RESEARCH ARTICLE

Amylose content, molecular structure, physicochemicalproperties and in vitro digestibility of starches fromdifferent mung bean (Vigna radiata L.) cultivars

Maninder Kaur1, Kawaljit Singh Sandhu2, Narpinder Singh1 and Seung-Taik Lim3

1 Department of Food Science and Technology, Guru Nanak Dev University, Amritsar, India2 Department of Food Science and Technology, Chaudhary Devi Lal University, Sirsa, India3 School of Life Sciences and Biotechnology, Korea University, Sungbuk-ku, Seoul, South Korea

Physicochemical and in vitro digestibility characteristics of starches isolated from six cultivars

of mung bean (Vigna radiata L.) were studied. Significant differences (p < 0.05) were

observed between the cultivars with respect to amylose content (29.9–33.6%), relative

crystallinity (29.0 to 31.7%), particle diameter (16.2–17.1 mm) and molecular weight of

amylopectin (260–289 � 106 g/mol). The scanning electron micrographs revealed the pres-

ence of large oval to small round shape granules with average particle diameter of 16.2–

17.1 mm. The X-ray diffraction pattern was of the C-type. The enthalpies of gelatinization and

retrogradation were 8.9–10.3 and 4.6–6.3 J/g, respectively. The amounts of slowly digesting

and resistant starch of mung bean followed the order: PBM-1 > SML-32 > ML-613 > SML-

134 > ML-267 > ML-5 and ML-5 > ML-267 > SML-134 > ML-613 > SML-32 > PBM-1,

respectively. The six starches exhibited significant (p < 0.05) differences in their pasting

parameters. Correlation analysis showed that amylose content, granule diameter and relative

crystallinity values were important in determining thermal, pasting and in vitro digestibility of

starches.

Received: April 11, 2011

Revised: May 18, 2011

Accepted: May 20, 2011

Keywords:

In vitro digestibility / Mung bean / Pasting / Physicochemical / Starch

1 Introduction

Mung bean (Vigna radiata L.) has been grown in India

since ancient times. It is also widely grown in Southeast

Asia, Africa, South and North America, and Australia [1].

Mung bean is an important pulse crop of India with an

annual production of 4.2 million tonnes. About 70% of the

world production of mung bean is in India. All mung bean

produced in India is for domestic consumption. It is con-

sumed mainly for its rich protein content (24%) but carbo-

hydrates (62–63%) are its major component [2]. Starch is

the major storage polysaccharide of higher plants and is

deposited in partially crystalline granules varying in

morphology and molecular structure between and within

plant species [3]. Besides being a major plant metabolite,

starch is also the dominating carbohydrate in the human

diet. Abdel-Rahman et al. [4] and Hoover et al. [5] reported

that mung bean contains about 31 and 26% starch con-

centration, respectively, on whole-seed basis with an amy-

lose content of 30–45% [6]. When heated, the starch

solution becomes a ‘transparent’ gel, a unique character-

istic of mung bean starch, while remaining resilient with

strong gel-strength [1].

The digestibility of starch in foods varies widely; there-

fore, a nutritional classification of dietary starch has been

proposed [7]. Most starch products contain a portion that

digests rapidly (rapidly digesting starch, RDS), a portion

that digests slowly (slowly digesting starch, SDS) and, a

Correspondence: Dr. Maninder Kaur, Department of FoodScience and Technology, Guru Nanak Dev University, Amritsar143005, IndiaE-mail: mandyvirk@rediffmail.comFax: þ91-183-2258820

Abbreviations: HI, hydrolysis index; RDS, rapidly digestingstarch; SDS, slowly digesting starch

DOI 10.1002/star.201100053Starch/Starke 2011, 63, 709–716 709

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fraction that is resistant to digestion (resistant starch, RS) [8].

RS has been defined as the sum of starch and the product

of starch degradation not absorbed in the small intestine

but is fermented in the large intestine of healthy individuals [9].

