Effect of Gaseous Chlorine Dioxide on Sterilization and Quality of Grapes

The dominant bacteria isolated from grape surface (Vitis vinifera cv. Kyoho) were identified as Escherichia coli and Kocuria and inactivated by treatment with gaseous chlorine dioxide (ClO₂) prepared by the indirect reaction between NaClO₂ and dry ice, and the effects of ClO₂ gas on bacterial inactivation were evaluated by measuring the logarithmic reduction of total bacterial counts. Meanwhile, during storage at 4 ℃ for 30 days, the color parameters, fruit hardness, percentage mass loss and total soluble solid (TSS) content of artificially inoculated grapes were measured to evaluate the effect of ClO₂ gas on the quality of grapes. The results showed that ClO₂ gas had a good inactivating effect on Escherichia coli and Kocuria inoculated on surface of grapes. When the cumulative concentration of ClO₂ was increased from 131 to 599 μL/(L·h), the logarithmic reduction of Escherichia coli increased from 1.6 (lg (CFU/g)) to 3.5 (lg (CFU/g)), and the logarithmic reduction of Kocuria increased from 1.0 (lg (CFU/g)) to 4.5 (lg (CFU/g)). During 30 days of storage, the color of grapes treated with ClO₂ gas did not obviously change compared with that of the untreated control group. The softening and mas loss were obviously inhibited and the consumption of soluble solids in grapes treated with the high cumulative concentration of ClO₂ was obviously reduced after storage at 4 ℃ for 30 days compared with that in the control and low cumulative ClO₂ concentration groups. Additionally, the residual ClO₂ on grapes treated by ClO₂ gas was less than 0.4 mg/kg during storage at 4 ℃ for 30 days. The ClO₂ gas treatment method is convenient, efficient, and low cost, which can effectively kill bacteria and improve the quality of grapes. This study provides a technical basis for the application of ClO₂ gas to fruits and vegetables.