Semester of Graduation



Master of Science (MS)


School of Nutrition and Food Sciences

Document Type



Bacterial attachment or biofilm formation on produce surfaces may result in limited penetration ability of sanitizers. This study examined the wet and dry contact time (WCT or DCT) of produce during washing with sanitizer and evaluated the effect of attachment level of Listeria monocytogenes during storage on the efficacy of chlorine treatment. Spinach and bell peppers were inoculated with Listeria monocytogenes and Salmonella enterica. The produce was then washed by dipping into a 100 ppm of chlorine solution for 1 min and an additional 1, 3, or 5 minutes (WCT) or removed from the chlorine solution and held for 1, 3, or 5 minutes (DCT). For the attachment study, bell peppers inoculated with L. monocytogenes were stored at 4 °C and 25 °C, and attachment strength (SR) and the efficacy of chlorine (100 ppm, 5 mins) was examined at 1, 24, 48, and 72 h. Chlorine wash at 100 ppm for 1 min resulted in a significant reduction (pL. monocytogenes and S. enterica population, with the highest reduction being 4.86 log CFU/g for Salmonella on spinach. No significant further reduction of pathogens was observed for an additional 5 mins with both WCT and DCT. Cross-contamination of L. monocytogenes (> 2.30 log CFU/g) from inoculated to un-inoculated samples was observed within 1 min during chlorine wash. Cross-contamination of S. enterica was 2.9 log CFU/g within 1 min and increased to 4.21 log CFU/g after six min. No cross-contamination of Salmonella was observed on bell pepper samples. The L. monocytogenes population at 4 °C decreased significantly up to 72 h while remaining constant at all times when stored at 25 °C. The attachment strength (SR value) of bacteria at 4 °C decreased significantly within 24 h and remain constant thereafter while the SR value for bacteria at 25 °C remained constant till 48 h and increased significantly. Chlorine outcompeted water wash for the samples stored for 1 h and all the samples stored at 25 °C. Chlorine wash is effective in minimizing microbial risk; however, its efficacy is affected by contact time and attachment of bacteria.

Committee Chair

Adhikari, Achyut