**4. Effects of ionizing radiation on structure**

The investigation of ionizing radiation effects on starch structure revealed information related to the granule morphology, crystalline structure, or structural characteristics as determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and chromatography.

the decrease or increase in crystallinity degree in accordance with the most affected region by irradiation dose. Anyway, the investigators considered even the possibility of crosslinking in

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Another study [17] stated that the crystallinity degree decreased more rapidly with irradiation dose increasing for bean starch (C-type pattern) than potato starch (A-type pattern), showing that the crystallographic patterns have different sensitivity to irradiation. Thus, the B-type pattern has been proven to be more sensitive to ionizing radiation processing than A-type pattern and justified the behavior of bean starch in which the B-type pattern degraded faster than A-type pattern from granule surface. It is noteworthy that recently an opposite behavior has been identified by Chung et al. [1] for corn starch with different content of amylose subjected to ionizing radiation processing, namely the high amylose corn starch showed a B-type pattern being more radiation resistant than the waxy corn starch with A-type pattern. Several works [3, 10, 17, 21, 33, 37] have reported results on the crystallinity degree of irradiated starch, estimated by using infrared spectroscopy, which involves the analysis of the absorption bands at 1047 cm−1 (crystalline structure) and 1022 cm−1 (amorphous region), and their respective ratio indicates the degree of starch order. The experimental data revealed that the ratio of 1047/1022 decreased with an increase of gamma radiation dose up to 50 kGy, and the starch granular crystallinity was affected [17, 21, 33, 37]. However, a couple of studies [3, 10] showed that the ionizing radiation processing (up to 50 kGy) had no influence on this ratio, suggesting that larger crystalline regions might be broken into small crystallites such

Morphology of starch granule exposed to ionizing radiation can be affected depending on starch type and irradiation parameters. For instance, studies on potato and rice starches [16, 38] reported the surface cracking of granules as well as deformation of granular structure were identified to increase with increasing irradiation dose in the range of 5–20 kGy at a dose rate of 2 kGy/h. Also, the extent of change depended on starch variety. Other studies on rice starches [14, 15] at lower irradiation doses (<10 kGy) and lower dose rate (0.4 kGy/h) also showed some modifications in the values of the mean sizes of the granules depending on irradiation dose and rice cultivars even if the irradiation apparently caused no change in the granule morphology. On the contrary, Shishonok et al. [18] reported that the surface structure of potato starch suffered no damage by electron beam irradiation even at high irradiation

For corn starch irradiated with gamma rays up to 50 kGy and dose rate around 1 kGy/h, an absence of notable changes on the shapes and sizes of starch granules has been noticed [1, 2]. These observations were confirmed and completed by another investigation [35], which reported that gamma irradiated corn starch retained the original shape and size without any granular cracking or roughness occurring on the surface, even for 500 kGy with a dose rate 83 Gy/min. On the other hand, other investigations found changes in corn starch morphology induced by ionizing radiation. Although the granule shape and sizes were apparently unaffected by electron

the case of the increase of crystallinity degree.

that the crystallinity degree was practically unaffected.

**4.2. Granule morphology**

doses (110–440 kGy).

### **4.1. Crystallinity**

Crystallinity and crystallinity degree of starch macromolecule can be evaluated by different analytical techniques of investigation, such as X-ray diffraction, infrared spectroscopy, or DSC. The same starch granule consists of both crystalline regions (crystalline lamellae of amylopectin) and amorphous regions (typical to amylose) without a net delimitation making the determination of its crystallinity actually difficult.

One of the most used method to analyze the crystallinity and crystallinity degree is the X-ray diffraction because it can provide the crystallographic patterns of starch granules. The crystalline lamellae show two types of polymorph structures that design different diffraction patterns: the A-type crystallinity with relatively compact structure, the B-type crystallinity with a more open structure, including a hydrated helical core, and the C-type crystallinity that is a mixture of A-type and B-type patterns [41]. The crystallinity and crystallinity degree depend on the botanical source of starch and amylose content [1] or distribution of chain length in amylose. The experimental data proved that the diffraction pattern remained generally unaffected even at very high irradiation doses up to 500 kGy [35]. However, Reddy et al. [19] reported alteration of crystallographic pattern of elephant foot yam starch by gamma radiation processing. Thus, the B-type pattern of native starch changed in the C-type in irradiated starch.

