**2. Fundamentals of radiation processing**

Radiation is generally a form of energy characterized by its ability to move from one location to another, and it can be divided into non-ionizing (ultraviolet light, visible light, infrared radiation, microwaves, etc.) and ionizing (X-rays, gamma rays, electron beams, etc.) ones [26]. Ionizing radiation—mainly gamma radiation and electron beam—is the most used to modify starch macromolecules and, further, the approach will be made in context of the processing procedures using ionizing radiation. Gamma rays—electromagnetic radiation—are emitted by radionuclides such as isotopes of cobalt-60 (60Co) and cesium-137 (137Cs). Electron beam consists of accelerated electrons, which are charged particles generated from regular electricity using linear accelerators, and do not involve radioactive isotope sources. It is noteworthy that electron beam irradiation is similar to gamma processing with basically the same interaction with materials to be subjected to irradiation processing [27].

#### **2.1. Interaction of radiation with matter**

The chapter gives an overview of the major findings in the last decade concerning the starches modified by ionizing radiation processing. Therefore, aspects strongly related to changes in physicochemical, functional, and structural properties of starches from various botanical origins are approached. The main key points of this topic are highlighted by a critical evaluation

Apparent amylose content Carboxyl content, pH, Amylose leaching and swelling

Water absorption capacity

Leaching of carbohydrates and

power

Syneresis Pasting properties Granule morphology and

crystallinity

amylose

Swelling volume

**Investigated properties Techniques of** 

**characterization**

Chemical methods, viscography, SEM, X-ray diffractometry

Viscography, chemical and spectroscopic methods

**References**

[23]

[13]

It is to be mentioned herein that in the last decade two other reviews regarding the impact of radiation processing on starch [24, 25] have been published, and the most recent one [25] has

Radiation is generally a form of energy characterized by its ability to move from one location to another, and it can be divided into non-ionizing (ultraviolet light, visible light, infrared radiation, microwaves, etc.) and ionizing (X-rays, gamma rays, electron beams, etc.) ones [26]. Ionizing radiation—mainly gamma radiation and electron beam—is the most used to modify starch macromolecules and, further, the approach will be made in context of the processing procedures using ionizing radiation. Gamma rays—electromagnetic radiation—are emitted by radionuclides such as isotopes of cobalt-60 (60Co) and cesium-137 (137Cs). Electron beam consists of accelerated electrons, which are charged particles generated from regular electricity using linear accelerators, and do not involve radioactive isotope sources. It is noteworthy that electron beam irradiation is similar to gamma processing with basically the same interac-

of the mentioned aspects and future perspectives are suggested.

**Table 1.** Studies relevant to effects of ionizing radiation on various starches.

summarized only the gamma radiation influence on starches.

tion with materials to be subjected to irradiation processing [27].

**2. Fundamentals of radiation processing**

**Type of starch Type of ionizing** 

54 Applications of Modified Starches

Lotus Gamma rays; 5–20 kGy,

content 12%

*Stem*

**radiation/processing parameters**

2 kGy/h, in air, moisture

Sago E-beam 3 MeV; 5–30 kGy Pasting profile

Gamma rays transfer energy by the photoelectric effect, Compton effect, and pairs generating, leading to liberation of fast electrons that lose energy by the same effects as accelerated electrons of the electron beams. Later on, the energy is absorbed by matter when electrons pass through it and two distinct primary effects, *ionization* and *excitation* of atoms and molecules of the substance occur as presented synthetically in **Figure 1**.

Ionization is the primary process by which a neutral atom or molecule becomes charged, and the resulting product is called *ion*. An ion formed by the loss or capture of an electron contains an unpaired electron, being actually a *free radical*, which is highly reactive chemical specie. The ejected electron may ionize further other atoms and molecules by successive collisions and ionizations. Excitation is another primary effect occurring when a high-energy charged particle passes through atoms imparting energy to atomic electrons without ejecting them and leads to an excited atom.

The secondary effects consist in different reactions of primary species (ions, excited molecules, or free radicals) that lead to the final products. These effects could be dissociation of an excited molecule into two radicals or into two different molecules. The free radicals participate further in recombination processes between themselves (radical-radical recombination) leading either to the initial molecule or new molecules. The formed radicals can also suffer a recombination with a new molecule abstracting a hydrogen atom forming a new free radical and a new molecule.

**Figure 1.** Fundamental processes of electrons passing through matter.

#### **2.2. Radiation quantities**

The most used dosimetric quantities and their units are the absorbed dose and the absorbed dose rate according to the International Commission on Radiation Units and Measurements (ICRU) Report no. 33 [28]. Moreover, these radiation quantities are the most important in the physical quantities used in the dosimetry field in order to optimize and control the irradiation process [29, 30].

