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Food
Chemistry
Food Chemistry 107 (2008) 92–97
www.elsevier.com/locate/foodchem
Structural characteristics and in vitro digestibility of Mango
kernel starches (Mangifera indica L.)
Kawaljit Singh Sandhu, Seung-Taik Lim
*
School of Life Sciences and Biotechnology, Korea University, 5-1 Anam-dong, Sungbuk-ku, Seoul 136-701, South Korea
Received 16 April 2007; received in revised form 5 June 2007; accepted 17 July 2007
Abstract
Structural characteristics and digestibility of starches isolated from the kernels of two mango cultivars (Chausa and Kuppi) were stud-
ied and compared with those of a commercial normal corn starch. Mango kernel starches showed an A-type X-ray diffraction pattern,
with relative crystallinities of 35.4% and 38.3%, respectively for Kuppi and Chausa cultivars. The structural characterisation obtained,
using high performance size exclusion column chromatography connected to multi-angle laser light scattering and refractive index detec-
tors (HPSEC-MALLS-RI), revealed that the mango kernel starches had lower molecular weight (M
w
) and radius of gyration (R
g
)of
amylopectin and amylose compared to those of corn starch. The M
w
of amylopectin for Chausa and Kuppi starches were 179
10
6
and 140
10
6
g/mol, respectively. The amounts of readily digestible starch (RDS) and slowly digestible starch (SDS) were lower for
mango kernel starch than those of corn starch. Resistant starch (RS) contents in the mango kernel starches (75.6% and 80.0%, respec-
tively) were substantially higher than those of corn starch (27.3%). The glycemic index (GI) values for mango kernel starches were 48.8
and 50.9 (for Chausa and Kuppi, respectively), whereas that of corn starch was 74.8, indicating that the mango kernel starch granules
were highly resistant to digestion with significant contents of RS.
2007 Elsevier Ltd. All rights reserved.
Keywords: Mango kernel starch; Crystallinity; Molecular weight; Digestibility
1. Introduction
Kaur et al. (2004)
studied the physicochemical, morpho-
logical, thermal and rheological properties of mango kernel
starches and found their properties to be comparable with
starches from other commercial sources.
Velan, Krishnan,
and Lakshmanan (1995)
studied the conversion of mango
kernel starch to glucose syrups by enzymatic hydrolysis.
Chowdary, Hari Krishna, and Hanumantha Rao (2000)
studied optimisation of enzymatic hydrolysis of mango
kernel starch by response surface methodology.
Tavares,
Bathista, Silva, Filho, and Nogueira (2003)
reported
molecular dynamic study of the starches obtained from
the mango and the Espada seeds by
13
C solid state NMR.
In recent years, glycemic index (GI) has become a poten-
tially useful tool in planning diets for patients suffering
from diabetes, dyslipidemia, cardiovascular disease and
even certain cancers (
Jenkins et al., 1981
). The digestibility
of starch in foods varies widely according to the nature of
the foods (
Bj¨ rck, Granfeldt, Liljeberg, Tovar, & Asp,
Mango (Mangifera indica L.) is one of the most
favoured and commercially valuable fruit growing
throughout the tropics and is used in a variety of food
products. Considerable amounts of mango kernels (seeds)
are discarded as waste after industrial processing of man-
goes (
Puravankara, Bohgra, & Sharma, 2000
). Approxi-
mately 40–60% waste is generated during processing of
mangoes, 12–15% and 15–20% of which consists peels
and kernels, respectively (
Kaur, Singh, Sandhu, & Guraya,
2004
). Depending on the variety, mango kernels contain
6.0% protein, 11% fat, 77% carbohydrate, 2.0% crude fiber
and 2.0% ash, based on the dry weight average (
Zein, El-
Bagoury, & Kassab, 2005
).
*
Corresponding author. Tel.: +82 2 3290 3435; fax: +82 2 927 5201.
E-mail address:
(S.-T. Lim).
0308-8146/$ - see front matter 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.foodchem.2007.07.046
K.S. Sandhu, S.-T. Lim / Food Chemistry 107 (2008) 92–97
93
1994
). Therefore, a nutritional classification of dietary
starch that takes into account both the kinetic component
and the completeness of its digestibility has been proposed.
