Following several recent outbreaks of foodborne illness from salad greens in the U.S., the fresh produce industry is looking for ways to more reliably ensure that its lettuce and spinach are safe for consumption.
A recent study published in the journal Applied and Environmental Microbiology examines one such method: electron-beam irradiation. Researchers from the collaborative study that included Texas A&M University inoculated samples of iceberg lettuce and baby spinach with either poliovirus or rotavirus two viruses that humans can contract from contaminated food. Electron-beam irradiation was then applied to the greens, successfully inactivating the viruses and significantly reducing the risk of infection from the contaminated samples. In fact, the risk of infection from a lettuce sample containing poliovirus was reduced from 20 percent to 6 percent, while the risk of rotavirus infection from contaminated spinach decreased from about 30 percent to 5 percent.
This is definitely a step forward, says ACSH s Dr. Ruth Kava. Before, it had only been possible to kill bacteria with irradiation; the dose necessary to kill viruses was just too high to use on leafy greens. So it s important to know that irradiation can kill viruses as well as bacteria without making the lettuce wilted and inedible.
However, ACSH s Dr. Josh Bloom points out that norovirus also known as the cruise ship virus was not included in this study, even though it is the leading cause of viral foodborne illness. There are vaccines for rotavirus, he says, and polio gastroenteritis is rare, at least in this country. Norovirus is the real problem to be addressed, and researchers will be publishing these data shortly.
And while some researchers are investigating the efficacy of irradiating viruses, others continue to look for more effective ways to eradicate bacteria from leafy greens. E. coli and salmonella are the most common concerns. Currently, most companies rinse their salad greens especially bagged salads with water that includes an antimicrobial agent, such as chlorine. But although these washes can remove most contaminants, some pathogens can remain and even spread.
Food companies are now looking for the perfect wash, and one new alternative that s shown promise is called T-128, or SmartWash. Studies have demonstrated that this compound enhances the power of chlorine when added to salad wash. Other options include biofilm disruptors that pull pathogens off of leaves, ultrasound, gaseous washes, and even cold plasma. Clearly, the damage a foodborne outbreak can do both in terms of public health and public relations has motivated industry researchers to explore a variety of possible methods.
It will be important to see what works best, and also what is the most cost-effective, because a lot of these methods are expensive, Dr. Kava observes. While certain new methods are promising, she notes, it's still a good idea to take precautions and wash fresh produce even when eating triple-washed bagged salad, since current methods to remove contaminants still are not 100 percent effective.