Chlorine Dioxide Gas Treatment of Cantaloupes and Quantification of Its Residues

Introduction: In previous studies, cantaloupes treated with chlorine dioxide (ClO₂) gas (5 mg/l, 10 min) showed 4.6 and 4.3 log reductions of Escherichia coli O157:H7 and Listeria monocytogenes, respectively. This could however result in residues of ClO₂ specifically, chloride (Cl^-), chlorite (ClO₂^-), chlorate (ClO₃^-) and perchlorate (ClO₄^-) in the treated product, of which, the latter three are a toxicity concern. 

Purpose: The purpose of this study was to treat cantaloupes with ClO₂ gas (5 mg/l, 10 min) and then identify and quantify its residues. 

Methods: Radiolabeled chlorine dioxide (³⁶ClO₂) gas was generated by an acidification reaction and used to treat a cantaloupe in six individual treatments. Cantaloupe flesh (~200 g) was also directly exposed to ³⁶ClO₂ remaining in the system after each of the last three treatments. Each treated cantaloupe was separated into rind, flesh and mixed (rind+flesh) samples. These were blended to give the corresponding ‘slurry’. Aliquots of slurry were centrifuged to obtain the supernatant ‘serum’. Serum aliquots were fractionated via ion chromatography and the fractions collected. Liquid scintillation counting was used to detect radioactivity in collected fractions, aliquots of serum and aliquots of slurry. Radioactivity detected and the ratio of radioactivity to ClO₂^- mass for the generation of ³⁶ClO₂ gas was used to calculate residue concentrations.

Results: Anions detected in the cantaloupe were Cl^-(~90%) and ClO₃^-(~10%). They were located primarily in the rind (19.26 ± 7.99 µg Cl^-/g rind slurry and 4.83 ± 2.26 µg ClO₃^-/g rind slurry, n = 6). Only Cl^- residues (8.12 ± 1.01 µg Cl^-/ g flesh, n = 3) were detected in cantaloupe flesh directly exposed to ClO₂ gas.

Significance: Transference of these residues from rind to flesh may occur during cutting, however, Cl^- is not considered toxic and ClO₃^- exposure is too low to be a cause for concern. This data suggests therefore that ClO₂ residues in cantaloupes do not pose a significant toxicological risk.