Evaluation of naturally occurring and inoculated microorganisms on stone fruit carriers

Fruit carriers are used in stone fruit packinghouses to size, sort, and convey fruit before packing fruit for the consumer. This study assessed the microbial levels naturally occurring on carriers, the growth potential of Salmonella enterica and Listeria monocytogenes on fruit carriers, and the use of humidity and temperature combinations as a possible treatment for pathogens on carriers. Environmental swabs of 192 carriers were taken from 8 commercial stone fruit packinghouses. Statistical analysis of the results indicated that routine cleaning significantly reduced total microbial and coliform counts on fruit carrier surfaces. In the laboratory, new and commercially used fruit carriers were inoculated with S. enteirca and L. monocytogenes to a surface attachment of ~2 log CFU/cm2 and then incubated at different humidity (65, 75, 85 or 95%) and temperature (22, 28, 34 or 40°C) combinations. There was a decline of both pathogens after 1-day exposure to 65% humidity at 40°C, 75% humidity at 34°C, or 85% humidity at 40°C for both used and new carriers. No growth of either pathogen was observed under all tested conditions. To examine the effect of humidity and temperature combinations as a possible treatment for pathogens, new fruit carriers were inoculated with S. enteirca or L. monocytogenes to a surface attachment of ~6.5 log CFU/cm2. In 4 hours exposure to 75% humidity at 34 or 40°C; 85% humidity at 34 or 40°C; and 65% humidity at 40°C a ≥ 3-log reduction was achieved. At 75% humidity and 40°C in 4 hours, both pathogens experienced a ≥ 5-log reduction. The results of this study indicate current sanitation practices for sorting system’s fruit carriers decrease the total microbial and coliform levels on the equipment. The study promotes the potential of using environmental conditions, such as humidity and temperature combinations, for the reduction of microbial contamination on carriers and possibly other food contact surfaces.