This classification consists of rapidly digestible starch
(RDS), slowly digestible starch (SDS) and resistant starch
(RS) (
Englyst, Kingman, & Cummings, 1992
).
Starches from fruits such as mango (
Iagher, Reicher, &
Ganter, 2002; Millan-Testa, Mendez-Montealvo, Ottenhof,
Farhat, & Bello-Perez, 2005
), apple (
Singh, Inouchi, &
Nishinari, 2005
), and banana (
N´˜ ez-Santiago, Bello-
P
´
rez, & Tecante, 2004; Zhang, Whistler, BeMiller, &
Hamaker, 2005
) have been characterised however, no stud-
ies concerning the structural characterisation and digest-
ibility of mango kernel starches have been reported to
date. Therefore, in this study structural properties and
in vitro digestibility of mango kernel starches were investi-
gated and compared with those of normal corn starch.
and degassed with a vacuum pump for 4 h before use.
The SEC column (2.6
70 cm) contained Toyopearl HW
65 F resins (Tosoch Corp. Tokyo, Japan) of particle and
pore sizes, 30–60 lm and 1000 A, respectively. The system
consisted of a pump (P2000, Spectra System, San Jose,
CA), an injector valve with a 1 ml loop (model 7072, Rhe-
odyne, Cotati, CA), a SEC column, a multi-angle laser
light scattering detector (MALLS, 632.8 nm, DAWN
DSP-F, Wyatt Technology, Santa Barbara, CA) and a
refractive index detector (RI, Optilab DSP, Wyatt Tech-
nology, Santa Barbara, CA). The flow rate and pump pres-
sure were 0.8 ml/min and 40 psi.
2.4. In vitro digestibility
In vitro starch digestibility was analysed following the
method described by
Englyst et al. (1992)
as modified by
Chung, Lim, and Lim (2006)
. Porcine pancreatic alpha-
amylase (No. 7545, Sigma–Aldrich, St. Louis, MO) and
amyloglucosidase (No. 9913, Sigma–Aldrich) (3.89 g) was
dispersed in water (25.7 ml) and centrifuged for 10 min at
2500g and 18.7 ml of supernatant was collected. Amyloglu-
cosidase (No. 9913, Sigma–Aldrich) (1 ml) and deionised
water (2 ml) were added to enzyme solution. The solution
was freshly prepared for the digestion analysis.
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, fol-
lowed by incubation in a water bath (37 C) 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).
The total starch content in the starch samples was mea-
sured according to
Englyst et al. (1992)
. The starch classi-
fication based on its digestibility was: RDS as the starch
that was hydrolysed within 20 min of incubation, RS as
the starch not hydrolysed with 120 min, and SDS as the
starch digested during the period between 20 and 120 min.
2. Materials and methods
2.1. Materials
Starches from the kernels of two mango cultivars (cv.),
i.e. Chausa and Kuppi were isolated as described previ-
ously (
Kaur et al., 2004
). Normal corn starch was provided
by Samyang Genex Co. (Seoul, Korea).
2.2. X-ray diffraction analysis
X-ray diffraction analysis was performed using an X-ray
diffractometer (Philips, X’pert MPD high resolution XRD,
Almelo, Netherlands) operated at 40 kV and 40 mA. Dif-
fractograms were obtained from 4 (2h)to30 (2h) using
a scanning speed of 4/min. The degree of relative crystal-
linity was quantitatively estimated following the method
described by
Nara and Komiya (1983)
using peak-fitting
software (Origin-Version 6.0, Microcal Inc., Northampton,
MA).
2.3. Molecular weight analysis
For measuring the structural properties, the starch sam-
ple was purified following the method described by
Han
and Lim (2004)
. For starch dissolution, the dry and pure
starch (5 mg, dry solids), in a glass vial, was wetted with
ethanol (50 ll) and then 1 M NaOH (1 ml), 50 mM NaNO
3
(3 ml) and 1 M HCl (1 ml) was added and mixed thor-
oughly. The starch solution was then autoclaved at
121 C/20 min and filtered through the mixed cellulose
ester filter (5 lm) while hot (
70 C), before injection into
the high performance size exclusion column chromatogra-
phy (HPSEC) system. The molecular structure of the starch
was analysed using a HPSEC, connected to a multi-angle
laser light scattering detector (MALLS) and a refractive
index (RI). The mobile phase used for HPSEC was an
aqueous NaNO
3
solution (0.15 M) that had been filtered
through 0.1 lm cellulose acetate filters (Whatman, UK)
2.5. Estimated glycemic index (GI)
Using the hydrolysis curve (0–180 min), the hydrolysis
index (HI) was calculated as the percentage of total glucose
released from the sample, to that released from white bread
(
Go˜ i, Garcia-Alonso, & Saura-Calixto, 1997; Granfeldt,
Bj¨ rck, Drews, & Towar, 1992
). The glycemic indices of
the samples were estimated according to the equation pro-
posed by
Go˜ i et al. (1997)
: GI = 39.71 + 0.549 HI.
