Carbon dioxide (CO2) is the single most important atmospheric gas that is used to control microorganisms in foods.15,35 It along with O2 are the two most important gases in modified atmosphere packaged (MAP) foods, and this is discussed in Chapter 14. Ozone (O3) is the other atmospheric gas that has antimicrobial properties, and it has been tried over a number of decades as an agent to extend the shelf life of certain foods.
It has been shown to be effective against a variety of microorganisms,9 but because it is a strong oxidizing agent, it should not be used on high-lipid-content foods since it would cause an increase in rancidity. Ozone was tested against Escherichia coli 0157:H7 in culture media, and at 3 to 18 ppm the bacterium was destroyed in 20 to 50 minutes.10
The gas was administered from an ozone generator and on tryptic soy agar, the D value for 18 ppm was 1.18 minutes, but in phosphate buffer, the D value was 3.18 minutes. To achieve a 99% inactivation of about 10,000 cysts of Giardia lamblia per milliliter, the average concentration time was found to be 0.17 and 0.53 mg-min/L at 25◦C and 5◦C, respectively.53
The protozoan was about three times more sensitive to O3 at 25◦C than at 5◦C. It is allowed in foods in Australia, France, and Japan; and in 1997 it was accorded GRAS (generally regarded as safe) status in the United States for food use. Overall, O3 levels of 0.15 to 5.00 ppm in air have been shown to inhibit the growth of some spoilage bacteria as well as yeasts. The use of ozone as a food sanitizing agent is presented in Chapter 13.