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A Closer Look at Produce Washes

Edited by: Mary Schroeder, M.S., R.D. & Pat Kendall, Ph.D., R.D., Colorado State - Winter/Spring 2005

Fresh and fresh-cut fruits and vegetables, traditionally considered "low risk," are becoming more of a food safety concern. Produce items associated with foodborne outbreaks in recent years have included berries, cabbage, cantaloupe, lettuce, raw sprouts, tomatoes and watermelon. Fortunately, consumers are getting the message that it is important to wash fruits and vegetables before eating. The term "wash", however, can have very different meanings even among the experts in the field.

What NOT to Use
Although fruit and vegetable processing plants routinely use chlorine as an effective antimicrobial agent in their produce washing operations, the amounts used and timing are carefully controlled to ensure safety. For consumers, use of detergent or laundry bleach for cleansing fruits and vegetables is highly risky. Fruits and vegetables are porous and can absorb the soap or bleach, which are not approved or labeled by the Foods and Drug Administration for use on foods. Therefore, these products should NEVER be recommended for home use in cleaning foods.

Running Water - the Reliable Standard
The U.S. Department of Agriculture recommends that consumers simply "rinse fresh fruits and vegetables well under running water prior to eating." More specifically, the University of Minnesota provides these tips on washing fresh produce:

• Before working with any foods, wash hands with soap and water. Also, make sure preparation areas are sanitary.
• Under clean, running water, rub fruits and vegetables briskly with your hands to remove dirt and surface microorganisms.
• Wash produce just before serving - not before storing, as washing will cause produce to spoil faster.
• Produce with a firm skin or hard rind like carrots, potatoes, melons or squash may be scrubbed with a vegetable brush and water.
• Discard the outer leaves of leafy vegetables such as lettuce and cabbage before washing.
• Always wash squash and melons, even if you don't eat the rind or skin because when cut, dirt or bacteria that is on the outer surface can be transferred to the inner flesh.
• DO NOT wash produce with detergent or bleach solutions. Fruits and vegetables are porous and can absorb the detergent or bleach, which is not intended for use on foods and consuming them on fruits and vegetables have the potential to make you sick.

Commercial Produce Washes
Several studies have looked at the effectiveness of produce washes. In most cases the produce washes have been found to be "equally effective or "slightly better" than tap or distilled water in removing microbes and pesticide resides. For example, in a study conducted at University of California-Riverside, one group of produce was washed with plain tap water, the second rinsed with both water and produce wash, and the third was not rinsed at all. The combined treatment of produce wash followed by water rinse reduced surface pesticide residues by 6% more than the water alone method, a difference too minor in the researcher's opinion to justify the purchase price of a produce wash.

Some produce washes recommend soaking the fruits and vegetables in the wash solution. This can be problematic if the water becomes contaminated. Also, prolonged soaking of fruits and vegetables in wash solutions can damage produce quality and contribute to nutrient losses. Because rinsing in tap water alone is still highly effective, most researchers agree that it comes down to personal preference as to whether produce washes are worth the purchase price.

Vinegar and Lemon Juice Treatments
A few studies have evaluated the effectiveness of vinegar and lemon juice (weak organic acids) as anti-microbial and anti-browning agents. In controlled studies, the best results in microbial reduction have been achieved when use of organic acids were combined with other treatments, such as a water rinse and/or agitation. In one such study, apples were spot inoculated with Salmonella enterica, wetted with 1 teaspoon of water or vinegar (5% acetic acid), rubbed for 5 or 30 seconds, rinsed with water, and dried with a paper towel. Dipping in vinegar, followed by rubbing for 5 seconds, rinsing with running water, and drying with a paper towel resulted in a reduction of 5.2 to 6.2 log CFU per apple, which was significantly (p<0.05) larger than reductions achieved with water washing alone (3.1 log CFU per apple).

Another study evaluated the effectiveness of household products, including lemon juice and vinegar, in reducing levels of E. coli on iceberg lettuce. E. coli reductions were 2.1 log CFU/g when inoculated lettuce samples were exposed to 13% lemon juice and 2.6 logs CFU/g when samples were exposed to 13% lemon juice and agitation (10 min.). The authors concluded that 13% lemon juice was significantly (P<0.05) more effective when combined with agitation.

Cold Storage
An additional factor in controlling bacterial populations on fresh produce is cold temperature storage. Studies have continued to show that cold storage slows the growth of pathogenic bacteria. For example, Salmonella Montevideo grew on tomatoes stored at 20 and 30ºC but not at 10ºC (Zhaung et al., 1995). Listeria monocytogenes grew well on fresh-cut cabbage and onions stored at 10ºC but not at 4 ºC (Farber et al., 1998) and Escherichia coli O157:H7 grew on fresh-cut melon at 12-25ºC but not at 5ºC (41ºF) (Del Rosario and Beuchat, 1995).

There is a need to continue exploring new methods to remove, inhibit and /or destroy pathogens on fresh and minimally processed fruits and vegetables. Consumer recommendations are likely to change as new treatments for produce washing are evaluated. The American Dietetic Association's Home Food Safety website offers general tips in Keeping Produce Safe.

1. Food Safety and Inspection Service (FSIS); United States Department of Agriculture. Food Safety Features. Does Washing Food Promote Food Safety? July 1999. Available at www.fsis.usda.gov/OA/pubs/washing.htm
2. Produce Washes Effective at Removing Pathogens. Center for Food Safety. University of Georgia. Available at www.griffin.peachnet.edu/cfs/hottopics/producewashes.html
3. Brackett, R.E. 1992. Shelf stability and safety of fresh produce as influenced by sanitation and disinfection. J Food Prot. 55: 808-814.
4. DeRoever, C. 1998. Microbiological safety evaluations and recommendations on fresh produce. Food Control. 9:321-347.
5. Parnell, T.L. and L.J. Harris. 2003. Reducing Salmonella on apples with wash practices commonly used by consumers. J Food Prot. 66 (5): 741-747.
6. Zhuang, R.Y., L.R. Beuchat and F.J. Angulo. 1995. Fate of Salmonella Montevideo on and in raw tomatoes as affected by temperature and treatment with chlorine. Appl. Environ. Microbiol. 61:2127-2131.
7. Del Rosario, B.A. and L.R. Beuchat. 1995. Survival and growth of enterohemorrhagic Escheria coli O157:H7 in cantaloupe and watermelon. J Food Prot. 58:105-107.
8. Farber, J.M., et al. 1998. Changes in populations of Listeria monocytogenes inoculated on packaged fresh-cut vegetables. J Food Prot. 61: 192-195.



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