2.6. Statistical analysis
The data reported in all the tables were subjected to one-
way analysis of variance (ANOVA) using Minitab Statisti-
cal Software version 15 (Minitab, Inc., State College,
USA).
94
K.S. Sandhu, S.-T. Lim / Food Chemistry 107 (2008) 92–97
3. Results and discussion
sity was higher for mango kernel starches than corn
starch (
Table 1
). Chausa starch had a higher crystallinity
(38.3%) than Kuppi starch (35.4%). The side chains of
amylopectin form the crystalline structure, it is therefore
expected that the crystallinity will be inversely related to
amylose content. It has been reported that the relative crys-
tallinity of normal corn starch was 30.3% (
Cheetham &
Tao, 1998
) and that of mango starch was 35% (
Millan-
Testa et al., 2005
).
3.1. Size distribution and amylose content
The mean granule diameters of the mango kernel
starches were slightly higher than those of corn starch
(
Table 1
): 15.8 and 16.3 lm, respectively, were observed
for Chausa and Kuppi cultivars. The amylose content of
the mango kernel starches (28.8% and 33.6%, respectively
for Chausa and Kuppi cultivars) measured using the
HPSEC-MALLS-RI system was slightly higher than that
of corn starch (26.7%).
3.3. Molecular characteristics
3.2. Crystallinity by X-ray diffraction
The structural data measured using an HPSEC-
MALLS-RI system for corn and mango kernel starches
are shown in
Table 2
and their representative curves are
shown in
Fig. 2
. Significant differences in the M
w
of amy-
lopectin and amylose were observed between corn and
mango kernel starches. Corn starch showed the higher
value of M
w
of amylopectin (200
10
6
g/mol) and amylose
(9.5
10
6
g/mol) than the mango kernel starches. Compar-
ing the mango kernel starches, the M
w
of amylopectin was
higher for Chausa (179
10
6
g/mol) than for Kuppi
(140
10
6
g/mol). The radius of gyration (R
g
) of amylo-
pectin was the highest for corn starch (348 nm) and the
lowest for Kuppi starch (293 nm) in the same order for
M
w
. A similar relation between M
w
and R
g
has been
The X-ray diffractograms of the corn and mango kernel
starches are shown in
Fig. 1
. Both corn and mango kernel
starches showed A-type X-ray diffraction patterns, which
are typically found in many cereal starches.
Millan-Testa
et al. (2005)
reported A-type X-ray diffraction patterns
for mango starch. Both corn and mango kernel starches
showed strong reflections at 15 and 23 (2h) and an unre-
solved doublet at 17 and 18 (2h). Mango kernel starches
showed an additional peak at 10 (2h) which was slightly
different from that of normal corn starch. The relative crys-
tallinity, which was measured, based on diffraction inten-
Relative
crystallinity (%)
Normal corn 13.6 ± 0.2
a
26.7 ± 0.6
a
30.1 ± 0.4
a
Chausa 15.8 ± 0.3
b
28.8 ± 0.7
b
38.3 ± 0.7
c
Kuppi 16.3 ± 0.3
c
33.6 ± 0.8
c
35.4 ± 0.9
b
Values with the same superscript within a column do not differ signifi-
cantly (p < 0.05).
Mean (±standard deviation) of triplicate analysis.
