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RESEARCH ARTICLE
Physicochemical properties and in vitro digestibility ofresistant starch from mung bean (Phaseolus radiatus)starch
Suling Li1, Qunyu Gao1 and Rachelle Ward2
1 Carbohydrate Laboratory, College of Light Industry and Food Sciences, South China University of Technology,Guangzhou, P. R. China
2 NSW Department of Primary Industries Yanco Agricultural Institute, Yanco NSW, Australia
RS from mung bean starch was prepared by autoclaving, pullulanase debranching, and
retrogradation. Physicochemical properties, crystalline structure, and in vitro digestibility of
selected RS samples with different RS content were investigated. Compared to native starch,
AAM content of RS increased but MW decreased greatly. SEM clearly showed RS samples
exhibited irregular shaped fragments with compact structure. XRD pattern indicated that RS
samples had typical B-type pattern with sharp peaks at 17.08, 22.28, and and 23.98 2u. Therelative crystallinity, gelatinization temperatures, and enthalpy increased with increasing RS
content. The a-amylase digestibility of RS was lower than that of native starch. The results
suggested that the decrease in enzymatic digestion of RS might due to compact and ordered
crystalline structures after debranching and recrystallization.
Received: August 15, 2010
Revised: November 28, 2010
Accepted: November 29, 2010
Keywords:
Digestibility / Mung bean starch / Properties / Pullulanase / Resistant starch
1 Introduction
In response to consumer awareness and demands for
healthy food options, great efforts have been made to
explore new sources to prepare nutraceuticals and func-
tional foods with beneficial physiological effects [1–4]. One
example of new nutrition-valued food is to increase the RS
within food products [5]. RS are the starch portions that
escape digestion in the small intestine, but might be
fermented and absorbed in the large intestine [6]. RS
imparts desirable physiological benefits to human health,
which mainly includes the increase in faecal bulk, and the
production of some SCFAs from fermentation in the
large intestine, improvement in cholesterol problem, the
reduction in glycemic and insulinemic response to food,
and the decrease in the risk of ulcerative colitis and colon
cancer [5, 7, 8]. RS features a unique combination of
physiological and functional properties, while traditional
fiber has a coarse texture [9]. These properties enable
RS to receive increasing attention as a beneficial food
component.
RS can be classified into five categories, as follows;
RS1: physically inaccessible starch; RS2: native granule or
ungelatinized starch; RS3: retrograded starch [10]; RS4,
chemically modified starch [4]; RS5, V-form, inclusion
complexes formed by AM and polar lipids [11]. RS3
remains thermally stable in normal cooking and it is the
most important type of starches in processed foods [1].
RS3 closely relates to highly retrograded AM fractions.
Different processing methods and conditions can
influence the formation and properties of RS. For example,
pullulanase debranching is an important technology for
gelatinized starch to produce linear glucans and therefore
helps starch recrystallization [5].
Correspondence: Professor Qunyu Gao, CarbohydrateLaboratory, College of Light Industry and Food Sciences, SouthChina University of Technology, 381 WuShan Road, Guangzhou510640, P. R. China.E-mail: [email protected]: þ86-020-87113848
Abbreviations: HPGPC, high performance gel permeationchromatography; RDS, rapidly digestible starch; SDS, slowdigestible starch.
DOI 10.1002/star.201000102Starch/Starke 2011, 63, 171–178 171
� 2011WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.com
Many studies about RS have been conducted on
starches from maize, wheat, potato, pea, and wx maize
[12]. It is necessary to look for alternative sources of starch
that have the potential to exhibit better physicochemical
and functional characteristics [13]. Mung bean (Phaseolus
radiatus) or green bean is native to the northeastern India–
Burma (Myanmar) region of Asia. It can be grown in Asia,
Africa, South America and Australia [14]. Traditionally,
mung bean starch is the best raw material for making
starch noodle due to the properties of high AM content,
restricted swelling and high shear resistance of its paste
[15].
Mung bean is mainly cultivated in China and a good
source of starch (�50%). The information regarding the
production and properties of RS from mung bean starch
is extremely scarce. Therefore, it is worthwhile to explore the
potential to derive value-added products from mung bean
starch. The purpose of this study was to evaluate physico-
chemical properties and structural characteristics of mung
bean starch with different RS content. The in vitro enzymatic
digestibility of RS was also studied. Understanding of the
properties and enzymatic digestibility of mung bean RS will
establish a foundation for further application.
