Pre-harvest contamination of produce has been a major food safety focus. Insight into the behavior of enteric pathogens on produce in pre-harvest conditions will aid in developing pre-harvest and post-harvest risk management strategies. In this study, the attachment strength (SR) and die-off rate of E. coli on the surface of watermelon fruits and the efficacy of aqueous chlorine treatment against strongly attached E. coli population were investigated. Watermelon seedlings were transplanted into eighteen plots. Prior to harvesting, a cocktail of generic E. coli (ATCC 23716, 25922 and 11775) was inoculated on the surface of the watermelon fruits (n = 162) and the attachment strength (SR) values and the daily die-off rates were examined up to 6 days by attachment assay. After 120 h, watermelon samples were treated with aqueous chlorine (150 ppm free chlorine for 3 min). The SR value of the E. coli cells on watermelon surfaces significantly increased (P<0.05) from 0.04 to 0.99 in the first 24 h, which was primarily due to the decrease in loosely attached population, given that the population of strongly attached cells was constant. Thereafter, there was no significant change in SR values, up to 120 h. The daily die-off rate of E. coli ranged from -0.12 to 1.3 log CFU/cm2. The chlorine treatment reduced the E. coli level by 4.2 log CFU/cm2 (initial level 5.6 log CFU/cm2) and 0.62 log CFU/cm2 (initial level 1.8 log CFU/cm2), on the watermelons that had an attachment time of 30 min and 120 h respectively. Overall, our findings revealed that the population of E. coli on watermelon surfaces declined over time in an agricultural environment. Microbial contamination during pre-harvest stages may promote the formation of strongly attached cells on the produce surfaces, which could influence the efficacy of post-harvest washing and sanitation techniques.

Produce growers using surface or well water to irrigate their crops may require an appropriate water treatment system in place to meet the water quality standard imposed by FSMA Produce Safety Rule. This study evaluated the potential of using ultraviolet (UV‐C) treatment in reducing the microbial population in agricultural water. Waters with turbidity levels ranging from 10.93 to 23.32 Nephelometric Turbidity Units (NTU) were prepared by mixing pond water and well water. The waters were inoculated with a cocktail of generic Escherichia coli (ATCC 23716, 25922, and 11775) and then treated with UV‐C light (20–60 mJ/cm2). All tested doses of the UV‐C treatment reduced the E. coli levels significantly (p < .05) in the water samples with the turbidity levels up to 23.32 NTU. The decrease in the turbidity from 23.32 to 10.93 NTU increased the level of reduction by more than 2.15 log most probable number (MPN)/100 ml). UV‐C treatment effectively reduces microbial load in agriculture water; however, turbidity of water may significantly affect the disinfection efficacy. The study also demonstrated that sprinkler system resulted in a higher level of contamination of cantaloupes compared with drip irrigation. The results indicated that UV‐C treatment could be a promising strategy in reducing the produce safety risks associated with irrigation water.

Preharvest contamination of produce with food borne pathogens has been a major food safety issue. In this study, we investigated the effect of surrounding vegetation on the survival of natural and inoculated generic Escherichia coli on watermelon rinds in an agricultural field setting. There was no significant difference (p > .05) on the populations of natural generic E. coli (1–1.46 log Most Probable Number (MPN)/sample) and coliforms (<3.99 log CFU/cm2) on watermelons harvested from low, medium, and high levels of vegetation. However, the survival rate of generic E. coli inoculated on watermelon rind discs was variable with the level of vegetation. A significant reduction in generic E. coli count was observed within 12 hr at all vegetation levels. After 108 hr, discs placed at low vegetation level had a highest die‐off reduction (3 log Colony Forming Units (CFU)/cm2) compared to medium and high vegetation levels. Practical applications To ensure preharvest produce safety, the Food Safety Modernization Act (FSMA) produce safety rule has suggested a time interval between last irrigation and harvest for potentially contaminating microorganisms to die‐off. However, a knowledge gap exists regarding the influence of surrounding vegetation on microbial die‐off rates on produce in the agricultural field. The findings of this study emphasize the importance of considering the surrounding vegetation while making decisions for developing preharvest risk management strategies based on microbial die‐off rate calculations.

Forty-five cultivars of lettuce (Lactuca sativa) were field-grown using best management practices at the Louisiana State University Agricultural Center (LSU AgCenter) Botanic Gardens in Baton Rouge during the Fall 2011 and Fall 2012 seasons. Recommended cultivars were selected for commercial production in Louisiana based on fresh weight and lettuce size (width and height). Nitrate (NO3–) concentration was analyzed for each cultivar, as lettuces are known to accumulate and concentrate NO3–, and were then compared with the U.S. Environmental Protection Agency’s (EPA) oral reference dose (RfD—the EPA’s maximum acceptable oral dose of a toxic substance) of 1.6 mg NO3-nitrogen (N) per kilogram body weight per day. Recommended butterhead cultivars were Caliente and Harmony (21.6 and 13.9 ppm NO3–, respectively); recommended green-leaf cultivars were Salad Bowl and Tango (10.6 and 4.6 ppm NO3–, respectively); recommended red-leaf cultivars were Red Salad Bowl, Red Sails, and New Red Fire (15.2, 15.4, and 24.0 ppm NO3–, respectively). The only recommended romaine cultivar was Green Towers (11.2 ppm NO3–), and recommended crisphead cultivars included Raider and Ithaca (17.6 and 14.9 ppm NO3–, respectively). Of the highest yielding cultivars, New Red Fire accumulated the greatest NO3– concentration: 24.0 ppm in both years 1 and 2. The NO3– concentration is less than the levels of concern for both men and women 20 to 74 years old, 3.9% of the RfD for men and 4.59% of the RfD for women.

for all the support and encouragement during the challenging times of my graduate studies. I am grateful for my lab mates Dorra Djebbi-Simmons and Mohammed Alhejaili who were there to guide and help me in my research work. I am thankful for Dr. Kathryn Fontenot, Mary Sexton, and Austin Wong for planting the strawberries for this study. I also thank the staff at the LSU AgCenter Botanic Gardens for all their help during fieldwork study. I would especially like to acknowledge my loving friends Kriza Calumba, Bennett Dzandu, and Johana Coronel for their continuous encouragement, motivation, and for their everlasting friendship. I would like to thank all the faculties of the School of Nutrition and Food Sciences at LSU for their support. Gratitude is also given to my parents for coming all the way from Sri Lanka to give me a helping hand in taking good care of my kids and by showering their unconditional love in my absence. They also helped me navigate through late night research experiments and weekend study. A very special thanks to my loving kids Aiza and Adeeb for patiently waiting until I complete graduate school so we can have ample happy family times together. Lastly, my deepest appreciation goes to my best friend who is also my loving husband Zowril Razik for his encouragement, determination, love, care, and patience. My academic achievements belong to him, if not for his faithful support and commitment I will not be able to come this far in accomplishing my graduate studies. This thesis was supported by the U.S. Department of Agriculture's (USDA) Agricultural Marketing Service through grant Agreement 2000241666. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USDA.