On the other hand, most investigations recorded the decrease in the crystallinity degree of starch as a result of irradiation. The reduction in crystallinity degree with the increasing irradiation dose has been explained by breaking of the crystalline regions. Conversely, some studies [2, 10] found out that the degree of crystallinity was insignificantly changed for cereal starches by gamma irradiation processing with irradiation doses up to 50 kGy and low irradiation dose rates (<19 Gy/min). In case of wheat starch, Kong et al. [39] reported that the gamma irradiation at a dose rate of 1 kGy/h moderately affected the crystallinity degree that increased continuously with irradiation dose increasing up to 7 kGy and decreased at 9 kGy. This behavior was attributed to the alterations predominantly in amorphous regions induced with irradiation dose up to 7 kGy, whereas the crystalline regions were more affected by irradiation dose of 9 kGy. Also, the irradiation at 10 kGy with dose rate of 0.4 kGy/h caused an increase of the crystallinity degree of corn starch indicating that a slower dose rate is able to induce more crystalline structure [37]. Moreover, the investigation on rice starch [14] revealed both reduction and an increase in crystallinity degree by irradiation up to 5 kGy with dose rate of 0.4 kGy/h depending on rice cultivars. Therefore, the ionizing radiation processing influenced both the crystalline region and amorphous region of starch granules, leading to the decrease or increase in crystallinity degree in accordance with the most affected region by irradiation dose. Anyway, the investigators considered even the possibility of crosslinking in the case of the increase of crystallinity degree.

Another study [17] stated that the crystallinity degree decreased more rapidly with irradiation dose increasing for bean starch (C-type pattern) than potato starch (A-type pattern), showing that the crystallographic patterns have different sensitivity to irradiation. Thus, the B-type pattern has been proven to be more sensitive to ionizing radiation processing than A-type pattern and justified the behavior of bean starch in which the B-type pattern degraded faster than A-type pattern from granule surface. It is noteworthy that recently an opposite behavior has been identified by Chung et al. [1] for corn starch with different content of amylose subjected to ionizing radiation processing, namely the high amylose corn starch showed a B-type pattern being more radiation resistant than the waxy corn starch with A-type pattern.

Several works [3, 10, 17, 21, 33, 37] have reported results on the crystallinity degree of irradiated starch, estimated by using infrared spectroscopy, which involves the analysis of the absorption bands at 1047 cm−1 (crystalline structure) and 1022 cm−1 (amorphous region), and their respective ratio indicates the degree of starch order. The experimental data revealed that the ratio of 1047/1022 decreased with an increase of gamma radiation dose up to 50 kGy, and the starch granular crystallinity was affected [17, 21, 33, 37]. However, a couple of studies [3, 10] showed that the ionizing radiation processing (up to 50 kGy) had no influence on this ratio, suggesting that larger crystalline regions might be broken into small crystallites such that the crystallinity degree was practically unaffected.

#### **4.2. Granule morphology**

**4. Effects of ionizing radiation on structure**

the determination of its crystallinity actually difficult.

(FTIR) spectroscopy and chromatography.

**4.1. Crystallinity**

60 Applications of Modified Starches

in irradiated starch.

The investigation of ionizing radiation effects on starch structure revealed information related to the granule morphology, crystalline structure, or structural characteristics as determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared

Crystallinity and crystallinity degree of starch macromolecule can be evaluated by different analytical techniques of investigation, such as X-ray diffraction, infrared spectroscopy, or DSC. The same starch granule consists of both crystalline regions (crystalline lamellae of amylopectin) and amorphous regions (typical to amylose) without a net delimitation making

One of the most used method to analyze the crystallinity and crystallinity degree is the X-ray diffraction because it can provide the crystallographic patterns of starch granules. The crystalline lamellae show two types of polymorph structures that design different diffraction patterns: the A-type crystallinity with relatively compact structure, the B-type crystallinity with a more open structure, including a hydrated helical core, and the C-type crystallinity that is a mixture of A-type and B-type patterns [41]. The crystallinity and crystallinity degree depend on the botanical source of starch and amylose content [1] or distribution of chain length in amylose. The experimental data proved that the diffraction pattern remained generally unaffected even at very high irradiation doses up to 500 kGy [35]. However, Reddy et al. [19] reported alteration of crystallographic pattern of elephant foot yam starch by gamma radiation processing. Thus, the B-type pattern of native starch changed in the C-type

