Effect of Citric Acid on Prolonging the Half-life of Dissolved Ozone in Water.

To elucidate the effect of citric acid on the stability of dissolved ozone, half-lives of ozone in a citric acid solution was investigated. Prolongation of the half-life of ozone was clearly shown in the presence of citric acid in ozonized water. In the presence of ethylenediaminetetraacetic acid (EDTA), the half-life of ozone was decreased. The addition of various concentrations of citric acid to the EDTA solution, however, reversed the half-life in a concentration-dependent manner. These indicate that citric acid suppresses ozone self-decomposition in water. A citric acid-mediated suppression mechanism of ozone self-decomposition involving hydroxy radical (HO•) was proposed as follows: HO• formed by the radical chain reaction process of ozone is scavenged by a way of abstracting the hydrogen atom bound to a carbon atom located α-position of a carbonyl group. The radical chain reaction of ozone is, thus, suppressed. These findings demonstrate that the addition of citric acid to ozonized water is useful for the stabilization of ozone. This ability may contribute to the application of ozone sterilization in food production processes.