RS has potential physiological benefits similar to dietary

fibre and unique functional properties. Legume starches

have been shown to have unique properties imparting

resistance to hydrolysis by digestive enzymes. Several

properties of legumes affect their starch digestibility,

including high content of viscous soluble dietary fibre

and relatively high amylose/amylopectin ratios. The high

RS content of legume seeds has significant impact in

eliciting a low glycemic response [10]. Mung bean starch

has the unique characteristics of having a low glycemic

index carbohydrate and containing a potentially high

resistant starch that have been attributed to its high

amylose content and the molecular structure of the amy-

lopectin [6, 11].

Studies on mung bean starches have been focused on

its physicochemical and rheological properties, as well as

structural characterizations [2, 4, 5, 10, 12]. To the best of

our knowledge no systematic work has been carried out on

digestibility of starch in relation to its structural and phys-

icochemical properties from different mung bean cultivars,

which is an important crop of economic significance in

India. Therefore, it was considered worthwhile to investi-

gate the in vitro digestibility characteristics of starches

separated from six mung bean cultivars grown in India

to relate the digestibility data to physicochemical proper-

ties and granule morphology.

2 Materials and methods

Representative samples of six improved mung bean culti-

vars viz. ML-5, SML-134, ML-613, ML-267, SML-32 and

PBM-1 were obtained from Punjab Agricultural University,

Ludhiana, India. Starches were isolated from mung

bean cultivars following the method as described by

Singh et al. [13].

2.1 Physicochemical properties

Amylose content of isolated starches was determined by

following the method of Williams et al. [14]. For the deter-

mination of molecular weight, starch was purified following

the method described by Han and Lim [15]. The filtered

sample (1 mL) was then immediately injected by syringe

into the high performance size exclusion column chroma-

tography (HPSEC), connected to a multi-angle laser light

scattering detector (MALLS). X-ray diffraction analysis

was conducted using an X-ray diffractometer (Philips,

X’pert MPD high resolution XRD, Almelo, Netherlands)

operated at 40 kV and 40 mA. Diffractograms were

obtained from 4 (2u) to 308 (2u) at a scanning speed

of 4o/min. The degree of relative crystallinity was deter-

mined quantitatively following the method described by

Nara and Komiya [16] using peak-fitting software

(Origin–Version 6.0, Microcal Inc., Northampton, MA,

USA).

2.2 Structural properties

Size distribution of mung bean starches was measured

using a Laser light scattering particle size analyser (1064

LD, CILAS, France) following the method described by

Kaur and Sandhu [17]. Scanning electron micrographs

were taken by a Jeol JSM- 6100 scanning electron micro-

scope (Jeol Ltd., Tokyo, Japan). Starch samples were

suspended in ethanol to obtain a 1% suspension. One

drop of the starch-ethanol suspension was applied

on an aluminium stub using double-sided adhesive

tape and the starch was coated with gold-palladium

(60:40 w/w). An accelerating potential of 15 kV was used

during micrography.

2.3 Thermal properties

Thermal properties of isolated starches were analysed

using a differential scanning calorimeter (Seiko

Instrument, DSC 6100, Chiba, Japan) following the

method described by Singh et al. [13]. After conducting

thermal analysis, sampleswere stored in the refrigerator at

48C for 7 days for retrogradation studies. Retrogradation

was measured by reheating the sample pans containing

the starches at the rate of 108C/min from 25 to 1008C.

2.4 Pasting properties

The pasting properties and viscosity profiles of starch

suspensions (8% w/w; 28 g total weight) were evaluated

using a Rapid Visco Analyser (RVA-3D, Newport Scientific,

Warriewood, Australia) following the method described by

Kaur and Sandhu [17].