Mean granule
diameter (lm)
Amylose
content (%)
Table 2
Molecular characteristics of starches from normal corn and mango kernels
of different cultivars
Starch
M
w
(
10
6
g/mol) R
g
(nm)
Amylopectin Amylose Amylopectin Amylose
Normal corn 200 ± 2.1
c
9.5 ± 0.9
c
348 ± 2.8
c
145 ± 0.9
c
Chausa 179 ± 2.5
b
4.8 ± 0.5
a
318 ± 2.1
b
124 ± 2.3
a
Kuppi 140 ± 1.7
a
6.2 ± 0.7
b
293 ± 1.9
a
134 ± 1.2
b
Values with the same superscript within a column do not differ signifi-
cantly (p < 0.05).
Mean (±standard deviation) of triplicate analysis.
2.5
2.0
Normal corn
1.5
Normal corn
Kuppi
Kuppi
1.0
Chausa
Chausa
0.5
0.0
0
5
10
15
20
25
30
35
120
140
160
180
200
Diffraction angle (2 theta)
Elution volume (ml)
Fig. 1. X-ray diffractograms of starches from normal corn, Chausa and
Kuppi.
Fig. 2. Molecular characterisation of starches from normal corn, Chausa
and Kuppi.
Table 1
Mean granule diameter, amylose content and crystallinity of starches from
normal corn and mango kernels of different cultivars
Starch
K.S. Sandhu, S.-T. Lim / Food Chemistry 107 (2008) 92–97
95
reported earlier for okenia, mango and banana starches by
Millan-Testa et al. (2005)
. It was noteworthy that the
mango kernel starch from the Kuppi cultivar contained
the greater amylose content and the molecular size of the
amylose was also greater in comparison to that of the
Chausa cultivar. The M
w
and R
g
of amylopectin were neg-
atively correlated to the amylose content (r =
0.999 and
0.963, p < 0.01). A similar inverse relationship between
the M
w
of amylopectin and amylose content has been pre-
viously reported for mango and banana (
Millan-Testa
et al., 2005
) and wheat starches (
Yoo & Jane, 2002
).
15.3%, respectively). These values were substantially lower
than those for normal corn starch (27.4% and 45.3%,
respectively). SDS is completely, but more slowly, digested
in the small intestine and attenuates postprandial plasma
glucose and insulin levels. It is generally the most desirable
form of dietary starch (
Jenkins et al., 1981
). RS has been
defined as the sum of starch and the product of starch deg-
radation not absorbed in the small intestine but is fer-
mented in the large intestine of healthy individuals (
Asp,
1992
). The lowest RS (27.3%) was observed for corn starch,
whereas Chausa starch contained a RS more than three
times that of corn starch (80.0%).
Zhang, Venkatachalam,
and Hamaker (2006)
followed the method of
Englyst et al.
(1992)
to determine the RDS, SDS and RS (%) for native
normal corn starch and reported values of 24.4%, 53.0%
and 22.6%. Corn starch granules had channels connecting
the internal cavity with the external environment (
Huber &
BeMiller, 1997
) therefore the hydrolytic enzymes had access
to the interior of the granules via channels (
Hood & Liboff,
1983
), which results in its high digestibility. Conversely,
mango kernel starches contain a high proportion of starch
granules with smooth surfaces, with very few granules hav-
ing surface pores (
Kaur et al., 2004
). Hydrolytic enzymes
act primarily through surface erosion of the starch gran-
ules, which may be the cause of their lower digestibility.
High RS contents due to hydrolytic enzymes acting on
the surfaces of starch granules have been reported for
banana (
Zhang et al., 2005
), yam and lily starches (
Jane,
Wong, & McPherson, 1997
). The differences in the
in vitro digestibility of native starches among species have
been attributed to the interplay of many factors, including
starch sources (
Ring, Gee, Whittam, Orford, & Johnson,
1988
), granule size (
Snow & O’Dea, 1981
), amylose/amylo-
pectin ratio (
Hoover & Sosulski, 1985
), degree of crystallin-
ity (
Chung et al., 2006; Hoover & Sosulski, 1985
) and type
of crystalline polymorphic forms (
Jane et al., 1997
). The
total amount of digestible starch (RDS + SDS) was nega-
tively correlated to starch granule diameter (r =
0.969,
p < 0.05). The size of starch granules may affect digestibil-
ity because as the size of the starch granule increases,
the contact between the enzyme and substrate decreases
(
Svihus, Uhlen, & Harstad, 2005
).
