Characterization of Physicochemical Properties of Starch in Barley Irradiated with Proton Beam

Sang Kuk Kim*, Shin Young Park**, and Hak Yoon Kim***†

*Division of Crop Breeding, Gyeongsangbuk-do Provincial Agricultural Research and Extension Services,

Daegu 702-708, Republic of Korea

**Department of Clinical Pathology, Jeju Halla University, Jeju 690-708, Republic of Korea

***Department of Global Environment, Keimyung University, Daegu 704-701, Republic of Korea

260

†Corresponding author: (Phone) +82-53-580-5918 (E-mail) hykim@kmu.ac.kr

<Received 25 March, 2013; Accepted 22 July, 2013>

한작지(Korean J. Crop Sci.), 58(3): 260~266(2013) DOI : http://dx.doi.org/10.7740/kjcs.2013.58.3.260

ABSTRACT The study was carried out to determine the gel pasting properties of barley (Hordeum vulgare L. cv. Geoncheonheugbori) as affected by different proton beam irradiation. The λmax, blue value, and amylose content were significantly associated with increasing proton beam irradiation. The pasting time in barley flour irradiated with proton beam ranged 0.09 to 0.16 min shorter than non- irradiated barley flour. Gel pasting temperature ranged 57.4 to 60.5℃. Gel pasting temperature in barley flour decreased with increasing proton beam irradiation. Proton beam irradiation caused a significant decrease in the onset temperature (To), peak temperature (Tp), conclusion temperature (Tc) and enthalpy change (ΔH). Gelatinization range (R) in barley starch was more broaden than that of non-irradiated barley starch. Barley starches gave the strong diffraction peak at around 2θ values15°, 18°, 20°, and 23° 2θ. Peak intensity tended to increase with increased proton beam irradiation. The granule crystallinity is closely associated with decreased amylose and increased amylopectin component. The crystallinity degree of barley starch irradiated with proton beam was significantly increased and it ranged from 24.9 to 32.9% compared to the non-irradiated barley starches. It might be deduced that proton beam irradiation causes significant changes of properties of starch viscosity in rice, especially at high irradiation of proton beam.

Keywords : barley, Hordeum vulgare, proton beam irradiation, starch properties

Barley is the world’s fourth most important cereal after

wheat, rice, and corn. It is the most widely cultivated but

for the most part, it is used for feed and brewing material

rather than as foodstuff for human consumption (Bhatty,

1993; Mitsunaga et al., 1994).

Irradiation is known to degrade the starch. Numerous

studies have been carried out on gamma-irradiated starch.

As a useful method for the production of modified starch,

gamma irradiation produces free radicals on starch molecules

that can alter their size and structure (Sabularse et al.,

1991). Several studies on the effects of ionizing radiation

on wheat starch (Lai et al., 1959; Milner, 1961) and barley

endosperm (Faust and Massey, 1966) have been conducted.

Gamma irradiation is capable of hydrolyzing chemical

bonds, thereby cleaving large molecules of starch into

smaller fragments of dextrin that may be either electrically

charged or uncharged as free radicals. These changes may

affect the physical and rheological properties of irradiated

foods, resulting in increased solubility of starch (Deschreider,

1959) and decreased swelling power (Tollier and Guilbot,

1970) and decreased relative viscosity (Vakil et al., 1973)

of starch paste. Very often the viscosity of cooked native

starch is too high to use in certain applications. Therefore,

it should be modified to meet such application.

Modified starch can provide a wide range of functions, from

binding to disintegrating, imbibing or inhibiting moisture.

Types of modification that are most often made, sometimes

singly, but often in combinations, are crosslinking of polymer

chains, non-crosslinking derivatization, pregelatinization and

depolymerization (Shelton and Lee, 2000).

This study aimed at elucidating the effect of proton

beam irradiation on the physicochemical characteristics of

black pigmented barley starch with higher doses in order

to find its potential in wide application.

Characterization of Physicochemical Properties of Starch in Barley Irradiated with Proton Beam 261

Table 1. Wavelength at maximum absorption (λmax), absorbance

at 680 nm (blue value, BV) and amylose content of

proton beam irradiated black pigmented barley starches.

Proton beam dose

(Gy)

λmax

(nm)

Blue value

(at 680 nm)

Amylose

content (%)

0

50

100

150

200

250

300

599a

598a

573b

564c

555d

546e

539f

0.29a

0.28a

0.23b

0.20c

0.16d

0.13e

0.09f

13.5a

13.4a

12.5b

12.1b

11.5c

11.0c

10.4d

Different letters within each column indicate significant differences

(P < 0.01). Amylose content was calculated by dry weight basis.

