A shocking new method of disinfecting produce
There’s a high-tech alternative for growers looking to clean and disinfect their produce, food-processing equipment and workplaces without adding harmful chemicals to their wastewater. It looks like ordinary water and tastes like ordinary water, but the USDA, FDA and EPA have approved it for a variety of uses, including killing E. coli O157:H7, Salmonella enteritidis, Campylobacter and Listeria monocytogenes.
It’s electrolyzed water (EW), combination of clean tap water and table salt, zapped by an electric current.
“I learned about it from a colleague in Japan and decided to check it out,” says Yen-Con Hung, a professor and food scientist at the Department of Food Science and Technology at the University of Georgia in Griffin, Ga. It’s been used in the medical and dental industries in Japan for years to sterilize medical equipment, treat wounds and wash hands. In the United States, it’s used in greenhouses and nurseries to prevent the spread of diseases and fungi and to extend the shelf life of cut flowers and ornamental plants. It’s also used in chicken-processing plants.
Hung has been researching EW since 1997. His work on its effects on shell eggs, apples, lettuce and cutting boards has been published in more than 25 scientific journals, and he’s currently working on a project funded by the USDA to show how it could be used by consumers. He has also developed a process that uses the water to destroy food-borne pathogens on produce, meat and poultry.
According to researchers, electrolyzed water keeps produce free from pathogens while leaving surfaces—including hands—free of residue and wastewater free of excess chemicals, without rinsing. It’s more effective at killing bacteria on foods than bleach or heat treatments, and because it doesn’t use heat it preserves heat-sensitive nutrients and can be used on fresh fruits and vegetables. EW is nontoxic and doesn’t irritate skin or eyes. Although the tap water is mixed with salt, EW isn’t salty, Hung says, because the concentration of salt is only about 0.1 percent.
“We’re focusing on finding safe, effective, economical and practical means of controlling food-borne pathogens as food moves from the farm, through postharvest operation and onto the table at home,” he says.
According to Joe Stapley, Senior Vice President of investor relations and business development with EAU Technologies, which manufactures, leases and maintains generators that produce EW, it does work.
“We have had to prove that the technology worked unequivocally on both sides [as a disinfectant and as a cleaner],” Stapley says. “It’s tough to get it by a scientist who believes it’s just glorified chlorine, but we’ve done it.”
Generators that electrolyze water range in size from refrigerator and tabletop models to small spray bottles used by the military. They all work on the same principle, he says. When the machine is turned on, a low-voltage electric current passes through the solution of salt and tap water, separating the salt, whose chemical name is sodium chloride, into two solutions that are produced simultaneously. One is sodium hydroxide, which is very alkaline and has a pH of about 11 or 12. It can be extremely caustic, but sodium hydroxide from the generators is very mild and works like soap. It can be used to clean and degrease food processing equipment as well as wash vegetables and fruit. The other product is chlorine, the active ingredient in bleach, which has a pH of about 14. The directions on bleach bottles tell you to add water, Stapley says, because bleach reacts with water, which has a pH of about 7, and is converted to hypochlorous acid (HOCl), a much more powerful disinfectant than straight bleach. EAU creates their disinfectant solutions at an even lower pH, between 1.7 and 5.
“We’re not talking about regular bleach,” he says. “That’s a very basic, high-pH solution. It’s a killer, but nowhere near ours. We’re able to use the low pH as part of the kill.”
This acid water is such an effective disinfectant because it’s a “triple cocktail,” he says. It includes the low pH, the HOCl and a very high ORP (oxidation-reduction potential), which is the ability of a solution to oxidize a cell’s membrane and change the cell itself, making it easier to kill pathogens.
“HOCl is only one part of the cocktail,” he says. “Our solutions have a high ORP. The ORP of bleach is between 700 and 800 millivolts. Ours is 1,000 to 1,150. Nothing can survive in 1,000 ORP and above.”
