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  • Author or Editor: Chris Ference x
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Laser labeling of fruit and vegetables is an alternative means of labeling produce in which a low-energy carbon dioxide laser beam etches the surface and reveals a contrasting underlying layer. These etched surfaces can promote water loss and may increase the number of entry sites for decay-promoting organisms. The long-term effects of laser labeling on produce quality during storage have not been examined. We conducted experiments to measure water loss, peel appearance, and potential decay in laser-labeled grapefruit (Citrus paradisi) during storage. Laser-labeled fruit stored at 10 °C and two relative humidities (i.e., 95% and 65%) for 5 weeks showed no increase in decay compared with nonetched control fruit, suggesting that laser labeling does not facilitate decay. This was confirmed by experiments where Penicillium digitatum spores were coated on fruit surfaces before and after etching. In either case, no decay was observed. In agar plates containing a lawn of P. digitatum spores, the laser etching reduced germination of spores in contact areas. Water loss from etched areas and label appearance were determined during storage. Water loss from waxed etched surfaces reached control levels after 24 h in storage. Label appearance slowly deteriorated during 4 weeks in storage and was proportional to laser energy levels and ambient relative humidity. Waxing the labeled surface reduced water loss by 35% to 94%, depending on the wax formulation used. We concluded that laser labeling provides the grapefruit industry a safe alternative to adhesive sticker labeling without enhancing decay susceptibility.

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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 citri ssp. 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. ClO2 packets 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 10 °C (to simulate storage and transportation) + 1 week of storage at 20 °C (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.

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