2.5 Digestibility studies

In vitro starch digestibility was analysed following the

method described by Englyst et al. [8] with slight modifi-

cations [18]. Amyloglucosidase (No. 9913, Sigma–Aldrich,

St. Louis, MO) (1 mL) was added to deionized water

(2 mL). Porcine pancreatic alpha-amylase (No. 7545,

Sigma–Aldrich, St. Louis, MO) (3.89 g) was dispersed in

water (25.7 mL) and centrifuged for 10 min at 2500 g, and

18.7 mL of supernatant was collected. This supernatant

was mixed with 1 mL of diluted amyloglucosidase for mak-

ing the enzyme solution. The solution was freshly prepared

for the digestion analysis.

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Aliquots of guar gum (10 mL, 5 g/L) and sodium acetate

(5 mL, 0.5 M) were added to the starch samples (0.5 g, db)

in a test tube. Seven glass balls (10 mm diameter) and

5 mL of enzyme solution were then added to each tube,

followed by incubation in a water bath (378C) with agitation

(170 rpm). Aliquots (0.5 mL) were taken at intervals and

mixed with 4 mL of 80% ethanol, and the glucose contents

in the mixture were measured using glucose oxidase

and peroxidase assay kits (No. GAGO-20, Sigma–

Aldrich, St. Louis, MO). The total starch (TS) content

was measured according to Englyst et al. [8]. The starch

classification based on its digestibility was: RDS as

the starch that was hydrolyzed within 20 min of incubation,

RS as the starch not hydrolyzed after 120 min, and SDS as

the starch digested during the period between 20 and

120 min.

2.6 Estimated glycemic index (GI)

The rate of starch digestion was expressed as the per-

centage of TS hydrolysed at different times (0–180 min)

and the hydrolysis curve was plotted. The area under

the hydrolysis curve was calculated. The hydrolysis

index (HI) was calculated as the relation between the

area under curve for a sample and the area under

curve for a reference material, white bread, expressed

as a percentage [19, 20]. The glycemic indices of

the samples were estimated from the HI according

to the equation described by Goni et al. [20]:

GI ¼ 39.71 þ 0.549HI.

2.7 Statistical analysis

The data reported in all the tableswere average of triplicate

determinations. The data were subjected to one-way

analysis of variance (ANOVA) using Minitab Statistical

Software version 13 (Minitab Inc., USA). Pearson corre-

lation coefficients (r) for the relationships between various

starch properties were calculated.

3 Results and discussion

3.1 Physicochemical properties

The amylose content of the six mung bean starches varied

from 29.9 (ML-5) to 33.6% (PBM-1) (Table 1). The values

obtained for the mung bean starches fall within the ranges

reported in other studies (31.6%) [18], (33.19%) [2] and

(31.7–33.8%) [12] for mung bean starches. Amylose con-

tent has a significant effect on functional and physico-

chemical properties, including pasting, gelatinization, ret-

rogradation and swelling behaviour of starch [3, 21]. The

structural data measured using the HPSEC-MALLS-RI

system for the six mung bean starches differed signifi-

cantly (p < 0.05) (Table 1). Molecular weight (Mw) of

amylopectin and amylose of mung bean cv. starches

ranged between 260–289 � 106 and 1.80–2.10 � 106 g/mol,

respectively. TheMw of amylopectin for ML-5 cv. starch was

significantly (p < 0.05) higher than SML-32 and PBM-1

starch, but was not different from other cv. starches. A

statistically significant negative correlation of Mw of amy-

lopectin with amylose content (r ¼ �0.942, p < 0.01) was

observed (Table 2). Similar inverse relationship

betweenMw of amylopectin and amylose content has been

reported earlier for different legume [18] and pigeon pea

starches [17]. The relative crystallinity measured, based

on diffraction intensity of the starches ranged between

29.0 and 31.7% (Table 1). Comparable relative crystallinity

values of 27.1–33.5% for C-type legume starches [22] and

27.5–33.1% for lentil starches [23] have been reported

earlier. PBM-1 cv. starch showed the lowest while ML-5

cv. starch had the highest values of crystallinity. The lower

relative crystallinity of PBM-1 cv. starch may be attributed

to its highest amylose content in comparison to other cv.

