Cherin studied BSc Hons (Genetics) at the University of Pretoria and was involved in the commercial sale of equipment to laboratories.
She obtained an MBA from the University of Cape Town and has been employed by HEPRO Cape (Pty) Ltd since 1992, where she is currently the Managing Director. She was instrumental in developing the company, involved in many research projects and, under the mentorship of the late Dr Rocco Basson (the father of irradiation in South Africa), was involved with the development of protocol for the irradiation of table grapes for export to the United States.

Throughout our existence, humans have developed technologies to prevent spoilage and enhance the safety of their food. These include drying, smoking, salting, heat pasteurisation, canning, refrigeration, freezing, chemical preservatives and irradiation.

The use of irradiation as a food safety method has been researched and been judged safe and effective. This technology, widely used in the medical industry for sterilising equipment and consumables, has been commended widely by international bodies, including the World Health Organization (WHO), the Food and Agriculture Organisation (FAO), the International Atomic Energy Agency (IAEA) and Codex Alimentarius, amongst others.

What is food irradiation?

Food irradiation is the process of exposing food to a controlled amount of energy in the form of high-speed particles or electromagnetic radiation.

Irradiation, carried out under conditions of Good Manufacturing Practice, is an effective technology, improving the safety of foods for human consumption by reducing or eliminating food spoilage microorganisms (thus extending shelf life) and insects.

At the correct doses, there is minimal effect on nutritional or sensory quality, as would be the case for all other food-processing techniques.

How Is food irradiated?

Three sources of radiation are approved for use on foods:

  • Gamma rays emitted from Cobalt 60: Gamma radiation is widely used for food irradiation; the medical, pharmaceutical and cosmetic industries; and in the treatment of cancer (at a lower intensity).
  • X-rays produced by reflecting a high-energy stream of electrons off a target substance into food: X-rays are also widely used in medicine and industry to produce images of internal structures.
  • Electron beam (or e-beam): a stream of high-energy electrons propelled from an electron accelerator into food.

Is irradiated food safe to eat?

Food that has been exposed to irradiation is safe to eat.

The European Food Safety Authority (EFSA 2011), the FDA, the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC) and the U.S. Department of Agriculture (USDA) have all concluded that irradiated food is safe to eat and that most of the chemical substances formed during irradiation were also formed in food that has been subjected to other processing treatments. The quantities in which they occur in irradiated food were not significantly higher than those being formed in heat treatments.

Irradiation does not make foods radioactive, compromise nutritional quality, or noticeably change the taste, texture, or appearance of food when correctly applied.

The food is never in contact with the source of the radiation, only the energy from it.

There are several applications of irradiation of food:

  • Food safety: Eliminating pathogens causing food-borne illness (e.g. (Salmonella, E. coli)
  • Preservation: Eliminating food-borne microorganisms responsible for food spoilage, thus extending shelf life
  • Control of Insects: Irradiating fruit at low doses sterilises insects in or on the fruit, thereby mitigating against pests that may be spread through global trade of these commodities
  • Delay of sprouting and ripening: Of garlic, onions, tubers, etc., for example
  • Sterilisation: Irradiated sterile (high-dose) foods for severely impaired immune system patients e.g. AIDS patients or patients undergoing chemotherapy. The NASA space programme also provides sterilised food

How does irradiation work?

High-energy (ionising) rays from a source (such as Cobalt 60 producing gamma rays, high-speed electrons from e-beams or X-rays) penetrate the food, producing highly reactive, very short-lived free radicals disrupting the DNA of dividing cells, causing the cells to stop dividing and cease functioning. Thus, bacteria, yeasts and moulds can be eradicated.

It is the action of the very transient free radicals that accounts for many of the effects (killing pathogenic bacteria) of irradiating food.

The dose of radiation received is commonly measured in Grays. One Gray corresponds to the absorption of one joule of energy in a mass of one kilogram (1Gy = 1J/kg). Depending on the purpose for the irradiation, doses will vary.

How will I know if my food has been irradiated?

Labelling legislation requires that irradiated foods bear the international symbol for irradiation, the Radura symbol, or the words “Radurised” or “Irradiated” on the food label.

Bulk foods, such as fruits and vegetables, are required to have a notice next to the display indicating that the product has been irradiated and giving reasons for the irradiation.

