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Abstract
Chlorine is the most widely used sanitizing chemical in the U.S. fresh produce industry. However, chlorine can react with organic matter and produce toxic disinfection by-products, which pose potential threats to consumer health. The main objective of this project was to evaluate the efficacy of activated persulfate as an alternative sanitizing chemical for pathogen inactivation and produce sanitation. Five research chapters were conducted. The first two research chapters systematically evaluated the efficacy of ferrous and alkaline activated persulfate in inactivating Escherichia coli O157:H7 and Listeria monocytogenes in pure solution. It was found that more than 8 log CFU/mL reductions can be achieved on the two pathogens by the two activation treatments. The efficacy was dependent on the persulfate to activator ratio, persulfate concentration, and treatment time. Free radicals were determined to be the primary compounds in pathogen inactivation. The third research chapter investigated the possible pathogen inactivation mechanisms. It was found that after activated persulfate treatment, there were significant intracellular leakage of protein and DNA. The dehydrogenase activity was also inhibited. Electron microscopy images further revealed the damage on cell surfaces and cytoplasm. Therefore, it was concluded that the major inactivation mechanism was through direct damage on cell envelope structures that caused intracellular material leakage and finally cell death. The fourth research chapter investigated the effectiveness of activated persulfate treatment for fresh romaine lettuce decontamination. It was found that up to 3.5 log CFU/g pathogen can be removed from romaine lettuce surface in 5 min without significant impact on the color quality. The efficacy was dependent on both persulfate concentration and treatment time. Furthermore, cross-contamination through wash water can be prevented at appropriate persulfate levels for both activation methods. The fifth research chapter evaluated the potential effect of organic load on activated persulfate. The overall results showed ferrous activation was easier to be affected by organic matter compared with alkaline activation. UV254 was deemed as an appropriate parameter to indicate the organic load effect. The overall findings of this project indicated activated persulfate has great potential to be applied as an alternative sanitizing chemical for fresh produce sanitation.