MATERIALS & METHODS

Black pigmented barley (Hordeum vulgare L. cv.

Geoncheonheugbori) seeds were exposed to proton beams

accelerated to 45 MeV (LET 1.57 keV/μm) with a dose of

0, 50, 100, 150, 200, 250 and 300 Gy. The LET values of

the beam were calculated at the surface of the seeds. After

treatment, 20 g of black pigmented barley seeds were ground

to pass through a 100-mesh sieve on Ball miller (Model

MM-400 Retsch, Verder Co., Germany), and these powders

were used for starch isolation.

Barley powder was dispersed in 200 ml 0.05% aqueous

NaOH at room temperature for 24 h. After draining off the

supernatant and washing with distilled water several times,

the grains were wet milled and filtered through a nylon

screen (53 µm). The slurry was centrifuged and the top yellow

layer was removed. The solid obtained by centrifugation

were sequentially purified five times by the toluene-salt

solution shaking procedure (McDonald and Stark, 1988).

The clean white layer of isolated rice starch was washed

with distilled water and ethanol before drying in a convection

oven at 32℃ for 48 h.

The absorption curves of starch and iodine complexes

were measured by a UV/VIS spectrophotometer (Model

Evolution 300, Thermo Electron Corporation, USA) at 700

to 500 nm. A solution containing 2 mg iodine and 20 mg

potassium iodate was added to 1 mg NaOH-gelatinized and

HCl-neutralized starch, and made up to 25 ml. The wavelength

at maximum absorption (λmax) and blue value (BV),

absorbance at 680 nm, were determined (Fujimoto et al.,

1972). According to the method of Kainuma (1977),

amperometric iodine titration of defatted starch was carried

out at 1A and 50 mV.

Barley flours were determined by using a Rapid Visco

Analyzer (RVA, Model 4, Newport Scientific, Sydney,

Australia). Each sample (flour 3 g, 12% moisture basis)

was mixed with 25 ml of deionized water in an RVA

sample canister. The idle temperature was set at 50℃, and

the following 12.5 min test profile was run: 50℃ held for

1.0 min, the temperature was linearly ramped up to 95℃

until 7.3 min, the temperature was linearly ramped down

to 50℃ at 11.1 min and held at 50℃ until 12.5 min.

Thermal properties of barley starch were determined by

using a differential scanning calorimeter (DSC-7, Perkin-Elmer,

Norwalk, CT, USA) equipped with an intracooling II

system. Starch (3 mg) was accurately weighed to 0.01 mg

in a hermetic aluminium DSC pan, mixed with 9 mg of

deionized water and sealed and equilibrated at room

temperature for at least one hour. The sample was allowed

to equilibrate for 1 h and scanned at a rate of 10℃/min

over a temperature range of 30-110℃. An empty aluminium

pan was used as the reference to balance the heat capacity

of the sample pan.

Gelatinization onset (To), peak (Tp) temperature, conclusion

(Tc) and enthalpy change (ΔH) were determined. X-ray

diffraction patterns of the barley starch were obtained with

copper Kα radiation in a diffractometer (D-500, Siemens,

Madison, WI). The analysis was conducted by following

the procedure of Yoo and Jane (2002).

The collected data were analyzed by using SAS package

(version 8.0, SAS Institute Inc., Cary, NC) for Dunkan’s

multiple range tests.

RESULTS & DISCUSSION

Gel pasting properties of barley starch was evaluated

from barley seeds irradiated with proton beam (Table 1).

The three parameters, λmax, blue value, and amylose

content were significantly associated with increasing proton

beam irradiation. In particular, amylose content was

significantly decreased by higher irradiation. Like a tendency

of gamma irradiation (Wu et al., 2002), the decreasing

effect of high proton beam irradiation on apparent amylose

한작지(KOREAN J. CROP SCI.), 58(3), 2013262

Table 2. Pasting properties of black pigmented barley flours.

Proton beam

dose (Gy)

Pasting time

(min.)

Pasting temp.

(℃)

Viscosity (RVU)

PKV HPV CPV Breakdown Setback

0

50

100

150

200

250

300

4.46

4.37

4.35

4.36

4.35

4.32

4.30

60.6

60.5

61.4

60.5

58.7

57.2

57.4

2,595a

2,443b

2,372c

2,290d

2,204d

2,176e

2,018e

1,977a

1,754b

1,673c

1,584c

1,495d

1,466d

1,301e

1,974

1,884

1,873

1,786

1,735

1,721

1,683

618d

689c

699b

706b

709ab

710a

717a

-621a

-559b

-499c

-504c

-469d

-455d

-335e

Different letters within each column indicate significant differences (P < 0.01).

