Irradiation is a topic of great interest to the industry, especially since the FDA has approved its use for pathogen reduction on iceberg lettuce and spinach. The other day we ran a piece, UC Davis Produce Curriculum Is Open To The Industry, which included information on a UC Davis webinar entitled, Produce Irradiation: Food Safety Solution? The webinar is co-sponsored by the UC Davis Center for Produce Safety, United Fresh, the Produce Marketing Association and the National Restaurant Association.
Several of the participants in the webinar have been mentioned in the Pundit, and we did full-blown interviews with both Christine M. Bruhn, Ph.D., UC Davis, and Harlan Clemmons, President & COO, Sadex Corporation, on the irradiation issue.
In fact, the Harlan Clemmons interview was run as part of a more comprehensive piece we entitled, Irradiation Kickstart, which also included interviews with Richard Hunter, President and CEO of Food Technology Service, and Dr. Jeffrey Barach, Vice President and Center Director of the Grocery Manufacturers Association, and that piece brought a note from one of the Pundit’s most thoughtful correspondents, Bob Sanderson of Jonathans Sprouts:
Relative to the “good bacteria” irradiation question raised in your piece, Irradiation Kickstart, Dr. Jeffery Barach seems to be suggesting that irradiation kills pathogens but not benign organisms:
Q: When the product is irradiated to get rid of E. coli, salmonella or other dangerous pathogens, are all bacterium eliminated? Could there be negative long-term affect if a person’s diet included a large percentage of irradiated products?
A: This is not a sterile product that is produced after irradiation. There are still normal bacteria that exist, but the foodborne pathogens have been eliminated. I’ve never seen any studies that show any dangerous cumulative effect of humans eating irradiated food products. There is no credible data suggesting this is an issue, nothing from FDA, no scientific data that has been peer-reviewed to demonstrate any issue whatsoever. FDA took an exhaustive look at the impact of irradiation. We’ve not seen any evidence pointing to irradiation compromising future resistance to pathogens.
Is this what he intends to say, and if so, could he elucidate how this selective sterilization works?
Richard Hunter proposes that all bacteria on food are bad:
Q: Is there a chance the irradiation process could kill off “good” bacteria as well as the bad bacteria? In other words, are you playing with nature’s circle of life, where certain bacteria are needed to ward off other problems?
A: My view is that anything living on your food, whether a pathogen or spoilage organism is bad. I wouldn’t view any bacteria on food as good bacteria.
In essence you have a lot more spoilage than pathogens on food. The magic in irradiation is in logarithmic reductions. If you start out with 1,000 organisms, bacteria divide dependent on temperature and species of bacteria. That’s why you have to be so careful about keeping product at the right temperature. Say at the end of the day, those 1,000 organisms have doubled to 2,000, and the next day to 4,000.
Starting with those 1,000 organisms, if you have a 4 log reduction, take the decimal and move it four places to the left, now you have .1 instead of 1,000. Instead of 1,000 doubling to 2,000, it takes so much longer for organisms to multiply to a dangerous level. Eventually you have the same spoilage indicators, but you’re slowing down the spoilage process significantly.
If this is the accepted frame of reference, then it is a moot point — in fact, any survivors such as what Dr. Barach mentions could be seen as a shortcoming of the irradiation process.
Some perspective on the question of the “pro” or “con” significance of non-pathogenic microorganisms on food (what might be called “normal flora”), might be gained from observations of laboratory animals that are fed a sterile diet:
First, is their general level of health and immune function similar to that of animals not fed a sterile diet?
Secondly, if you raise a lab animal on a sterile diet, and then expose it to pathogens, is it more likely to have an adverse reaction than an animal would that had been fed a “normal” diet rich in many kinds of microorganisms?
I have not found a source for this information, and so, like many people, am left to my “intuitions,” which I find are shared by many: exclusively sterile food, or an overly sanitized environment, are not healthy for people who are not seriously immune-compromised, and their increasing introduction into the diet and lifestyle may have pervasive adverse health effects that are difficult if not impossible to accurately trace back to their causes.
— Bob Sanderson
Bob Sanderson often raises intriguing questions, and we have featured his insights in pieces such as these:
In this case we thought Bob’s question were sufficiently intriguing to lead us to ask Pundit Investigator and Special Projects Editor Mira Slott to, once again, speak with Dr. Jeffrey Barach and try to get some clarification:
| Dr. Jeff Barach
Vice President and Center Director
Grocery Manufacturers Association (GMA)
Member, Executive Committee
Creating Sustainable Outcomes for Agriculture
The Keystone Center
Q. In your interview, you point out that after irradiation there are still normal bacteria that exist, but the foodborne pathogens have been eliminated. Could you elaborate on how this selective sterilization works?
