Food Safety Focus (41st Issue, December 2009) – Food Safety Platform
Reported by Ms. Shuk-man CHOW, Scientific Officer,
Risk Assessment Section, Centre for Food Safety
As introduced in the last issue, there are a number of food processing technologies that can be used to maintain the post-harvest quality and safety of our food. Among these, irradiation seems to be a relatively new technology to the public. Irradiation, in fact, has been used for food treatment for more than five decades.
Irradiation is a processing technology which involves treating food with ionising radiation. Since irradiation does not substantially raise the temperature of food products under treatment, it is also called "cold pasteurisation". During the process of irradiation, food under treatment is usually packed in its final packaging and transported by a conveyor system into a closed room where the food is exposed to ionising radiation, such as gamma rays, x-rays or high energy electron beams. The duration and energy for irradiation is carefully adjusted according to the size, food type and purpose for treatment. When the ionising radiation passes through, DNA in the food, bacteria, insects or parasites will be broken. These organisms will then be killed or sterilized and thereby the shelf-life of the irradiated food products can be extended. However, viruses and bacterial spores are typically more resistant to ionizing radiation that may survive through the irradiation process.
Illustration :Examples of the application of food irradiation
1. Limit unwanted sprouting of potato tubers, garlic and onion bulbs
2. Decontaminate herbs and spices
3. Delay ripening in bananas, papayas and mangoes
4. Reduce pathogenic microorganisms in fresh produces
Application of Food Irradiation
Currently, over 50 countries have approved the use of ionising radiation to control the post-harvest quality of foods and for satisfying quarantine requirements in trade.
Reduce pathogenic microorganisms in fresh and frozen food
As treatment of food with ionising radiation does not result in significant temperature increase, it is of particular importance to control food-borne illnesses in fresh and frozen food products such as seafood, fresh produces, and frozen meat products. In the wake of E. coli O157:H7 outbreaks linked to spinach and iceberg lettuce in the United States in 2006, the U.S. Food and Drug Administration (FDA) has recently approved the use of ionising radiation for the treatment of fresh spinach and iceberg lettuce to protect consumers from the disease-causing bacteria.
Decontaminate herbs and spices
Spices, herbs and seasonings are valued for their distinctive flavours, colours and aromas. However, they are often contaminated with microorganisms from the environment and during processing. Since heat treatment can lead to a significant loss of flavour and aroma, a "cold process", like irradiation may be a good choice to decontaminate dried herbs and spices before incorporating into other food products.
Extend shelf-life of perishable produces
Extending the durable life of commercially important plant commodities is always desirable. Exposure to low dose of ionising radiation can help improve the shelf-life and maintain the post-harvest quality of some perishable produces. For example, irradiation can inhibit cap opening and stem elongation of mushrooms, limit unwanted sprouting of potato tubers and onion bulbs, and delay ripening in bananas, mangoes, and papayas.
Control insect infestation in fruits and grain products
A major problem encountered in preservation of fruits and grain products is insect infestation. Irradiation has been shown to be an effective alternative to the physical and chemical methods currently used for insect control. Commodities such as cereal grains, dried fruits, flour and coffee beans have been successfully disinfested by irradiation. However, it is worth mentioning that proper packaging of irradiated food products is required to prevent reinfestation of insects.
Despite the fact that irradiation has been used for decades for food disinfection and satisfying quarantine requirements in trade, health concerns over the consumption of irradiated food continue to attract attention. In the coming issue, we will have a more in-depth discussion on the safety and nutritional quality of food after irradiation treatment.
For details of the basic principles and application of food irradiation, please refer to our literature review on "Safety of Irradiated Food" .