Classification of rice cultivars based on cluster analysis of hydration ...

<strong>Classification</strong> <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong> <strong>based</strong> on cluster analysis <strong>of</strong> hydration and pasting
properties <strong>of</strong> their starches
Inae Lee a , Gyoung Jin We a , Dong Eun Kim a , Yong-Sik Cho b , Mi-Ra Yoon c , Malshick Shin d ,
Sanghoon Ko a, *
a Department <strong>of</strong> Food Science and Technology, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, Republic <strong>of</strong> Korea
b National Academy <strong>of</strong> Agricultural Science, Rural Development Administration, Suwon 441-707, Republic <strong>of</strong> Korea
c National Institute <strong>of</strong> Crop Science, Rural Development Administration, Suwon 441-707, Republic <strong>of</strong> Korea
d Department <strong>of</strong> Food and Nutrition, Chonnam National University, Gwangju 500-757, Republic <strong>of</strong> Korea
article info
Article history:
Received 22 September 2011
Received in revised form
16 February 2012
Accepted 2 March 2012
Keywords:
Rice
Starch
Pasting property
Cluster analysis
Cultivars
<strong>Classification</strong>
1. Introduction
abstract
Rice starch has attracted attention for use in baby foods, extruded
products, soups, and dressings due to its small-size starch granules,
neutral taste, and s<strong>of</strong>t mouth feel (Mitchell, 2009). However, Rice
starch industry is suffering from inefficiency in securing the uniform
quality ingredient since <strong>rice</strong> commodities that are traded involve
a wide variety <strong>of</strong> <strong>cultivars</strong>, and each <strong>rice</strong> cultivar possesses unique
processability. Especially, there exists a significant difference in
physicochemical properties even among the starches obtained from
<strong>rice</strong> <strong>cultivars</strong> with similar amylose content (Choi, 2002; Ha et al.,
2007; Yoon, Koh, & Kang, 2009). From the industrial standpoint, it
is a realistic approach to simplify <strong>rice</strong> <strong>cultivars</strong> categorization in
order to control the <strong>rice</strong> quality at all times. Thus, it is plausible to
classify the <strong>rice</strong> starches categorized by similarity on the processability
<strong>of</strong> their species after selecting those by its food-applicable
properties for appropriate management <strong>of</strong> <strong>rice</strong> starch quality. It is
* Corresponding author. Tel.: þ82 2 3408 3260; fax: þ82 2 3408 4319.
E-mail addresses: cwddzz@naver.com (I. Lee), playmaker11@navr.com (G.J. We),
idb7576@daum.net (D.E. Kim), yscho@rda.go.kr (Y.-S. Cho), mryoon12@rda.go.kr
(M.-R. Yoon), msshin@jnu.ac.kr (M. Shin), sanghoonko@sejong.ac.kr (S. Ko).
0023-6438/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.lwt.2012.03.002
LWT - Food Science and Technology 48 (2012) 164e168
Contents lists available at SciVerse ScienceDirect
LWT - Food Science and Technology
journal homepage: www.elsevier.com/locate/lwt
The aim <strong>of</strong> this study was to classify different <strong>rice</strong> <strong>cultivars</strong> <strong>based</strong> on their starches processability indicators
such as hydration and pasting properties instead <strong>of</strong> conventional approach <strong>based</strong> on amylose
content. Hydration and pasting properties <strong>of</strong> <strong>rice</strong> starches from 12 different <strong>cultivars</strong> (A to L) were
analyzed, and corresponding parameters were used to classify the <strong>cultivars</strong> by a hierarchical cluster
analysis. Twelve <strong>rice</strong> <strong>cultivars</strong> were classified <strong>based</strong> on the pasting parameters (AJ/B/CDGI/EFH/K/L), the
hydration parameters (ACDGJ/BEFHI/K/L), and their combination (ACDGJ/BEFHI/K/L). The classification
<strong>based</strong> on the amylose content (AB/CDEFGHIJ/KL) is different from that <strong>based</strong> on hydration and/or pasting
characteristics. Especially, <strong>cultivars</strong> C, D, and G and <strong>cultivars</strong> E, F, and H have been separated into different
groups although they were found to possess similar amylose content. The group having <strong>cultivars</strong> E, F, and
H showed higher water absorption index, swelling power, and pasting viscosities than the group <strong>of</strong> C, D,
and G <strong>cultivars</strong>. This study provides a resolution to standardize purpose-specific starches from a variety
<strong>of</strong> <strong>rice</strong> <strong>cultivars</strong>.
Ó 2012 Elsevier Ltd. All rights reserved.
necessary to reflect their actual competence in order to distinguish
<strong>based</strong> on the characteristics <strong>of</strong> <strong>rice</strong> starch. So far, amylose content
and amylose/amylopectin ratio have been used to distinguish the
<strong>rice</strong> starch characteristics (Hall & Johnson, 1966; Juliano, 1985; Kum,
Lee, Lee, & Lee, 1996). However, neither amylose content nor
amylose/amylopectin ratio <strong>of</strong> <strong>rice</strong> starch has reflected properly the
processing suitability parameters such as swelling power and
pasting property. A wide variety <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong> can be classified into
several groups <strong>based</strong> on their processability instead <strong>of</strong> amylose
content or amylose/amylopectin ratio.