2 Materials and methods
2.1 Materials
Native mung bean starch was purchased from Hada
Starch Factory (Harbin, China) to prepare a series of
products with different RS content. The RS products were
labeled as RS 11.7%, RS 29.9%, RS 36.8%, RS 43.0%,
and RS 51.0%. The samples with RS 29.9–51.0% were
subjected to autoclaving, pullulanase debranching, and
crystallization processes. An aqueous slurry of starch
(8% w/w, dry basis) was added with an acetate-acetate
buffer solution and autoclaved at 1218C for 20 min. After
cooling to 558C, pH was adjusted to 4.6 with 0.5 N acetic
acid. The gelatinized starch was treated with different
concentrations of pullulanase (20, 40, 60, and 50 ASPU/
g dry starch, Diazyme1 P10, Danisco) and incubated at
558C for 24 h to prepare RS 29.9%, RS 36.8%, RS 43.0%,
and RS 51.0%, separately. The enzyme was inactivated at
1008C for 15 min and then the debranched starch was
stored at 48C for 24 h. The retrograded starch waswashed
with 90% ethanol to pH 7 and dried at 458C to �10%
moisture content. Sample RS 11.7% was not debranched
by pullulanase, but underwent autoclaving and crystalliza-
tion. The undebranched starch (RS 11.7%) was the control
sample. The RS samples were ground and packed in
plastic bags for further analysis.
RS assay kit was brought from Megazyme International
Ireland Ltd. (Wicklow, Ireland). Porcine a-amylase (260 U/g),
AM and AP were obtained from Sigma Chemical Company
(St. Louis, MO, USA). Standard dextrans were purchased
from Pharmacia Ltd. (Germany). All other chemicals and
solvents in this work were of analytical grade.
2.2 Resistant starch determination
The RS content was determined using a Megazyme
Resistant Starch Assay Kit with the description of
Association of Official Analytical Chemists (AOAC)
2002.02 [16]. In short, starch (100 mg) and 4 mL of
enzyme mixture (pancreatic a-amylase, 10 mg/mL, and
amyloglucosidase, 3 U/mL) was added to each test tube,
and then incubated in a shaking water bath (Wisebath@,
Feedback Control Digital Timer Function, Sweden) for
16 h (378C, 200 strokes/min) to hydrolyze digestible
starch. The resistant portion was precipitated with 95%
ethanol and the residue obtained was washed with 50%
ethanol twice, and treated with potassium hydroxide
solution (4 M, 2 mL) to solubilize the RS. The RS solution
obtained was adjusted to pH 4.75 with 8 mL of 1.2 M
sodium acetate buffer (pH 3.8). After incubation with amy-
loglucosidase (0.1 mL, 3300 U/mL) at 508C for 30 min,
the samples were centrifuged at 3000 � g for 10 min.
Threemilliliter of glucose-oxidase-peroxidase-aminoantipyrine
(GOPOD) was added to aliquots (0.1 mL) of the super-
natant, and the mixture was incubated at 508C for 20 min.
Absorbance was measured using a spectrophotometer
(Model 722, Shanghai Analytical Instrument Company,
China) at 510 nm. The analyses were determined in
triplicate and the average value was recorded.
2.3 Apparent amylose content
Apparent AM content in the sampleswas determined using
themethod of Juliano et al. [17]. Starch (100 mg, dry basis)
was wetted with 1 mL ethanol (95%) and gelatinized by
treatment with 9.2 mL of 1 N NaOH and storage for 24 h at
ambient temperature. After adjusting to 100 mL of distilled
water, an aliquot of 5 mL of the solution was transferred to
100 volumetric flasks and 1 mL of 1 N acetic acid was
added. Then 2 mL of 0.2% w/v I2 and 2% w/v KI were
added to the volumetric flask and the volume was adjusted
to 100 mL with distilled water. The solution was allowed to
stand for 20 min at ambient temperature prior to absorb-
ance measurements at 620 nm. A standard curve was
plotted for mixtures of pure AM and AP from potato starch.
AAM content was calculated from the standard curve.
2.4 High-performance gel permeationchromatography (HPGPC)
Sample (50 mg) was dissolved in 10 mL of 90% DMSO
and the solution was centrifuged at 3000 � g for 20 min.
