Cantaloupes—scrubbing the rind may not wash away contamination

photo of cantaloupe in a bowl

Seems impossible that bacteria could get past that thick rind and into the fruit. Surely a good scrubbing is enough… WRONG!

UNEXPECTED: Salmonella-contaminated cantaloupes have killed two people and sickened more than a hundred in 20 U.S. states, according to the US Centers for Disease Control and Prevention (CDC). Per CDC recommendations, “consumers who recently purchased cantaloupes grown in southwestern Indiana are advised not to eat them and discard any remaining cantaloupe. … Washing them will not completely eliminate the contamination. Cutting, slicing and dicing may also transfer harmful bacteria from the fruit’s surface to the fruit’s flesh.”

OK, this makes sense. This morning on Good Morning America, Dr. Richard Besser, ABC News’s Chief Health and Medical editor, said pretty much the same thing. Dr. Besser was at one time the acting director of the CDC.

But despite all the media focus on cantaloupes and Salmonella, nobody is talking about how salmonella can get inside a cantaloupe before it is ever cut open. But Chuck Schuster, Montgomery County horticulture extension educator for the University of Maryland Extension, explained it at one of the classes that Barry and I took this year. The class was called “Starting a Second Career in Local Food—Commercial Food Production and Marketing for the New Farmer on Small Acreage.” I think of it as our “Beginning Farmers” classes. The information stuck in my mind because I always thought I could scrub away contamination on a melon.

Chuck told us that commercial growers of cantaloupes cool the melons after they are picked and brought in from the fields. One of the cooling methods is to dunk the melons in cold water with disinfectant. Sounds OK. But the rind of a melon is somewhat porous, and the recently broken area where the stem was attached is like a fresh wound (cantaloupe stem scars may pro­vide a potential route for entry of human pathogens to the edible flesh of melons1). When you dunk a warm melon that has been sitting out in the sun (and just happens to be contaminated with Salmonella or e coli) into cold water, water is absorbed into the melon through the stem scar, along with any contaminants that are on the rind or in the water. Bacteria may also continue to multiply on the rind, given suitable temperatures during shipping and storage.

An explosive situation occurs when the internal portions of the melon are exposed to Salmonella from the external surfaces. Melons provide a rich source of nutrients for bacteria, along with more than adequate moisture. If conditions of temperature are hazardous (above 41° F and below 135° F), bacterial multiplication will occur, and this can be very rapid in the range of 70° F to 120° F.2

So it’s not enough to just scrub your melons. The solution may be for growers to implement a brief hot water bath—three minutes at 168°—according to U.S. Department of Agriculture microbiologist Bassam Annous, Ph.D. This surface pasteurization treatment eliminates 99.999 percent of salmonella bacteria3 and does not damage the flesh.

Sources:

1) US FDA Guidance for Industry: Guide to Minimize Microbial Food Safety Hazards of Melons; Draft Guidance

2) Food Safety News, Melons Stand Out As Produce Safety Problem

3) Food Safety News, Hot Water Bath Eliminates Pathogens on Cantaloupe

JOURNAL OF FOOD SCIENCE, Vol. 71, Nr. 2, 2006, Thermal Inactivation of Salmonella on Cantaloupes Using Hot Water (2.8 MB PDF)

This entry was posted in The Unexpected. Bookmark the permalink.