By Jessica Knoblauch
Environmental Health News
February 24, 2009
Researchers are experimenting with x-ray technology to zap dangerous bacteria that hide in foods such as leafy greens, tomatoes, ground beef and, most recently, peanuts.
A new x-ray machine being tested at Michigan State University can reduce pathogens 99.999%, a higher percentage than traditional methods such as chlorine washes, food experts say. The technique, which uses a low-dose form of irradiation
, destroys the bacteria on delicate foods without turning them to mush.
As such methods improve, some food safety experts say irradiation is a necessary step that could prevent many illnesses and deaths tied to E. coli and salmonella. In August, the Food and Drug Administration approved
irradiation for iceberg lettuce and spinach, which have been responsible for some of the worst outbreaks in recent years. That approval is expected to open doors to more irradiated foods.
About 76 million Americans are stricken with food-borne illness each year. In the increasingly global food economy, a single head of contaminated lettuce can spread across state lines and contaminate many people.
Peanut products contaminated with salmonella have sickened more than 650 people in 44 states and killed at least nine since December. And in 2006, spinach tainted with E. coli
from one field in California caused one of the worst nationwide food-poisoning outbreaks in recent years, killing three people and sickening at least 205. A few months after that, in two separate outbreaks, at least 150 people became ill from eating iceberg lettuce at Taco Bell
and Taco John's
restaurants. As each recall is issued, consumer confidence in food safety diminishes.
Irradiation, also known as cold pasteurization, kills harmful bacteria by briefly exposing food to ionizing radiation, or short energy wavelengths. Irradiation has already been approved for use on many foods, including spices, poultry, wheat flour and ground beef. FDA officials, who have conducted irradiation safety evaluations for more than 40 years, say they have "determined the process to be safe for use on a variety of foods."
But there are many barriers to irradiating foods on a larger scale, particularly fresh produce. Some experts say it’s not ready for mass production due to a lack of major facilities. Also, irradiation is not permitted on certified organic products. And much of the public is still uneasy about buying foods that carry an international symbol for irradiation.
“The recent FDA approval for irradiating spinach and iceberg lettuce is misleading to the public because it’s not ready for industrial use by any means,” says Will Daniels, who oversees food safety at organic leafy greens producer Earthbound Farm. “There are some food items currently irradiated, but by no means are these irradiation facilities geared up to irradiate everybody’s fresh produce.”
Salmonella and E. coli 0157:H7-- involved in many of the recent outbreaks --are two of the pathogens targeted by the new technology at MSU.
The x-ray machine uses a higher dose of irradiation than medical x-ray imaging, yet less than competing irradiation methods such as gamma ray and electron beam. So far, the researchers have proved that x-rays can kill bacterial pathogens on ground beef, leafy greens and nuts.
The MSU researchers are concentrating on x-ray irradiation because most research to date has been almost exclusively conducted with gamma ray or e-beam. According to the Centers for Disease Control and Prevention, only four commercial x-ray irradiation units
have been built in the world since 1996.
“Our overall goal is not to promote a particular technology, but to give food processors the best information available so that they can decide which irradiation technology is best for their process,” Marks says.
Currently, the MSU researchers are testing their technology’s ability to kill pathogens in nuts such as walnuts or almonds, with a possibility for future work on peanuts.
Nuts, because of their high fat and oil content, tend to become rancid after irradiation. “High fat/oil products naturally become rancid over time. Irradiation could speed up that process,” Marks says, adding, “I’m not saying that it will happen, but we just need to test for that.”
Patrick Archer, President of the American Peanut Council
, says irradiation has been tested on peanuts in the past, but was “found unacceptable because it degraded the taste of the nut.”
However, MSU’s preliminary tests show no major quality problems such as rancidity, possibly due to the different nature of x-ray irradiation, which is lower energy than other methods.
To determine the proper dosage, the researchers first inject food with bacteria. The contaminated food is then put in a prototype machine that’s about the size of three home refrigerators hooked together. After the food is irradiated, the researchers count any surviving bacteria and look for physical changes in the food product.