172 S. Li et al. Starch/Starke 2011, 63, 171–178
� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.com
Sample solution (100 mL) was filtered through cellulose–
acetate membrane filters with 0.45 mm pore size. The
solution was fractionated through Waters 600 HPLC sys-
tem (Waters Corp., Milford, MA, USA) with analytical col-
umns (UltrahydrogelTM Linear 300 mm � 7.8 mm). The
column temperature was maintained at 458C. The mobile
phase of 100 mM NaNO3 containing 0.02% NaN3 at a rate
of 0.9 mL/min and monitored by differential RI detectors
(Model 2410, Waters Corps., Milford, MA, USA). Standard
dextrans with different MWs were used for MW calibration.
The average of duplicate of MW was recorded.
2.5 Scanning electron microscopy (SEM)
RS and native samples were mounted on an aluminum
specimen holder by double-sided tape. The samples were
coated with gold palladium, with a thickness of about 30 nm.
The specimen holder was then transferred to an environ-
mental scanning electron microscope (Quanta 200, FEI,
Holland) and examined at an accelerating potential of 20 kV.
2.6 X-ray diffraction (XRD)
XRD analysis of native and RSs was examined by a D/
Max-2200 X-ray diffractometer (Rigaku Denki Co., Tokyo,
Japan). The samples were scanned with a CuKa target at
40 kV and 30 mA. XRD patterns were recorded using a
scintillation detector scanning from 48 to 358 (2u) with the
speed rate of 48/min. The degree of relative crystallinity of
the samples was quantitatively estimated following the
method of Nara and Komiya (1983) [18].
2.7 Differential scanning calorimeter (DSC)
Thermal properties of starches were measured by a differ-
ential scanning calorimeter (DSC) (Perkin-Elmer DSC 8000,
Norwalk, CT, USA). Starch (7.5 mg) was weighed into high-
pressure screw type DSC pans and distilled water (15.0 mg)
was added tomake suspensionswith 70%moisture content.
Pans were hermetically sealed and equilibrated for 2 h at
ambient temperature before heating in the DSC. The scan-
ning temperature range and the heating rate were 30–1808Cand 108C/min, respectively. Indium and zinc were used for
the calibration and an empty pan was used as a reference.
Onset temperature (To), peak temperature (Tp), conclusion
temperature (Tc), and enthalpy (DH, J/g) for gelatinization
were determined. Results were presented as an average of
four repeats.
2.8 In vitro a-amylase hydrolysis rate ofdigestion
The determination of in vitro enzymatic hydrolysis index
was conducted according to the modified method of
Jenkins et al. (1987) and Fredriksson et al. (2000) [19,
20]. Briefly, 4 mL of a-amylase solution (100 U/mL) was
added to RS samples held in 15 cm dialysis bag. The
dialysis bag was placed into a beaker containing
400 mL distilled water at 378Cwith agitation. The dialysate
was obtained every 30 min from 0.5 to 5 h. The enzyme
was inactivated at boiling water for 5 min to ensure further
hydrolysis did not occur after the prescribed time. Maltose
concentration was determined by phenol–sulfuric acid
reagent method. The rate of starch digestion was calcu-
lated as the percentage of starch digestion products to
maltose (maltose equivalents) at the different incubation
times. The samples were run in triplicate.
2.9 Statistical analysis
The test data were statistically analyzed using one-way
analysis of variance (ANOVA) on SPSS version 13.0 soft-
ware for Windows (USA). Least significant difference
(LSD) test was used to determine differences between
means. p < 0.05 was considered to be significant. The
results reported were average and SD values.
3 Results and discussion
3.1 Apparent AM content
Native starch of AM content in this study was 30.1%
(Table 1), which is comparative to previous mung bean
AM contents of 30.9–34.3% [21] and defatted mung bean
starch 32.7–34.3% [14]. The AM content of unbranched
RS 11.7% was 6.0% greater than native starch, and the
debranched RS samples were 22.7–28.7% greater than
native starch. Results show that AM content increased with
the enhancement of RS, that AM content was somewhat
related to RS and that the RS could be further enhanced
by debranching with pullulanase. Upon retrogradation,
rearrangement or recrystallization of starch fractions
would generate RS3 resulting from highly retrograded
AM chains [22].
