Efficacy of washing with a commercial flatbed brush washer, using conventional and experimental washing agents, in reducing populations of Escherichia coli on artificially inoculated apples

Conventional and experimental washing formulations were applied with a comm ercial flatbed brush washer under conditions representative of commercial p ractice to determine their efficacy in decontaminating apples inoculated wi th a nonpathogenic Escherichia coli strain. Golden Delicious apples (18 kg) inoculated with E. coli were mixed with approximately 109 kg of uninoculat ed Fuji apples (distinctly different in appearance) in a wet dump tank cont aining 1.325 liters of water at 20 degreesC for 15 min. The combined apples were washed in a flatbed brush washer with the following washing solutions : water at 20 degreesC, water at 50 degreesC, 200 ppm of chlorine (pH 6.4) at 20 degreesC, 8% trisodium phosphate at 20 degreesC, 8% trisodium phospha te at 50 degreesC, 5% hydrogen peroxide at 20 degreesC, 5% hydrogen peroxid e at 50 degreesC, 1% APL Kleen 245 at 50 degreesC, and two-stage washing tr eatments using the combination of 1% APL Kleen 245 at 20 or 50 degreesC fol lowed by 5% hydrogen peroxide at 35 or 50 degreesC. None of the washing tre atments tested under the conditions of this experiment significantly reduce d the E. coli populations on the inoculated apples or in cider made from th ese apples, probably as a consequence of the inability of this washing syst em to inactivate or remove the bacterial cells in inaccessible calyx and st em areas of apples. These results are important because they demonstrate th e need for new fruit washing technology that can overcome this limitation. Also, there was no significant cross-contamination of the Fuji apples in th e dump tank. Significant cross-contamination of cider, made with uninoculat ed apples, occurred in the hammer mill and/or the press cloth when these un its were not sanitized following a trial with inoculated apples.