Chlorine dioxide gas treatment of cantaloupe and residue analysis

Simran Kaur, Purdue University

Abstract

Chlorine dioxide is a selective oxidant and powerful antimicrobial agent. Previous work has shown that treatment of cantaloupe with chlorine dioxide gas at 5 mg/L for 10 minutes results in a 4.6 and 4.3 log reduction of E. coli O157:H7 and L. monocytogenes respectively. A significant reduction (p<0.05) in the initial microflora and an increase in the shelf life by six days without altering the color of the cantaloupe (as compared to the untreated control) were also reported. In the past two decades, cantaloupes have been associated with numerous foodborne illness outbreaks in the United States. The use of chlorine dioxide treatment may help mitigate this problem, however, it could result in the presence of chloroxyanions residues (chloride, chlorite, chlorate or perchlorate) in the treated product. These residues, at certain levels, are a toxicity concern. The objective of this project was to identify and quantify chloroxyanions in cantaloupes treated with chlorine dioxide gas at the relevant conditions. Current analytical methods for chlorine dioxide and chloroxyanions are only applicable to aqueous samples. Some of these methods have been used to determine surface residues in treated products by analyzing rinse-water. In order to quantify residues in the tissues of a more complex food matrix, while reducing interference from natural organic matter, an analysis method that used radiolabeled chlorine [36Cl] was implemented. Radiolabeled chlorine dioxide gas was generated by a reaction between hydrochloric acid and a mixture of radiolabeled and nonradiolabeled sodium [36Cl] chlorite. This gas was used to treat the cantaloupe for 10 minutes such that the initial concentration of chlorine dioxide, during treatment, was 5 mg/L. The treated product was then separated into rind, flesh and mixed (rind+flesh) samples that were blended separately to give corresponding slurry samples. Aliquots of slurry were centrifuged and liquid supernatant (serum) was obtained. Separate aliquots of serum were fractionated via ion chromatography and the fractions were collected. Liquid scintillation counting was used to detect radioactivity in the slurry, serum and collected fractions. Based on the radioactivity detected, and the ratio of radioactivity to chlorite mass used in the chlorine dioxide generation reaction, the distribution of chloroxyanions and their concentrations could be determined. The only anions detected were chloride and chlorate, with ~90% of the anions in the chloride form. These residues were located primarily in the rind of the cantaloupe. Six different cantaloupes (Melon1 to Melon6) were individually treated. The concentration of residues in the rind for all six cantaloupes was 19.26±7.99 ug chloride/g rind slurry and 4.83±2.26 ug chlorate/g rind slurry. Residues were also detected in the flesh for Melon1, 2 and 3 (0.13±-.07 ug chlorite/g flesh) but were present at very low concentrations such that the anionic species could not be identified, so total residues were reported in terms of chlorite equivalents. These residues were believed to have been caused by contamination of the flesh from residues in the rind, via the knife used for cutting during sample preparation. For Melon4, 5, and 6 a different cutting technique was employed to prevent residue crossover and consequently no residues (at the limit of detection) were detected in the flesh . A worst-case scenario wherein flesh of cantaloupe was directly exposed to chlorine dioxide gas showed that in this case, the only residue formed was chloride (8.12 ±1.01 ug Cl-/g flesh). Chlorite and chlorate are the two anions of concern, of which, chlorite was not detected and chlorate was only present in the rind. The concentration of chlorate residues that were transferred to the flesh, when the treated cantaloupe was cut, was too low to be of concern. The limit of detection using this method was also significantly lower than other reported methods.

Degree

M.S.

Advisors

Morgan, Purdue University.

Subject Area

Food Science

COinS