Table 1. AAM content of native and RSs
Samples AAM content (%)
Native starch 30.1 � 0.2a
RS 11.7% – undebranched 36.1 � 0.6b
RS 29.9% – debranched 52.8 � 0.8c
RS 36.8% – debranched 58.9 � 0.9d
RS 43.0% – debranched 57.6 � 0.6d
RS 51.0% – debranched 58.8 � 1.1d
Mean values with different letters within each column aresignificantly different (p < 0.05).
Starch/Starke 2011, 63, 171–178 Properties and digestibility of mung bean resistant starch 173
� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.com
Pullulanase can not only catalyze hydrolysis of a-D-
glucosidic linkages of pullulan, but also cleave
a � (1 ! 6) branch linkages of AP and glycogen [23,
24]. The resulted short linear chains had similar molecular
characteristics to AM and mainly linked by a � (1 ! 4)
linkage. Guraya et al. [25] (2001) suggested that amount of
debranching would affect the retrogradation process
during storage because shorter chain length was favorable
for precipitation, rather than longer chain length. This was
due to strong gel networks between AM interaction of AM
or AP during retrogradation [26]. Thus, treatment of mung
bean starch with pullulanase can produce RS3 starch
by chain elongation and folding, which will promote
recrystallization.
Addition of excess pullulanase does not increase the
RS of the mung bean starch; e.g., 50 and 60 ASPU/g (dry
starch) of pullulanase resulted in the samples with RS
content of 51.0 and 43.0%, respectively. Eerlingen et al.
[27] (1993) indicated that too many number of short chains
were unfavorable for nucleating and propagating into
stable crystallites whereas appropriate starch chain length
was good for starch recrystallization. In other words,
pullulanase treatment could generate appropriate chain
lengths of AM that helps starch recrystallization.
3.2 Molecular weight distribution by HPGPC
The elution profiles of MW of RSs were examined by
HPGPC (Table 2). Native mung bean starch was a complex
molecule with high Mw and it was difficult to fraction. The
Mw of debranched products showed a dramatic decrease
in Mw with increasing RS content. These results suggested
that themolecule of starch decreased greatly after debranch-
ing. Pullulanase can rapidly hydrolyze a�(1!6) glucosidic
bonds from the parent AP molecule. The technology of
pullulanase debranching is promising for producing linear
and low Mw chains. With the degradation of polymer,
debranching treatment might provide sufficient AM chains
for the crystallization process. When the debranched
starch was recrystallized, the short linear chains would
aggregate and realign into double helical strands and be
stabilized by hydrogen bonds [28]. This result is consistent
with the study of Leong et al. [24] (2007), which showed
that a 20–25 glucose residue was favorable for starch
retrograded or recrystallized and resulted in RS formation.
The aggregated starch chains with suitable Mw could lead
to precipitation and formation of denser structures during
the periods of retrogradation. The potential substrates in
RS3 with double helical aggregations might increase its
resistance to enzyme hydrolysis [29].
3.3 Morphology (SEM)
Morphology of native and RS was obtained from SEM
(Fig. 1). Native mung bean starch granules appeared small
and either elliptical or spherical shape. Large granules
displayed kidney-shaped or oval, whereas small granules
exhibited spherical. The granular size of mung bean starch
ranged from 7.9 to 31.6 mm.However, granular structure of
starch was destroyed after modifications. RS3 samples
showed bigger, irregular shaped fragments with compact
structure (Figs. 1B, C, and D). The size of large fragments
ranged from 30 to 80 mm, and that of the smaller ones
varied from 10 to 30 mm. For RS samples, the difference in
microscopic appearance was influenced by autoclaving
and retrogradation relative to crystalline structure in RS
samples [30].
When starch was heated in excessive water at gelati-
nization temperature, Ratnayake and Jackson [31]
observed that molten starch granules or beams would
connect with one another to form a sponge-like structure
observed from different starch. Previous studies
suggested that starch molecules re-associated as double
helices, and formed tightly packed structures stabilized by
hydrogen bonding upon retrogradation. RS was charac-
terized as an ordered double helix structure and appeared
to be located in inner regions [31–33]. Thus, the newly
formed structure with irregular shape of RS would
decrease enzymatic hydrolysis.