Recently, hydration and rapid visco analysis (RVA) parameters
have been considered to study the processability <strong>of</strong> starches
(Adebowale & Lawal, 2003). Herein, we hypothesize that proper
interpretation <strong>of</strong> the analytical results <strong>of</strong> <strong>rice</strong> processability indicators
such as hydration and pasting parameters could provide a new
classification <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong> fulfilling food industry needs. The RVA is
one <strong>of</strong> major analytical methods to determine starch quality in food
industry. The RVA pr<strong>of</strong>iles have been extensively used for pasting
comparison studies in starch applications (Bhattacharya, Zee, &
Corke, 1999; Limpisut & Jindal, 2002; Wiesenborn, Orr, Casper, &
Tacke, 1994). Starch processability characteristics can be indirectly
inferred from the quantitative RVA pr<strong>of</strong>ile parameters such as peak

time, pasting temperature, peak viscosity, trough viscosity, final
viscosity, breakdown, and setback. Other important parameters
which represent processability are hydration properties: water
absorption index, water solubility, and swelling power (Crosbie,1991;
Li & Yeh, 2001). The hydration properties <strong>of</strong> starches can be correlated
with their pasting behaviors which are important for the determination
<strong>of</strong> starch quality. In many cases, a single parameter from
different measures rarely reflects whole characteristics <strong>of</strong> a starch. In
addition, it is difficult to classify the <strong>rice</strong> starches intuitively <strong>based</strong> on
the parameters because <strong>of</strong> the complexity <strong>of</strong> them.
To overcome these issues, statistical categorization such as
clustering can be used as an alternative approach to obtain
a common pattern from complex data sets <strong>of</strong> hydration and pasting
parameters. Cluster analysis is a statistical method to convert
various characteristics <strong>of</strong> objects to quantitative measures (so
called similarity distance) and correspondingly to cluster them at
relatively close distances into a category (Endo, Okada, Nagao, &
D’applonia, 1990). We hypothesize that the cluster analysis can be
used to categorize the <strong>rice</strong> <strong>cultivars</strong> having similar hydration and
pasting parameters into single group. In this approach, starches
from different <strong>cultivars</strong> but with similar processability properties
can be assumed as a single commodity for easy identification and
selection by starch industry for specific application purposes.
In this study, <strong>rice</strong> starches were extracted from 12 different
<strong>cultivars</strong> and their processability parameters were measured; they
are categorized into several groups by cluster analysis <strong>of</strong> the processability
parameters. In addition, the texture properties <strong>of</strong> these <strong>rice</strong>
starches were also determined to validate the categorization.
2. Materials and methods
2.1. Materials
Twelve <strong>rice</strong> <strong>cultivars</strong> are listed in Table 1 and were grown at the
National Institute <strong>of</strong> Crop Science, Rural Development Administration,
Korea in 2009. The grains <strong>of</strong> each <strong>rice</strong> cultivar was polished
to separate husk and bran and subsequently stored for further
starch preparation.
2.2. Rice starch preparation
Rice starch from each cultivar was isolated by an alkaline
steeping method (Yamamoto, Sawada, & Onogaki, 1973).
2.3. Amylose content measurement
Amylose content <strong>of</strong> the <strong>rice</strong> starches was determined by using
the iodine test (Williams, Kuzina, & Hlynka, 1970).
Table 1
Amylose contents <strong>of</strong> <strong>rice</strong> starches extracted from different <strong>cultivars</strong>.
Symbols Amylose content (g/100 g) Name <strong>of</strong> the cultivar
A High amylose 33.84 0.47 a
Goami
B 29.16 0.71 b
Thailand
C Medium amylose 22.05 1.33 c
Seolgaeng
D 21.73 0.51 dc
Hiami
E 21.44 0.2 d
Ilmi
F 21.35 0.32 d
Hanareum
G Low amylose 19.44 0.17 e
Hopyeong
H 17.97 0.37 f
Deuraechan
I 17.92 0.18 f
Hanmauem
J 17.62 0.23 f
Dongjin 1
K Waxy 1.70 0.12 g
Boseokchal
L 1.32 0.56 g
Shinseonchal
Means with the different letters in the same column are significantly different at the
5% level.
