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.  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 .
Moreover, Liew and Prange  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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