Chapter 1: Introduction

For newcomers, food irradiation is a promising innovative food processing technology. However, those that have spent their lives working in this field since its first industrial use, around the 1950s, may consider that everything has already been done. In fact, the application of ionizing radiation for food preservation started immediately after its discovery. In 1895, W. R. Röntgen observed the existence of non-visible radiation, as disclosed by the famous picture of the first radiography of his wife's hand, where her bones and wedding ring could be discerned. The following year, H. Becquerel discovered the radioactivity of atoms, and the first patents on the use of ionizing radiation for food preservation were claimed in 1905.

Experiments with ionizing radiation have continued until the present day. Its use at industrial scale proliferated after the 1960s. In the US, ionizing radiation was first applied to develop sterile meat products to substitute canned and frozen military rations.

US astronauts have been using irradiated food since 1972. Also in 1972, the Japanese government allowed the irradiation of potatoes for sprout inhibition. With the progress of the technology, certain countries started to authorize its use at higher doses and application to other food items, contributing to the marketing of this technology (see Chapter 17).

Gamma rays, accelerated electrons (e-beam), and X-rays have been successfully tested for food processing, insect disinfestation (see Chapter 9), microbial decontamination (see Chapter 10), or to extend the shelf life of food (see Chapter 12). Their use is regulated (see Chapter 2), with all three types of irradiation processing (see Chapters 3 and 4) having enough energy to ionize atoms and break molecules without interfering with the nucleus, consequently not inducing radioactivity in food, the main concern of non-informed consumers (see Chapters 17 and 20).

In parallel, several materials have been tested in order to irradiate packed food (see Chapter 8), one of the main advantages of this technology, contributing to guarantee that a product meets the high standards of safety and quality, which, together with irradiation processing, is an essential tool to prevent food outbreaks with invaluable costs for the industry and, sometimes, also in terms of human lives (see Chapter 10). The industrial use of irradiation for food processing also follows a strict protocol under the qualification and certification of irradiation facilities (see Chapter 19).

Due to public misconceptions about ionizing radiation and the strong uproar of anti-science movements, some countries have reversed or halted the progress in this area, as is the case with the European Union (see Chapter 2).¹ In the EU, a white list of irradiated products was established, with only one type of products in the list, spices and dried herbs. However, some countries have their own list, authorized by the EU, allowing the irradiation of several food products, such as vegetables, fish, or meat (see Chapters 2 and 20). Currently, its potential contribution to food processing is not fully exploited to reduce or eliminate the use of chemicals for postharvest food processing, which could be a driven force for the technology, so as to reduce the obvious adverse effects of some chemicals on the environment and humans. In addition, irradiation could be a feasible alternative for postharvest processing, such as hot water or steam treatments, with less impact on the food properties.

Although there are several qualified and certified gamma and e-beam irradiation facilities for food irradiation processing (see Chapters 2 and 19), some technical limitations still exist. Not all food products can be processed by this technology, as high doses would be needed to achieve the desired effect, potentially compromising the quality and shelf life of the product. Namely, foods with high fat content may be oxidized and doses above 5 kGy may also change certain organoleptic properties of fruits (see Chapter 11).

Ionizing radiation applications for food preservation are more than a century old and its industrial use has been around for more than half a century. However, the interaction of ionizing radiation (gamma, e-beam, and X-rays) with natural matrices is a complex phenomenon, not as easily interpreted as the interaction with inorganic and single molecule materials, depending also on the irradiation conditions (dose rate, product temperature, and moisture content) (see Chapter 11).

The food product type (fruit, vegetable, fish, or meat), size (physical dimensions), state (solid or liquid), temperature (ambient or frozen), and irradiation conditions (dose rate or modified atmosphere) can be optimized to minimize the irradiation effects and improve its application for the desired purpose. These parameters, along with new trends in packaging materials (see Chapter 8), are the object of current research, maintaining the scientific community alive and working in this field so as to validate processes and study their effect on several natural matrices and under different irradiation conditions and technologies. This research is also contributing to maintaining the focus on the safety of this promising technology (see Chapter 16), albeit underused and still not fully accepted due to ignorance and/or misconceptions, as discussed above.

The dose ranges for a variety of purposes are more or less well established: for sprout inhibition, less than 0.5 kGy; for insect disinfestation, up to 0.5 kGy; for shelf-life extension, 1 to 2 kGy; for microbial decontamination, up to 5 kGy; and for food sterilization, more than 5 kGy. With such food processes already under control by several methods (see Chapters 13, 14, and 15) and the technological applications so well defined, has everything been done?

In fact, this is not the case. As discussed in the previous section, the interaction of ionizing radiation with natural products is multifactorial, where some molecules may protect others from ionizing radiation effects, requiring case-by-case studies. The referred dose ranges should not be assumed to be universal for all food products. Even at low doses, such as those recommended for fresh fruit or vegetable preservation (about 1 or 2 kGy), certain adverse effects have been observed, such as organoleptic changes, compromising the use of this technology in such particular cases. Its combination with other technologies or processes could overcome these side effects, allowing its application for food preservation (see Chapter 12).

To fully understand the impact of ionizing radiation in products where radiosensitive molecules are present, the combination with molecules able to protect the former from radiation effects and to increase the extractability of natural compounds with added value is still an open field. Not only the interaction of radiation with natural matrices needs to be studied, but also the technology for food irradiation is continually under development to make it more economically feasible (see Chapter 18). There is also a current tendency to test X-ray processing, limited in some countries to energies below 5 MeV, with ongoing research aimed at extending its use to higher energies (7.5 MeV), as authorized in the US but not in the EU. Recently, in 2015, the IAEA started a Collaborative Research Project (CRP) involving 13 countries with the objective of developing new technological solutions and simultaneously validating their application for different food items.

There is still room to continue research in this field, namely to optimize the irradiation conditions using the output of reliable dosimetry systems (see Chapter 5), to assess other beam energies to lower the cost of the processes, and to use mobile systems that may be applied in close proximity to the food production station (see Chapters 3 and 4).

Let's go through the book, chapter by chapter, contributing to the comprehension and recognition of such a global technology, able to foster and/or open new markets to guarantee the safety and quality of food.