70 Handbook of herbs and spices
This difficulty can be overcome by converting electrons into X-rays by fitting a
water-cooled converter plate to the scanner. The electrons, upon striking the metal
plate, are converted into X-rays. The conversion efficiency depends on the material
of the converter plate and the energy of the striking electrons. The X-rays are as
penetrating as gamma rays.
3.3.3 The choice of an irradiator
A number of aspects are considered during the choice of an irradiator. These include:
∑ the type of commodity
∑ whether loose bulk or packages
∑ throughput required
∑ thickness and shape of the product
∑ the size and shape of the container
∑ the packaging density of the product
∑ techno-economic feasibility
∑ socio-political implications.
3.3.4 Process control
During irradiation processing the aim is to expose the material to at least the minimum
required dose that governs the effectiveness of the process. Correct measurement of
dose and dose distribution in the product ensures that the radiation treatment is both
technically and legally correct. Application of an experimentally established dose for
the purpose of radiation processing of a specific food is important both technologically
and economically. Dose and dose distribution are determined by product and source
parameters. Product parameters are primarily the density of the commodity and packages.
The source parameters vary with the facility or the type of radiation being used.
3.3.5 Mechanism of action of ionizing radiations
Ionizing radiations bring about the desired effects by different mechanisms in different
foods, depending upon the dose of radiation. The ionizing radiations cause these
effects by causing changes in bio-molecules, primarily DNA, either by direct deposition
of energy or indirectly through production of radiolytic product of water, that interact
with the bio-molecules. The extent of radiation effect depends on the radiation energy
absorbed. It increases linearly with the dose in the dose range normally employed in
food irradiation. Water is an abundant component of food. Therefore, interaction of
water with radiation has a major role to play during irradiation. The radiolytic products
of water such as hydroxyl radical, hydrated electrons, hydrogen atoms, and peroxides
are highly reactive and play a major role in bringing out the effects of irradiation. The
effects brought about by the interaction of radiolytic products of water with bio-
molecules are also called indirect effects.
3.4 Nutritional and safety aspects........................................................
No other method of food processing has been subjected to such a thorough assessment
of safety as radiation processing. The various aspects of wholesomeness and safety