On the other hand, most investigations recorded the decrease in the crystallinity degree of starch as a result of irradiation. The reduction in crystallinity degree with the increasing irradiation dose has been explained by breaking of the crystalline regions. Conversely, some studies [2, 10] found out that the degree of crystallinity was insignificantly changed for cereal starches by gamma irradiation processing with irradiation doses up to 50 kGy and low irradiation dose rates (<19 Gy/min). In case of wheat starch, Kong et al. [39] reported that the gamma irradiation at a dose rate of 1 kGy/h moderately affected the crystallinity degree that increased continuously with irradiation dose increasing up to 7 kGy and decreased at 9 kGy. This behavior was attributed to the alterations predominantly in amorphous regions induced with irradiation dose up to 7 kGy, whereas the crystalline regions were more affected by irradiation dose of 9 kGy. Also, the irradiation at 10 kGy with dose rate of 0.4 kGy/h caused an increase of the crystallinity degree of corn starch indicating that a slower dose rate is able to induce more crystalline structure [37]. Moreover, the investigation on rice starch [14] revealed both reduction and an increase in crystallinity degree by irradiation up to 5 kGy with dose rate of 0.4 kGy/h depending on rice cultivars. Therefore, the ionizing radiation processing influenced both the crystalline region and amorphous region of starch granules, leading to Morphology of starch granule exposed to ionizing radiation can be affected depending on starch type and irradiation parameters. For instance, studies on potato and rice starches [16, 38] reported the surface cracking of granules as well as deformation of granular structure were identified to increase with increasing irradiation dose in the range of 5–20 kGy at a dose rate of 2 kGy/h. Also, the extent of change depended on starch variety. Other studies on rice starches [14, 15] at lower irradiation doses (<10 kGy) and lower dose rate (0.4 kGy/h) also showed some modifications in the values of the mean sizes of the granules depending on irradiation dose and rice cultivars even if the irradiation apparently caused no change in the granule morphology. On the contrary, Shishonok et al. [18] reported that the surface structure of potato starch suffered no damage by electron beam irradiation even at high irradiation doses (110–440 kGy).

For corn starch irradiated with gamma rays up to 50 kGy and dose rate around 1 kGy/h, an absence of notable changes on the shapes and sizes of starch granules has been noticed [1, 2]. These observations were confirmed and completed by another investigation [35], which reported that gamma irradiated corn starch retained the original shape and size without any granular cracking or roughness occurring on the surface, even for 500 kGy with a dose rate 83 Gy/min. On the other hand, other investigations found changes in corn starch morphology induced by ionizing radiation. Although the granule shape and sizes were apparently unaffected by electron beam processing, the appearance of small circular perforations on the granule surface could be observed for irradiation of 50 kGy (dose rate of 2 kGy/min) [3]. Moreover, Kamal et al. [8] showed that the shape of corn starch granule was somewhat deformed by both gamma rays and electron beams for doses up to 100 kGy. It is noteworthy that the different content of amylose in corn starch had no influence on morphological aspects of irradiated starch; the granules remained intact and visually unchanged by gamma irradiation up to 50 kGy with dose rate around 1 kGy/h [1].

Microscopic observation of bean starches indicated surface cracking of granule with irradiation in a dose-dependent manner in the irradiation dose range of 5–25 kGy (<185 Gy/h) without significant changes in granule dimensions [20, 21]. However, in an earlier study, Gani et al. [22] have found the deformation of granule increased with increasing irradiation dose in the range of 5–20 kGy (dose rate of 2 kGy/h), the extent of change depending on starch variety. Other starches extracted from different botanical sources (lotus, chickpea) also presented surface fissures induced by irradiation [23, 32], while the ionizing radiation processing had no influence on the morphological characteristics for starches from elephant foot yam, Indian horse chestnut, and sago [19, 33, 36].

