Making Food Safer

Agricultural research in a variety of disciplines makes food safer for consumers

Reconciling wild bird conservation with farm food safety concerns

Following the onset of several major outbreaks of foodborne pathogens traced back to wildlife, buyers of farm-fresh produce began encouraging the removal of natural habitats and nesting areas on farms to discourage wildlife intrusion.

This tactic became a preventative measure meant to reduce farmland contamination due to wildlife presence, and Olivia Smith, a postdoctoral researcher in the University of Georgia’s College of Agricultural and Environmental Sciences, began to focus her research on identifying the food safety risks posed by wild birds due to agricultural intensification — examining the various relationships between farming practices, land-use practices around farms, and crop contamination by birds.

Olivia Smith smiles while holding a bird

Olivia Smith, a postdoctoral researcher in UGA’s College of Agricultural and Environmental Sciences, focuses her research on identifying the food safety risks posed by wild birds due to agricultural intensification — examining the various relationships between farming practices, land-use practices around farms and crop contamination by birds.

With populations of birds already rapidly declining due to repercussions from agricultural intensification, removing nesting areas is particularly problematic because farmland remains an important habitat for many species of birds.

“Birds provide important insect pest control services to sustainable farmers, so removing birds makes it harder for these farmers to farm without pesticides,” said Smith. “Therefore, it is extremely important to understand how much of a problem birds are likely to be for food safety and how we might reduce that risk.”

With foodborne illness remaining a major concern in the U.S. and abroad, this in-depth research is important for harmonizing food production and wildlife conservation while preserving the general health of consumers around the globe. Despite widespread fear that birds are a major cause of foodborne illness, Smith’s studies showed only one conclusive study linking foodborne illness back to birds.

“One of the greatest challenges of our time is to figure out how to feed 8 billion people while supporting a healthy environment for future generations,” said Smith. “Bird populations have been rapidly declining, with an estimated 3 billion birds lost over the last several decades. Meanwhile, a growing body of research has shown that biodiversity provides important pest control services to farmers. Thus, it is timely and imperative to understand how to best comanage conservation, food production and food safety.”

Smith’s findings, which were published in the Journal of Applied Ecology, suggest that these natural habitats around farms should be preserved, as they may be beneficial for both food safety and wildlife conservation efforts, despite current recommendations for promoting food safety within the industry.

“We began the research to understand how much of a problem birds are likely to be for food safety for small-scale, organic farmers and how farm management and land use surrounding a farm impact that risk,” said Smith, who works with Department of Entomology Professor Bill Snyder. “It is extremely important to understand the risk wild birds pose to food safety for several reasons.”

Snyder echoed the importance of the study and the impact it will have on the food production industry and wildlife worldwide.

“Wildlife is thought to be a key threat to food safety, which has led to pressure for growers to remove natural habitats from their farms,” said Snyder. “Olivia has made a major contribution by showing the natural habitats on farms are the solution to, rather than the cause of, food safety threats posed by wild birds. This is because diversified farms attract the native bird species least likely to spread human pathogens. So Olivia has shown that there is no conflict between food safety and bird conservation — quite the opposite, as the two actually go hand in hand.” — Sean Montgomery

New method may make tomatoes safer to eat

When vegetable farmers harvest crops, they often rely on postharvest washing to reduce any foodborne pathogens, but a new University of Georgia study shows promise in reducing these pathogens — as well as lowering labor costs — by applying sanitizers to produce while it is still in the fields.

Tong Zhao is pictured in the lab

Tong Zhao, associate research scientist with the UGA Center for Food Safety, demonstrated that the preharvest application of a bactericide solution can control Salmonella, Shiga toxin-producing E. coli and Listeria monocytogenes on tomato plants.

Salmonella, Shiga toxin-producing E. coli and Listeria monocytogenes are major causes of foodborne diseases and of public health concern in the U.S. Tomato-associated Salmonella outbreaks reported to the Centers for Disease Control and Prevention have increased in frequency and magnitude in recent years, and fresh produce accounted for 21% of E. coli outbreaks reported to the CDC over a 20-year span.

Initially researchers planned to study the use of a nonchlorine-based sanitizer made of two food additives approved by the U.S. Food and Drug Administration — levulinic acid and sodium dodecyl sulfate — as a postharvest wash solution. However, at the suggestion of a producer involved in the study — Bill Brim of Lewis Taylor Farms in Tifton, Georgia — they designed the study using the solution in a preharvest spray, said Tong Zhao, associate research scientist with the Center for Food Safety on the UGA Griffin campus.

While producers commonly use chlorine-based disinfectants — including chlorine gas, sodium hypochlorite, calcium hypochlorite and chlorine dioxide — to treat produce postharvest, the preharvest application of bactericides is not a common practice, Zhao said.

Building on previous studies of levulinic acid and sodium dodecyl sulfate that showed that the combination substantially reduces both Salmonella and E. coli on romaine lettuce without adversely affecting lettuce quality, Zhao hoped to prove the combination’s effectiveness on reducing foodborne pathogens on tomato plants contaminated with Salmonella, Shiga toxin-producing E. coli and Listeria monocytogenes.

In the field studies, the spray treatment significantly reduced the total bacterial population on the surface of tomatoes, determining that this preharvest treatment is a practical, labor-cost effective and environmentally friendly approach for the control and reduction of foodborne pathogens. The study was recently published in the journal Food Control.

“This combination of chemicals had never been used for preharvest treatment,” said Zhao, who studied the combination 10 years ago as an alternative to chlorine treatment as a postharvest wash. “Free chlorine is easily neutralized by organic material, which is a big problem when you are using it to reduce pathogens.”

In both laboratory and field tests, tomato plants were sprayed all over with a solution containing five strains of E. coli, five strains of Salmonella and five strains of Listeria specially grown for the study in the lab.

Spraying tomatoes in the field

UGA research showed that the preharvest application of a bactericide solution can control Salmonella, Shiga toxin-producing E. coli and Listeria monocytogenes on tomato plants.

To test the effectiveness of the chemicals in the lab as a preventative and as a treatment, tomato plants were separated into three equal groups then sprayed with the bacteria solution. The first group was treated with acidified chlorine as the positive control, the second with a treatment solution containing levulinic acid and sodium dodecyl sulfate as the test group, and the third treated with tap water only as the negative control.

For the three plots used for farm application testing, the positive and negative control groups were treated the same way, and a commercial product — Fit-L — was diluted according to the manufacturer’s label and used as the treatment solution. Before treatment studies on the farm, two concentrations of the treatment solution were tested for safety on tomato seedlings in the greenhouse.

Results from the studies showed that the application, used either as a preventative or as a treatment, significantly reduced the populations of inoculated Shiga toxin-producing E. coli, Salmonella and L. monocytogenes on tomato plants.

In addition to being effective and affordable, preharvest treatment with levulinic acid and sodium dodecyl sulfate to reduce pathogens also saves labor costs for producers who need workers to perform postharvest washing and drying of produce before packaging.

“This method can easily be adopted using equipment that most farms are already using,” Zhao said. “Preharvest treatment is very effective, efficient and easy considering the amount of labor needed for postharvest washing.” — Maria M. Lameiras