Table 3. Thermal properties of black pigmented barley starches irradiated with different proton beam doses.

Proton beam dose

(Gy)

Gelatinization parameters

To (℃) Tp (℃) Tc (℃) ΔH gel (J/g) PHI R

0

50

100

150

200

250

300

54.2a

53.7a

53.1ab

52.5b

50.1b

48.7b

48.5b

58.6a

58.9a

59.4ab

59.9b

61.6c

62.9cd

63.5d

64.3a

64.5a

64.4a

64.7a

65.2ab

64.9a

65.9b

8.3a

8.1a

7.7b

7.4b

7.0c

6.8c

6.9c

1.89a

1.56b

1.22c

1.00c

0.61d

0.48e

0.46f

10.1f

10.8e

11.3e

12.2d

15.1c

16.2b

17.4a

Different letters within each column indicate significant differences (P < 0.01).To, onset temperature; Tp, peak temperature; Tc,

conclusion temperature; R, gelatinization range (Tc-To); ΔH, enthalpy of gelatinization (based on starch dry weight); PHI, peak

height index ΔH gel/(Tp-To).

content was associated with the structure of starch. The

results were also in agreements with those reported by Jane

et al. (1992) and MacGregor and Fincher (1993).

As we know, starch can be chemically fractionated into

two types of distinct glucopyranosyl polymers: amylose,

which is the smaller one essentially linear in structure, and

amylopectin, which is a very large polymer with extensive

branching resulting from (1–6) linkages. In an amylopectin

molecule, short glucan chains (chains) are unbranched, but

linked to multiple branched B chains, and there is a single

reduction end to the C chain glucan (Ball et al., 1996).

With the analysis of RVA, seven major parameters of

barley flour pasting properties, peak viscosity (PKV), hot

pasting viscosity (HPV), cool pasting viscosity (CPV),

setback (CPV minus PKV), breakdown (PKV minus HPV),

pasting time and temperature were significantly decreased

with the increasing proton beam irradiation (Table 2).

The pasting time in barley flour irradiated with proton

beam ranged 0.09 to 0.16 min shorter than non-irradiated

barley flour. Gel pasting temperature ranged 57.4 to 60.

5℃. Gel pasting temperature in barley flour decreased with

increasing proton beam irradiation. These changes in pasting

properties were referred to the breakage of starch granules

caused by proton beam irradiation (Yu and Yang, 2007).

The peak viscosity, hot peak viscosity, cool peak viscosity

and setback were considerably decreased with increasing

proton beam irradiation dose. The setback is mainly due to

a re-ordering or polymerization of leached amylose and

long linear amylopectin (Wu et al., 2002).

It is therefore likely that degradation or shortening of

amylose and longer amylopectin branch chains by proton

beam irradiation was responsible for the decrease in setback.

The parameter setback viscosity that is often used as an

indicator of the firmness of cooked rice, with higher values

indicating firmer texture (Bason et al., 1994; Juliano et al.,

1990; Shu et al., 1998), was reduced with dose increases.

In our previous studies, change of properties of starch

viscosity in rice (Kim et al., 2012) and Chinese yam (Kim

Characterization of Physicochemical Properties of Starch in Barley Irradiated with Proton Beam 263

Table 4. X-ray diffraction data of black pigmented barley starches irradiated with proton beam.

Proton beam dose (Gy)Diffraction peaks at 2θ values

15° 17° 18° 20° 23°

0

50

100

150

200

250

300

15.2

14.9

14.9

15.0

15.2

15.1

15.1

17.2

17.1

16.9

17.0

17.1

17.3

17.2

18.1

18.0

18.2

18.1

18.2

17.9

18.2

20.0

20.1

20.2

20.1

20.0

20.0

20.1

23.1

23.1

22.8

23.0

23.1

23.2

23.1

Table 5. Crystal pattern and relative crystallinity at different dose of black pigmented barley.