“This technology is not plug and play and walk away,” Stapley says. “It’s a paradigm shift for food processing.” Electrolyzed water has a short shelf life and it has to be monitored regularly to ensure it’s at the right strength. Acid water can be stored for three to five days in a closed container, but only about one day in the open.
On the other hand, batches of EW are easy to make up, according to Hung. When you want to use it, you just push a button and you don’t have to worry about mixing concentrated liquids. Growers and food processors can use the alkaline water to clean surfaces first, and follow up with the acid water to kill pathogens, either by immersion in the water or by spraying from processing equipment or spray bottles.
Acid water has a short residual effect once it’s applied to a surface. With EW, you’ll probably have to spray more frequently than with other sanitizers and pesticides to prevent cross-contamination. Some growers might see this as a disadvantage, Hung says, but it benefits farmers because they can spray closer to harvest.
Acid water is good at increasing germination rates in greenhouses because it kills bacteria and pathogens. “You can see the difference in the health of the seedlings,” Stapley says. However, it probably won’t be cost-efficient when plants are in the ground, for two reasons: first, the environment isn’t controlled, and second, electrolyzed water can’t be combined with any other solution, including fertilizers or pesticides, so they’d have to be sprayed separately.
Another problem is the initial expense. Some processing plants will have to be retrofitted because the acid solution would most likely eat through lower-grade metals, he says.
And the generators currently cost $10,000 or more because so few are made, Hung says, but once they’re mass-produced the technology would be cost-effective. In addition, he adds, the electrodes should last between 3,000 and 5,000 hours of operation. Assuming that growers use them for four hours a day, that comes to three and a half years.
EAU’s high-volume cells will last for 15,000 hours, Stapley says, and the benefits of EW can compensate for the cost. It can extend the shelf life of produce like strawberries and tomatoes so they stay fresh in the stores longer and can be shipped farther. Growers would be able to market their produce as being free of chemical disinfectants and cleaners—and possibly pesticides.
“Here’s where I get excited,” he says. “I want these processors using our solutions on the floor, on workers’ hands, on walls, on the equipment, on produce—and they won’t have any chemicals going down the drain. All they’re left with is dirty water.”
Yen-Con Hung’s first research paper found that electrolyzed water reduced the counts of E. coli O157:H7, Salmonella enteritidis and Listeria monocytogenes from 8.0 CFU/ml (colony forming units/milliliter) to undetectable levels after just 10 minutes. (Applied and Environmental Microbiology, with Kumar S. Venkitanarayanan, Gabriel O. Ezeike and Michael P. Doyle, 1999.)
In Japan, researchers sprayed electrolyzed strong acid water on the leaves of cucumbers with downy mildew every three or four days. The incidence of downy mildew was controlled almost perfectly by the end of the 17-day experimental period, regardless of the amount sprayed. (Fundamental Studies on Crop Disease Control By Spraying Electrolyzed Strong Acid Water, by K. Doi Fujiwara and M. Shi Q-C Iimoto, Environmental Control in Biology, 1998.)
In Taiwan, researchers showed that electrolyzed water decreased the coliform count in purple cabbage, lettuce and leeks by 98 percent within minutes. The color didn’t change during 10 minutes of soaking if the surface wasn’t damaged. (Evaluation of the Washing and Sterilization of Vegetables Using Electrolyzed Strong Acid Aqueous Solution, C-C Huang, T-C Cheng, Y-R Yang, Y-H Chung and J-R Chi, Journal of the Chinese Agricultural Chemical Society, 1998.)
In Japan, researchers found that microbial contamination by spore-forming bacteria that were heat-resistant could be effectively eliminated on soybeans after being soaked in electrolyzed water for 30 minutes. The physicochemical characteristics of both tofu and soy milk were unchanged. (Eizo Tatsumi, JIRCAS Newsletter, Control of Microbial Contamination by Electrolyzed Water in Tofu Manufacturing, 2002.)
The author is a freelance writer based in Altadena, Calif.