starches. A negative correlation of relative crystallinity with

amylose content (r ¼ �0.910) at a significance level of

p < 0.01 was observed (Table 2). Since the side chains

of amylopectin form the crystalline structure, the crystal-

linity will be inversely related to amylose content. The

Table 1. Physicochemical properties of starches from different mung bean cultivarsa,b)

Parameters ML-5 SML-134 ML-613 ML-267 SML-32 PBM-1

Amylose content (%) 29.9 � 0.3a 30.5 � 0.4ab 31.6 � 0.5b 31.1 � 0.3ab 33.3 � 0.6c 33.6 � 0.5c

Mean granule diameter (mm) 17.1b 16.9b 16.5ab 16.7ab 16.5ab 16.2a

Relative crystallinity (%) 31.7 � 0.4c 30.9 � 0.3bc 29.7 � 0.5ab 30.1 � 0.4b 29.6 � 0.2ab 29.0 � 0.3a

Molecular weight ofamylopectin (�106 g/mol)

289 � 2.9b 283 � 2.8b 269 � 3.1ab 271 � 3.0ab 263 � 2.7a 260 � 3.3a

Molecular weight ofamylose (�106 g/mol)

2.02 � 0.3b 2.10 � 0.4c 1.80 � 0.4a 1.98 � 0.5b 1.83 � 0.3a 1.81 � 0.3a

a) Means followed by same superscript within a row do not differ significantly (p > 0.05).b) Means (�SD) of triplicate analyses.

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crystalline order in starch granules is often the basic under-

lying factor influencing its functional properties [23]. Mung

bean starches exhibited the characteristic C-type X-ray

diffraction pattern of legume starches. In the diffraction

spectra of the six mung bean cultivar starches, there were

strong diffraction peaks at 15.0, 17.2, 18.0 and 23.28 (2u).A C-type X-ray pattern for mung bean starches has been

previously reported [1, 5, 12].

3.2 Structural properties

The starches separated from the six mung bean cultivars

differed significantly in their granule diameter. Particle

diameter of the majority of the starch granules ranged

between 10 and 37 mm with a few granules having

diameter in the range of 1–8.5 mm. The average particle

diameter of the mung bean starches ranged between 16.2

and 17.1 mm, the largest for ML-5 cv. starch and the small-

est for PBM-1 cv. starch (Table 1). Granule diameter of

7.1–26 [5], 10–30 [12] and 7.65–33.15 mm [4] in mung

bean starches has been observed earlier. Starch granule

size may affect its physicochemical properties, such as

gelatinization and pasting, enzyme susceptibility, crystal-

linity and solubility [24]. A negative correlation of particle

diameter with amylose content (r ¼ �0.924) and a positive

correlation with Mw of amylopectin (r ¼ 0.964) and relative

crystallinity (r ¼ 0.986) at a significance level of p < 0.01

was observed (Table 2). The scanning electron micro-

graphs (SEM) of starches showed the presence of large

oval to small round shape granules with smooth surface

(Fig. 1). The surface of the granules appeared to be

smooth with no evidence of any fissures. Mung bean

starch has been reported to have smooth-surfaced oval

to round to bean shaped granules [4, 5, 12].

3.3 Thermal properties

The six mung bean starches had an initial gelatinization

temperature (To) in the range of 63.8–69.18C, a maximum

peak temperature (Tp) of 69.7–74.68C and a final con-

clusion temperature (Tc) in the range of 76.0–80.38C(Table 3). These gelatinization temperatures were higher

than those observed earlier in mung bean starches by

Abdel-Rahman et al. [4] (To, 65.0; Tp, 69.0; and Tc,

75.08C), Ohwada et al. [2] (To, 59.0; Tp, 69.0; and Tc,

75.08C), and Hoover et al. [5] (To, 58.0; Tp, 67.0; and

Tc, 82.08C). ML-613 cv. starch showed the lowest To, Tp

and Tc whereas the highest was observed for SML-32 cv.