Proton beam dose (Gy) Relative crystallinity (%) Crystal patterns

0

50

100

150

200

250

300

24.5g

24.9f

26.7e

28.3d

29.3c

32.2b

32.9a

A

A

A

A

A

A

A

Different letters within each column indicate significant differences (P < 0.01). Crystallinity was determined following equation

as Xc=Ac/(Ac+Aa); Ac: the crystallized area; Aa: the amorphous area on the X-ray diffractogram.

et al., 2011), it concluded that proton beam treatment like

a gamma irradiation caused a significant decrease in starch

viscosity. The present study was considerably in agreement

with previous results (Kim et al., 2011; Kim et al., 2012).

It was generally accepted that the increase in viscosity

that occurs during heating of starch suspension is mainly

due to the swelling of the starch granules and breakdown

of viscosity was caused by rupture of the swollen granules

(Sandhya Rani and Bhattacharya 1995; Vandeputte et al.,

2004).

It is also accepted that the swelling degree of starch

granules was directly proportion to the average size of

starch granules in rice (Vandeputte et al., 2004). It was

therefore likely that the observed decrease in peak viscosity,

hot pasting viscosity was due to the decreased of size of

starch granules caused by proton beam irradiation. The

parameters of cool pasting viscosity, setback and peak time

must be correlated with the degree of polymerization after

RVA processing (Sandhya Rani and Bhattacharya, 1995).

Table 3 shows thermal properties of barley starches as

affected by proton beam irradiation. Proton beam irradiation

caused a significant decrease in the onset temperature (To),

peak temperature (Tp), conclusion temperature (Tc) and

enthalpy change (ΔH). Gelatinization range (R) in barley

starch was more broaden than that of non-irradiated barley

starch.

The onset temperature (To) of wheat and rice decreased

after gamma irradiation (Bao et al., 2005; Ciesla and

Eliasson, 2002). Rombo et al. (2004) reported that the

onset temperature (To) decreases in maize flour after

gamma irradiation. The ΔH was reported to decrease in

potato and wheat starches (Ciesla and Eliasson 2002, 2003)

and bean flour (Rombo et al., 2004) after gamma

irradiation. As DSC thermal properties reflect gelatinization

of the crystalline of starch, our results indicate a significant

decrease in the crystalline ordering in barley starch after

proton beam irradiation.

The X-ray diffraction data and degree of crystallinity in

barley as affected by proton beam irradiation was shown in

Table 4 and Table 5. Barley starches gave the strong

diffraction peak at around 2θ values 15°, 18°, 20°, 23° and

a small peak at 17° 2θ.

The X-ray diffraction patterns of proton beam irradiated

barley starches are shown in Fig. 2. In all of the starches,

한작지(KOREAN J. CROP SCI.), 58(3), 2013264

Fig. 1. Scanning electron micrograph of black pigmented barley starch granules irradiated with proton beam (2.0kX). 1:

non-irradiated; 2: 50Gy; 3: 100Gy; 4: 150Gy; 5: 200Gy; 6: 250Gy, 7: 300Gy. The endosperm of barley shows starch granules

of various sizes embedded in a protein matrix containing numerous protein bodies.

Characterization of Physicochemical Properties of Starch in Barley Irradiated with Proton Beam 265

Fig. 2. X-ray diffraction patterns of two rice varieties as affected by different proton beam irradiation.

major peaks were observed at d-spacing of 5.8, 5.2, 4.8,

4.4 and 3.8 Å are characteristic of an A-type starch crystal

that is common to most cereal starches. The d-spacing of

4.4 Å is characteristic of amylose-lipid complex. Furthermore,

large starch granules in each fraction had a peak at 4.4 Å.

Peak intensity tended to increase with increased proton

beam irradiation. The granule crystallinity is closely associated

with decreased amylose and increased amylopectin component.

The crystallinity degree of barley starch irradiated with

proton beam was significantly increased and it ranged from

24.9 to 32.9% compared to the non-irradiated barley starches.

It is can be explained possibly that decreased amylose

content is attributed to increase their crystallinity under

proton beam irradiation.

The changes in size of starch granules represented effect

of irradiation on microstructure of barley starch as affected

by different proton beam irradiation (Fig. 1). The size of

starch granules of non-irradiated barley starch was partially

large, and small size granules could be found. With

increasing proton beam irradiation, the amount of small

size granules was to some extent increased. These changes

were due to the free radicals generated by high proton

beam irradiation, cleaving large starch molecules like some

results (Grant and G’Appolonia, 1991; Sabularse et al.,

1991). In conclusion, it might be deduced that proton beam

irradiation causes significant changes of properties of

starch viscosity in rice, especially at high irradiation of

proton beam.

한작지(KOREAN J. CROP SCI.), 58(3), 2013266

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