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Post-harvest Interventions and Food Safety of Leafy Green Vegetables

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2011, Doctor of Philosophy, Ohio State University, Food Science and Technology.
Foodborne illness outbreaks associated with the consumption of leafy green vegetables are a growing public health concern worldwide. While there has been great progress in using practical and cost-effective interventions to reduce the risk of contaminations and prevalence of pathogens on farm, effective post-harvest interventions to remove field acquired contamination are still lacking. The body of literature related to microbial hazards in leafy green vegetables has accumulated since 1990, offering often contradictory information on the efficacy of food safety interventions. In this work, I identified, characterized, and assessed the quality of available research on prevalence, risk factors, and interventions for 16 microbial hazards in leafy green vegetables. Systematic literature review, a replicable two-level relevance screening, and a two-phase quality assessment and data extraction procedure were performed by two independent reviewers following general principles of systematic review methodology. A lack of well designed, executed, and reported prevalence studies on efficacy of intervention(s) under real-life conditions was observed. Additional knowledge gaps and research areas included equipment sanitation and cross-contamination potential, survival of pathogens in organic vegetables, and the lack post-harvest intervention studies applicable to the developing regions. Several identified knowledge gaps were further addressed. The concentration of coliforms and Escherichia coli and prevalence of E. coli O157:H7, Salmonella spp., Shigella spp. and Listeria monocytogenes in spianch before and after minimal processing under commercial conditions was investigated. A total of 1356 spinach samples were collected daily in two processing plants over a period of 14 months. The proportion of coliform positive samples increased from 53% before to 79% after minimal processing. Generic E. coli prevalence was 8.9% (mean 1.81 ± 0.14 log CFU/g) with no difference after processing. Salmonella spp. and L. monocytogenes were isolated from 0.4% and 0.7% of samples, respectively. The contribution of each commercial processing step to generic E. coli, coliform, and total aerobic bacterial load on fresh-cut lettuce and food contact surfaces in a processing plant were further quantified. Plausible bacterial populations on fresh-cut, minimally processed lettuce using T-RFLP analysis were identified. Washing initially decreased coliforms on lettuce but microbial populations increased during subsequent steps. Peak contamination on food contact surfaces was detected after two hours of processing, then declined after 4-6h of processing without intermediate sanitation interventions. No association between coliform increase on lettuce and contact-surfaces was found. Removal of outer leaves was the single most effective step of large-scale minimal processing. T-RFLP analysis identified representatives of 12 phyla/classes of bacteria on minimally processed lettuce. The ability of E. coli O157:H7 to survive in processed packed organic and conventional baby spinach during storage conditions during the shelf life was compared. Epiphytic bacteria present and the effect of leaf size on survival of E. coli O157:H7 were assessed. E. coli O157:H7 survived similarly on both spinach types. Finally, existing data pertaining to post-harvest interventions was compiled and synthesized. The options for post-harvest risk reduction were summarized and the existing information was translated to vegetable production conditions in developing countries. The applicability of multiple-barrier approach in developing regions was discussed.
Jeffrey LeJeune, PhD (Advisor)
Brian McSpadden-Gardener, PhD (Committee Member)
Douglas Doohan, PhD (Committee Member)
Kenneth Lee, PhD (Committee Member)
213 p.

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Citations

  • Ilic, S. (2011). Post-harvest Interventions and Food Safety of Leafy Green Vegetables [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1313509920

    APA Style (7th edition)

  • Ilic, Sanja. Post-harvest Interventions and Food Safety of Leafy Green Vegetables. 2011. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1313509920.

    MLA Style (8th edition)

  • Ilic, Sanja. "Post-harvest Interventions and Food Safety of Leafy Green Vegetables." Doctoral dissertation, Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1313509920

    Chicago Manual of Style (17th edition)