New Treatment for Fruits Could Extend Shelf Life, Reduce Food-borne Illness

Wet steam processing of fruits has the potential to significantly reduce the incidence of food-borne illness associated with contaminated fresh-cut fruits, a new study has suggested.

Dike O. Ukuku, PhD, from the United States Department of Agriculture (USDA), Agricultural Research Service (ARS), Wyndmoor, Pennsylvania, and colleagues, published the results of their study in the International Journal of Food Microbiology.

“Wet steam processing inactivated and reduced the populations of Salmonella, E. coli O157:H7, and L[isteria] monocytogenes bacteria on contaminated whole melons and those transferred to fresh-cut pieces during fresh-cut preparation,” the authors write.

Fresh produce is exposed to microbial contamination during growth, harvesting, and processing. Indeed, according to the authors, “[f]resh fruit and vegetable produce are ranked the fourth food category responsible for food-borne illnesses in the United States, implicated in 1.2 million illness, 7,100 hospitalizations, 134 human deaths, and $1.4 billion in associated illness costs each year.”

Thus, the ability of pathogenic bacteria to adhere to surfaces of fruits and vegetables poses a food safety problem of significant concern to the produce industry. Various methods of cleaning produce—such as by using chlorine washes, hydrogen peroxide washes, hot water decontamination, and vacuum-steam-vacuum treatment—have been described, all of which typically only achieve approximately 2 to 3 log reductions of surface bacteria. There is therefore a continued need for a better way to treat the surfaces of fresh products, in order to reduce this safety problem.

With this in mind, Dr. Ukuku and colleagues conducted a study to investigate the efficacy of flash wet steam treatments in reducing bacterial populations from the surface of cantaloupes.

They initially tested cantaloupes for the presence of bacterial pathogens, and all were negative for Salmonella, E. coli O157:H7, and L. monocytogenes. Next, they inoculated cantaloupes with these three bacterial organisms, exposed the rinds to wet steam processing for 3 minutes, and then stored the treated cantaloupes at different temperatures for different periods of time.

They found that wet steam processing killed the Salmonella, E. coli O157:H7, and L. monocytogenes bacteria on the surface of cantaloupe rinds. In particular, steady application of wet steam treatment for 3 minutes at a particular spot on the surface of rind resulted in approximately 4 log reductions of each of the three bacterial pathogens.

The group also found that wet steam treatment reduced transfer of the bacterial pathogens to pieces of melon that were cut immediately after treatment. After 9 days of storage at both 4°C and 10°C, populations of these three bacteria were significantly lower in pieces of fruit that were cut from treated melons than in those from untreated melons.

In addition, Dr. Ukuku and colleagues found no visible signs of damage on treated melons, either immediately after treatment or during storage. Fresh-cut pieces of treated melon showed no signs of spoilage during storage at 5° C for up to 7 days—suggesting that wet steam treatment of the surface of melon rind before immediately cutting the fruit can slow microbial growth and extend the shelf life of fresh-cut pieces.

“This process holds the potential to significantly reduce the incidence of food-borne illness associated with fresh-cut fruits,” the authors conclude.

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.