Remember the 2011 outbreak of listeriosis traced to cantaloupes from Colorado? Thirty-three people died, making it the second deadliest recorded U.S. foodborne disease outbreak since the CDC began tracking outbreaks in the 1970s.
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Such killer produce catastrophes could be history, courtesy of a nisin-EDTA (ethylenediaminetetraacetic acid) based sanitizing wash developed by Dike Ukuku, PhD, a food technologist at the USDA Agricultural Research Service Food Safety and Intervention Technologies Research Unit, Wyndmoor, Penn.
Dr. Ukuku demonstrated that his landmark solution, which contains specific short chain organic acids, rids cantaloupes, honeydew melons, and other produce of bacteria that migrate to cut pieces of the fruit.
“We found that our solution works better than chlorinated water or hydrogen peroxide at ridding surface bacteria from produce,” he reports.
Because the wash worked so well, Dr. Ukuku named it “Lovit.”
Nisin is a polycyclic antibacterial peptide produced by the bacterium Lactococcus lactis used as a food preservative. In particular, nisin is used in processed cheese, meats, beverages, etc. during production to extend shelf life by suppressing Gram-positive spoilage and pathogenic bacteria.
Specifically, while in general most bacteriocins inhibit only closely related species, nisin is a rare example of a “broad-spectrum” bacteriocin effective against many Gram-positive organisms, including lactic acid bacteria (which are commonly associated with spoilage), Listeria monocytogenes (a known pathogen), Staphylococcus aureus, Bacillus cereus, Clostridium botulinum, etc. Nisin is also particularly effective against spores.
EDTA is a colorless, water-soluble solid that is widely used to dissolve limescale. It can be a chelating agent, with the ability to sequester metal ions. After being bound by EDTA, metal ions remain in solution but exhibit diminished reactivity.
In his study, Dr. Ukuku inoculated the rinds of cantaloupes with E. coli, Salmonella, and Listeria. He washed them for 5 minutes in either Lovit, hydrogen peroxide, or chlorinated water (at 1,000 milligrams/liter). He allowed the rinds to dry before cutting them into pieces. He then stored some pieces from each of the treatments in plastic tubs with covers at room temperature (68 degrees Fahrenheit) for 24 hours, and others at chilled temperatures of either 41 or 50 degrees Fahrenheit for 15 days.
The results showed Lovit to be the most effective treatment of the three different washes, and it reduced pathogen levels to below detection levels required by food safety standards.
“The nisin-based sanitizer prevented transfer of bacteria from melon rind surfaces to fresh-cut pieces, and the populations in fresh-cut pieces were below detection even by enrichment,” Dr. Ukuku elaborates.
In the fresh-cut cantaloupe pieces washed with chlorinated water, only Salmonella was found (0.9 log CFU/gram), whereas E. coli O157:H7 and L. monocytogenes were positive only when fresh-cut pieces were enriched to encourage recovery of injured or undetectable cells, Dr. Ukuku reports, noting that the results with chlorinated water treatments were similar to hydrogen peroxide treated melons.
“The results of this research indicate that Lovit is a better sanitizer for inactivating bacteria on melon rind surfaces than chlorine.” Dr Ukuku says. “Its use holds promise to reduce the number of foodborne illnesses caused each year by E. coli, Salmonella, and Listeria from fresh-cut produce.”
The study, “Efficacy of Sanitizer Treatments on Survival and Growth Parameters of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on Fresh-Cut Pieces of Cantaloupe During Storage,” was published in the Journal of Food Protection in July 2015.