Aug 22, 2003 (CIDRAP News) Supporters of irradiation as a tool for preventing foodborne disease are dismayed by a generally negative evaluation of irradiated meat in the August issue of Consumer Reports.
"There's no real reason to [buy irradiated meat] if you cook meat thoroughly," the article says. "Irradiation actually destroys fewer bacteria than does careful cooking." In addition, Consumer Reports taste tasters found a "slight but distinct off taste and smell" in irradiated beef and chicken servings they sampled.
The report says the magazine's microbiologic tests showed that irradiated raw ground beef and chicken had much lower bacteria counts than nonirradiated meat did, but some bacteria remained. The writers also mention recent European research suggesting that 2-alkylcyclobutanones (2-ACBs), chemicals found in irradiated meat, may promote tumors in laboratory rats.
Public health professionals who support irradiation say the article ignores the reality that many people don't handle and cook meat properly. "They say that it's [irradiation] not necessary for a careful cook, but the bottom line is that most people are not careful cooks. And we see that again and again with the people who get sick," Minnesota State Epidemiologist Dr. Harry Hull told CIDRAP News.
In addition, irradiation experts like Michael T. Osterholm, PhD, MPH, charge that the article seriously understates the benefits of irradiation. They say the article wrongly suggests that irradiation at permitted doses is not very effective because it doesn't kill all bacteria in meat. The article also underplays the potential role of irradiation in preventing the most serious foodborne illnesses, in Osterholm's view. Osterholm, director of the University of Minnesot's Center for Infectious Disease Research and Policy, which publishes this Web site, critiqued the article in a recent letter to Consumer Reports.
Irradiation proponents take issue with the article on several other counts as well. The report, they contend, largely ignores the weight of scientific literature over the past 50 years demonstrating the safety of irradiated food. They also say the report's discussion of 2-ACBs leaves out crucial information supporting the safety of irradiated meat, including evaluation of the 2-ACB research by food safety authorities.
Further, irradiation supporters found the information about the taste tests too sketchy to be convincing. They say most taste tests have found no significant off taste or smell in irradiated meat. And, among various other objections, they critique the magazine for not reporting levels of most of the specific human pathogens in irradiated and nonirradiated meat.
Consumer Reports officials defended their article, titled "The Truth About Irradiated Meat," as an accurate and unbiased report on the subject. Geoffrey Martin, PhD, director of consumer sciences at the magazine, responded by e-mail to a CIDRAP News summary of the points made by irradiation supporters and provided more information on how the taste tests were conducted. In addition, Julia Kagan, vice president and editorial director of Consumer Reports, responded to some of Osterholm's criticisms in a reply to his letter. Following is a report on the main criticisms of the article and the responses from the magazine.
The disease-preventive benefits of irradiation
The article acknowledges that irradiation reduces the risk of illness from eating ground beef. It states that because irradiated meat has much lower levels of bacteria than nonirradiated meat, "It may reducebut not eliminatethe risk of illness if your food is undercooked." The article further states, "Used in institutions such as cafeterias, irradiated meat could help reduce widespread foodborne illness, some experts predict. That's worth knowing if you are among those, such as the immunocompromised, at greatest risk from foodborne illness or if you want an extra measure of safety." The magazine goes on to note that irradiation at approved doses "doesn't wipe out all bacteria in meat," a task that would require much higher doses, which would change the taste.
The article quotes an estimate by Robert Tauxe, a foodborne disease expert at the Centers for Disease Control and Prevention, that irradiating half of all ground beef, poultry, pork, and processed meat would prevent 900,000 illnesses and 350 deaths in the United States each year. On the other hand, the report says, other experts worry that some retailers' promotional statements about irradiated meat give consumers a false sense of security and that irradiation "takes the focus off preventing contamination in the first place."
Osterholm said the statement that irradiation doesn't kill all bacteria in meat is misleading because it implies that irradiation must sterilize meat to be effective. The purpose of the process is not to sterilize meat, but to kill or inactivate specific pathogens that could be present, just as milk pasteurization kills pathogens while permitting some harmless bacteria to survive, he asserted. "At no time do we attempt to sterilize meat with a pasteurization process," he wrote.
