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| Fig. 1: Radiation Damages DNA (Source: Wikimedia Commons) - This figure dangles - RBL |
Recently, outbreaks of E. coli infections have been reported in multiple states. In 2018 alone, 2,925 cases (per 100,000) of infection with Shiga toxin producing E. coli were reported in 10 different states. [1] Even more severely, 9,723 cases (per 100,000) of infection with Campylobacter were reported across 10 different states. As such, foodborne diseases continue to have a large impact on the health of U.S. population. Foodborne diseases are caused by consumption of foods contaminated with viruses, pathogenic bacteria, and/or parasites. Common symptoms include diarrhea, vomiting, nausea, fever, abdominal cramps, and can even lead to death in severe cases when compounded with age and/or other existing health problems.
Scallan et al. used 31 major pathogens in the United States to calculate the number of cases and related incidents and found that these pathogens caused 9.4 million cases of foodborne illness, 55, 961 hospitalizations, and 1,351 deaths. [2] As such, preventing foodborne illnesses continue to be a nation-wide health priority. One widely used technology to decrease the number of foodborne illnesses is food irradiation.
Food irradiation is one of the technologies developed for safe food processing. It is the process of treating food by ionizing radiations to kill microbes and to improve storage. Ionizing radiation used in food irradiation uses γ photons emitted by Co-60 or Cs-137 radioisotopes, X-rays of maximum of 5 MeV, or accelerated electrons of maximum of 10 MeV. [3] While γ photons and X-rays of 5 MeV have been shown to have high penetrability, accelerated electrons have been shown to have lower penetrability.
The science behind using ionizing radiation in food processing is that ionizing radiation damages the DNA, releasing oxidative radicals and prompting apoptosis and necrosis of living cells, as shown in Fig. 1. As such, ionizing radiation prevents microbial species from reproducing and by killing the vectors by which viral particles can reproduce, eliminate the mechanism by which virus can survive. The dose required to result in a specific preservative effect is known as well. For instance, it takes about 3 to 10 kGy of radiation to reduce or eliminate microbes in dry food ingredients. [3]
Furthermore, the D10 value (radiation dose required to inactivate 90% of the microbial load) for different bacterial strains is known as well. For instance, the D10 value for Salmonella spp. is 0.30.8 kGy whereas Clostridium sporogenes is 1.5-2.2 kGy. [3]
It is important to note that the process of irradiation does not kill the food itself even though food has living cells, which are just as vulnerable to the process as parasites, insect pests, and bacteria. In fact, if the process of irradiation does reach those living cells, then it may delay the processes of sprouting or ripening in certain foods.
While there are many hypotheses surrounding why irradiation does not kill the food itself, one of the plausible explanations may come from the fact that it takes more irradiation to kill cells with less DNA. Just as it takes more irradiation to kill bacterial cells than parasitic cells and it takes even more irradiation to kill viruses than bacterial cells, the living cells in foods may harbor the least amount of DNA. This may incur some protective effects against irradiation process killing the food itself. Another plausible explanation may come from the fact that the cells in foods are not actively dividing. Bacterial and parasitic cells are actively dividing and viral particles are looking for host cells to make more copies of its nucleic acid. As such, the amount of dosage required for eliminating most of the bacteria, viruses, and parasites without killing the food cells may be known, but it stems from largely empirical data.
© Anika Kim. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] D. M. Tack et al., "Preliminary Incidence and Trends of Infections with Pathogens Transmitted Commonly Through Food - Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 2015-2018," MMWR-Morbid. Mortal. W. 68, 369 (2019).
[2] E. Scallan et al., "Foodborne Illness Acquired in the United States - Major Pathogens," Emerg. Infect. Dis. 17, 7 (2011).
[3] J. Farkas, "Irradiation for Better Foods," Trends Food Sci. Tech. 17, 148 (2006).