The *absorbed dose*, *D*, is the amount of energy absorbed per unit mass of irradiated matter at a point in the region of interest [29]:

$$D = \frac{d\vec{\varepsilon}}{dm} \tag{1}$$

**3. Effects of ionizing radiation on functional properties**

presented.

**3.1. Physicochemical properties**

by avoiding the microorganisms' development.

The physicochemical and functional properties of starch in various applications are of great interest, especially for manufacturers of starch-based products. Aspects related to the ionizing radiation effects on physical, chemical, and functional characteristics of starch are onward

Aspects on Starches Modified by Ionizing Radiation Processing

http://dx.doi.org/10.5772/intechopen.71626

57

The moisture contents of starches extracted from various botanical sources (lotus, sago, tapioca, wheat) were insignificantly affected by gamma radiation up to 20 kGy (dose rate ≤ 9 kGy/h) and electron beam up to 30 kGy [13, 23]. On the other hand, the moisture contents of rice starches were also insignificantly affected by gamma radiation at low doses (<1.5 kGy with dose rate of 0.63 kGy/h) [31], whereas a significant reduction in moisture content occurred at irradiation doses >2 kGy (dose rate of 0.4 kGy/h) as a result of radiation energy dissipation while ionizing radiation penetrates the starch sample [15]. Also, for starch extracted from elephant foot yam, the amount of moisture decreased significantly by gamma irradiation up to 25 kGy with dose rate of 2 kGy/h [19]. According to Reddy et al. [19], the reduction in the moisture content of starch sample by radiation processing may improve the shelf life of starch

pH of aqueous starch solutions decreased with increase of irradiation dose regardless of the botanical origin of the starch [5, 14, 16, 19, 23, 31–33]. The descending change of solution pH after irradiation could be attributed to the formation of chemical groups with acidic character such as carboxyl, carbonyl, or peroxide groups. Moreover, this behavior is sustained due to the fact that radiation processing of starch was generally performed in the presence of oxygen, thus promoting the appearance of free radicals, compounds with carbonyl bonds (aldehydes/ketones), organic peroxides, or other polysaccharide degradation products [34] that can lead to the increase of starch acidity. Therefore, the reduction of solution pH is strongly correlated with the increase of carboxyl content by the ionizing radiation processing of starch.

The water solubility can be improved concomitantly with the reduction of swelling power of granule by ionizing radiation processing for all starches. Therefore, the solubility value increased with the increase of irradiation dose for starches extracted from various botanical sources (corn, wheat, rice, potato, bean, elephant foot yam, lotus, chickpea, and Indian horse chestnut) [5, 9, 10, 15, 16, 18, 19, 21–23, 31–33, 35, 36]. The increase in solubility was due to the increase in polarity as a result of chain scission under irradiation and the decrease in inter-chain hydrogen bonds [35]. Such behavior demonstrates clearly that the starch molecules suffered important changes as a

The ionizing radiation processing of all types of starches caused the reduction of **swelling power** as the increase of the irradiation dose, especially at higher doses [5, 9, 10, 15–17, 19, 21, 22, 31, 32, 36–38]. This evolution could be attributed to the fact that starch granules become sensitive being weaker and easier to break after irradiation. In addition, a consequence of starch radiation-induced degradation can be also the inhibition of granule ability to trap water and provoke the swelling explaining thus the reduction of swelling power by irradiation.

consequence of a degradation phenomenon induced by ionizing radiation processing.

where *dε* ¯ is the mean energy imparted by ionizing radiation to the matter in a volume element and d*m* is the mass of that volume element.

The SI derived unit of absorbed dose is the *gray* (Gy), which replaced the earlier unit of absorbed dose, the *rad* that is still tolerated, but less used:

$$1\,\text{Gy} = 1\,\text{J/kg} = 100\,\text{rad}$$

For this absorbed dose, the rate of change of it with time can be defined as the absorbed dose rate, *D*̇ :

$$
\dot{D} = \frac{dD}{dt} \tag{2}
$$

The SI derived unit of absorbed dose rate is the *Gy/s*.

The absorbed dose and the absorbed dose rate will be hereinafter referred as irradiation dose and irradiation dose rate, respectively.

#### **2.3. Advantages and disadvantages of ionizing radiation processing**

Ionizing radiation has many advantages in material processing, being an effective tool to induce changes in structure and functional properties of materials without environmental negative implication. Thus, it is an environmentally friendly process that involves no use of polluting agents, no generation of undesirable residual products, and no penetration of toxic substances in treated products. Despite the advantages, ionizing radiation processing is accompanied by some disadvantages as shown in **Table 2**.


**Table 2.** Ionizing radiation processing: Advantages and disadvantages.