starch. High gelatinization temperature of starch makes it

useful in foods subjected to thermal processing such as

canned foods. The enthalpy of crystallite melting (DHgel) of

starches from different mung bean cultivars varied from

8.9–10.3 J/g and followed the order: ML-5 > SML-

134 > SML-32 > ML-267 > ML-613 > PBM-1. ML-5 cv.

starch displayed the highest DHgel, which is indicative of a

higher proportion of relative crystallinity in ML-5 starch;

consequently higher energy is needed to break the inter-

molecular bonds in its starch granules to achieve gelati-

nization. The gelatinization properties of starch have been

related to characteristics of the starch granule such as

size, proportion and kind of crystalline organization, and

ultra structure of the starch granule [24]. DHgel exhibited a

Table 2. Pearson correlation coefficients between various properties of starches from different mung bean cultivars

Aml Mwt. AP Dia Crys To DHgel DHret PV BD RS RDS SDS

Mwt. AP�0.942 ��

Dia �0.924 �� 0.964 ��

Crys �0.910 �� 0.984 �� 0.986 ��

To 0.402 �0.232 �0.126 �0.175DHgel �0.678 �� 0.825 � 0.895 �� 0.887 �� 0.228DHret �0.613 0.787 � 0.843 � 0.852 � 0.226 0.988 ��

PV �0.210 0.045 0.012 0.035 �0.824 � �0.163 �0.110BD �0.155 0.032 0.053 0.056 �0.569 0.018 0.090 0.930 ��

RS �0.940 �� 0.903 �� 0.935 �� 0.912 �� �0.323 0.698 0.614 0.072 0.000RDS 0.918 �� �0.932 �� �0.959 �� �0.942 �� 0.173 �0.775 � �0.693 0.088 0.131�0.982 ��

SDS 0.934 �� �0.872 � �0.908 �� �0.882 �� 0.402 �0.645 �0.560�0.159 �0.073�0.994 �� 0.957 ��

GI 0.790 � �0.726 �0.849 � �0.779 � 0.122 �0.664 �0.559 0.057 0.074 0.930 �� 0.910 �� 0.927 ��

Aml, Amylose content; Mwt. AP, Molecular weight of amylopectin; Dia, Particle diameter; Crys, Relative crystallinity; To, Onsetgelatinization temperature; DHgel, Enthalpy of gelatinization; DHret, Enthalpy of retrogradation; PV, Peak viscosity;BD, Breakdown viscosity; RDS, Rapidly digestible starch; SDS, Slowly digestible starch; RS, Resistant starch;GI, Glycemic index.� p < 0.05,�� p < 0.01.

712 M. Kaur et al. Starch/Starke 2011, 63, 709–716

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statistically significant positive correlation with particle

diameter (r ¼ 0.895), molecular weight AP (r ¼ 0.825)

and relative crystallinity (r ¼ 0.887) (Table 2). The enthalpy

of retrogradation (DHret) during storage of gelatinized

mung bean starches at 4oC for 7 days followed the order:

ML-5 > SML-134 > SML-32 > ML-613 > ML-267 > PBM-1

(Table 3). DHret of 4.6–6.3 J/g observed for the six mung

bean starches in the present study corroborated well with

that observed earlier in mung bean by Kim et al. [12] (5.5–

6.6 J/g) and Sandhu and Lim [18] (5.0 J/g). The difference

inDHret among the variousmung bean starches suggested

difference in their tendency towards retrogradation. ML-5

cv. starch displayed the highest DHret (6.3 J/g) and %

retrogradation (61.2%) in comparison to other mung bean

cv. starches. A statistically significant correlation of DHret

with DHgel (r ¼ 0.895, p < 0.01) was observed (Table 2).