Because changes known to occur in irradiated foods are so minimal and often similar to changes due to other processes, very sensitive tests have been developed to prove that a product has been irradiated: electron spin resonance spectroscopy (ESR – detects free radicals in bones, seeds and shells), luminescence methods (thermo-luminescence or TL, using mineral grains present in herbs, spices, vegetables, fruit and shrimps), photostimulated luminescence (PSL) and the detection of long-chain volatile hydrocarbons and 2-alkylcyclobutanones (used for foods containing fat).

Nutritional quality of irradiated food

There is no significant loss of macronutrients during irradiation. The nutritional value of proteins, fats and carbohydrates undergoes little change during irradiation though there may be sensory changes (depending on the conditions).

The essential amino acids, essential fatty acids, minerals and trace elements are also unaffected by irradiation.

A decrease in certain vitamins (particularly thiamin) may result from irradiation. To put this into perspective, these decreases are of the same order of magnitude as occurs in other manufacturing processes such as drying or canning (thermal sterilisation).

Sensory quality of irradiated food

As with most food processing technologies, irradiation is not suitable for all products.

The correct dose, temperature, packaging and timing of irradiation in the product’s life cycle determine the success of the process.

Those products with high-fat contents (fatty fish, some dairy products, some nuts) may develop off-odours and tastes due to the acceleration of rancidity, even at relatively low doses.

The dose is a very important aspect as some products respond well at lower doses but not at the higher doses, e.g. loss of firmness can occur with some fruits and vegetables at higher doses.

Irradiation combined with refrigeration or freezing can deliver good results in certain protein product types, e.g. pork, beef, chicken, ostrich, etc.

Packaging

Food is often pre-packaged before irradiation to prevent re-contamination. The possibility that irradiation might either affect barrier properties or that radiolytic products formed in the packaging might be absorbed into the product has to be investigated before irradiation.

Consumer attitudes

Irradiation and thermal pasteurisation of milk share very similar attitudes, with opponents claiming that:

  • The nutritional value will be compromised and vitamins will be destroyed
  • Not enough research has been done regarding the long-term effects of consuming irradiated foods – it may be unsafe
  • The price of irradiated items will be higher
  • Irradiation will be used to cover up poor GMP
  • Irradiated food has a longer shelf life; old food could be sold in the supermarkets
  • Food becomes radioactive.

In consumer studies, it was found that having been supplied with good information and an opportunity to try irradiated products, consumers were more likely to accept the technology and to buy irradiated products.

International trends

Some countries still do not allow irradiation of foodstuffs while others (over 60 countries) have embraced the technology.

The UK and EU countries have strict regulations regarding the importation of irradiated foodstuffs and allow only herbs and spices that have been irradiated.

Other countries have recognised the value of the technology in combating food-borne diseases by providing safe food to their citizens.

South Africa has been at the forefront of the technology providing irradiation services from as early as the 1960s.

Why the scepticism still?

Perhaps it is human nature to be sceptical of things that cannot be seen, or pasteurisation technologies simply take a long time to take hold. Or is it that consumers need to be better educated about the benefits of food irradiation?

Is the word “irradiated” frightening? Should the benefits more clearly highlight that food is never contaminated or rendered radioactive, and that the energy used results in a superior final product?

The irradiation industry and professional bodies have much work to do in changing these perceptions by educating consumers

The future

Whatever the case, the advantages of providing safe food that has been treated by gamma rays, e-beam or X-rays cannot be dismissed.

With a rising urban population, incidents of food-borne diseases are on the increase. Greater focus will be on food safety. It is comforting to know legislation and manufacturers do turn to irradiation/radurisation/cold sterilisation to ensure the consumer enjoys safe food.

Safety of food supply is becoming increasingly important. The use of irradiation as a phytosanitary mitigation against spreading of pests globally is an important application. South Africa has been at the forefront in promoting this application and since 2010 the export of irradiated table grapes to the USA has been allowed – this market was closed due to the strict phytosanitary requirements of cold sterilisation (i.e. –0.55°C for 22 consecutive days) too robust for the fruit to bear. Other fruits such as litchis, persimmons, plums and mangoes have been proposed for this method of phytosanitary control.

As the incidences of food-borne disease increase, the requirement for cross-border phytosanitary controls is intensified and irradiation of foodstuffs has a radiant future.