3.4. Digestibility studies
The digestibilities of the corn and mango kernel starches
and starch fractions differ in digestion behavior (readily
digestible starch, RDS; slowly digestible starch, SDS; and
resistant starch, RS) as shown in
Table 3
and
Fig. 3
.
RDS is rapidly and completely digested in the small intes-
tine and is associated with more rapid elevation of post-
prandial plasma glucose. The mango kernel starches
showed lower values for RDS and SDS but very high RS
compared to normal corn starch. The Chausa starch
showed the lowest amounts of RDS and SDS (4.7% and
Table 3
Digestibilities of starches and starch fractions from normal corn and
mango kernels of different cultivars
Starch
Digested starch
RS (%)
RDS (%) SDS (%)
Normal corn 27.4 ± 0.7
b
45.3 ± 2.6
c
27.3 ± 2.1
a
Chausa 4.7 ± 0.4
a
15.3 ± 1.1
a
80.0 ± 2.9
c
Kuppi 5.2 ± 0.3
a
19.2 ± 1.3
b
75.6 ± 1.7
b
Values with the same superscript within a column do not differ signifi-
cantly (p < 0.05).
Mean (±standard deviation) of triplicate analysis.
100
80
Normal corn
3.5. Hydrolysis index (HI) and estimated glycemic index
(GI)
60
40
The hydrolysis index (HI) is a useful tool, from a nutri-
tional point of view, for comparison of starch digestibility.
This index expresses the digestibility of the starch in foods
in relation to the digestibility of starch in a reference mate-
rial, namely white bread. Glycemic index (GI) is calculated
from HI and is defined as the incremental postprandial
blood glucose area after injection of the test product, as a
percentage of the corresponding area after injection of an
equicarbohydrate portion of the reference product (
Jenkins
et al., 1983
). The HI and GI of corn and mango kernel
starches are shown in
Table 4
. Corn starch showed a higher
Kuppi
20
Chausa
0
0
20 40 60 80 100 120 140 160 180 200
Hydrolysis time (min)
Fig. 3. Enzymatic digestion of starches from normal corn, Chausa and
Kuppi.
96
K.S. Sandhu, S.-T. Lim / Food Chemistry 107 (2008) 92–97
Table 4
Hydrolysis index (HI) and estimated glycemic index (GI) of starches from
normal corn and mango kernels of different cultivars
Starch
HI
GI
d
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Normal corn
64.0 ± 1.5
c
74.9 ± 1.1
c
Chausa
16.7 ± 0.9
a
48.8 ± 0.6
a
50.9 ± 1.0
b
Values with the same superscript within a column do not differ signifi-
cantly (p < 0.05).
Mean (±standard deviation) of triplicate analysis.
d
GI was calculated by the equation proposed by
Go˜ i et al. (1997)
:
GI = 39.71+0.549 HI.
20.5 ± 1.3
b
HI and GI (64.0% and 74.9%, respectively) compared to
mango kernel starches. The HI of mango kernel starches
was 16.7 and 20.5, respectively and the estimated GI based
on HI were 48.8% and 50.9%, respectively for Chausa and
Kuppi. The HI and GI of Kuppi were higher than those of
Chausa. The hydrolysis rate was significantly different for
corn and mango kernel starches: the highest rate was for
corn (77.0%) and the lowest was for Chausa (28.6%). After
20 min of hydrolysis, mango kernel starches showed a
hydrolysis rate of less than 5.3%, whereas that of corn
starch was 27.5%. After 120 min, the hydrolysis rate of
corn starch (72.7%) remained substantially greater than
those of the mango kernel starches (24.5% and 20.1%,
respectively). The greater amylose content and crystallinity
observed for the mango kernel starches, in comparison to
the normal corn starch, may be a major contributor to
the greater resistance of the digestive enzymes for mango
kernel starches.
4. Conclusion
Mango kernel starches showed an A-type X-ray diffrac-
tion pattern, typically found in many cereal starches. The
M
w
of the mango kernel starches were lower whereas the
amylose content and crystallinity were higher than that
of normal corn starch. The mango kernel starches con-
tained higher RS leading to lower GI values compared to
normal corn starch. Therefore, mango kernels wasted after
industrial processing of mango could become a useful
source of starch, especially in terms of its beneficial digest-
ibility behavior and high RS content.
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