3.4 X-ray diffraction (XRD)
Figure 2 shows the XRD patterns and relative crystallinity
(%) of native starch and the selected RS3 samples. Native
mung bean starch showed strong diffraction peaks at
15.08, 17.18, 19.78, 23.08 2u (Fig. 2, curve A). Native mung
bean starch exhibited A-type crystalline pattern. Some
confusion in literature about the crystalline pattern of mung
bean starch is reports of C-type and A-type [34, 35].
The difference in diffraction pattern of native mung bean
starch might due to the starch origin, isolation method,
sample preparation method, and X-ray analysis operation
conditions.
Compared to native starch, the sample of RS 11.7%
(non-debranched) had additional diffraction peak at 5.88 2u(Fig. 2, curve B). The debranched starch products dis-
played similar XRD patterns with sharper peaks (Fig. 2,
curve C, D, E, and F). The RS samples with pullulanase
Table 2. Summary of MW distributions of RS
Samples Mwa)
RS 29.9% 3.50 � 103
RS 36.8% 3.70 � 103
RS 43.0% 3.90 � 103
RS 51.0% 3.97 � 103
a) Mean values of average MW.
174 S. Li et al. Starch/Starke 2011, 63, 171–178
� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.com
debranching had sharp peaks at 17.08, 22.28, 23.98 2u, andnew peaks occurred at 5.78, 14.08, and 25.98 2u (Fig. 2,
curve C, D, E, and F). The result showed that RS3 dis-
played a typical B-type diffraction pattern. The typical B-
type X-ray pattern was the result of the retrogradation of
both AM and AP.
Miao et al. [36] reported that the differences in starch
crystallinity could mainly due to crystal size, amount of
crystalline regions affected by AP content and AP chain
length, orientation of the double helices within the crystal-
line domains, and degree of interaction between double
helices. The hydrolysis of a�(1!6) glycosidic bondswould
produce more free linear chains in the hydrolysate and RS
crystallites exhibited more tightly packed structure and/or
more arranged to XRD than did native starches. Wu and
Sarko [32] suggested that the extent of diffraction intensity
could reflect the change in retrograded AM. During
heating and cooling, AM chains were recrystallized and
even debranched AP chains were re-crystallized [5].
Therefore, the change in starch crystalline structure will
cause difference in diffraction pattern.
The relative crystallinity of nativemung bean starch was
the lowest value (21.6%) of all samples. With increasing
RS content, the relative crystallinity of samples increased.
The value of relative crystallinity (21.9%) of un-debranched
sample was similar to native starch (Fig. 2, curve B).
However, the debranched RS samples showed much
higher value in relative crystallinity and the relative crys-
tallinity ranged from 38.8 to 42.8%. (Fig. 2, curve C, D, E,
Figure 1. Micrographs of native and RSs. (A) Native (T3000), (B) RS 11.7% (T600), (C) RS 36.8% (T600), (D) RS 51.0%(T600).
5 10 15 20 25 30 35
FEDCBA
Inte
nsity
Diffraction angle
Figure 2. XRD patterns of native and RSs. (A) Native,(B) RS 11.7%, (C) RS 29.9%, (D) RS 36.8%, (E) RS43.0%, (F) RS 51.0%.
Starch/Starke 2011, 63, 171–178 Properties and digestibility of mung bean resistant starch 175
� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.com
and F). The increase in relative crystallinity was found on
the debranched and recrystallized cassava starch [37].
The increased relative crystallinity further illustrated the
ordering arrangement of starch chains in RS.
3.5 Thermal analysis by DSC
Thermal properties of native and the resistant products
were determined by DSC analysis. The native mung bean
starch showed a clear gelatinization peak at 76.58Cwith an
endothermic enthalpy of 2.3 J/g (Table 3). This gelatiniza-
tion enthalpy reported here were lower than previous
studies with the difference in results, attributed to different
starch source, isolation methods and/or DSC pan. After
gelatinization and retrogradation treatment, the RS prod-
ucts exhibited broader peaks and the gelatinization tem-
peratures shifted to higher temperatures. The enthalpy of
RS product increased from 4.1 to 14.1 J/g with increasing
RS content. The RS product showed obvious endothermic
transition temperatures ranging from 65.3 to 103.38Cwith the peak temperatures of 66.0–109.98C. The result
can be mainly associated to the dissociation of AM double
helices and formation of the re-association of leached
AM upon retrogradation. Hence, the gelatinization
temperature of RS was increased and RS products exhib-
ited more thermal stability than that of native starch.