3.4 Pasting properties

Pasting viscosity profiles of starches from different mung

bean cultivars are illustrated in Fig. 2. Mung bean starches

differed significantly with respect to their peak (PV) (3208–

3977 cP), breakdown (BD) (800–1252 cP), final (FV)

(4277–4609 cP) and setback (SB) (1743–2101 cP) vis-

cosities (data not shown). All the samples showed a grad-

ual increase in viscosity with the increase in temperature

Figure 1. Scanning electron micrographs of starches separated from the six mung bean cultivars (A) ML-5, (B) SML-134,(C) ML-613, (D) ML-267, (E) SML-32, (F) PBM-1; magnification: � 1000; scale bar: 10 mm.

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and this could be advantageous when thickening is

required in utilization. ML-613 cv. starch exhibited the high-

est PV, BD and the lowest SB, while SML-134 cv. starch

showed the lowest values for PVand BD (data not shown).

A significant positive correlation of BD and PV (r ¼ 0.930)

at a significance level of p < 0.01 was observed (Table 2).

Changes in viscosity during cooking period give indications

of the stability and the changes occurring during cooling

show the consistency of the product when consumed [23].

The high retrogradation tendency of mung bean starches

as evident from high values of SB might be useful in

products where a gelling is desired.

3.5 Digestibility studies

The rapidly digesting starch (RDS), slowly digesting starch

(SDS) and resistant starch (RS) contents of the six mung

bean starches are shown in Table 3. RDS, SDS and RS

represented 9.8–11.1, 39.9–42.3 and 46.6–50.3%,

respectively, of the TS content in different mung bean

cultivars. SDS content, which is generally the most

desirable form of dietary starch, followed the order:

PBM-1 > SML-32 > ML-613 > SML-134 > ML-267 > ML-5.

RS content of different mung bean starches measured as

the residue resistant to 120 min of enzymatic hydrolysis

followed the order: ML-5 > ML-267> SML-134 > ML-

613 > SML-32 > PBM-1. High RS content of mung bean

starches makes them equally beneficial as dietary fibre

with physiological functions. RDS, SDS and RS contents of

9.7, 40.0 and 50.3%, respectively, in mung bean [18] and

5.2–8.1, 29.6–31.0 and 60.9–65.2%, respectively, in

pigeon pea starches [17] have been reported. RS content

showed a significant (p < 0.01) negative correlation with

amylose content (r ¼ �0.940), RDS (r ¼ �0.982) and

Table 3. Gelatinization, retrogradation and digestibility properties of starches from different mung bean cultivarsa,b)

Parameter ML-5 SML-134 ML-613 ML-267 SML-32 PBM-1

To(8C) 63.9 � 0.2a 67.6 � 0.3c 63.8 � 0.4a 64.5 � 0.3ab 69.1 � 0.5d 65.3 � 0.4b

Tp(8C) 69.8 � 0.4a 73.1 � 0.5c 69.7 � 0.3a 70.8 � 0.4b 74.6 � 0.5d 70.6 � 0.5b

Tc(8C) 76.1 � 0.3a 78.9 � 0.2c 76.0 � 0.4a 77.6 � 0.3b 80.3 � 0.4d 76.1 � 0.4a

DHgel (J/g) 10.3 � 0.4c 10.0 � 0.2c 9.3 � 0.5ab 9.4 � 0.4ab 9.8 � 0.4b 8.9 � 0.5a

DH ret(J/g) 6.3 � 0.2c 5.8 � 0.3b 5.1 � 0.2ab 5.0 � 0.3ab 5.7 � 0.4b 4.6 � 0.3a

% R 61.2 � 0.5d 58.0 � 0.6c 53.7 � 0.5b 54.3 � 0.4bc 58.1 � 0.5c 51.7 � 0.3a

RDS (%) 9.8 � 0.1a 10.0 � 0.3a 10.9 � 0.2b 10.2 � 0.4ab 10.9 � 0.3b 11.1 � 0.4b

SDS (%) 39.9 � 0.4a 40.7 � 0.5ab 41.6 � 0.3b 40.3 � 0.5ab 42.1 � 0.6c 42.3 � 0.6c

