradiation was assessed for reduction of microbial contamination in pre-formed food packaging cartons. There was a synergistic effect between low concentrations (0 – 5% wt/vol) of hydrogen peroxide and UV-C irradiation (10 s) on spores of Bacillus subtilis, the maximum lethality occurring between 0.5 and 1% peroxide. A combined treatment using 1% hydrogen peroxide and 10 s of UV-C irradiation was also effective against a variety of other organisms (spores and vegetative cells). The efficiency of the treatment was dependent on the type of inner surface of the carton. A greater lethal effect was obtained against B. subtilis spores in polyethylene-lined cartons than in aluminium/polyethylene laminate-lined cartons (5.1 and 3.5 decimal reductions in numbers respectively, using a combined treatment with 1% peroxide and 10 s of UV-C).
Reflectivity, smoothness and geometry of several types of food packaging board were studied in relation to the effectiveness of decontamination treatments involving ultraviolet (UV-C, 254 nm) irradiation. Surfaces containing aluminum in the laminate reflected more light in the 325 to 550 nm range and showed a lower lethal effect when Bacillus subtilis spores were irradiated. Visible light of wavelengths between 325 and 550 nm is known to cause photoreactivation of UV damage in vegetative cells. It was suggested that a similar phenomenon might occur in spores on reflective surfaces. Smoothness of the board surface was not an important factor in the extent or the variability of the lethal effect. The geometry of the irradiated surface was shown to be important for aluminum/polyethylene laminatelined surfaces only, as more spores were killed on board normal to incident UV-C irradiation than in cartons with reflective angles. Spores on the inner sides of this type of carton may have received more reflected light of photoreactivation wavelengths.
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