Irradiation may help control pathogens associated with fruits, vegetables.

We have linked foodborne pathogens to a variety of fruits, vegetables and juices. It is often difficult or impossible to wash pathogens off the produce or inactivate them by using chemical treatments. The pathogens may be located in inaccessible areas, or they may have penetrated the product.

Ionizing radiation can penetrate the entire product and inactivate pathogens that have contaminated the food. While pasteurizing some products, such as juices, involves the use of heat and may alter their flavor, ionizing radiation may offer an alternative that doesn't change a product's flavor.

Several studies have been undertaken in the past on the irradiation of seeds to control plant pathogens. But relatively little work has been done to control foodborne pathogens on fresh foods. Recently though, ionizing radiation was used to eliminate E. coli O157:H7 from apple juice, T. gondii and C. cayetanenis from raspberries, and E. coli O157:H7 and Salmonella from seed and sprouts.

Research is ongoing in several countries to determine techniques for controlling foodborne pathogens that are associated with fresh fruits, fruit juices, freshly cut vegetables or salads, sprouts and seed. Combining irradiation with other processes, such as chlorination, appears to hold potential for combating the problem.

In contrast to extensive studies on irradiation for controlling pathogens on meat and poultry products, there have been few studies on the value of ionizing radiation for eliminating foodborne pathogens on or in fruit juice, fruits, vegetables and seed used to grow sprouts. Such leafy vegetables as lettuce have been considered not suitable for irradiation treatment because of phytotoxic damage that occurred during early studies with high-dose irradiation intended to produce a sterile product.

Modified atmosphere packaging (MAP) systems often find use in extending the shelf life of sprouts and precut salads. But both have been linked to outbreaks of foodborne disease caused by E. coli O157:H7, Salmonella and L. monocytogenes. Treating product with disinfectants has not completely eliminated these pathogens from seeds. They also have not been very effective in decontaminating sprouts that may be internally contaminated and which probably won't respond well to chemical decontamination efforts.

Basic studies are needed for fresh produce, including those determining optimum harvest times, specific varieties that best withstand treatment with radiation, the doses required to inactivate common pathogens, the variables that may alter the percentage of bacterial killed and interactions of radiation injury of the pathogen with other treatments, we're told.

The irradiation of grain, fruits and vegetables is approved in the United States by the FDA to a maximum dose of 1 kGy for disinfestation. Fruits and vegetables also may be irradiated to inhibit sprouting and to alter the rates of maturation to obtain longer shelf life. The current regulations do not include the use of irradiation to control foodborne pathogens on fruits and vegetables.

Further information. Donald W. Thayer, USDA/ARS, Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038; phone: [phone]; fax: [phone]; email: [e-mail].