Advisory technological dose limits

These dose limits are recommended by the ICGFI solely on the basis of technological data available in the literature. The lowest absorbed dose required to achieve a desired effect is termed in this book the lowest acceptable dose. The highest absorbed dose acceptable is determined by the sensory and functional properties of the product that must not be impaired by too high a dose. Their values are based on food irradiation experience and are specified by food technologists for each combination of process and product on the basis of the results obtained in experimental research preceding commercial scale application. It should be kept in mind, however, that the radiation effect on a product is a continuous function and not a step function of the applied dose, so that the lowest acceptable dose is not stringently defined but must be derived from other considerations. The collection of such results (see Bibliography for ICGFI publications) defines GIP in radiation processing of food, which is the same as good manufacturing practice (GMP) in other food processing. GIP is always considered an integral part of GMP. These advisory technological dose limits are given in Table I [3].

Much has been published on food irradiation, and several international conferences sponsored by FAO/IAEA/WHO have taken place.¹It is not the aim of

1 At Karlsruhe in 1966, at Bombay in 1972, at Wageningen in 1977, at Washington in 1985, at Geneva in 1988, at Aix-en-Provence in 1993 and at Antalya in 1999; the proceedings of these conferences are available through the IAEA.

TABLE I. ADVISORY TECHNOLOGICAL DOSE LIMITS [3]

Classes of food Purpose Maximum dose ICGFI^a

(kGy) document No.

Class 1: Bulbs, roots To inhibit sprouting 0.2 8

and tubers during storage

Class 2: Fresh fruits and To delay ripening 1.0 6

vegetables (other Insect disinfestation 1.0 3, 7, 17

than Class 1) Shelf life extension 2.5 6

Quarantine control^b 1.0 7, 13, 17

Class 3: Cereals and their Insect disinfestation 1.0 3, 20

milled products, Reduction of microbial 5.0 3, 20

nuts, oil seeds, load pulses, dried fruits

Class 4: Fish, seafood and Reduction of certain 5.0 10 their products pathogenic micro-organisms^c

(fresh or frozen) Shelf life extension 3.0 10

Control of infection 2.0 10

by parasites^c

Class 5: Raw poultry and Reduction of pathogenic 7.0 4 meat and their micro-organisms^c

products (fresh and Shelf life extension 3.0 4

frozen) Control of infection by 2.0 4

parasites^c

Class 6: Dry vegetables, Reduction of certain 10.0 5, 19 spices, condiments, pathogenic

animal feed, dry micro-organisms^c

herbs and herbal teas Insect disinfestation 1.0 5, 19

Class 7: Dried food of animal Disinfestation 1.0 9

origin Control of moulds 3.0 9

Class 8: Miscellaneous foods, Reduction of >10 including, but not micro-organisms

limited to, honey, Sterilization >10 space foods, hospital Quarantine control >10 foods, military rations,

spices, liquid egg, thickeners

a See list of ICGFI documents in the Bibliography.

b The minimum dose may be specified for particular pests. For fruit flies, the minimum dose is at least 0.15 kGy.

c The minimum dose may be specified depending on the objective of the treatment to ensure the hygienic quality of food.

Notes:

1. Product grouping into classes (except Class 8) is on the basis of similarity of chemical compositions.

2. The maximum dose limits have been set for good irradiation practice and not from a food safety viewpoint.

this book to provide a full bibliography on the subject; however, more detailed information on food irradiation and effects achieved may be found elsewhere [12–17]

and by reference to some of the published food irradiation bibliographies².

The dose ranges given in the literature should not be understood to be rigid; the lowest acceptable dose may vary in either direction depending on the conditions of production and harvesting, on the state of ripeness and on the environmental conditions.

This is also true for the maximum tolerable dose, which may be quite low in some applications in order to avoid damage to radiation sensitive products. Consequently, any reference to such values is as ‘advisory technological dose limits’ only. Such dose data are, in principle, not suitable for regulatory purposes, but only for guidance.

The ranges of dose commonly used in food irradiation to achieve various effects can be classified as given in the following sections.

1.4.1. Applications at low dose levels (10 Gy–1 kGy)

Sprouting of potatoes, onions, garlic, shallots, yams, etc. can be inhibited by irradiation in the dose range 20–150 Gy. Radiation affects the biological properties of such products in such a way that sprouting is appreciably inhibited or completely prevented. Physiological processes such as ripening of fruits can be delayed in the dose range 0.1–1 kGy. These processes are a consequence of enzymatic changes in the plant tissues.

Insect disinfestation by radiation in the dose range 0.2–1 kGy is aimed at preventing losses caused by insect pests in stored grains, pulses, cereals, flour, coffee beans, spices, dried fruits, dried nuts, dried fishery products and other dried food products. A minimum absorbed dose of about 150 Gy can ensure quarantine security against various species of tephretid fruit flies in fresh fruits and vegetables, and a minimum dose of 300 Gy could prevent insects of other species from establishing in non-infested areas. In most cases irradiation either kills or inhibits further development of different life-cycle stages of insect pests.

The inactivation of some pathogenic parasites of public health significance such as tapeworm and trichina in meat can be achieved at doses in the range 0.3–1 kGy.

1.4.2. Applications at medium dose levels (1–10 kGy)

Radiation enhances the keeping quality of certain foods through a substantial reduction in the number of spoilage causing micro-organisms. Fresh meat and seafood, as well as vegetables and fruits, may be exposed to such treatments with

2 For example, Bibliography on Irradiation of Foods, Bundesforschungsanstalt für Ernährung, Karlsruhe, Germany (published at irregular intervals until No. 40 in 1996, now available on-line at http://www.dainet.de/8080/BFELEMISTW/SF).

doses ranging from about 1 to 10 kGy, depending on the product. This process of extending the shelf life is sometimes called ‘radurization’.

Pasteurization of solid foods such as meat, poultry and seafoods by radiation is a practical method for elimination of pathogenic organisms and micro-organisms except for viruses. It is achieved by the reduction of the number of specific viable non-spore-forming pathogenic micro-organisms such that none is detectable in the treated product by any standard method, for which doses range between 2 and 8 kGy.

The product will usually continue to be refrigerated after the radiation treatment. This process of improving the hygienic quality of food by inactivation of food-borne pathogenic bacteria and parasites is sometimes called ‘radicidation’. This medium dose application is very similar to heat pasteurization, and is hence also called radiopasteurization.

1.4.3. Applications at high dose levels (10–100 kGy)

Irradiation at doses of 10–30 kGy is an effective alternative to the chemical fumigant ethylene oxide for microbial decontamination of dried spices, herbs and other dried vegetable seasonings. This is achieved by reducing the total microbial load present in such products including pathogenic organisms.

Radiation sterilization in the dose range 25–70 kGy extends the shelf life of precooked or enzyme inactivated food products in hermetically sealed containers almost indefinitely. This is valid independent of the conditions under which the product is subsequently stored as long as the package integrity is not affected. This effect is achieved by the reduction of the number and/or activity of all organisms of food spoilage or public health significance, including their spores, to such an extent that none are detectable in the treated product by any recognized method. This process is analogous to thermal canning in achieving shelf-stability (long term storage without refrigeration) and is sometimes called ‘radappertization’.