In response, Kagan wrote, "We never suggest it [is] necessary to 'wipe out all bacteria in meat.'" She said one purpose of the report was to investigate advertising claims about irradiated meat, including one supermarket's claim that irradiation eliminates all bacteria. She continued, "Our tests showed that while bacteria levels were generally lower in irradiated meat, irradiatioin didn't kill all bacterianor did it kill all pathogenic bacteria. In one sample of irradiated, nonfrozen ground beef, we found evidence of the pathogen Listeria monoctyogenes."
Osterholm also criticized the article's use of Tauxe's estimate of the preventive benefits of irradiation. By itself, the statement that irradiation could prevent 6% of foodborne illnesses underrates the benefits, because irradiation targets the most serious illnesses, he contends. For example, more than 40% of all foodborne illnesses are minor ones caused by noroviruses, usually spread to food by infected workers who prepare or serve it. "By far, the most serious infectious agents that we encounter with foodborne disease in this country are caused by the very pathogens that are routinely eliminated with the use of food irradiation, such as Listeria monocytogenes, E. coli O157:H7, Salmonella, and Campylobacter," Osterholm wrote. Irradiation wouldn't prevent norovirus cases because it is applied before the food preparation stage, but it would prevent many of the serious illnesses, he said.
Kagan did not comment on this point in her reply to Osterholm.
Further, Osterholm asserted that irradiation is significantly more effective than such low-tech measures as spraying beef with lactic acid before grinding. The Consumer Reports article says that step has been shown to eliminate 99.9% of E coli O157:H7 in spiked beef samples. According to Osterholm, irradiation effects an average 5-log (99.999%) reduction in pathogens, a 100-fold improvement over the spray treatment. This difference is significant, he wrote, because many outbreak investigations have shown that extremely low doses of E coli O157:H7fewer than 10 cells per gram of meatcan cause illness.
"Short of pasteurization (i.e., 5-log reduction in pathogen levels), we will never be able to assure the public of a safe red meat product," Osterholm wrote.
However, Kagan said Consumer Reports' tests did not show a 5-log difference in bacteria levels. "In our tests, we did not get results that approached a five-log difference between the irradiated and nonirradiated samples we acquired at retail or at the FTS plant," she wrote. "We found differences of about two logs or less for all enumerated test organisms, and suggest that claims for higher levels of bacterial inactivation may be misleading to consumers."
Overall scientific support for the safety of irradiated meat
The article says that between 1964 and 1992, five expert committees convened by the United Nations evaluated the literature and concluded that irradiated foods are safe to eat. However, it gives no details about the number or kinds of studies that have focused on irradiation safety.
Chris Sommers, PhD, the lead scientist in the US Department of Agriculture's (USDA's) food irradiation research program, found some good points in the article but felt that it would give most readers a negative view of irradiated meat. "I'd have concern that the layperson reading the article would conclude that irradiated foods are harmful in some way, which has not been indicated by approximately 45 years' worth of safety studies pertaining to irradiated food," Sommers told CIDRAP News. He works at the USDA's Eastern Regional Research Center in Wyndmoor, Pa.
In studies since the 1950s, animals including rats, mice, dogs, primates, and guinea pigs have been fed irradiated foods for up to three generations without showing any ill effects, Sommers said. He added, "In many countries human tests have been conducted using irradiated foods. So there is a huge literature base on the safety of irradiated foods."
Martin, in reply to the assertion that the article largely ignored the scientific record on irradiation safety, said, "Our article states that federal and world health officials say irradiated food is safe to eat. We never say otherwise."
Research on 2-ACBs
The Consumer Reports article says recent European research suggests that 2-ACBs, "unique byproducts created by irradiating fat in a food such as ground beef, may act as tumor promoters in laboratory rats. Authors of the report [on the European research] . . . say their findings show the need for further study. Meanwhile, the European Parliament in December halted new approvals of irradiated foods going to member nations of the European Union pending more safety studies." The magazine also notes that the Food and Drug Administration is reviewing the 2-ACB studies.
Sommers called this version of the 2-ACB question incomplete and misleading. "The European Commission released a statement after reviewing the data, in which they said they basically could not support the conclusions of those studies," he said. "Also, Health Canada reviewed the work on ACBs and their conclusion was that the conclusion of the authors that the ACBs were potentially toxic could not be supported."
Sommers added that the USDA recently conducted toxicologic tests on ACBs and found no evidence that they cause mutations or chromosome damage. One report on that research is currently in review and another is still being written, he said. "The cyclobutanones are a very, very old story," he added. "[In] all of those feeding studies, all of those foods by definition contained cyclobutanones, and again there were no adverse effects."