13.84 Gy/min. These results were attributed to the breaking of chemical bonds by irradiation. Besides, the botanical source of starch and the irradiation dose rate influenced the degree of the radiation-induced changes. Also, the findings [2] showed a decrease in peak intensity of the bending mode of the glycosidic linkage (C─O─C) with 13.4% explained by a depolymerization of amylose chains of starch and/or the amylopectin double helices within the amorphous regions after irradiation due to the breaking of glycosidic linkages [2, 10]. Conversely, an increase in the intensity of the characteristic peak at 1647 cm−1 ascribed to carbonyl groups was also observed [8] for e-beam irradiated corn starch, suggesting that the starch degraded

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At the same time, the band intensity of the bending mode of water was also affected by a decreasing trend as the irradiation dose increased [2, 10]. This change occurred by water radiolysis that involves the breakdown of the water structure under the action of ionizing energy

Molecular weight of polymers influences most of their physicochemical and functional properties, and its investigation can reveal information useful to understand the behavior of macromolecules to ionizing radiation processing. Unfortunately, one can notice the lack of interest in this subject and the existence of only a few papers [4, 5, 12, 17] that have approached the study of the influence of the electron beam or gamma radiation on the starch molecular weights. The experimental data showed the decreasing evolution of the molecular weights with the irradiation dose independently of the starch botanical source. This kind of behavior indicated the break of polymeric chain and formation of the fragments with different molecular weights, which modified the mass molecular distribution of starch. However, the radiation-induced changes were correlated with the structural organization of starch, especially the branched structure component of starch (amylopectin). Hence, for cereal starches having short chains, the molecular weight distribution was affected mainly by the formation of the fractions with higher molecular weight than the formation of the fractions with low molecular weight. Instead, for tuber starch having long chains, the molecular weight distribution was slightly modified by irradiation, namely the scissions in fractions with high molecular weight being closer to that of the fractions with

and leads to the formation of hydroxyl and hydrogen radicals.

1550–1800 O─H vibrations from bound water molecules

Below 800 Pyranose ring of the glycosidic unit

**Table 3.** Band region frequencies and assignments of FTIR absorption of starch.

**4.4. Molecular weight and molecular weight distribution**

by free radical reaction.

**Frequency region [cm−1] Assignment** 3000–3700 O─H stretch 2800–3000 C─H stretch

800–1550 Fingerprint region

low molecular weight.

Consequently, the ionizing radiation is an energetic penetrating radiation that able to produce effects in the whole volume of the samples, so that the radiation-induced changes may occur both in the central regions and in the peripheral regions of the starch granules. However, the fact that microscopic methods reveal no damage to the granule outer layer for some starches leads to the conclusion that the radiation-induced changes might occur at a more intimate level of matter in the form of structural changes depending on starch granular structure.

#### **4.3. Spectral characteristics**

Generally, the analytical evaluation of FTIR spectrum of native starch must show five different frequency regions as presented in **Table 3** [42–44]. Therefore, potential modifications induced by ionizing radiation processing of bands assigned to those frequency regions should be evaluated.

The spectral features of the irradiated starch were apparently similar to native starch and no bands of new functional groups were found in spectrograms [3, 9, 10, 15, 18, 19, 33, 35]. For instance, Liu et al. [35] found that all spectral patterns for corn starch irradiated with gamma radiation were similar to those of control sample even after 500 kGy irradiation. However, some differences related to the frequency and intensity of some bands were identified after irradiation indicating radiation-induced alteration of the macromolecule structural integrity. Thus, slight shifts of some peaks and the decrease in intensity of some bands or the increase in intensity of other bands with the irradiation dose increasing have been noticed for all types of starches. The most affected bands were especially those assigned to O─H and C─H bonds [2, 3, 8], indicating that the stability of the inter- and intramolecular hydrogen bonds of starch structure was affected by ionizing radiation processing [3]. As an example, Bettaïeb et al. [2] found intensity decrease with 38.4 and 19.6%, respectively, for corn starch after irradiation with 50 kGy at 19 Gy/min. Instead, for wheat starch [10], the absorbance intensity of the same bonds decreased dramatically about 70 and 67%, respectively, after irradiation with 50 kGy at


**Table 3.** Band region frequencies and assignments of FTIR absorption of starch.

beam processing, the appearance of small circular perforations on the granule surface could be observed for irradiation of 50 kGy (dose rate of 2 kGy/min) [3]. Moreover, Kamal et al. [8] showed that the shape of corn starch granule was somewhat deformed by both gamma rays and electron beams for doses up to 100 kGy. It is noteworthy that the different content of amylose in corn starch had no influence on morphological aspects of irradiated starch; the granules remained intact and visually unchanged by gamma irradiation up to 50 kGy with dose rate

