2017 ASHS Annual Conference

The Food Safety and Modernization Act (FSMA) Produce Safety Rule specifies certain requirements for agricultural water, when directly applied to covered produce during growing activities. The Food and Drug Administration (FDA) uses generic E. coli as the indicator of potential pathogen contamination in the water. Overhead evaporative cooling (EC) using surface water is frequently used in Washington to decrease sunburn in apples to prevent economic losses, but it’s influence on food safety risk is uncertain.

This study examined the influence of the EC on the survival of generic E. coli on Fuji apples in two different regions in central Washington (Sunrise orchard near Wenatchee, WA and Roza orchard near Prosser, WA). A generic E. coli cocktail (four-strains, rifampicin-resistant) was applied onto apples using a backpack sprayer after sunset. In both regions, replicated blocks of Fuji apples were either treated with EC or without EC water treatment (UC); an additional mist treatment (MIST) was utilized at the Roza orchard. In the two-year study, Fuji apples were harvested at 0, 2, 10, 18, 34, 42, 58, 82, 106, and 154 hours post inoculation (PI). After each harvest period, apples were immediately put on ice and transported to a microbiology lab for microbial testing. Uninoculated control apples were tested for indicator organisms as well as for pathogenic E. coli and Salmonella spp.

The average initial generic E. coli levels in log of colony forming units per apples (log CFU/apple) at each region for untreated fruit were 7.40±0.05 (UC, Sunrise) and 7.52±0.03 (UC, Roza), and the final concentration at 154h PI was 2.11±0.17 (UC, Sunrise) and 2.20±0.17 (UC, Roza). Initial concentration for treated fruit were 7.33±0.05 (EC, Sunrise), 7.47±0.05 (EC, Roza) and 7.60±0.06 (MIST, Roza) log CFU/apple, with the final concentrations of 1.90±0.16 (EC, Sunrise), 2.66±0.17 (EC, Roza) and 2.46±0.17 (MIST, Roza) log CFU/apple.

In all treatments, a rapid reduction in generic E. coli levels was observed between 10-18h PI. Average generic E. coli reductions at 18h PI were 3.4 and 2.8 log CFU/apple for UC in Sunrise and Roza respectively. For apples receiving water treatment, average generic E. coli reductions at 18h PI were 2.7 and 3.0 log CFU/apple for EC treatment in Sunrise and Roza, respectively, with 3.0 log CFU/apple of reduction for MIST treatment. Generally, the type of overhead treatment, EC or MIST, did not appear to affect survival of generic E. coli on Fuji apples.