Hull commented that the research on 2-ACBs "has to be put in context with all the chemicals produced by cooking as well as other forms of food preservation." Some compounds produced by cooking, especially barbecuing, pose a risk of cancer, and there may be compounds in cooked food that are still unknown, he said.
In addition, Henry Delincee, one of the authors of the European studies on 2-ACBs, has warned against using the findings to argue that irradiated foods are unsafe. In a statement to the Minnesota Beef Council and available on the council's Web site, Delincee said the studies used purified 2-ACBs in high concentrations, not irradiated foods containing many complex components. Consequently, the studies do not justify any conclusions about the safety of irradiated foods, he said. "In my viewand this is also the opinion of WHO and other international and national organizationsthe benefits far outweigh the risks," Delincee said. Delincee made the points in response to statements from the consumer group Public Citizen, which has cited the European studies in statements opposing food irradiation. Osterholm's letter to Consumer Reports also cited Delincee's statement.
Martin rejected the assertion that Consumer Reports' treatment of the 2-ACB issue was incomplete. He said, "We believe it important that our readers know of the latest research concerning 2-ACBs. To that end, we accurately characterized that research, and the scientists' recommendation that more research is needed on the topic. We also accurately characterized the action of the European Parliament on the matter."
Kagan's letter echoed Martin's statement that consumers need to know about the research on 2-ACBs. She added, "Nowhere in the article did we include Public Citizen's interpretation of the research; hence, there was no reason to include the comments of the researcher concerning Public Citizen's interpretation."
Negative taste-test results
Consumer Reports asked trained taste testers to sample 72 pairs of irradiated and nonirradiated ground beef and chicken samples after they were cooked according to package directions. The beef samples had similar leanness. In all but six pairs, the testers could identify the irradiated meat, "describing it as having a slightly scorched taste and a smell reminiscent of singed hair," the article states. But the taste was described as subtle enough that some people might not notice it.
Critics of the report say it doesn't give enough details about how the taste tests were done. For example, Hull said he wondered if the pairs of beef samples were really the same in fat level and other characteristics. Others have questioned whether the reported differences achieved statistical significance. And Osterholm questioned the appropriateness of using trained taste testers, since they would be more likely to detect very slight changes in taste that average consumers wouldn't notice.
Irradiation supporters also contend that most published taste studies have not found a significant off taste in irradiated beef. "There's a great deal of literature on the palatability of irradiated ground beef, and at the doses these products are being irradiated to, there should not be any problem with any off odors or off flavors," said Sommers. "I was actually very surprised to see any complaints concerning that." He said excessive doses of radiation would change the taste, but that should not have been the case with commercial products.
Supporters also find the report at odds with their own experience. For example, Kirk Smith, DVM, PhD, supervisor of the foodborne disease unit at the Minnesota Department of Health, said he has never noticed an unusual taste in irradiated ground beef. He said he has participated in several blind taste tests of irradiated beef. "When I could tell the difference, I thought it was the irradiated stuff that was better," he said.
In response to these points, Martin provided more details on how the taste testing was done. His explanation follows:
"Two experienced, trained tasters were used.
"When we reported 66 of 72 pairs where the irradiated sample was identified, it means that both expert tasterstasting independentlyagreed 66 times on which sample was irradiated. For the 6 pairs where a sample was not 'identified as irradiated,' there may have been disagreement between the tasters, but it does not mean that neither taster could identify a distinct 'irradiated' flavor.
"According to chance alone, the tasters would have chosen the irradiated sample correctly half the time, or 36 of 72 pairs. Since our tasters correctly identified the irradiated sample in 66 of 72 pairs, there is something more than luck at work. The probability of 'guessing' the correct answer that many times is much less than one in a trillion. Hence the results are highly significant.
"The paired samples were matched as closely as possible for fat content, and were handled similarly, stored at identical temperatures and for the same short length of time. Ground beef was made into patties of uniform size and weight before cooking, and the burgers were cooked on two identical grills. For a sample pair, the irradiated burgers were cooked on one grill, while the non-irradiated burgers were cooked on the other grill. All meat was cooked to proper serving temperatures.
"Except for the chicken samples obtained at the irradiation plant, it is not possible to know what the radiation doses were, since that information is not revealed on the packaging."
