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FIGURE 18.9 Effects of ozone gas concentration, % RH, and treatment time on log reductions of E. coli O157:H7 on green peppers at 22°C. (From Han, Y. et al., J. Food Sci., 67, 1188, 2002. With permission.)

Ishizaki et al. [82] reported that the efficacy of ozone gas for inactivation of bacillus spores on filter paper increased as ozone concentration (0 to 3.0 g/l), time (0 to 6 hours), and RH increased (54 to 90%). The spores were more resistant on a glass fiber filter than on filter paper. At a RH of 50% or below, there was no appreciable decrease in the number of survivors within 6 hours exposure to 3.0 mg/l ozone. Other researchers also reported that RH is an important factor for microbial inactivation by ozone gas, and ozone is less effective to inactivating dehydrated microorganisms [64].

Moreover, Liew and Prange [84] reported that temperature played an important role in the storage of carrots treated by ozone gas. The ozone concentration at 2° C was higher than that at 16° C, hence providing a greater reduction in fungal growth rate on carrots. A different linear effect of ozone concentration was found for each temperature. Significant (P < 0.05) effects of temperature and linear and quadratic effects of ozone on the growth rate of Botrytis cinerea on carrots were also observed.

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