Log time (min)

FIGURE 18.6 Effects of ClO2 gas concentration (0.1 to 0.5mg/l), RH (55 to 95%), time (15 to 135 minutes), and temperature (10 to 20°C) on log reductions of E. coli O157:H7 on inoculated green peppers. Shaded areas represent reductions greater than 5 logs. Log time at 1.2, 1.4, 1.6, 1.8, and 2.0 correspond to 15.8, 25.1, 39.8, 63.1, and 100 minutes, respectively. (From Han, Y. et al., J. Food Prot., 64, 1128, 2001. With permission.)

studied using response surface methodology [34]. A predictive model developed in this study suggests that increasing ClO2 gas concentration, treatment time, RH, and temperature all significantly (P <0.01) increased the inactivation of E. coli O157:H7. Contour plots (Figure 18.6) for E. coli O157:H7 log reduction, generated using a predictive model, showed a good comprehensive picture of the model, in which the shaded areas indicate treatment conditions that give greater than a 5 log reduction. ClO2 gas concentration was the most important factor in the predictive model followed by time, RH, and then temperature. The interaction between ClO2 gas concentration and RH indicated a synergistic effect. Other research also indicates that a higher RH results in a higher bacterial inactivation rate by ClO2 gas [1-3,5]. High RH can moisturize treatment surfaces possibly leading to a thin layer of water droplets. These water droplets can further absorb and dissolve large amounts of ClO2 gas due to high water solubility. Thus, the localized and concentrated ClO2 contributes to microbial inactivation on the surfaces of fruits and vegetables. This may explain why ClO2 gas is unique and more effective compared to other gaseous disinfectants.

Similar to aqueous sanitation treatments, ClO2 gas treatment may also be less effective in reducing microorganisms on cut produce surface compared

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