Inactivation Kinetics of Escherichia coli O157:H7 on Baby-Cut Carrots During Gaseous Chlorine Dioxide Treatment: The Impact of Relative Humidity

The objective of this study was to model the inactivation of Escherichia coli O157:H7 under varying relative humidity and gaseous ClO₂ concentrations. E. coli was spot-inoculated onto baby-cut carrots and exposed to ClO₂ gas at concentrations of 100 ppm, 200 ppm, and 300 ppm, within relative humidity ranges of 50 to 90%. The results demonstrate that the germicidal efficacy of gaseous ClO₂ significantly increases with both ClO₂ concentration and relative humidity increase (p < 0.05). Two different non-linear inactivation models, the Weibull model and the modified Chick model, were employed to describe the inactivation kinetics of E. coli. The modified Chick model, based on chemical reaction kinetics, proved more suitable (RMSE < 0.356) than the Weibull model (RMSE < 0.469). A multiple regression analysis was subsequently conducted, utilizing the modified Chick model to describe the inactivation of E. coli under varying relative humidity and ClO₂ concentrations. At 50% relative humidity and 100 ppm ClO₂ concentration, the inactivation rate constant of the modified Chick model was 1.04 × 10⁻³ min⁻¹. The inactivation rate constant increased to 3.63 × 10⁻³ min⁻¹ and 0.0668 min⁻¹ as ClO₂ gas concentration increased from 100 to 300 ppm and relative humidity increased from 50 to 90%, respectively. The model developed in this study describes the inactivation of E. coli as a function of relative humidity and ClO₂ concentration (R² of 0.985) and can be utilized by the food processing industry to design gaseous ClO₂ processes for achieving desired levels of E. coli inactivation.