Response surface modeling for the inactivation of Escherichia coli O157:H7 on green peppers (Capsicum annuum L.) by chlorine dioxide gas treatments

The effects of chlorine dioxide (CIO2) gas concentration (0.1 to 0.5 mg/liter), relative humidity (RH) (55 to 95%), treatment time (7 to 135 min), and temperature (5 to 25 degreesC) on inactivation of Escherichia coli O157:H7 on green peppers were studied using response surface methods. A four-factor, central, composite, rotatable design was used. The microbial log reduction was measured as a response. A direct membrane-surface-plating method with tryptic soy agar and sorbitol Mac-Conkey agar was used to resuscitate and enumerate CIO2-treated E. coli O157:H7 cells. The statistical analysis and the predictive model developed in this study suggest that CIO2 gas concentration, treatment time, RH, and temperature all significantly (P < 0.01) increased the inactivation of E. coli O157:H7. CIO2 gas concentration was the most important factor, whereas temperature was the least significant. The interaction between CIO2 gas concentration and RH indicated a synergistic effect, The predictive model was validated, and it could be used to determine effective CIO2 gas treatments to achieve a 5-log reduction of E. coli O157:H7 on green peppers.