Bacteria under threat with new packaging device – study

By Jane Byrne

- Last updated on GMT

Related tags E. coli Escherichia coli Bacteria Escherichia coli o157:h7

Researchers claim to have discovered a method to eliminate bacteria in packaged foods such as spinach and tomatoes, a process that could reduce the number of food-borne outbreaks linked to the produce.

The findings have been published in the journal, LWT - Food Science and Technology.

The device, according to researchers Kevin Keener and Paul Klockow, consists of a set of high-voltage coils attached to a small transformer that generates a room-temperature plasma field inside a package, ionizing the gases inside.

They maintain that the process kills food contamination causing pathogens such as E. coli​ and Salmonella​.

Demand for natural

According to the 2007 US Department of Agriculture (USDA) Economic Research Service statistics, fresh spinach reached a record consumption in 2005, up more than 12 times the amount consumed in 1970, while processed spinach consumption has declined over the last few decades.

The authors of the study claim that this high demand puts pressure on producers and processors to ensure that products are safe for consumption and still retain nutritious and aesthetic qualities, so while minimal processing and treatment is needed to ensure this there are many sources of contamination that can affect produce before, during, and after harvest.

Sanitation methods

Conventional methods of sanitizing fresh produce involve various washing procedures. Typically, fresh produce is washed with plain water or water containing a sanitizer, such as chlorine; however, the researchers claim that chlorine has a minimal effect in killing bacteria on these surfaces.

Non-thermal processing, of which ozone gas is an example, can enhance food safety without compromising quality and desirability of the food, claim the researchers.


The goal of this study, said Keener and Klockow, was to analyse the effectiveness of a novel ‘in package’ ozone gas treatment PK-1 system, which uses a pair of electrodes with an adjustable gap inside a package, in eliminating E. coli 0157:H7 on individual spinach leaves.

The authors said that another objective was the analysis of the effects of the treatment and storage on the quality of the spinach leaves.


Individual, fresh, prepackaged, whole spinach leaves inoculated with E. coli ​O157:H7 were treated in packaging with ozone generated in air and oxygen. Samples were treated for five minutes and stored at room temperature (22°C) or refrigeration (5°C) for 30 minutes, two hours and 24 hours.

Gas composition and relative humidity were measured.


All treated samples showed reductions in E. coli ​O157:H7 populations with the largest reductions (3-5 log10 CFU/leaf) after 24 hours of storage.

After five minutes of treatment, ozone concentrations were 1.6 and 4.3 mg/L for air and oxygen gas, respectively.

The concentrations of ozone decreased with time and were not detectable after 24 hours.

A five point Spinach Color Quality (SCQ) scale was also established (5-best, 1-worst). Treated spinach showed discoloration with SCQ-values of 3.83 and 1.00 for air and oxygen gas exposed leaves after 24 hours, found the scientists.

The authors concluded that the results indicate that the PK-1 system is capable of reducing E. coli ​O157:H7 in packaged spinach; however, minimizing quality changes after treatment requires further research.

Source: LWT - Food Science and TechnologyPublished online ahead of print: ​10.1016/j.lwt.2009.02.011Title: Safety and Quality Assessment of Packaged Spinach Treated with a Novel Ozone-Generation System​Authors: P.A. Klockow, K. M. Keener.

Related topics Food Safety & Quality

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