A. Irradiation treatment will reduce both pathogenic and non-pathogenic (spoilage or normal) organisms.
In real life on a food product, such as fresh vegetables and fruits, the number of the pathogenic bacteria is a lot lower than the number of spoilage organisms.
In addition to that, different microorganisms have different sensitivity to irradiation. In an irradiation treatment, the dose chosen for a specific food product will target a specific organism, which is the pathogen most likely to contaminate that product.
Since many spoilage organisms are more resistant and are in numbers more prevalent than pathogens, the targeted treatment kills the pathogens and some of the spoilage (normal) organisms, but not all.
Q. Richard Hunter proposes that all bacteria on food are bad. If this is the case, could any survivors be seen as a shortcoming of the irradiation process?
A. The comment that all bacteria on food are bad is not exactly correct. I think he wanted to point out he would prefer not to have any kind of bacteria on his food, which is hardly possible, unless the food is “commercially sterilized” (such as with canned foods).
All produce, vegetables, fruits, bakery products, dairy products, etc., have some microorganism load. There are many food products that are purposely inoculated with bacteria, yeast or moulds (i.e., fermented meats, cultured dairy products, fermented drinks, etc).
Irradiation is used for the purpose of reducing the harmful bacteria (the life-threatening pathogens) and not to sterilize the food. Bacteria come in good and bad varieties, or more to the point, bacteria can be helpful or harmful.
Q. Have there been any scientific studies conducted on the significance of non-pathogenic microorganisms on food? For example, would general health and immune functions be similar between animals fed a sterile diet and animals not fed a sterile diet?
If you raise a lab animal on a sterile diet and then expose it to pathogens, is it more likely to have an adverse reaction than an animal that had been fed a “normal” diet rich in many kinds of microorganisms?
A. That is an interesting question but beyond the scope of our discussions here. Irradiated produce is not sterile and will contain some bacteria (of the non-pathogenic type). The remaining “normal” bacteria on the irradiated produce are the same ones you would find on unirradiated produce — there are just fewer of them.
This whole issue is reminiscent of the debate over sterile environments and allergies and asthma in children. There is an interesting little video on the “Hygiene Hypothesis” that focuses on the idea that farmer’s children have fewer incidences of allergies and asthma. You can see the video here.
Doctors describe the Hygiene Hypothesis this way:
Here’s the theory: The newborn immune system is tolerant and non-allergic to most anything (which is why it sometimes does such a lousy job of fighting off infection). When it is exposed to the usual allergy-causing antigens (such as dust and mold and dogs and cats), the immune system and allergens become lifelong buddies: a long-lasting acceptance and tolerance between them develops.
On the other hand, when an allergy-prone infant is raised in a very clean — almost sterile — environment, the immune system remains unfamiliar with these allergens. Then, when exposed later on, it reacts to them as it would to any alien invader, triggering allergies and/or asthma.
There have been a number of studies and some do make such a finding. One source says that as “…the hepatitis A infection rate has dropped from nearly 100 percent to less than 30 percent; meanwhile, the incidence of asthma has doubled. After analyzing hundreds of DNA samples, Umetsu found a link. More than half of Americans carry a variant of an immune-response gene, TIM-1, that makes people much less likely to get asthma — but only if they have been exposed to hepatitis A.”
Still the research is problematic, the data establishing an epidemic of childhood asthma and allergies is unclear often relying on patient self-diagnosis. There are also many variables. Children on farms may have fewer allergies — but maybe parents with severe allergies don’t become farmers. The role of antibiotics in both animals and people may affect this whole line of inquiry. And of course cleanliness can have positive attributes in preventing infection. As a result of all this, public health authorities are not urging parents to have their children eat dirt.
When it comes to irradiation, Bob Sanderson’s concern strikes us as intriguing, and we would like to see animal studies done such as he suggests. Yet it does not strike us as an important concern regarding the irradiation of iceberg lettuce and spinach.
Even if irradiation was to render produce completely sterile — which it does not — and even if bacteria wouldn’t start growing the minute that bag is open and the produce touches the air, a bowl, a fork, etc. — which it would — iceberg lettuce and spinach are just too small a portion of a person’s diet to make this much of a concern. “It strikes us as an argument against irradiating or otherwise rendering sterile the whole food supply as we do for astronauts, whose confined environment makes diarrhea a very serious problem.”
Today we are a long way from that; in fact, at this point the Pundit proposed just making a line of produce available for use by immune-compromised individuals or institutions that serve such people.
Since there is no danger anytime soon of the whole diet being “sterilized,” we can proceed with irradiation of higher risky items, such as leafy greens, in full confidence that the known benefits in terms of food safety outweigh any even hypothetical risk to society at large.
We thank both Bob Sanderson and Jeffrey Barach for their assistance with this challenging topic.