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Pros and Cons of Commercial Irradiation of Fresh Iceberg Lettuce and Fresh Spinach: A Literature Review

This is the first part of a multi-part series on the Pros and Cons of Commercial Irradiation of Fresh Iceberg Lettuce and Fresh Spinach.  Given the recent outbreaks, hopefully this is timely.

On August 22, 2008, FDA published a final rule for the safe use of ionizing radiation (also termed irradiation, irradiation pasteurization, cold pasteurization) of fresh iceberg lettuce and fresh spinach for control of foodborne pathogens, and extension of shelf-life. A few weeks later, the US Government Accountability Office (GAO) released a report entitled, “Improvements Needed in FDA Oversight of Fresh Produce.” This report states that FDA’s intervention efforts for reducing the risk of contamination during the processing of fresh-cut produce have been limited. Interestingly, the GAO reviewers only briefly mention irradiation, and brought little context to the implications of introducing irradiation as a potential control (“kill”) step during produce processing.

Currently, a serious outbreak of E. coli O157:H7, possibly linked to iceberg lettuce, is unfolding in Michigan and other parts of the United States. Since 1995, the FDA has documented at least 22 other E. coli O157:H7 outbreaks traced to leafy greens likely contaminated before retail distribution, including a number of outbreaks involving fresh iceberg lettuce and spinach. Clearly, there is a need for improved methods to prevent contamination of produce before it reaches the consumer.

Most food safety experts would agree that there is no silver bullet (defined by Webster’s dictionary as “a magical weapon ; especially : one that instantly solves a long-standing problem”) to guarantee protection of any food from contamination. The use of comprehensive “farm-to-table” approaches is well accepted as the best way to combat the complex problems in food safety.

Where does irradiation of food fit into this evolving continuum including the new rule in the United States for lettuce and spinach?

Irradiation is probably the most studied, and the most controversial, food processing method in history. Several years ago, two renowned food safety leaders, Drs. Robert Tauxe (2001) and Michael Osterholm (2004), published elegant summaries describing the role of irradiation in food safety and protecting the public health. They did not promote irradiation as a silver bullet, but their commentaries suggested the process is one tool in the toolbox, and may be a silver lining (defined as “a hopeful side of an otherwise desperate or unhappy situation”) in the burgeoning problem of foodborne disease.

To better understand the implications of FDA’s new rule, I hit the books with the goal to examine the “pros and cons,” (perhaps more appropriately described as “advantages and limitations”) of using irradiation as a control step during fresh lettuce and spinach processing. The following is the first in a series summarizing the findings.

Part I. Historical Perspective and Definitions

Irradiation as a processing method for food is not a new technique. Indeed, research into using ionizing radiation to improve food quality and shelf-life began in the late 1800’s. In 1905, scientists received the first patents for application of ionizing radiation as a food preservation process to kill bacteria. In the 1940’s, the term “irradiation” was first used in the literature, but some have since questioned using this language to describe the technology. Molins (2001a), an expert in the field of radiation, characterized the term as: “a most unfortunate occurrence because it brought a direct and conceptually misleading association of a food processing technique with the nuclear establishment.” He suggested use of the word “irradiation” was inappropriate because “it does not describe the actual process of applying ionizing radiation in ways that would set it apart from other processes used in the food industry. Thus, microwaves and infrared light – both of which generate heat – are also forms of radiation, and their use in cooking, heating foods in a microwave oven, or simply keeping the food warm under infrared light – as is customary in many restaurants – could just as properly be termed “food irradiation.”

Fifty years ago, the FDA defined food irradiation as a “food additive” in the Food, Drug, and Cosmetic Act. Tauxe (2001) made this comment on the classification in his review paper: “By an historical quirk, the use of irradiation on food was formally approved as though it were something added to food, rather than a process to which the food is subjected.”

Regardless of the potential pros and cons of food irradiation, poor terminology is a disservice to the scientific community, industry, and the public; furthermore, the “mystery” surrounding food irradiation has potentially lead to unnecessary controversy and miscommunication. Before beginning this review into the potential advantages and limitation of food irradiation, it seems critical to review some definitions and basic chemistry behind the process.

