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theses

Foodborne illnesses caused by viruses and STEC contaminated fresh produce are currently a world concern. Strawberries are delicate and could be contaminated at any point during the farm to fork continuum. Typically, fresh strawberries would be stored at refrigerated temperature and not washed until immediately prior to serving. In contrast, strawberries are typically washed prior to freezing at -¬40 °C or even lower temperature. Washing and low temperature storage are two common practices utilized by commercial processors and in-home to enhance safety and quality of strawberries. The efficacy of two combining practices: washing with a commercial water antimicrobial and freezing/refrigeration were investigated.
In the present study, MS2 bacteriophage was used as a surrogate for Norovirus and Hepatitis A virus. The microorganisms were spot inoculated onto strawberries to
achieve 6.6 log PFU/g. The inoculated strawberries were washed with tap water, electrolyzed water or 50 ppm free chlorine solution for 90 seconds prior to and after storage. After initial washing, the strawberries were separately stored at −20 °C and −80 °C for 30 days, and at 4 °C for 2 days. Change in MS2 populations on strawberries was evaluated by plaque assay on pre-determined sampling days. The same experiment was conducted independently using E. coli O157:H7 and E. coli O26:H11.
The results showed that washing with antimicrobials provided a significant decrease of MS2 and STEC populations (p < 0.05). The log reduction of MS2 was approximately 1 log PFU/g and that of STEC was 2.5 log CFU/g. Frozen storage had minor effect on inactivating MS2, resulting in 0.5 log PFU/g reduction at the end of storage. In contrast, freezing successfully reduced the population of E. coli O157:H7/O26:H11 on strawberries and the maximum reduction was up to 3 log CFU/g achieved by the electrolyzed water treatment. The second wash conducted following storage provided an additional 1 log reduction in the population of MS2 and STEC. The influence of refrigeration on populations of MS2 and STEC was similar to frozen storage.
Collectively, population of MS2 bacteriophage did exhibit remarkable decrease following exposure to water antimicrobials and low temperature. STEC were more susceptible to these conditions. The utilization of multiple hurdles may result in greater reduction of MS2 and STEC. Based on results of the present study, it is recommended that water antimicrobials are used particularly when strawberries are washed using an immersion process.

ETD_9661

M.S.

Includes bibliographical references

doi:10.7282/t3-9kpe-kg59

ETD graduate

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