Extrinsic control parameters for ozone inactivation of Escherichia coli using a bubble column

Aims: To investigate the effect of extrinsic control parameters for ozone inactivation of E. coli in a bubble column. Methods and Results: Ozone inactivation of Escherichia coli ATCC 25922 in Tryptic Soya Broth was examined. The parameters studied included temperature (ambient, 20, 25 and 30°C), exposure time (up to 30 min), gas flow rate (0·03, 0·06, 0·12, 0·25, 0·5 and 0·75 l min^-1) and concentration level (five different levels). The efficacy of ozone treatment was a function of the parameters investigated and optimum control parameters of flow rate (0·12 l min^-1), temperature (ambient) and ozone concentration (75 μg ml^-1) resulted in a t_d5 (time required to achieve 5 log reduction) of 20 min. Conclusions: Optimum control parameters of gas flow rate, ozone concentration and temperature are reported for E. coli inactivation within a bubble column. Significance and Impact of the Study: In 2001, the FDA approved use of ozone as a direct additive to food and in 2004, issued guidelines for the use of ozone in liquid systems. However, these guidelines highlighted gaps in the literature for ozonation of liquid foods. This study provides useful information regarding optimum extrinsic control parameters for E. coli inactivation in liquid media using a bubble column to ensure microbiological safety.