How does food irradiation work?

Food irradiation is based on the principle of using energy to ionize a material, in this case food. Ionizing irradiation treatment involves chemical reactions with microbes, but these reactions are not dissimilar to chemical reactions induced by cooking, canning, curing, drying, freezing, or other food processing techniques. There are pros and cons to every food processing technique. In food irradiation, high speed particles or rays are harnessed by a machine. The particles used for this purpose are common in nature, and part of the energy that comes from the sun. These particles are focused in the process to penetrate the food, and result in the creation of free radicals that damage the DNA of organisms, especially microbial contaminants at the doses used for food. Depending on the organism and irradiation dose, this process is capable of enhancing food safety and quality of the food (the nature of this process as it applies to food safety and comparison with other food processing methods such as cooking, and effects on food quality such as nutrients, are described in subsequent parts of this review).

There are 3 sources of ionizing radiation approved in the context of food processing:

1. Gamma rays
2. X-rays
3. Electronic beams (E-beams)

Only gamma rays require the use of radioactive material (Cobalt 60), but the levels required are too low for creation of “radioactivity” in the food or packaging. Thus, the food or packaging are not radioactive. In contrast, X-ray and electronic beam applications do not involve the use of radioactive material. For example, with E-beam technology, electricity is the source for generating electrons that damage DNA of certain microbes that contaminate food. Photons are generated by gamma and x-ray technology, and these methods provide deeper penetration into the food compared with E-beam, but the difference in penetration is not significant in the context of fresh lettuce and spinach. None of these methods for food irradiation create neutrons, the particles associated with nuclear technologies.

The “dose” applied to the food is an important consideration in understanding the chemistry of food irradiation. There are three general categories for irradiation dose in food processing. The dose of ionizing radiation is measured in units called gray.

1. Low (< 1kGy) is used mostly to kill insects that infest foods
2. Medium (1-10 kGy) is used primarily to reduce pathogens and prolong shelf-life of foods
3. High (>10 kGy) is used to reduce organisms resistant to low-medium doses, or to sterilize food

FDA currently permits food irradiation in the “medium” dose range to control pathogens (primarily bacteria and parasites) for the following foods:

• Fresh, non-heated processed pork
• Fresh or frozen, uncooked poultry products
• Refrigerated and frozen, uncooked meat products
• Fresh shell eggs
• Seeds for sprouting
• Fresh or frozen molluscan shellfish
• Fresh iceberg lettuce and spinach

The susceptibility of organisms to different doses of irradiation varies based on the biology of the organism. Damage is greatest in more complex organisms that may be a problem in food. The required dose to reduce or eliminate pests, pathogens, or spoilage organisms is generally in decreasing order as follows:

Insects < parasites < molds/yeasts < vegetative (non-spore forming) bacteria < spore forming bacteria < viruses < prions

Implications for the Lettuce and Spinach Industry

The new FDA rule for food safety and quality in fresh lettuce and spinach allows a maximum dosage of 4 kGy, which has been shown to be effective at reducing or eliminating the major pathogens linked to produce outbreaks (for example, E. coli O157:H7 and other STECs, Salmonella).

In Part II of this review, the pros and cons (advantages and limitations) of commercial irradiation of fresh iceberg lettuce and spinach relating to microbial contamination and food safety will be explored. Part III examines the food quality and food security considerations. Part IV concludes with an overview of the cost-benefit considerations that both industry and consumers must face in deciding how food irradiation fits into the big picture of prevention and control of foodborne illness.

References

1.    Anonymous.  Questions and answers about final rule on irradiation of fresh iceberg lettuce and fresh spinach, U.S. Food and Drug Administration, August 21, 2008.  Available at:  http://www.cfsan.fda.gov/~dms/cfsup185.html

2.    Anonymous.  Improvements needed in FDA oversight of fresh produce, U.S. Government Accountability Office, September 2008.  Available at:  http://www.marlerblog.com/2008/10/articles/lawyer-oped/pros-and-cons-of-commercial-irradiation-of-fresh-iceberg-lettuce-and-fresh-spinach-a-literature-review/

3.    Cleland, M. R.  2006.  Advances in gamma ray, electron beam, and X-ray technologies for food irradiation.  In:  Food Irradiation Research and Technology.  Sommers, C. H. and X. Fan (ed).  Blackwell Publishing, Ames , Iowa , p. 11-35.

