You've probably heard of product recalls involving lettuce, spinach, or other leafy greens. Consuming these popular vegetables are among the main causes of food poisoning, affecting thousands of people every year. Leafy greens can become contaminated with pathogenic E. coli or other bacteria through splashes of soil or contaminated irrigation water in the field, or through processing and handling. Growers and processors work hard to implement multiple safety procedures, but contaminated products still slip through the cracks and reach consumers.
- Marianne Stein
A new study from the University of Illinois Urbana-Champaign looks at control measures and product testing in the produce supply chain, aiming to determine the most effective risk management strategies under a range of scenarios.
"The goal of this project is to give the produce industry a tool to estimate microbial risk and help them make decisions around food safety. We developed a framework for the model, and then demonstrated use by modeling a test case for leafy greens. That way, we could evaluate different food safety practices and the trade-offs between them," said lead author Gabriella Pinto, a doctoral student in the Department of Food Science and Human Nutrition, part of the College of Agricultural, Consumer and Environmental Sciences at Illinois.
There are other risk assessment tools available, but they are created to address specific purposes, noted co-author Gustavo Reyes. He was a graduate student in FSHN when conducting the research, and he now works as a food safety manager for Western Growers Association.
"This model is flexible and allows users to simulate different systems and potential organisms that may affect the produce environment, as well as assessing the effect of different interventions. The results can lead to improved risk management decisions," Reyes said.
The model framework includes five stages: primary production, harvesting, processing, retail, and consumer handling. At any stage, the user can estimate the possibility of contamination; increase or reduce contamination; or add product testing. The model's output measure is the risk of a product testing positive for microbial contamination when it reaches consumers.
"We chose leafy greens as a test case because they are frequently implicated in outbreaks and recalls. And the produce industry is always trying to figure out why these events are happening. Furthermore, the practices we evaluate are not only unique to leafy greens; they may be applied across many different commodities," Pinto stated.
Leafy greens such as fresh cut lettuce will usually undergo a washing process with food safe acid to reduce any microbial contamination that may be present. Processors can manage risk by improving these process controls, or by conducting product testing towards the end to prevent contaminated products from going out to consumers.
"We wanted to put those two approaches side by side and assess which would be better at managing risk under different contamination scenarios," Pinto said.
The researchers found that improved process controls (washing) provided a greater reduction in the overall risk of a positive test at retail (a proxy for recall risk) than additional product testing at the end of processing. They conclude that although product testing at the end of processing does reduce public health and recall risk, this is at the expense of rejecting many lower-risk lots. When contamination is detected, the entire product lot is discarded; however, high-level contamination events that drive both recall and public health risks are rare.
"The model doesn't tell you exactly how much microbial reduction you would see from these strategies, but it allows you to make relative comparisons in order to better guide your management decisions, and that's very valuable for the industry. Our work helps growers and processors divert resources where they can make the most meaningful difference," Reyes said.
The researchers have created an interactive webpage, SCRM-Lite, that gives outside users a way to explore the published test case contamination scenarios and intervention strategies.
"Food is produced mostly outside, in open systems that are in nature, so we're never going to get to a food system with zero risk of contamination. People are working on both preventing contamination and processing methods that reduce it," said Matt Stasiewicz, associate professor in FSHN and corresponding author on the paper.
"We're not going to find the perfect method that sterilizes every product, so we need to come up with a menu of options and then find the practices that work best. A lot of what we work on in my lab is thinking about risk, better decision making, and how we can use modern computation for risk modeling. "
The paper, "Development of a flexible produce supply chain food safety risk model: Comparing tradeoffs between improved process controls and additional product testing for leafy greens as a test case," is published in the Journal of Food Production [DOI:10.1016/j.jfp.2024.100393]. Funding was provided by The Center for Produce Safety project 2023CPS08.