“Our preliminary results have shown that x-ray technology is at least as effective at killing bacteria as e-beam or gamma ray, and in some cases it might be more effective,” Marks says.
A major advantage is that its low energy requires less protective shielding which means the equipment is more compact and can be installed right in the processing plants. Other irradiation methods have to be located in specialty facilities.
One downside, however, is that the x-ray can only process small quantities of food at a time, such as five-pound bags of lettuce. “You have to treat the product in single servings,” Marks says. Other technologies can irradiate food by the pallet.
Rayfresh Foods Inc
., a technology start-up company that provided MSU with an x-ray prototype machine, is looking to ramp it up to a commercial scale. Recently, the company landed its first contract to build an x-ray machine to treat ground beef for Omaha Steaks.
“We feel very strongly that if we’re going to sell ground beef, it’s going to be irradiated because that’s the highest level of food safety that we can provide to our customers,” says Beth Weiss, public relations director at Omaha Steaks
The steak company has been irradiating its ground beef since 2000, but currently the meat has to be sent on a five-day road trip to Florida to be irradiated at a separate facility. Using Rayfresh’s machine, on the other hand, will allow the process to be in-house.
Chris Schoch, the vice president of sales at Rayfresh, said the third-party testing MSU performs helps establish credibility for the technology. Schoch said irradiation is ideal for high-risk products such as ready-to-eat foods like bagged lettuce and raw nuts because there is currently no other kill step that’s as effective at wiping out bacteria.
Rayfresh has proven the x-ray process can cut pathogens like E. coli and salmonella from 100,000 microbes per product sample to one. “We have had success with complete sterilization,” says Schoch.
But irradiation is no silver bullet.
Instead, many said it should serve merely as an additional step to complement other food safety practices. “If you irradiate a product but then expose that product to other contamination risks, then irradiating the product was a waste of your time,” Marks says.
For example, irradiation probably would not have been able to prevent the recent salmonella outbreak in peanuts, where poor sanitary conditions and employee negligence were the culprits.
The public is still unsure about irradiated foods, despite the fact that some food products like spices have been irradiated since the 1900s. No radioactive substances remain in irradiated foods. Irradiation is a type of energy that disappears when the energy source is removed.
However, the public’s uneasiness could change as more foodborne illness outbreaks occur.
“After a foodborne illness outbreak, if people hear irradiation will increase safety, the majority are interested in trying irradiated food,” says Dr. Christine Bruhn, director of the Center for Consumer Research at the University of California, Davis.
Bruhn said health authorities need to take a more active role in advising the public that they can choose irradiated ground beef, poultry, spinach and lettuce and that supermarkets should offer them at reasonable prices.
Many food processors believe that irradiation is not the only answer to eliminating pathogens.
Organic producers such as Earthbound Farm are not allowed to use irradiation under the National Organics Program standards.
Earthbound Farm, which packaged the spinach responsible for the 2006 E. coli outbreak, has since put in place the industry’s most aggressive testing and safety program. Included is a process of triple-washing foods with a chlorine rinse and pathogen-testing at every step of production. In 2008, 0.14% of the leafy greens that arrived at Earthbound Farm’s plant tested positive for salmonella or E. coli and was destroyed.
Many leafy greens producers have signed onto a California agreement that verifies that growers follow food safety practices. So far nearly 120 members have signed on, representing over 99 percent of the volume of California leafy greens. Recently, the USDA expressed interest in nationalizing the program.
The peanut outbreak has also renewed interested in revamping what food safety experts believe to be an outdated food safety system. Agriculture Secretary Tom Vilsack said he supports merging the nation's food-safety system, which is currently divided into the US Department of Agriculture and the FDA, into one agency.
Meanwhile, some food safety experts maintain that any tool demonstrated to be safe and effective should be available to protect the public from harmful bacteria. Said Bruhn, “The goal is to protect the public while permitting the consumption of healthful tasty foods.”