Inactivation of E-coli O157 : H7 in apple cider by ozone at various temperatures and concentrations

The effect of temperature (5-20C) at 860 ppm (v/v) ozone and different gaseous ozone concentrations above 1,000 ppm on inactivation of E. coli O157:H7 in apple cider was studied. Lag times ranged from 3.5 min at 20C to 6.7 min at 10C before the on-set of E. coli O157:H7 inactivation. D-values ranged from 0.6 to 1.5 min at 20C and 5C, respectively. After ozone treatment of cider for 14 min, dissipation of ozone from cider was slow, decreasing to about 5 mg/L after 2 h at 5C. At high gaseous ozone concentration, lag time was shortest and D-value lowest. There was a critical concentration of dissolved ozone of about 5-6 mg/L at 20C, before the on-set of E. coli O157:H7 inactivation in the cider. Total processing times, based on lag time plus 5D, ranged from about 4 to 14 min depending on temperature and ozone concentration. Overall, inactivation of E. coli O157:H7by ozone was fast enough to allow practical applications in cider production, and it should be considered as an alternative to thermal pasteurization.