Concerning the objection that most taste studies in the literature have not found unusual tastes or odors in irradiated meat, Martin stated, "Most of the literature we have seen was conducted using untrained consumer panels."
Kagan, echoing Martin's comments, also defended the taste tests as being careful and methodical. "We stand behind our test methodology of using paired comparisons," she wrote.
The Consumer Reports article says a contract laboratory was used to test 400 samples of irradiated and nonirradiated ground beef and chicken tenders for total bacterial plate count, enterococci, L monocytogenes, and generic E coli. Bacteria levels were "significantly lower" in the irradiated meat, with total plate count and enterococci averaging 90% to 99% lower. But meaningful differences could not be seen for some organisms because levels in the nonirradiated samples were so low, the report says.
The tests detected L monocytogenes in 25% of nonirradiated fresh ground beef packages, but the report doesn't mention tests for any other specific pathogens, such as E coli O157:H7 or Campylobacter. The magazine also randomly tested samples of chicken at an irradiation plant and found that 21 of 25 pre-irradiation samples contained L monocytogenes, versus none of 25 irradiated packages. Other laboratory tests revealed no evidence that irradiation increased the level of trans (hydrogenated) fats in the meat samples, contrary to some recent research, the article notes.
Critics such as Smith speculated that the magazine actually tested for additional pathogens, such as Salmonella and Campylobacter, but didn't include the findings. And Hull commented that the report seemed to play down the finding of Listeria in nonirradiated meat, instead of citing it as a reason to support irradiation.
In responding to these concerns, Martin said L monocytogenes was the only specific pathogen tested for. He further stated, "We also tested samples for generic E coli and enterococci, positive results for which indicate possible fecal contamination and the possibility that a pathogenic strain of these organisms may also be present. Since ground beef was the principal meat we tested, we expected that the incidence of Salmonella in the nonirradiated samples was likely to be very low, and of E coli O157:H7, hopefully nonexistent. Given the number of samples we had to test, and the extremely low prevalence of these pathogens in nonirradiated meat, the power to detect any statistically significant difference that may exist between irradiated and nonirradiated samples would have been extremely low and would not have justified the expense."
Preventing contamination versus eliminating it
Another point that drew criticism from Osterholm is the article's inclusion of the argument by Carol Tucker Foreman, director of the Food Policy Institute at the Consumer Federation of America, that "It's better to take steps to avoid contaminating food to begin with than it is to try to clean it up afterwards." She made the oft-heard assertion that the meat industry wants to use irradiation as a substitute for proper food safety measures in packing plants.
Osterholm wrote that while it is important to strive to prevent contamination, the reality is that it's simply not possible to remove all the microbes from cattle carcasses in a slaughterhouse. He said the problem is illustrated by the difficulty of eliminating contamination in hospitals. Each year 3% of surgical patients suffer a surgical site infection, despite having undergone surgery in a setting where all sterile precautions where taken, he wrote. If hospitals can't eliminate contamination of surgical sites, "how can one ever imagine the complete elimination of possible pathogens from an animal carcass being disemboweled in a slaughtering plant?" he asked.
Kagan did not comment specifically on this point in her letter.
Cooking recommendation and labeling issues
The Consumer Reports article includes a brief list of safety tips for handling and preparing meat. One of them advises consumers not to rely on color to judge whether meat is cooked, but instead to use a meat thermometer to make sure ground beef is heated internally to at least 160ºF. Another tip says, "Order ground beef medium or well done." Osterholm criticized these suggestions as inconsistent.
"In many restaurants hamburger ordered medium will come with a pink internal core," he wrote. "The consumer will not have ready access to a meat thermometer in that setting. . . . Frankly, if consumers were to routinely order ground beef done to a medium level you would be contributing to the occurrence of E coli O157:H7, Salmonella and other serious foodborne illnesses."
Osterholm also objected to the magazine's statement that irradiated foods should continue to be labeled "irradiated" and that "calling them pasteurized or anything else is misleading." He observed that one definition of "pasteurization" in Webster's dictionaries is "partial sterilization of perishable food products (as fruit or fish) with radiation (as with gamma rays)." "In other words, Webster's concludes that food irradiation is a form of pasteurization," he stated.
Kagan's reply to Osterholm did not comment specifically on either of these objections.
Full text of Michael Osterholm's letter to Consumer Reports