Washing, sanitizing techniques to make produce safer.

Several outbreaks of food poisoning in recent years have been linked to cantaloupes, sprouts, lettuce, tomatoes and other fresh produce. Conventional commercial washing and sanitizing methods that remove microbial contaminants from produce surfaces are marginally effective.

USDA-ARS scientists are conducting experiments to understand how these microorganisms survive and grow on produce surfaces even after exposure to sanitizing solutions. Understanding how microbial contaminants survive during washing and sanitizing will help researchers develop new technologies for removing or inactivating microbes on fresh and minimally processed produce. Researchers are trying to obtain a patent covering the equipment used in their treatment and are signing a cooperative agreement with industry in order to validate the technology.

Salmonella usually is behind produce-related outbreaks of foodborne illness. It's an important concern in ensuring microbiological safety of fresh-cut cantaloupe. The bacteria quickly cling to the rind and form a biofilm. Then, Salmonella cells present on the rind can be transferred to the melon's internal tissues when it is cut.

Salmonella cells produce fimbriae (hairlike structures) and cellulose that help them attach, colonize and survive on the melon's surface. Once attached to the outside of the rind, the cells grow and excrete polymers, forming the biofilm that shields the bacteria from harsh sanitizing solutions. Researchers will collaborate with scientists at the University of Navarra, Spain, to determine how Salmonella cells develop fimbriae as they grow, and how they use them to cling to surfaces. They will also determine the role of specific bacterial polymers involved in surface attachment and biofilm formation by using Salmonella cells that are defective in producing fimbriae or cellulose.

Scientists recently developed a commercial-scale surface-pasteurization treatment that resulted in a 5-log (99.999%) reduction in a population of S. poona on the surface of artificially contaminated cantaloupe. The process involves immersing melons in water at 169 F for 3 minutes to kill the pathogens, then sealing each melon in a plastic bag before rapidly cooling it in ice water. The plastic bag prevents the fruit from potential recontamination in the cold water. The treatment not only enhances the safety of the fruit, but also extends its shelf life by reducing native microflora that may cause spoilage. And the process does not harm melon quality.

Further information. Bassam Annous, USDA-ARS Food Safety Intervention Technologies Research Unit, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038; phone: [phone]; fax: [phone]; email: [e-mail].