Characterization and control of food safety risks associated with indoor leafy green growing and harvest

By including growth, harvesting, and post-harvest handling in one controlled environment, CEA operations offer the advantages of reducing exposure to human factors, soilborne pathogens and wildlife intrusion. However, CEA faces challenges due to the lack of literature about food safety risks associated with its unique operational components. This proposal investigates the food safety risks associated with the use of nutrient solutions (NS), growth substrates (GS), and LED lights, as well as the impact of higher facility relative humidity on food safety. Objective 1 is to evaluate the survival of common foodborne pathogens in recirculating NS using a model deep water hydroponic system. Objective 2 is to characterize the cross- contamination risks between NS, GS, food contact surfaces and produce under high relative humidities. Objective 3 is to study the impact of LED light on the survival of pathogens on produce leaves. The team has discussed the proposal with the technical committee and obtained strong support from the CEA industry, manufacturers of CEA systems, and CEA organizations. The insights this project can provide are of importance to CEA’s sustainable advancement. The data generated not only directs the development of food safety plans but also builds the data foundation for CEA system automation.

Controlled environment agriculture (CEA) is an innovative approach that uses controlled conditions to optimize plant growth and maximize yield. While CEA offers potential food safety advantages by reducing exposure to human factors, soilborne pathogens and wildlife intrusion, it faces unique challenges because of the lack of scientific data about food safety risks associated with the specific components used by CEA. CEA systems are very diverse, and the design and automation of facilities differ quite significantly. However, they do share several common components, including the use of nutrient solutions (NS), growth substrates (GS), and LED lights. In addition, CEA facilities tend to have higher relative humidity (RH) compared to field agriculture because of the presence of a large volume of water and low air exchange. This proposal seeks to bridge the knowledge gaps associated with these unique components of CEA systems and provide the data needed to develop food safety plans. Objective 1 is to evaluate the behavior of common foodborne pathogens (Salmonella and Listeria monocytogenes [LM]) in recirculated NS by using a model hydroponic system. NS is used by the CEA for providing essential nutrients for plants, however, if not handled properly or contaminated, NS can serve as a contamination source or cross- contamination vehicle. Our preliminary data showed that pathogens behaved differently in fresh and used NS in a static system. While Salmonella and generic E. coli declined faster in used NS than in fresh NS, no difference in LM behavior was observed between fresh and used NS. Pathogen behavior in a dynamic recirculating system needs further evaluation, and the data will be of critical importance for developing NS handling practice standards. Objective 2 is to investigate cross-contamination risks among different components in CEA systems, including the potential transfer of pathogens between NS and plants, GS and plants, and different types of food contact surfaces and plants under high humidity. This information is of great importance for CEA because preventing cross-contamination is a challenge in an enclosed system. Objective 3 is to study the impact of LED light exposure on the survival of pathogens on produce leaves. Artificial LED lighting, particularly of red and blue spectra, is widely used in CEA to enhance crop growth and nutritional quality. However, its potential role in food safety remains underexplored. While light exposure may lead to the opening of stomata, it is also known that LED lights, such as blue lights, have bactericidal effects. Therefore, how do different light sources and dark and light cycles impact the microbial safety of fresh produce needs to be thoroughly evaluated. This proposal directly addresses the needs of the CEA industry by providing science-based insights into the food safety risks associated with unique yet common CEA components. These data are of great importance for the sustainable development of CEA, as the automation of CEA systems is expected to continue to increase, and the design of CEA facilities needs to be data driven, ensuring both produce quality and safety.

Objective 1: Investigate the survival of foodborne pathogens in recirculating nutrient solution using a model hydroponic system.

Objective 2: Identify cross-contamination risks during the cultivation and harvesting of hydroponic-grown leafy greens by assessing potential transfers between NS, GS, food-contact surfaces, and plants.

Objective 3: Evaluate the impact of different LED light exposures, including red-blue light ratios, light-dark cycles, and light intensities, on the behavior of foodborne pathogens on edible leaves during produce cultivation.

This project is ongoing. A final report will be provided when the project is finished.