APPLICATION OF OZONE FOR INACTIVATION OF ESCHERICHIA COLI O157:H7 ON INOCULATED ALFALFA SPROUTS

摘要

Chemical treatments to eliminate pathogens on inoculated seed sprouts have shown little success. This study investigated the effectiveness of aqueous ozone in killing Escherichia coli O157:H7 on alfalfa sprouts. Alfalfa sprouts inoculated with a five strain cocktail of E. coli O157:H7 were immersed in water containing 21 ppm ozone for 2, 4, 8, 16, 32, 64 min at 4C. To increase availability and accessibility of ozone into sprout crevices, alternative treatments with continuous ozone sparging with and without pressurization were evaluated. Ozone treated sprouts were subjected to 12 psi hydrostatic pressure with pressurized ozone gas for 5 min to aid introduction of aqueous ozone into areas where pathogens may be hidden. Immersion of inoculated alfalfa sprouts (～10~7 CFU/g) in water containing 21 ppm ozone reduced the population of E. coli O157:H7 by 0.85 log_(10)CFU/g after 64 min. There were no significant differences in log_(10) reductions between the ozone treatments and control or between treatment times. With the exception of 2 min treatments, continuous ozone sparging resulted in reductions of 0.83 - 2.20 log_(10) CFU/g, significantly higher (P ≤ 0.05) than reductions obtained by sparging with air (0.83 -1.29 log_(10) CFU/g). Application of low hydrostatic pressure (12 psi) for 5 min subsequent to continuous ozone sparging for 2 to 64 min reduced E. coli O157:H7 populations by 2 log_(10) CFU/g. Reductions resulting from pressurized ozone treatments did not differ significantly from those resulting from unpressurized ozone treatments, except at 32 min. Ozone treatments did not exhibit a visible detrimental effect on sprout quality. Further investigation is required to develop methods applying ozone for the purpose of decontaminating sprouts and reducing health risks. Ozone exhibits the potential for successful post harvest treatment of sprouts and also to replace other chemical treatments currently being used in the seed sprout industry.