Survival dynamics of Salmonella enterica, Listeria monocytogenes, and Escherichia coli in wash water during simulated chlorine depletion and replenishment processes

Authors: ZHOU, BIN - University Of Maryland; Luo, Yaguang - Sunny; Nou, Xiangwu; LYU, SHUXIA - Shenyang Agricultural University; WANG, QIN - University Of Maryland

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2015
Publication Date: 4/2/2015
Publication URL: http://handle.nal.usda.gov/10113/61203
Citation: Zhou, B., Luo, Y., Nou, X., Lyu, S., Wang, Q. 2015. Survival dynamics of Salmonella enterica, Listeria monocytogenes, and Escherichia coli in wash water during simulated chlorine depletion and replenishment processes. Food Microbiology. 50:88-96.

Interpretive Summary: Chlorine is the most common sanitizer used in the produce industry. An effective level of chlorine in produce wash water is critical to prevent cross-contamination of fresh and fresh-cut produce; therefore, it is imperative to determine what parameters will define the sanitary status of a washing system. USDA-ARS scientists at the Beltsville Agricultural Research Center simulated the chlorine depletion and replenishment processes during produce washing and investigated the relationship between microbial populations and water quality parameters. The researchers identified the key parameters for monitoring the quality of produce wash water, and determined the threshold levels of free chlorine for complete inactivation of human pathogens. This study provides critical information to the fresh-cut produce industry to implement performance standards for produce wash water sanitation and to develop improved strategies to maintain a stable chlorine concentration during commercial produce wash operations.

Technical Abstract: Maintaining effective sanitizer concentration is of critical importance for preventing pathogen survival and transference during fresh-cut produce processing and for ensuring the safety of finished products. However, maintaining an adequate level of sanitizer in wash water can be challenging for many processors due to the large organic load in the wash system. In this study, we investigated how the survival of human pathogens was affected by the dynamic changes in water quality during chlorine depletion and replenishment in simulated wash water. Lettuce extract was added incrementally into water containing pre-set levels of free chlorine to simulate the chlorine depletion process, and sodium hypochlorite was added incrementally into water containing pre-set levels of lettuce extract to simulate chlorine replenishment. Key water quality parameters were closely monitored and the bactericidal activity of the simulated wash water was evaluated using three-strain cocktails of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes. In the free chlorine depletion process, survival of bacterial pathogens was observed when wash water free chlorine dropped to under 3.7 mg/L; and in the free chlorine replenishment process, survival of bacterial pathogens dropped to below the detection limit when wash water free chlorine reached 3.7 mg/L. This study established the correlation between chlorination parameters and survival of human pathogens in simulated produce wash water. It highlights the importance of establishing performance standards for produce wash water sanitation and developing improved strategies to maintain a stable chlorine concentration during commercial produce wash operations.