Doctor of Philosophy (PhD)


School of Nutrition and Food Sciences

Document Type



The fertilizers solution used in hydroponic systems may also provide a favorable condition for the growth of environmental pathogens. This study examined the growth and survival of L. monocytogenes in hydroponic fertilizer solutions at different pH and the distribution of Listeria from contaminated lettuce and tomato seeds to seedlings in a hydroponic system. UV-C light (1.32 mW/cm2) and chemical sanitizers such as chlorine (1000, 10,000, and 20,000 ppm) and chlorine dioxide (100, 200, and 300 ppm) were evaluated against Listeria monocytogenes contaminated in fertilizer solutions and lettuce seeds respectively. Fertilizer solutions provided a favorable environment for the growth of Listeria monocytogenes. Listeria levels increased from 2.80 Log CFU/ml to 4.94 Log CFU/ml and 5.21 Log CFU/ml in lettuce and strawberry fertilizer solutions, respectively. However, Listeria levels remained similar in tomato fertilizer solutions. The highest growth of Listeria was observed in fertilizer solutions maintained at pH 6. UV-C light treatment for 5, 10, and 15 seconds on lettuce fertilizer solution reduced Listeria levels from 5.7 log CFU/ml to 4.61, 2.26, and 1.38 log CFU/ml, respectively. Similarly, on tomato and strawberry fertilizer solution to 4.49, 2.14, and 1.04 log CFU/ml, and to 4.50, 2.19, and 1.75 log CFU/ml, respectively. Listeria from contaminated seeds was able to spread to the seedlings. At day 50, the number of cells in tomato leaves increased significantly (pL. monocytogenes levels were significantly reduced after seeds were treated with chlorine and chlorine dioxide solution. Chlorine solution at 1000, 10,000, and 20,000 ppm significantly reduced Listeria levels in the seeds from 4 log CFU/g to 1.65 log CFU/g, 2.12 log CFU/g, and 2.13 log CFU/g respectively. Similarly, chlorine dioxide at 100, 200, and 300 ppm reduced Listeria levels to 2.34 log CFU/g, 1.87 log CFU/g and 1.73 CFU/g, respectively. UV-C light and chemical sanitizers (chlorine, and chlorine dioxide) are effective in reducing Listeria levels from contaminated fertilizer solutions and seeds, respectively. Appropriate use of physical and chemical treatment could minimize the food safety risk and maintain the quality of hydroponic crops.



Committee Chair

Adhikari, Achyut



Available for download on Saturday, June 30, 2029