Course:FNH200/Lessons/Lesson 10/Page 10.5

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10.5 Changes that can Occur in Food during Irradiation

Another concern expressed about food irradiation is the possible formation of unique radiolytic products. However, in fact, the molecular changes in foods treated with ionizing energy are not usually unique or distinct from those found in non-irradiated foods such as those treated by thermal processing. The few unique radiolytic products that have been found are at such trace levels, that they are not considered to be of any significance, and so far toxicological studies have not found evidence of any harmful effects.

Other changes can occur in foods during irradiation with ionizing energy via indirect effects. These changes can involve the radiolysis of water molecules to produce reactive hydroxyl radicals, or reactions in foods of peroxides and peroxide free radicals with fats, leading to lipid oxidation(rancidity). Some vitamins are also sensitive to radiation. The extent of effects on both macronutrients and micronutrients are, of course, dependent on the dose of irradiation. Page 51 of Irradiation and Food Safety describes the effects of food irradiation on macro- and micro- nutrients. It also describes some of the sensory changes that have been perceived and their implications for the consumer.

Want to learn more?
  • Read: the IFT Scientific Status Summary on "Irradiation and Food Safety" by Smith and Pillai.
  • Try to answer the following questions (keep in mind the radiations doses being used):
    • What are the two groups of compounds (radiolytic products) that have generated concern?
    • Of these two groups, only one is considered as "unique radiolytic products" - which one?
    • What are the opinions of Health Canada and of the European Commission's Scientific Committee on Food on potential toxicity concerns based on mutagenicity/genotoxicity studies?
    • What was the role of Health Canada in the mutagenic/genotoxic studies?
    • Which nutrients are less sensitive to irradiation? Which are most sensitive?
    • What effects could irradiation have on sensory properties?

Below are three proposed methods of minimizing the "undesirable" changes during food irradiation:

Irradiation in the frozen state

  • When water is frozen free radicals are produced at a lesser extent
  • The frozen state will delay free radical diffusion and migration to food constituents beyond the site of free radical production.
  • However, as we learned in the required reading by Smith and Pillai (2004), the D10 values also change as the water in the product freezes.

Irradiation in a vacuum

  • Removing O2 from the system may minimize reactions; however,
  • Removal of oxygen could also confer a protective effect on microorganisms.

Addition of free radical scavengers

  • Ascorbic acid has a great affinity for free radicals.
  • Addition of free radical scavengers to food systems results in consumption of the free radicals via reactions between the scavengers and the free radical(s).