Purpose: Chlorine and chlorine dioxide were evaluated as post-harvest antimicrobials for whole, fresh apples in laboratory and commercial settings.
Methods: In replicated laboratory studies, apples (560-850) inoculated with generic Escherichia coli (E. coli) or E. coli O157:H7 were randomly assigned to: inoculated untreated, chlorine or chlorine dioxide (oxidation-reduction potential {ORP} of 665mV, 750mV and 850mV), phosphoric acid (pH 3.5) or water, for 2, 3.5 and 5 minutes. Samples were enumerated on violet red bile agar and Cefixime-Tellurite Sorbitol-MacConkey agar. At commercial facility 1, 975 apples (3 replications) were randomly assigned to: inoculated untreated, or inoculated and treated in a dump tank containing water, phosphoric acid (pH 3.5), chlorine (targeted 750 and 850mV ORP), chlorine dioxide (750 and 850mV ORP) or peroxyacetic acid (80ppm). At commercial facility 2, 1,600 apples (4 replications) were examined at: 1) chlorinated dump tank with low or high organic loads 2) hyperwash containing chlorine dioxide with low or high organic loads 3) chlorinated flume system at high organic load, low organic load-750mV ORP chlorine and low organic load-850mV ORP chlorine.
Results: For laboratory studies, microbial levels after treatment with water, phosphoric acid, chlorine (665mV, 750mV, or 850mV) or chlorine dioxide were statistically similar. At facility 1, chlorine (targets of 750 and 850mV) in the dump tank achieved a significant, 0.9 log reduction in generic E. coli levels on apples in low organic load water. At facility 2, in the presence of low organic load, generic E. coli levels on apples collected after the chlorine dump tank treatment were significantly reduced (1.5 log), while in the presence of high organic loads, generic E. coli levels on apples collected after the dump tank were reduced 0.8 log.
Significance: Commercial experiments demonstrated larger antimicrobial reductions than laboratory experiments. Antimicrobial effectiveness in commercial facilities depends on multiple factors.