Date of Award

Spring 5-22-2019

Document Type


Degree Name

Master of Science (MS)


Food Science

First Advisor

Dr. Anuradha Prakash

Second Advisor

Dr. Donna Williams-Hill

Third Advisor

Dr. Denise Foley

Fourth Advisor

Dr. Kirsten Hirneisen


Escherichia coli O157:H7 can contaminate dropped apples used for juicing via contact with manure or fecally tainted 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 1000 Gy to inactivate Escherichia 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 1000 Gy. The D-value of the E.coli O157:H7 strain was 334 Gy indicating that irradiation at 1000 Gy would result in a 3-log reduction of this pathogen. Contaminated apples were also stored for 3 weeks at refrigerated temperature during which time E.coli O157:H7 survived but did not grow. The inoculated apples were juiced, and the juice was stored up to 72 h. There was no change in counts of E.coli O157:H7 in the juice from the control apples, but irradiation at >600 Gy reduced counts by >3 logs, and survivors were not detected after 72 h storage. Sensory testing of juice treated at 652 Gy indicated 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 at 1000 Gy 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.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.



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