|Authors: ||C.F. Forney, L. Fan, P.D. Hildebrand, J. Song|
|Keywords: ||ozone, air ions, bacteria, mold, decay, produce.|
Positive and negative air ions are generated through ion generators or as byproducts of other industrial processes.
Air ions are short lived, lasting only minutes before they lose their charge.
Their life-time is reduced by contacting walls or surfaces, or by interactions with pollutants or humidity in the air.
Negative air ions (NAI) reduce airborne mold and bacterial contaminants.
The growth of cultured bacteria is retarded and the viability of bacteria and fungal spores in aerosols is reduced by exposure to NAI in concentrations ranging from 5 x 104 to 5 x106 ions/cm3. A combination of ozone (O3) with NAI is reported to be more effective than either of them alone, in suppressing microbial growth and decay of fresh produce.
When cultures of Erwinia caratovora were exposed to 106 NAI/cm3 and/or 50 ppb O3 at 10 °C for 6 hours, viability of O3 treated bacteria was 70%, whereas viability of those treated with O3 and NAI was only 4%. The synergistic effect of NAI with O3 could explain the variable effectiveness of O3 in reducing decay of stored produce.
In two separate studies, the lesion growth rates of Botrytis cinerea and Sclerotinia sclerotiorum on fresh carrots was reduced by 12% and 16%, respectively, when held in 1ppm O3 without NAI. However, in a similar trial where carrots were held in 0.1 - 0.5 ppm O3 in combination with 2x104 to 7x104 NAI/cm3, growth rates of B. cinerea and S. sclerotiorum were reduced by 69% and 57%, respectively.
The apparent synergism of NAI with O3 could provide an effective method to reduce postharvest decay of fresh produce.
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