How You Can Be Proactive in Preventing Greenhouse Food Safety Problems
September 1, 2021 
Photo: Adobe Stock Images
There’s an underlying assumption that vegetable crops produced in a controlled environment have a much lower risk of contamination than crops grown outdoors. While this may be true when it comes to some risk factors, Dr. Sanja Ilic, Associate Professor and Food Safety State Specialist in the Department of Human Sciences at The Ohio State University (OSU), says growers still need to be cautious.
“Contrary to the popular opinion that protected-environment produce is safer, we know that the conditions that are allowing for optimal yields in hydroponics are also conducive for human pathogens,” Ilic says. “Outbreaks have been linked to greenhouse produce, and our team has isolated pathogens such as Listeria monocytogenes from greenhouses.”
Eight Areas Growers Should Track
Most fresh tomatoes sold in the U.S. are grown using protected agriculture, and the risk of contamination and severe disease outbreaks in humans due to foodborne pathogens linked to fresh produce are a constant threat to the public and the industry.
“To date, there are limited tools to prioritize food safety management practices in commercial greenhouses to reinforce food safety in a timely manner,” Ilic says. “One rapid cost-effective approach, originally applied in education and health care, is the Delphi method that uses expert opinion to quantify and rank priorities.”
Working with a team of researchers at OSU, Ilic used an iterative systematic Delphi expert elicitation approach to prioritize management factors for the reduction of foodborne pathogen contamination in tomato greenhouses in the U.S. The project started with an online survey addressing eight areas (water management, workers, environment and greenhouse design, equipment sanitation, waste management, animal intrusion, traceability, and propagation). A group of 20 individuals internationally recognized as experts in fresh produce production in protected agriculture, foodborne pathogens, and food safety theory and practice then ranked the activities and practices most likely contributing to microbial contamination and its mitigation.
Food safety priorities to prevent contamination of greenhouse tomatoes, in order of significance, included water quality, handwashing, environmental controls, enforceable worker health policy, cleaning and sanitation of reusable plastic containers, reused retail-ready containers, and irrigation water testing for human pathogens to prevent contamination.
The majority of the experts indicated that contaminated greenhouse surfaces that are in contact (direct or indirect) with the fruits are important sources of pathogen transfer to fresh tomatoes, highlighting the need for environmental controls in greenhouses.
“The importance of adequate worker management practices, including handwashing and health policy, highlights the role of worker education in reducing the risks of foodborne outbreaks linked to greenhouse-grown produce,” Ilic says.
How Long Can Pathogens Survive?
Dr. Ilic, who is a faculty member in Human Nutrition, along with Dr. Melanie Lewis-Ivey from OSU Plant Pathology, also teamed up to look at how long pathogens might survive in water used in hydroponic leafy greens production, since lettuce ranks as one of the most susceptible crops when it comes to contamination.
The team installed an NFT system at one of OSU’s research greenhouses, and inoculated the water with Listeria and Salmonella to simulate what might happen if there were a storm that affected water stored in the ground. They then measured contaminant levels on leaves, roots, and the rockwool medium used to grow the crop.
Results indicated that Listeria survived through the entire production time frame at both low and high inoculation rates. Salmonella did not survive as long, but it was still detectable.
“We especially noticed high levels of pathogens in the rockwool, almost as if it was trapping the bacteria,” Ilij says.
You can learn more about Ilic’s research on both projects in a YouTube video at https://is.gd/gKeDS6.
Easy Rules to Follow
When it comes to practical solutions, Ilic points out three factors growers should monitor:
- Water: “Because hydroponics is water intensive, contaminated irrigation water poses serious risk for foodborne pathogens. It is important that growers understand the quality of the water they use in their system and do their best to prevent any contaminants from reaching their production water. Often, growers may recirculate water or use multiple sources. They should remember that the water is just as safe as the water from the lowest quality water source.”
- Worker hygiene: “It is important to implement and enforce workers’ health and hygiene practices. Workers can track the pathogens from the environment or contaminate the product if they carry pathogens. This is also an important COVID-19 prevention strategy.”
- Cleanliness: “Finally, regular cleaning and sanitation of surfaces in the greenhouse is critical for the safety of the product. Complete clean out and regular sanitation of food contact and other surfaces will ensure the prevention of cross-contamination.”
Get to Know the CEA Food Safety Coalition
Lettuce and leafy greens growers who produce a crop in a greenhouse certainly have an inherent advantage over field growers when it comes to food safety concerns. However, it doesn’t hurt to be proactive, which is why a group of growers formed the CEA (Controlled Environment Agriculture) Food Safety Coalition.
If you missed our recent series on the coalition, get caught up here.
Any time a recall happens (such as BrightFarms’ voluntary leafy greens recall earlier this year), Marni Karlin, Executive Director of the CEA Food Safety Coalition, says we are reminded as an industry that we must always prioritize greenhouse food safety and continue to improve.
“While indoor growing significantly reduces the structural risks of contamination, indoor farms are not invincible to food safety concerns, Karlin says. “Managing food safety requires non-stop, rigorous diligence and it’s hard. Pathogens are resilient and always changing, but the U.S. food supply is extremely safe.”
As a whole, Karlin says the sector can come together to share information, which will make everyone’s efforts to keep food safe more successful.
“The CEA Food Safety Coalition was created to serve this goal, because indoor growers recognized the need to hold controlled-environment agriculture to a food safety standard that asks CEA-specific questions. The Coalition looks forward to its members choosing to be externally audited to a CEA-specific food safety addendum, further communicating to consumers that certified growers are complying with rigorous food safety standards.”
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