4.    Josephson, E. S.  1983.  An historical review of food irradiation.  J Food Safety 5:161-89.

5.    Molins, R. A.  2001a.  Historical notes on food irradfiation.  In:  Food Irradiation:  Principles and Applications.  R. A., Molins (ed).  John Wiley & Sons, Inc., New York , New York .p. 1-21.

6.    Molins, R. A, Y. Motarjemi, F. K. Kaferstein.  2001b.  Irradiation:  a critical control point in ensuring the microbiological safety of raw foods.  Food Control 12:347-56.

7.    Murano, E. A.  1995.  Microbiology of irradiated foods.  In:  Food Irradiation:  A sourcebook.  E. A. Murano (ed).  Iowa State University Press, Ames, Iowa, p. 29-61.

8.    Niemira, B.A. and X. Fan.  2006.  Low-dose irradiation of fresh and fresh-cut produce:  safety, sensory, and shelf life.  In:  Food Irradiation Research and Technology.  Sommers, C. H. and X. Fan (eds).  Blackwell Publishing, Ames, Iowa, 169-84.

9.    Olson, D. G.  1995.  Irradiation Processing.  In:  Food Irradiation:  A sourcebook.  E. A. Murano (ed).  Iowa State University Press, Ames, Iowa, 3-28.

10.    Osterholm, M. T. and A. P. Norgan. 2004. The role of irradiation in food safety. N Engl J Med 350:1898-901.

11.    Osterholm, M. T., and M. E. Potter. 1997. Irradiation pasteurization of solid foods: taking food safety to the next level. Emerg Infect Dis 3:575-7.

12.    Paquett, K. E.  2004.  Irradiation of prepackaged food:  evolution of the Food and Drug Administrations’s Regulation of the packaging materials.  In:  Irradiation of Food and Packaging.  Komolprasert, V. and Morehouse, K. M. (ed).  American Chemical Society, Oxford University Press, Washington, DC, 182-202.

13.    Shea, K. M.  2000.  Technical report:  irradiation of food.  Pediatrics 106:1505-1510.

14.    Tauxe, R. V. 2001. Food safety and irradiation: protecting the public from foodborne infections. Emerg Infect Dis 7:516-21.

  • Irradiating food moves Eating into the category of activities that should require informed consent. From an ethical eating standpoint, the only way irradiating food should possibly be thrust on the public is if there is a strictly enforced requirement for labeling that persists even when irradiated ingredients are processed into other food products. This kind of labeling is highly unlikey; the US can’t even manage to get tiny stickers on produce that accurately track origin and packing. It’s something of a public health–and moral–disaster to be exposing unwitting populations to irradiated foods, particularly since the long-term effects of ingesting irradiated foods have yet to be studied.

  • I’m not saying I want the stuff banned, or that I even believe that it’s dangerous – but I have enough concerns that I don’t want anything to do with it.
    We know there is some vitamin loss by the process. We know that the product looks better longer, which may lead to situations where nutritional value has decreased beyond what would be visually apparent. We know the process changes proteins. These are just the known issues.
    And I don’t believe for a second that efforts to fight contamination in the first place will continue to be a priority if the use of this technology becomes widespread.
    And who will operate the machines? The same skilled workforce that the meat processing plants use? Good luck with that.
    I’m sorry but I just see this as yet another perfect example of agriculture failing to scale up to big business size. Eat whole foods, eat local foods, and eat what’s in season. KNOW where your food comes from.
    I got my chicken and some really nice bib lettuce lettuce from her:
    http://www.carrborofarmersmarket.com/castlemaine.html
    It’s a great feeling; the food is incredible, the money stays in the local economy, the farm is sustainable and if I can do this, you can too.

  • Thank you
    This is very important for every American to know what we eat.

  • D. Ehlermann, food irradiation expert

    This citation to a first US patent on food irradiation is totally false; it concerned mixing radioactive material with the food in order to preserve it. The first US patent on irradiation is of 1918 (Gillet), quite ingenious, about using a grid of X-ray bulbs. And the real first patent is from the UK in 1905/1906.

