The Texas A&M researchers inoculated frankfurters manufactured under commercial processing with a four-strain L. monocytogenes "cocktail," which contained 10 million microorganisms per gram.
You wouldnt expect to find levels that high. Its a worst-case scenario, so if youre going to get protection, you should get it at this point," Keeton said.
Each group was then treated with either with a saline solution (the control group); with acidified calcium sulfate; potassium lactate; or lactic acid.
The frankfurters were then vacuum-packaged much like they would have been processed commercially, stored under refrigeration 40 F for 12 weeks, and evaluated at 2-week intervals.
What researchers found was the acidified calcium sulfate killed the Listeria on the surface and also had a residual effect on the surface. "The organism didn't come back," Keeton said.
The lactic acid initially reduced the number of organisms, but it didn't kill all of them. Also, the Listeria started growing on the frankfurter again during refrigerated storage.
The potassium lactate was not effective at all, he said.
Researchers also tested the sensory and physical properties and found the acidified calcium sulfate changed the product very little. It had the same taste, even though the pH was reduced. It also slightly increased the calcium content of the frankfurters, Keeton said. Researchers also noticed a slight amount of moisture released in the packaging.
We attributed this to the fact the material was acidic, and it remained acidic throughout the storage period, he said.
Listeria can be introduce
Contact: Dr. Jimmy Keeton
Texas A&M University - Agricultural Communications