No abstract

Salmonella enteriditis and Staphylococcus aureus were separately inoculated onto fresh chicken thighs prior to dipping in 0, 1.0,2.5, or 5.0% potassium sorbate solutions adjusted to pH 6.0. Treated samples were packaged in Nylon/Plexar/Surlyn bags under air, vacuum, 20%, 60%, or 100% CO2 atmospheres and stored at 10°C ? l.O"C for 10 days. Changes in gaseous headspace composition, sorbate concentrations, surface pH, and microbial numbers were monitored during the storage period. S. enteriditis was more sensitive to potassium sorbate than S. aureus; growth on poultry of the latter organism was more effectively inhibited by exposure to high levels of CO2. Increased concentrations of sorbate dip solutions in combination with higher concentrations of CO2 in the package environment provided a more effective inhibitory system against growth of both pathogens on fresh poultry.

Four species of fish from Atlantic waters, Meronia americanus (perch), Cynoscion regalis (seatrout), Micropogon undulatis (croaker) and Pomatomus saltatrix (bluefish), were processed (gutted or filleted), packaged under carbon dioxide and refrigerated. Stability of the fish under the modified atmosphere preservation (MAP) system was compared to that of fish stored conventionally. Use of the MAP system resulted in a 45 to 55% increase in stability, primarily due to an extension in the lag phase of psychrotrophic organisms and to their reduced growth rate in the logarithmic phase. By the 10th day of storage, the conventionally packed fish always exhibited a 100-fold higher psychrotroph count than the CO2-packed fish. Levels of Vibrio parahaemolyticus were negligible in this MAP system and no Salmonella spp. or Staphylococcus aureus was detected, even at an abuse temperature (10°C) of storage. Positive evidence for preformed Clostridium botulinum toxin was lacking.

Thermally injured cells of Staphylococcus aureus lack the ability to grow on tryptic soy agar containing 7.5% NaCl. This injury phenomenon was examined in three strains ofS. aureus: MF-31; H (Str); and, isolated from H (Str), 52A5, a mutant which lacks teichoic acid in the cell wall. Temperatures for sublethal heat treatment were selected to produce maximum injury with minimum death for each strain. Examination of isolated cell walls showed that magnesium was lost from the wall during heating, and that the degree of cell injury was accentuated when magnesium ions were either removed from or made unavailable to the cell. S. aureus 52A5 was more heat sensitive than its parent strain. Cells containing higher levels of wall teichoic acid generally showed less injury than normal cells. Cells with the weaker cation-binding polymer, teichuronic acid, in the cell wall generally showed greater injury. These data suggest that cell wall teichoic acid of S. aureus aids in the survival of the cell by the maintenance of an accessible surface pool of magnesium.

The effects of potassium sorbate combined with vacuum or carbon dioxide modified atmosphere packaging on natural poultry spoilage flora were examined. Fresh chicken thighs were dipped into either 2.5% potassium sorbate solution or distilled water, adjusted to pH 6.0 and packaged on trays in Nylon/Plexar/Surlyn bags. Atmospheres of either air, vacuum or 100% CO2 were created in the packages which were then stored at 10 2 1°C for 10 days. Changes in aerobic plate counts, lactic acid bacteria and pseudomonads were monitored. The combination of CO, packaging and sorbate treatment provided the most effective inhibitory system against the poultry spoilage organisms, especially Pseudomonas species, without creating a selective enviroriment for the growth of lactic acid bacteria and premature souring of the product. The shelf life of the sorbate/COz samples was extended 3 days over the control/air samples at 10°C.