2019 ASHS Annual Conference

Escherichia coli O157: H7 can contaminate dropped apples used for juicing via manure or irrigation water and attach to the flesh of the apple through bruises and wounds where surface sanitizers are not effective. The goal of this project was to determine the efficacy of gamma irradiation at the maximum allowed dose of 1kGy to inactivate E.coli O157: H7 in whole apples used for juicing. Whole apples were punctured to simulate wounds which were then inoculated with an outbreak strain of E.coli O157: H7 and subjected to gamma irradiation at doses upto 1 kGy. The D-value of the E.coli O157: H7 strain was 334 kGy indicating that irradiation at 1 kGy would result in a 3-log reduction of this pathogen . Contaminated apples were also stored for 3 weeks in cold temperatures during which E.coli O157: H7 survived but did not grow. The inoculated apples were juiced, and the juice was stored upto 72 hours. There was no change in counts of E.coli O157: H7 in the juice from the control apples, but irradiation at 800 Gy reduced counts by 3 logs, and these cells did not survive the 72 hour storage. Sensory testing of juice treated at 1000 Gy indicated that consumers could tell the difference from control juice, due mostly to greater sweetness of the juice from irradiated apples. These results show that E.coli O157: H7 can easily survive in bruised apples and the juice made from them. Irradiation can provide significant lethality of E.coli O157: H7 in apples and juice conferring a greater level of safety without negative effects on sensory quality.