3.6 In vitro a-amylase hydrolysis rate ofdigestion
In vitro a-amylase hydrolysis (0–5 h) of RS is presented in
Fig. 3. With increasing RS content, the a-amylase hydroly-
sis rate of RS decreased. The control sample (RS 11.7%)
had the highest a-amylase hydrolysis rate among RS
samples. Moreover, a rapid hydrolysis rate of all samples
was observed within the first 2 h of incubation. This result
might mainly ascribe to hydrolysis of rapidly digestible
starch (RDS) and slow digestible starch (SDS). After
2.5 h, the enzymatic digestion rate slowed down to a
plateau. The a-amylase hydrolysis rate of RS 29.9%,
RS 36.8%, RS 43.0%, and RS 51.0% was lower than
that of RS 11.7%. The enzymatic digestibility decreased
as RS content increased and the sample of RS 51.0%
showed lowest enzymatic digestion of all starch samples.
Pongjanta et al. [5] reported similar results that the incom-
pletely debranched RS3 sample from high amlyose rice
starch had stronger resistance to a-amylase digestion
than native starch. The enzyme hydrolysis rate of banana
RS products was less than in native starch [30]. The
resistance to enzymatic hydrolysis is due to starch recrys-
tallization with tight and packed structures [1]. Shin et al.
[38] suggested that RDS, SDS, and RS fractions formed
into a single crystallite structure. RDS and SDS mainly
consisted of amorphous regions, while RS considered as
an arrangement and ordered double helix structure in
inner regions. Thick and dense crystallites would make
it difficult for a-amylase to access the double helices in a
crystalline structure [32], which decreased the hydrolysis
rate of starch digestion and even enhanced the resistance
to a-amylase hydrolysis.
Table 3. Thermal properties of native and RSs
Samples T0a) (8C) Tp
a) (8C) Tca) (8C) DHb) (J/g)
Native starch 76.5 � 0.3a 81.0 � 0.2a 86.1 � 0.2a 2.3 � 0.1a
RS11.7% 65.3 � 0.3b 66.0 � 0.3b 68.3 � 0.2b 4.1 � 0.1b
RS29.9% 90.2 � 0.2c 104.4 � 0.5c 109.8 � 0.2c 9.2 � 0.1c
RS36.8% 93.8 � 0.4d 106.3 � 0.1d 111.8 � 0.2d 11.0 � 0.1d
RS43.0% 94.0 � 0.3d 109.9 � 0.3ab 114.4 � 0.3ab 12.0 � 0.2ab
RS51.0% 103.3 � 0.2ab 108.7 � 0.1bc 115.2 � 0.1bc 14.1 � 0.2bc
a) To, Tp, and Tc indicate the temperature of the onset, peak, and conclusion of gelatinization, respectively.b) DH indicates enthalpy of gelatinization.Average values in the column with different superscripts are significantly different (p < 0.05).
0
2
4
6
8
10
12
14
16
0 1 2 3 4 5 6Time (h)
Hyd
roly
sis r
ate
(%)
Native11.6%29.9%36.8%43.0%51.0%
Figure 3. In vitro �-amylase hydrolysis rate of native andRS samples.
176 S. Li et al. Starch/Starke 2011, 63, 171–178
� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.com
4 Conclusions
Mung bean RS products with various RS contents pos-
sessed differences in physicochemical properties, crystal-
line structure, and enzyme hydrolysis profiles. The
differences in properties amongst debranched RS
starches indicated that the debranching technique com-
bined with crystallization could be used to design different
RS products.With respect to AAM content andMWresults,
pullulanase was an effective method to yield short chain
AM, which was helpful for RS formation during retrogra-
daton. After recrystallization, compact and ordering crystal
structure of starch might be developed and it led to a
decrease in a-amylase hydrolysis rate of starch. In
addition, RS products exhibited thermal stability with
increasing RS contents, which was favorable for food
processing. RS products with different properties and in
vitro digestion profiles are desired for satisfying different
marketing demand.
The study was carried out with financial support
of the National High-tech R&D Program of China
(2007AA10Z309), and Guangdong Province Program
of China (2009B090300274).
The authors declared no conflict of interest.
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