Decontamination of strawberries using batch and continuous chlorine dioxide gas treatments

Efficacy of chlorine dioxide (CLO(2)) gas in reducing Escherichia coli O157:H7 and Listeria monocytogenes on strawberries was determined using batch and continuous flow CLO(2) gas treatment systems. Effects of continuous CLO(2) gas treatment on total aerobic plate count, color, and residual ClO(2) and chlorite on strawberries were also evaluated. Strawberries were spot inoculated with 7 to 8 log CFU per strawberry of each pathogen (E. coli O157:H7 and L. monocytogenes), stored for I day at 4degreesC, and treated at 22degreesC and 90 to 95% relative humidity with 0.2 to 4.0 mg/liter ClO(2) gas for 15 or 30 min using a batch treatment system or with 0.6, 1.8, and 3.0 mg/liter for 10 min using a continuous treatment system. Surviving microbial populations were determined using a membrane-transfer plating recovery method. Increased ClO(2), gas concentrations resulted in increased log reductions of each pathogen for both the batch and continuous systems. A batch treatment of strawberries with 4 mg/liter ClO(2) for 30 min and continuous treatment with 3 mg/liter ClO(2) for 10 min achieved greater than a 5-log reduction for both E. coli O157:H7 and L. monocytogenes. After continuous exposure to 3.0 mg/liter ClO(2) gas for 10 min followed by I week of storage at 4degreesC, no aerobic microorganisms were detected and the color of the strawberry surface did not change significantly (P > 0.05). Residues of ClO(2) and chlorite on strawberries after the treatment were 0.19 +/- 0.33 mg ClO(2), per kg and 1.17 +/- 2.02 mg Cl(2) per kg, respectively, whereas after I week of storage no ClO(2), residues were detected and residual chlorite levels were down to 0.07 +/- 0.12 Mg Cl(2) per kg. These results suggest that ClO(2) gas treatment is an effective decontamination technique for improving the safety of strawberries while extending shelf life.