Image edited with the permission of Adam Simpson
Following the major Cyclospora outbreak linked to iceberg lettuce, consumers might assume that produce labeled “triple-washed” offers greater protection from foodborne illness.
But industrial washing cannot necessarily eliminate pathogens already established on produce. At the same time, the disinfectants used during processing may react with the food itself, creating new compounds whose effects on human health are not yet fully understood.
That hidden chemistry is the focus of research led by Adam Simpson, assistant professor in the Sonny Astani Department of Civil and Environmental Engineering at the USC Viterbi School of Engineering.
“Food processing is an engineered unit process, similar to processes in heavy industry,” Simpson said. “If we manipulate the matrix, we may transform its chemical groups and incorporate chemicals into the food.”
Looking beyond chemical residues
Food-safety testing commonly looks for known contaminants, such as pesticides or PFAS, on a food’s surface or within its tissues. Simpson instead investigates “transformation products”: new compounds created when processing chemicals react with proteins, fats and other components of food.
The organization of those components is known as the food matrix. Its structure determines how a disinfectant enters the food, which molecules it encounters and what reactions follow.
Simpson began studying these reactions during his doctoral research, examining triple-washed vegetables and the chlorinated water used to disinfect meat. He found that chlorine can alter amino acids and fats, forming compounds known as chlorotyrosines and fatty acid chlorohydrins.
Because these compounds can remain bound within proteins and fats until digestion, tests designed to detect dissolved contaminants or surface residues may miss them.
In a recent study published in the Journal of Hazardous Materials, Simpson and his research team examined fatty acid chlorohydrins formed when tree nuts are bleached with sodium hypochlorite, the active ingredient in many chlorine-based disinfectants. They also tested the compounds’ effects on cells.
The results identified a potential hazard, to consumers. Researchers must still determine how the body metabolizes it and whether these exposures cause long-term health effects.
Through a pilot collaboration with the Southern California Center for Chronic Disease Research and Prevention, Simpson’s lab is now working with Ana Claudia Maretti-Garcia, assistant professor of research medicine at the Keck School of Medicine of USC. The researchers are testing synthesized fatty acid chlorohydrins on hepatocytes, the liver’s primary functional cells.
“We want to know how these compounds affect the consumer,” Simpson said. “We do basic toxicology in our lab, but now we want to move toward medical research.”
Different foods, different reactions
Simpson’s research also shows that disinfectants do not interact with every food in the same way.
In another recent study, his team examined chlorine treatment in chicken, beef, fish and raw milk. The researchers expected treatment to increase chlorotyrosines and fatty acid chlorohydrins, as earlier studies had found in vegetables.
Instead, meat and fish already contained substantial amounts before treatment, and standard chlorine doses added little. The compounds may also form through immune responses while animals are alive, a pathway plants do not share.
The unexpected result shows why findings from one food cannot automatically be applied to another. How food is prepared can change the chemistry further. Cutting or shredding produce ruptures plant cells, releasing organic matter that reacts with chlorine. This can leave less disinfectant available to control pathogens while increasing reactions that produce chemical byproducts.
Industrial washing remains valuable because it can prevent microbes released from one item from spreading through processing water. But it is less effective against pathogens already present in produce. Cyclospora, for example, resists the chlorine concentrations commonly used in processing.
“Triple washing is effective at preventing cross-contamination, and the mechanical action of the water probably helps remove debris,” Simpson said. “But if a head of lettuce is already contaminated with a high load of pathogens, it is highly unlikely that triple washing will completely inactivate them. Prevention has to start at the farm.”
The “triple-washed” label also does not describe a standardized process. Chemicals, concentrations and contact times can vary among processors and products.
Balancing known and potential risks
Simpson recognizes that processors must balance the possible long-term effects of transformation products against the immediate danger of foodborne disease. He questions that calculation, however, when chemicals are used primarily to alter a food’s appearance.
“I can understand balancing the risk of pathogens against the chronic risk of these byproducts, because the yields are very low,” Simpson said. “But the industry is also bleaching tree nuts, whey protein and many other foods with chlorine and similar oxidants for aesthetic purposes that have no nutritional value.”
Simpson is not advising consumers to avoid fresh produce. He recommends washing produce and choosing whole foods when practical, without allowing cost or convenience to become barriers to a healthy diet.
“Eating washed, organic or nonorganic fresh produce is better than not eating vegetables at all,” he said.
The objective of his research is not to declare processed foods unsafe, but to understand an overlooked aspect of food production: what happens when chemical oxidants used during processing become incorporated into the food’s chemistry, leaving what he calls a “hidden chemical memory.” Ultimately, Simpson aims to make these processes safer, reducing potential health risks while preserving the benefits of both fresh and processed foods.
Published on September 10th, 2026
Last updated on September 10th, 2026