Viable microbial loads on citrus carpoplane during packhouse processing and survival of foodborne pathogens in reconstituted postharvest fungicides

This study investigated microbial population shifts on citrus carpoplane and the impact of irrigation and packhouse processing water in four commercial farms. Samples included oranges (n=450) and water (n=230). Mean microbial concentrations ranging from 1.6 to 3.6 log colony forming units (CFU)/cm(2) were detected on unwashed fruit and were reduced at least by 2.0 log CFU/cm(2) for bacteria, 0.8 log CFU/cm(2) for fungi and 1.3 log CFU/cm(2) for yeasts during washing with disinfectants and/or fungicides. Occasional spikes in concentration (mostly for bacteria) were observed following some packing steps including washing, fungicide treatment, waxing, and final packing. Evaluation of Escherichia coli O157:H7 and S. Typhimurium survival in fungicides typically used during packhouse processing showed them to be susceptible to guazatine, imazalil, philabuster, and ortho-phenyl phenate. Both tested pathogens were able to survive in thiabendazole, fludioxinil and pyremethanil, except for S. Typhimurium in fludioxinil where it died within 4 hr of incubation. Practical applicationsUnderstanding the impact of current intervention strategies on the ecological balance of the citrus carpoplane may provide a more durable approach to reduced losses and spoilage and in developing crop-specific management systems for food safety assurance. Our study showed process-by-process changes in microbial loads naturally present on healthy citrus fruit at harvest. Washing baths containing a sanitizing agent consistently reduced initial microbial loads on the citrus carpoplane. Further, potential survival of E. coli O157:H7 and S. Typhimurium in currently registered commercial postharvest fungicides, was demonstrated. The pesticide fludioxinil was observed to be effective against, S. Typhimurium providing some potential use as a kill step agent, which, however, needs further investigation.