The Effect of Controlled-release Chlorine Dioxide on the Preservation of Grapefruit

Abstract

The effect of controlled-release chlorine dioxide(ClO₂) gas on the safety and quality of grapefruit was studied. The experiments were run under controlled chamber systems with inoculated fruit, and in boxed fruit under commercial conditions. For the inoculation test, fruit artificially inoculated with either Escherichia  coli or Penicillium  digitatum, or naturally inoculated Xanthomonas citris sp. Citri (Xcc) (fruits with citrus canker lesions), were incubated in a chamber containing a dose equivalent to 0–60 mg·L^—1 of pure ClO₂ as an antimicrobial agent. After 24 hours, the microbial population on treated grapefruit was significantly reduced compared with that of control fruit: a dosage of 5 mg·L^—1 completely inhibit the growth of E.coli and P. digitatum, but a dosage of 60 mg·L^—1 was needed to completely kill Xcc. For the simulated commercial experiment, fruit were harvested in late Oct. 2015 passed through a commercial packing line, and packed in 29 L citrus boxes. ClO2packets were attached to the top lids with the following five treatments: fast-release, slow-release, slow/fast-release combination (each containing 14.5 mg·L^—1 of pure ClO2), double dose fast-release (containing 29 mg·L^—1 of ClO₂), and control. After 6 weeks of storage at 108⁰C (to simulate storage and transportation) +1 week of storage at 208⁰C (to simulate retail marketing), the fruit quality was evaluated. The slow-release treatment at standard dose exhibited the best antimicrobial activity, reducing total aerobic bacterial count and yeast/mold count by 0.95 and 0.94 log colony-forming units (cfu)/g of fruit, respectively, and maintained the best visual, sensory, and overall quality. However, the higher dosage treatments resulted in phytotoxicity as evidenced by peel browning.