RS (%) 50.3 � 0.7c 49.3 � 0.4b 47.5 � 0.7ab 49.5 � 0.6b 47.0 � 0.8ab 46.6 � 0.6a

HI (%) 18.9 � 0.6a 19.3 � 0.5ab 20.4 � 0.4bc 18.7 � 0.6a 20.0 � 0.4b 20.8 � 0.6c

GI c) (%) 50.09 � 0.6a 50.31 � 0.2ab 50.91 � 0.3b 49.98 � 0.4a 50.69 � 0.5ab 51.13 � 0.4b

To, Onset gelatinization temperature, Tp, Peak gelatinization temperature, Tc, Conclusion gelatinization temperature,DHgel, Enthalpy of gelatinization, DHret, Enthalpy of retrogradation,%R, Ratio of enthalpy of retrogradation to enthalpy of gelatinization.RDS, Rapidly digestible starch; SDS, Slowly digestible starch; RS, Resistant starch, HI, Hydrolysis index, GI, Glycemic index.a) Means followed by same superscript within a row do not differ significantly (p > 0.05).b) Means (�SD) of triplicate analyses.c) GI was calculated using the equation proposed by Goni et al. [20]: GI ¼ 39.71 þ 0.549 HI.

0 0

1000

2000

3000

4000

5000 5000

0

30

60

90

120

00 3 6 9 12 1515

Visc

osity

(cP)

Time (minutes)

Tem

pera

ture

(o C)

Temperature C

A

D F

E

B

Figure 2. Rapid visco analyser pasting profiles ofstarches from different mung bean cultivars (A) ML-5,(B) SML-134, (C) ML-613, (D) ML-267, (E) SML-32,(F) PBM-1.

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SDS (r ¼ �0.994), and a positive correlation with granule

diameter (r ¼ 0.935) and relative crystallinity (r ¼ 0.912)

(Table 2). Total digestibility of starches (RDS þ SDS) var-

ied from 49.7 to 53.4%, the lowest for ML-5 cv. and the

highest for PBM-1cv. starch was observed. Raw starch

digestibility is greatly influenced by granule size, amylose/

amylopectin ratio and degree of crystallinity [10]. Both

RDS and SDS contents showed a negative correlation

with starch granule diameter (r ¼ �0.959, �0.908,

respectively), and relative crystallinity (r ¼ �0.942,

�0.882, respectively), and a positive correlation with amy-

lose content (r ¼ 0.918, 0.934, respectively), at a signifi-

cance level of p < 0.01 (Table 2). In relation to HI of the

starches, the values for the six cultivars ranged from 18.7

to 20.8%. The six cultivars showed estimated glycemic

index (eGI) values ranging between 49.98 and 51.13%.

PBM-1 cv. starch exhibited significantly higher eGI and HI

values than ML-5 and ML-267 cv. Starches. eGI was posi-

tively correlated to RDS and SDS (p < 0.01) content and

negatively to particle diameter and relative crystallinity of

the starch.

4 Conclusions

The results showed that starches from different mung

bean cultivars had significant differences with respect to

amylose content, granule diameter, crystallinity and mol-

ecular weight which consequently influenced the observed

variations in pasting, gelatinization and digestibility

parameters. All the six mung bean starches showed a

characteristic C-type X-ray diffraction pattern. Starch from

cv. PBM-1 exhibited the highest amylose content, RDS,

SDS and eGI and the lowest granule diameter, crystallinity,

DHgel, DHret and retrogradation rates in comparison to

other mung bean starches. The low RDS and the high

RS and SDS content of mung bean starches makes them

useful in planning diets for patients with diabetes, dyslipi-

demia and cardiovascular diseases. Correlation analysis

data indicated a significant interdependence of physico-

chemical and structural properties with digestibility proper-

ties of mung bean starches.

The authors have declared no conflict of interest.

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