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Making Produce Safer

Research focuses on safety of consumer-purchased produce

By Brittany P. Newman

Recent food safety scares have raised consumer concerns about the quality of store-bought produce. Media coverage that often exaggerates the seriousness of the situation has heightened the public’s sensitivity to food safety. In actuality, the U.S. food supply is safer than in years past due to improved disease surveillance and monitoring, as well as to a more rapid response on the part of regulatory and public health departments.

An important part of this system includes ongoing research, education, and outreach efforts to reduce risks from pathogens in our food sources. A thorough evaluation of production and distribution processes can identify specific food hazards and help industry find ways to eliminate them from our food supply.

For example, the Salmonella enterica outbreak associated with jalapeno and serrano peppers affected 35 states during the spring and early summer months of 2008. Initially, the outbreak was incorrectly attributed to the consumption of tomatoes. Many grocers and restaurants discontinued their sale and use of tomatoes; the United Fresh Produce Association estimates that the tomato industry lost close to $100 million. Before food safety officials identified the contamination source, consumers also began to lose confidence in Virginia’s tomato industry.

Such incidents encourage extensive research into the causes of outbreaks and the possible measures that could prevent them in the future. Food scientists at Virginia Tech are working to inform both producers and consumers about minimizing risks of food-borne illnesses.

Three faculty members in the Department of Food Science and Technology have initiated projects geared toward produce safety. Monica Ponder, assistant professor of food science and technology, focuses on the molecular interactions between microbial populations on spinach. Ponder’s research group is characterizing the microbial ecology of spinach plants to identify the particular types of naturally occurring bacteria that could compete with pathogens on the surface of spinach leaves. Her research determined that 35 species of bacteria typically found on spinach leaves inhibit growth of the pathogens E. coli and Salmonella in laboratory conditions. “The ability to identify and quantify the antimicrobial effects of these bacteria on the safety of the spinach plant holds the promise of natural controls over food-borne pathogens in fresh spinach,” says Ponder.

In addition, Ponder and Greg Welbaum, professor of horticulture, are examining whether or not seeds are vehicles for food pathogens in spinach. They are soaking seeds in a Salmonella solution to determine whether the pathogen will be translated to the leaf of the plant.

Renee Boyer, assistant professor of food science and technology and Extension food safety specialist, is studying the effect that modified-atmosphere packaging has on the survival of the pathogen E. coli O157: H7 on lettuce and spinach. The packages of bagged spinach and lettuce sold at grocery stores use a modified atmosphere to extend shelf life.

According to Boyer, samples of cut and whole leaf lettuce and spinach were maintained under normal and modified atmospheric conditions and held at 4ºC or 10ºC. Spoilage began to occur on the seventh day for the lettuce and on the ninth day for the spinach. Populations of E. coli O157: H7 survived at high levels during this time, indicating the pathogen’s ability to flourish under standard distribution conditions. “The study shows that the modified atmosphere packaging will not control or reduce populations of E. coli once they are present,” says Boyer. “This stresses the importance of preventing contamination at the farm and packinghouse level.”

Boyer is also collaborating with Associate Professor and Extension Food Safety Specialist Robert Williams to determine the effect of high-pressure processing on whole and diced red tomatoes contaminated with Salmonella. This initiative, funded in part by the Virginia Agriculture Council, involves inoculating store-bought tomatoes with Salmonella, exposing the tomatoes to three different pressures, and examining the microbial counts and quality of the tomatoes after treatment. Williams notes, “Although food safety is our primary objective, we aren’t really helping the fresh tomato industry unless we develop a process that can preserve the high quality and flavor of a fresh tomato. A safe product that tastes bad is not a viable solution.”

The researchers are also interested in the effect of high pressure on green, unripened tomatoes, and whether the pressure treatment will inactivate the enzymes that ripen the tomato. The results of this research will help determine ways for industry to make their products safer with high-pressure processing.

Although U.S. Food and Drug Administration and U.S. Department of Agriculture guidelines cannot guarantee food safety, consumers deserve the latest information about potential risks associated with store-bought produce. Producers must also educate themselves about specific handling practices that minimize the risks to consumers, including field preparation, harvest, distribution, and worker hygiene. Interventions to remove contamination from fresh produce are limited; therefore, prevention is essential.
Virginia Tech, in collaboration with Cornell University and North Carolina State University, has established the Good Agricultural Practices program, which trains farmers in ways to prevent pathogenic contamination of their food crops. Williams has conducted farm assessments on the Eastern Shore of Virginia to collect data on production practices for tomato crops. This data can provide the produce industry with updated procedures that will help reduce crop contamination and offer guidance for future regulatory measures.

In 2007, Williams participated in FDA’s Tomato Safety Initiative (TSI), a collaborative effort between FDA, Virginia Department of Agriculture and Consumer Services, Virginia Department of Health, and Virginia Tech. The project assessed tomato production and handling practices with special attention to the levels of implementation of the Good Agricultural Practices and Good Manufacturing Practices programs.

The group met at the Eastern Shore Agricultural Research and Extension Center and visited several tomato producers throughout all phases of production (planting, growing, and harvesting). The TSI group also visited packinghouses and observed washing, sorting, and packing of tomatoes. According to Williams, these visits were used to assess current fresh tomato production practices in Virginia, with the ultimate goal to strengthen Extension programs for fresh tomato producers.

Preliminary results from TSI revealed a significant need for more research in the area of fresh fruit and vegetable safety; many answers are needed before an overhaul of the production industry can proceed. However, two important recommendations have already emerged from TSI. First, due to findings that contaminated water may play a major role in the contamination of fresh produce, growers have increased their focus on water quality. Second, the industry has refocused efforts to improve the hygiene of workers who come in contact with fresh produce.