Microscopic observation of bean starches indicated surface cracking of granule with irradiation in a dose-dependent manner in the irradiation dose range of 5–25 kGy (<185 Gy/h) without significant changes in granule dimensions [20, 21]. However, in an earlier study, Gani et al. [22] have found the deformation of granule increased with increasing irradiation dose in the range of 5–20 kGy (dose rate of 2 kGy/h), the extent of change depending on starch variety. Other starches extracted from different botanical sources (lotus, chickpea) also presented surface fissures induced by irradiation [23, 32], while the ionizing radiation processing had no influence on the morphological characteristics for starches from elephant foot yam, Indian

Consequently, the ionizing radiation is an energetic penetrating radiation that able to produce effects in the whole volume of the samples, so that the radiation-induced changes may occur both in the central regions and in the peripheral regions of the starch granules. However, the fact that microscopic methods reveal no damage to the granule outer layer for some starches leads to the conclusion that the radiation-induced changes might occur at a more intimate level of matter in the form of structural changes depending on starch granular structure.

Generally, the analytical evaluation of FTIR spectrum of native starch must show five different frequency regions as presented in **Table 3** [42–44]. Therefore, potential modifications induced by ionizing radiation processing of bands assigned to those frequency regions should

The spectral features of the irradiated starch were apparently similar to native starch and no bands of new functional groups were found in spectrograms [3, 9, 10, 15, 18, 19, 33, 35]. For instance, Liu et al. [35] found that all spectral patterns for corn starch irradiated with gamma radiation were similar to those of control sample even after 500 kGy irradiation. However, some differences related to the frequency and intensity of some bands were identified after irradiation indicating radiation-induced alteration of the macromolecule structural integrity. Thus, slight shifts of some peaks and the decrease in intensity of some bands or the increase in intensity of other bands with the irradiation dose increasing have been noticed for all types of starches. The most affected bands were especially those assigned to O─H and C─H bonds [2, 3, 8], indicating that the stability of the inter- and intramolecular hydrogen bonds of starch structure was affected by ionizing radiation processing [3]. As an example, Bettaïeb et al. [2] found intensity decrease with 38.4 and 19.6%, respectively, for corn starch after irradiation with 50 kGy at 19 Gy/min. Instead, for wheat starch [10], the absorbance intensity of the same bonds decreased dramatically about 70 and 67%, respectively, after irradiation with 50 kGy at

around 1 kGy/h [1].

62 Applications of Modified Starches

horse chestnut, and sago [19, 33, 36].

**4.3. Spectral characteristics**

be evaluated.

13.84 Gy/min. These results were attributed to the breaking of chemical bonds by irradiation. Besides, the botanical source of starch and the irradiation dose rate influenced the degree of the radiation-induced changes. Also, the findings [2] showed a decrease in peak intensity of the bending mode of the glycosidic linkage (C─O─C) with 13.4% explained by a depolymerization of amylose chains of starch and/or the amylopectin double helices within the amorphous regions after irradiation due to the breaking of glycosidic linkages [2, 10]. Conversely, an increase in the intensity of the characteristic peak at 1647 cm−1 ascribed to carbonyl groups was also observed [8] for e-beam irradiated corn starch, suggesting that the starch degraded by free radical reaction.

At the same time, the band intensity of the bending mode of water was also affected by a decreasing trend as the irradiation dose increased [2, 10]. This change occurred by water radiolysis that involves the breakdown of the water structure under the action of ionizing energy and leads to the formation of hydroxyl and hydrogen radicals.

#### **4.4. Molecular weight and molecular weight distribution**

Molecular weight of polymers influences most of their physicochemical and functional properties, and its investigation can reveal information useful to understand the behavior of macromolecules to ionizing radiation processing. Unfortunately, one can notice the lack of interest in this subject and the existence of only a few papers [4, 5, 12, 17] that have approached the study of the influence of the electron beam or gamma radiation on the starch molecular weights. The experimental data showed the decreasing evolution of the molecular weights with the irradiation dose independently of the starch botanical source. This kind of behavior indicated the break of polymeric chain and formation of the fragments with different molecular weights, which modified the mass molecular distribution of starch. However, the radiation-induced changes were correlated with the structural organization of starch, especially the branched structure component of starch (amylopectin). Hence, for cereal starches having short chains, the molecular weight distribution was affected mainly by the formation of the fractions with higher molecular weight than the formation of the fractions with low molecular weight. Instead, for tuber starch having long chains, the molecular weight distribution was slightly modified by irradiation, namely the scissions in fractions with high molecular weight being closer to that of the fractions with low molecular weight.
