Ozone technology advance for packaged foods

 Packaged foods have had a rough ride but new ozone technology is delivering a healthier approach.

Ozone in a bag. That's the novel method being developed by the food process engineer Dr Kevin Keener, of Purdue University, Indiana, to eliminate harmful bacteria on packaged foods such as spinach, tomatoes, and whole fruit. But rather than use an ozone generator to pump it in, Keener creates the ozone inside the bags only after they are sealed.

The rising popularity of fresh, packaged foods, from mixed-herb salads to fruit has its health dangers. Supermarket suppliers may use water washes enhanced with chlorine or ozone to eliminate possible bacterial contamination before packaging. However, a quick rinse might not be enough to dislodge powerful pathogens such as E coli O157.

Keener's idea of creating ozone inside food packaging came from his work with atmospheric, non-equilibrium plasmas (ANEP). Ionisation generates free electrons that react with gas molecules in the air to become reactive molecules such as ozone, which then attack bacteria. To form ozone, oxygen (O2) splits into single atoms that reform in threes as ozone (O3). But ANEP requires a special treatment chamber for containment.

"I started thinking about what we could do to recreate ANEP without the costly chamber process," says Keener. "My question became: 'Can we place the generation method outside the container and, if so, what would be our limitations?'"

He turned to the Purdue University research engineer Paul Klockow for help and, using off-the-shelf components costing less than $1,000, built a demonstration device. The prototype generates a high voltage potential (12kV) between electrodes consisting of coils of wire wrapped around dielectric (insulator) plates.

The electrode plates are placed above and beneath a sealed food bag and, once the device is turned on, generate a room-temperature plasma field inside, partly ionising the air and producing ozone. While the outside of the package may increase slightly in temperature, the contents are unaffected by this.

Bacteria are normally killed by a combination of concentration and time so a quick ozonated rinse before bagging won't necessarily do the job. "In a standard food manufacturing process using ozone, wash water or ozonated rinses only contact fruit or vegetables for seconds to minutes. Thus limiting the total concentration-time effect," says Keener.

Those limits are now overcome as the ozone reverts to oxygen over many hours. "In our system, because we are doing it in-package, we can deliver a specific ozone concentration which natural decay processes will convert back to normal after a known time," says Keener.

The longer the gaseous ozone remains present, the more bacteria - such as E coli and salmonella - will be killed. To test their system, Keener and Klockow placed a deadly strain of E coli O157 on spinach leaves. Food safety experts talk of achieving a minimum "5-log" standard, which means reducing bacterial numbers by 100,000-fold - killing an impressive 99.999% of them.

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