1a. Objectives (from AD-416):
Studies have conclusively demonstrated that treatment of a variety of commercial fruits and vegetables with low concentrations of chlorine dioxide gas (ClO2) increases produce shelf-life. In addition, ClO2 treatment decreases the incidence and concentrations of food-borne pathogens such as E. coli and Salmonella on produce. Although the chemical properties of ClO2 suggest that its presence on produce subsequent to treatment would be transient, studies proving such have not been conducted due to technical difficulties. The objective of this work is to determine the magnitude and chemical nature of residues in produce after treatment with radioactive ClO2 gas. The use of radioactive gas is necessary so that metabolites of ClO2 may be unambiguously identified and quantified.
1b. Approach (from AD-416):
Sealable Plexiglas chambers will be constructed to hold produce and a ClO2 generating system. Radioactive ClO2 will be produced by chemical reaction of sodium 36Cl-chlorite in the closed system. Produce will be bathed in 36Cl-ClO2 gas for a fixed duration period. Concentrations of gaseous 36Cl-ClO2 will be measured periodically. At the end of the reaction, radioactive gasses will be collected into chemical traps and exposed produce will be harvested. Harvested fruit will be analyzed for total radioactive residues by radiochemical techniques and the chemical identifies of radioactive metabolites will be identified and quantified by ion chromatography and radiochemical techniques, respectively. Some samples will be rinsed to determine the quantity of surface residues that are removable by water; surface residues will be speciated.
3. Progress Report:
Subsequent to experiments investigating the fate and disposition of labeled chlorine dioxide gas on vegetables and melons, studies were conducted to determine the major factors that caused the formation of undesirable chlorine-dioxide byproducts. Laboratory scale studies showed that chloroxyanion by products of chlorine dioxide could be prevented completely by protecting fumigations from illumination. Further studies with large-scale fumigations of produce showed that chloroxyanion residues are either not detectable or are at background levels in vegetables and melons fumigated with chlorine dioxide gas. Collectively, the data generated to date suggest that chlorine dioxide treatment may be a safe and economical method for the elimination of pathogens and spoilage organisms in commercially important crop groups.