Effects of adding either C[O.sub.2] or air during high-pressure processing.

The high-pressure processing of food products is highly dependent on the processing pressure itself, but also temperature and time. The addition of gas with the sample may enhance the destruction of microorganisms. This approach may lower operating process parameters and result in products of fresh quality.

Scientists at the National Center for Food Safety and Technology wanted to determine if adding either carbon dioxide or air during high-pressure processing could increase the rate of inactivation of E. coli K12 ATCC 25253 and L. innocua. Their research shows that it is possible to use high-pressure processing with Listeria as a target microorganism at lower operating parameters. The inactivation of both microorganisms increased with increasing pressure levels.

In experiments, the researchers inoculated distilled deionized water with either E. coli K12 ATCC 25253, a Gram-negative bacterium, or L. innocua, a Gram-positive bacterium. The solution was first filled into a plastic syringe fitted with a miniature valve, into which the appropriate volume of gas was pulled. The gas contents were evaluated at 0, 2, 4 and 6 volumes and high pressures ranging from 250 MPa to 400 MPa. The samples were processed using a 35-liter high-pressure vessel for up to five minutes.

Carbon dioxide was slightly effective against E. coli K12 ATCC 25253 and extremely effective against L. innocua. The gas slightly enhanced the inactivation of E. coli K12 ATCC 25253 at 300 MPa but was ineffective at higher pressures. Against L. innocua, carbon dioxide was effective at all pressure levels tested. At 250 MPa, there was total inactivation--greater than a 7-log reduction--after 300 seconds with carbon dioxide. There was only a 1-log reduction when no gas was added. The addition of air was not effective against both E. coli K12 ATCC 25253 and L. innocua. L. innocua was slightly more sensitive to high pressure than E. coli K12 ATCC 25253.

Further information. Edgar Murakami, National Center for Food Safety and Technology, FDA, IIT Moffett Campus, 6502 S. Archer Rd., Summit-Argo, IL 60501; phone: [phone]; email: [e-mail].