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The objectives of this project were to evaluate the efficacies of electrolyzed
oxidizing (EO) and ozonated waters as antimicrobial agents for enhancing the
microbiological safety of fresh strawberries (Fragaria x ananassa). The influence of
sodium chloride (NaCl) concentrations used for preparing EO water was evaluated on
their bactericidal activities against naturally occurring aerobic mesophiles on
strawberries with a contact time of 5, 10, or 15 min. EO water and ozonated water
containing about 1.90 ppm ozone were evaluated and compared with sodium
hypochlorite (NaOCl) solution on their capabilities to inactivate and control the
growth of Listeria monocytogenes and Escherichia coli O157:H7 inoculated onto
strawberries stored at 4 ± 1 °C for up to 15 d, respectively. Post-treatment
neutralization of fruit surfaces by washing was also investigated. More than 2 log₁₀
CFU/g reduction of mesophilic aerobic bacteria was achieved in samples washed for
10 or 15 min in EO water prepared from 0.10% (w/v) NaCl solution. Bactericidal
activity of treatment solutions against L. monocytogenes and E. coli O157:H7 was not
affected by post-treatment neutralization, and their effectiveness against both
pathogens in whole fruit tissues did not significantly increase with increasing exposure
time. The EO water had an equivalent antibacterial effect as compare with NaOCl in
eliminating L. monocytogenes and E. coli O157:H7 on whole strawberry tissues. Fruit
surfaces washing with distilled water resulted in 1.90 and 1.27 log₁₀ CFU/ml of rinse
fluid reduction of L. monocytogenes and E. coli O157:H7, respectively, whereas ≥
2.60 log₁₀ CFU/ml of rinse fluid reduction of L. monocytogenes and up to 2.35 and
3.12 log reduction of E. coli O157:H7 were observed on fruit surfaces washed with
EO water and NaOCl solution, respectively. However, EO water and NaOCl solution
treatments did not exhibit a higher microbicidal activity than water treatment during
refrigeration storage. The ozone treatment on inoculated strawberries was not
remarkably effective in removing and eliminating pathogens on the whole fruit tissues,
but the populations of L. monocytogenes and E. coli O157:H7 were significantly
decreased after ozone treatment regardless of the exposure time. The number of L.
monocytogenes and E. coli O157:H7 on fruit surfaces was decreased by 2.17 and 2.02
log₁₀ CFU/ml of rinse fluid, respectively, after washing with ozonated water for 10
min. |
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