Response surface modeling for the inactivation of Bacillus subtilis subsp. niger spores by chlorine dioxide gas in an enclosed space

In Vitro and In Vivo Inhibitory Effects of Gaseous Chlorine Dioxide against Fusarium oxysporum f. sp. batatas Isolated from Stored Sweetpotato: Study II

Chlorine dioxide (ClO₂) has been widely used as an effective disinfectant to control fungal contamination during postharvest crop storage. In this study, Fusarium oxysporum f. sp. batatas SP-f6 from the black rot symptom of sweetpotato was isolated and identified using phylogenetic analysis of elongation factor 1-α gene; we further examined the in vitro and in vivo inhibitory activities of ClO₂ gas against the fungus. In the in vitro medium tests, fungal population was significantly inhibited upon increasing the concentration and exposure time. In in vivo tests, spore suspensions were drop-inoculated onto sweetpotato slices, followed by treatment using various ClO₂ concentrations and treatment times to assess fungus-induced disease development in the slices. Lesion diameters decreased at the tested ClO₂ concentrations over time. When sweetpotato roots were dip-inoculated in spore suspensions prior to treatment with 20 and 40 ppm of ClO₂ for 0-60 min, fungal populations significantly decreased at the tested concentrations for 30-60 min. Taken together, these results showed that ClO₂ gas can effectively inhibit fungal growth and disease development caused by F. oxysporum f. sp. batatas on sweetpotato. Therefore, ClO₂ gas may be used as a sanitizer to control this fungus during postharvest storage of sweetpotato.

Disinfection efficiency of positive pressure respiratory protective hood using fumigation sterilization cabinet

Concerns have been raised about both the disinfection and the reusability of respiratory protective equipment following a disinfection process. Currently, there is little data available on the effects of disinfection and decontamination on positive pressure respiratory protective hoods (PPRPH). In this study, we evaluated the effect of vaporized hydrogen peroxide (VHP) on the disinfection of PPRPH to determine applicability of this method for disinfection of protective equipment, especially protective equipment with an electric supply system.

A hydrogen peroxide-based fumigation sterilization cabinet was developed particularly for disinfection of protective equipment, and the disinfection experiments were conducted using four PPRPHs hung in the fumigation chamber. The pathogenic microorganism Geobacillus stearothermophilus ATCC 7953 was used as a biological indicator in this study and the relationship between air flow (the amount of VHP) and disinfection was investigated. Both function and the material physical properties of the PPRPH were assessed following the disinfection procedure. No surviving Geobacillus stearothermophilus ATCC 7953, both inside and outside of these disinfected PPRPHs, could be observed after a 60 min treatment with an air flow of 10.5–12.3 m³/h. Both function and material physical properties of these PPRPHs met the working requirements after disinfection.

This study indicates that air flow in the fumigation chamber directly influences the concentration of VHP. The protective equipment fumigation sterilization cabinet developed in this paper achieves the complete sterilization of the PPRPHs when the air flow is at 10.5–12.3 m³/h, and provides a potential solution for the disinfection of various kind of protective equipment.

In Vitro and In Vivo Inhibitory Effects of Gaseous Chlorine Dioxide Against Diaporthe batatas Isolated from Stored Sweetpotato

Chlorine dioxide (ClO₂) can be used as an alternative disinfectant for controlling fungal contamination during postharvest storage. In this study, we tested the in vitro and in vivo inhibitory effects of gaseous ClO₂ against Diaporthe batatas SP-d1, the causal agent of sweetpotato dry rot. In in vitro tests, spore suspensions of SP-d1 spread on acidified potato dextrose agar were treated with various ClO₂ concentrations (1-20 ppm) for 0-60 min. Fungal growth was significantly inhibited at 1 ppm of ClO₂ treatment for 30 min, and completely inhibited at 20 ppm. In in vivo tests, spore suspensions were drop-inoculated onto sweetpotato slices, followed by ClO₂ treatment with different concentrations and durations. Lesion diameters were not significantly different between the tested ClO₂ concentrations; however, lesion diameters significantly decreased upon increasing the exposure time. Similarly, fungal populations decreased at the tested ClO₂ concentrations over time. However, the sliced tissue itself hardened after 60-min ClO₂ treatments, especially at 20 ppm of ClO₂. When sweetpotato roots were dip-inoculated in spore suspensions for 10 min prior to treatment with 20 and 40 ppm of ClO₂ for 0-60 min, fungal populations decreased with increasing ClO₂ concentrations. Taken together, these results showed that gaseous ClO₂ could significantly inhibit D. batatas growth and dry rot development in sweetpotato. Overall, gaseous ClO₂ could be used to control this fungal disease during the postharvest storage of sweetpotato.

Distribution, Identification, and Quantification of Residues after Treatment of Ready-To-Eat Salami with 36Cl-Labeled or Nonlabeled Chlorine Dioxide Gas

When ready-to-eat salami was treated in a closed system with ³⁶Cl-labeled ClO₂ (5.5 mg/100 g of salami), essentially all radioactivity was deposited onto the salami. Administered ³⁶ClO₂ was converted to ³⁶Cl-chloride ion (>97%), trace levels of chlorate (<2%), and detectable levels of chlorite. In residue studies conducted with nonlabeled ClO₂, sodium perchlorate residues (LOQ, 4 ng/g) were not formed when reactions were protected from light. Sodium chlorate residues were present in control (39.2 ± 4.8 ng/g) and chlorine dioxide treated (128 ± 31.2 ng/g) salami. If sanitation occurred under conditions of illumination, detectable levels (3.7 ± 1.5 ng/g) of perchlorate were formed along with greater quantities of sodium chlorate (183.6 ± 75.4 ng/g). Collectively, these data suggest that ClO₂ is chemically reduced by salami and that slow-release formulations might be appropriate for applications involving the sanitation of ready-to-eat meat products.