  • D. Ehlermann, food irradiation expert

    Correction: FDA has approved in the high-dose area the treatment of ‘spices’ up to 30 kGy.

  • D. Ehlermann, food irradiation expert

    References: your list lacks the most important book:
    J.F. Diehl, The safety of irradieted food, Marcel Dekker, 1995 (2nd edition)

  • Thanks for your comments.
    Comment 1.
    As clarification, the historical perspective in this review was meant to give a couple brief, general highlights from the fascinating history of food irradiation and its origins. The sentence (and reference) that you refer to states: “In 1905, scientists received the first patents for application of ionizing radiation as a food preservation process to kill bacteria.”
    This was not meant to be interpreted as US Patent. Indeed, the citation was Molins (2001a) and the original list from the introduction read: “1905: A British patent was issued for use of ionizing radiation to kill bacteria in food through food irradiation.”
    Comment 2.
    Are you referring to this part of the review? “FDA currently permits food irradiation in the ‚Äúmedium‚Äù dose range to control pathogens (primarily bacteria and parasites) for the following foods: ‚Ä¢ Fresh, non-heated processed pork
    • Fresh or frozen, uncooked poultry products
    etc.”
    Because this article is focused on the new FDA rule, which addresses a medium dose application, I did not list low or high dose uses, including spices. Because there is such a huge volume of literature on the subject, this review was meant to provide a relatively succinct and focused look at implications for fresh lettuce/spinach.
    Comment 3.
    You are correct. Diel (1995) is an excellent reference. It was included in my most recent installment to the series (see reference 6):
    http://www.marlerblog.com/2008/11/articles/lawyer-oped/pros-and-cons-of-commercial-irradiation-of-fresh-iceberg-lettuce-and-fresh-spinach-a-literature-review-part-iii-food-quality
    Diehl, J. F. 1995. Nutritional adequacy of irradiated foods. In: Safety of Irradiated Foods, 2nd edition. Diehl, J. F. (ed). Marcel Dekker, New York. p. 241-282.

  • philG

    Having done a lot of reading on various sites like Time to Awaken my views on irradiation are as follows:
    1) There simply is not enough know about the way free radicals alter food chemistry.
    2) It would appear that irradiation, while prolonging the shelf life of food (and indirectly increasing the profits on food) in actual fact destroy the nutritional value of the product, depleting vitamins A, thiamin, B2, B3, B6, B12, folic acid, C, E, and K.
    3) The amount of radiation pumped into the product seems excessive
    4) The safety studies I have read seem to be classed as flawed
    5) The only beneficiaries appear to be the retailer and the food manufacturer.”Time to Awaken]http://the-future.uphero.com/food/irradiation/[/link] my views on irradiation are as follows:
    1) There simply is not enough know about the way free radicals alter food chemistry.
    2) It would appear that irradiation, while prolonging the shelf life of food (and indirectly increasing the profits on food) in actual fact destroy the nutritional value of the product, depleting vitamins A, thiamin, B2, B3, B6, B12, folic acid, C, E, and K.
    3) The amount of radiation pumped into the product seems excessive
    4) The safety studies I have read seem to be classed as flawed
    5) The only beneficiaries appear to be the retailer and the food manufacturer.

  • deniseK

    I agree with Phil. I would also have to say that the FDA is not releasing enough information on research done on the effects of the irradiation on humans. In the “Hidden Harm”, written in December 2001, it speaks of just three things that are/can cause genetic and cellular damage in humans. These three things, 2-DCB, 2-TCB, and 2-TDCB (all cyclobutanones) could very well be largely responsible for the increase of cancer along with a lot of other diseases. I have not been able to find one thing that the FDA has done in this area nor have I found anything that would prove to me that they were investigating other possibilities that could occur from other fats. It has been proven that these three (above mentioned) cause genetic and cellular damage since 1971. Why does it appear that things have stalled since 2008 in research? (“Hidden Harm”, written by “Public Citizen and The Center for Food Safety”, both out of Washington, D.C.)