Science and Technology

NewsOK | BLOGS

Irradiation of food is a safe means for preservation

Robert Hayes Published: August 31, 2013

A cost effective method of killing both E-coli and salmonella bacteria from food in a safe way is available for many foods.  This method is that of exposing the food to large doses of ionizing radiation, in much the same way that medical utensils are sterilized when using this approach.  Exposing things to ionizing radiation is known as irradiation.

By irradiating food, many food borne pathogens can be safely killed leaving the food largely unaffected.  The effect on the food is a milder version of the effects caused when you cook the food so that the change in nutritional value from the exposure is inconsequential.  The texture can be effected and the nutritional value will be reduced slightly.  When food is cooked, many intermolecular bonds are broken including those of the proteins and vitamins but not to the point of making food unsafe.  Just as cooking food does not make it unsafe due to the molecular changes in proteins and vitamins, the same applies with exposure to large doses of ionizing radiation.  In fact, many foods are considered unsafe unless they are cooked, irradiation of food has a similar effect in its ability to kill bacteria, fungus and can weaken or even break up virus molecules.  The US Food and Drug Administration actually goes so far as to say on their website the following, “Irradiation does not make foods radioactive, compromise nutritional quality, or noticeably change the taste, texture, or appearance of food. In fact, any changes made by irradiation are so minimal that it is not easy to tell if a food has been irradiated” (http://www.fda.gov/Food/ResourcesForYou/Consumers/ucm261680.htm)

Some people have a fear that exposure to ionizing radiation will cause the exposed item to be radioactive itself.  When sterilizing food in this way, the types of radiation which would be used are not capable of inducing radioactivity in the exposed food.   Besides the fact that all food is already radioactive from naturally occurring radioisotopes such as carbon-14 and potassium-40, the methods used for food irradiation have been evaluated by the US Centers for Disease Control, World Health Organization along with pretty much all respectable similar scientific organizations.  These recognize the inability of the process to create more radioactivity in the food above and beyond that which is already naturally present.

Only three kinds of radiation are used for food preservation, these are gamma, electron and x-ray sources.  The key feature in all of these forms of radiation required to prevent radioactivity being created in the food during this process is that of limiting the maximum energy of the radiation used.  If the energy does not get above a certain level (around 10 MeV), then interaction with the atomic nucleus is no longer an issue as the radiation can only interact with the electrons orbiting the nucleus which is what causes molecular bonds to be broken.  These molecular bonds can easily cause death at large doses in living bacteria cells but in dead cells such as food, the effect is very small in terms of changing its nutritional content.  In other words, two or three bond breaks in a DNA strand can effectively kill a cell but slightly disassembling two or three proteins in a dead cell from a food item is entirely negligible regarding the overall food content of that cell.  To put this in a more realistic perspective, even though only two or three breaks in a DNA strand can kill the cell, there are many billions of individual bonds making up the entire DNA strand.  This applies to cells from fruit, vegetables, meat, beans, nuts or any other food item as well as bacteria and fungi which may be living on that food.   So if the food is not growing, irradiation will have an inconsequential effect on the food but any living organisms such as fruit flies or bacteria will be destroyed through radiogenic cell death.

Although there are some types of food which have slightly noticeable effects from food irradiation, most do not.  Special quality testing methods have been and are continuing to be developed to independently verify whether foods claimed to be treated actually were.  If too much irradiation is used, the changes will be more evident, much like boiling or microwaving food will cause easily detectable changes after substantial cooking and baking take place.  In this sense, this leaves food irradiation as a much preferable method to sterilize food over boiling or cooking it.