I. Lee et al. / LWT - Food Science and Technology 48 (2012) 164e168 165
2.4. Measurement <strong>of</strong> water absorption index, water solubility, and
swelling power
Water absorption index (WAI) was measured according to the
method <strong>of</strong> Medcalf and Gilles (1965). Water solubility (WS) and
swelling power (SP) were determined following the method <strong>of</strong>
Schoch (1964). For the analysis <strong>of</strong> hydration properties, starch
suspension was heated at 80 C. Three hydration parameters were
calculated using the following equation:
Water Absorption Index ðWAIÞ ¼
Water Solubility ðWS; %Þ ¼
wet sediment weight
dry sample weight
dry supernatant weight
dry sample weight
100
wet sediment weight
Swelling Power ðSPÞ ¼
WS ð%Þ
dry sample weight 1
100
2.5. Measurement <strong>of</strong> pasting properties
Pasting properties <strong>of</strong> starch samples were measured using
a rheometer equipped with a starch pasting cell (AR 1500ex, TA
instrument, New Castle, DE, USA) which can be operated like
a rapid visco-analyzer (RVA). Three grams (dry weight) <strong>of</strong> starch
sample was added to 25 g <strong>of</strong> distilled water in a aluminum vessel
(37 mm internal diameter and 65 mm height) installed on the
rheometer. The starch suspension was stirred at 25 C for 1 min by
a plastic paddle. During the measurement, a time-temperature
schedule was applied; the starch suspension was heated to 95 C
(starting from 25 C, at a rising temperature rate <strong>of</strong> 12 C/min), held
at 95 C for 2.5 min, cooled down to 50 C at a rate <strong>of</strong> 12 C/min,
and held at that temperature for 2 min. The pasting parameters,
peak time, pasting temperature, and peak (P), trough (T), final (F),
breakdown (PeT), and setback (FeT) viscosity parameters were
determined in situ for the starch suspension.
2.6. Texture pr<strong>of</strong>ile analysis <strong>of</strong> starch gels
For the texture pr<strong>of</strong>ile analysis, 2.4 g <strong>of</strong> each starch sample (dry
weight) was added to 27.6 mL <strong>of</strong> distilled water in a 100 mL screw
cap bottle (40 mm opening) at 25 C under stirring conditions
(700 rpm for 30 min). The bottles were heated by immersion in
a water bath at 85 C for 30 min and then cooled to 25 C. Subsequently,
the bottles were sealed with screw cap and stored at 4 C
for 24 h. Each bottle including the starch gel prepared was placed
on a texture analyzer (TMS-Pro, Food Technology Co., Sterling, VA,
USA) equipped with a 25 N load cell. The starch gel was compressed
5 mm at pretest a speed <strong>of</strong> 50 mm/min, test speed <strong>of</strong> 20 mm/min,
and post-test speed <strong>of</strong> 20 mm/min using a 20 mm diameter
cylindrical probe with a flat end. Texture parameters, hardness
(maximum peak during first compression), cohesiveness (the area
under the second peak/the area under the first peak), and
gumminess (hardness cohesiveness) were determined for individual
samples.
2.7. Duncan’s multiple range tests
The hydration and the pasting parameters were statistically
analyzed on the basis <strong>of</strong> the Duncan’s multiple range tests using
SAS s<strong>of</strong>tware (v. 9.1, SAS Institute Inc., Cary, NC, USA).

166
2.8. Cluster analysis for <strong>rice</strong> <strong>cultivars</strong> classification
Hierarchical clustering method was applied to the processability
data for classification <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong>. The processability data sets,
the hydration and the pasting parameters <strong>of</strong> the starch suspensions,
were used to classify 12 <strong>rice</strong> <strong>cultivars</strong> into several groups.
Hydration parameters were normalized whereas other parameters
were the values measured instrumentally. Hierarchical clustering
method is <strong>based</strong> on the average linkage clustering a method <strong>of</strong>
calculating mean (Euclidean) distance between elements <strong>of</strong> each
cluster. The average linkage clustering was carried out using SPSS
s<strong>of</strong>tware (v. 12.0, SPSS Inc., Chicago, IL, USA).
3. Results and discussion
3.1. Amylose content <strong>of</strong> <strong>rice</strong> starches
Amylose content <strong>of</strong> <strong>rice</strong> starches are listed in Table 1. Rice
<strong>cultivars</strong> are generally classified depending on the amylose content
<strong>of</strong> their starches into waxy, low amylose, medium amylose, and
high amylose varieties which contain 0e2, 9e20, 20e25, and over
25 g/100 g amylose, respectively (Mitchell, 2009). In this study, the
<strong>rice</strong> starches <strong>of</strong> <strong>cultivars</strong> A and B, <strong>cultivars</strong> C, D, E and F, <strong>cultivars</strong> G,
H, I and J, and <strong>cultivars</strong> K and L were categorized into groups <strong>of</strong> high
amylose, medium amylose, low amylose, and waxy <strong>rice</strong> starches,
respectively.
3.2. Hydration properties <strong>of</strong> <strong>rice</strong> starches
Hydration properties including WAI, WS, and SP <strong>of</strong> <strong>rice</strong> starches
at 80 C are showed in Table 2. The WAI values <strong>of</strong> the <strong>rice</strong> starches
from the <strong>cultivars</strong> B, E, and H were similar but their amylose levels
showed a significant difference as shown in Table 1. Especially, the
WAI <strong>of</strong> the starch in cultivar B was relatively high in spite <strong>of</strong> containing
high amylose content. These results are not in agreement
with previous findings that the WAI <strong>of</strong> the starches with high
amylose content tend to be relatively low since amylose is hardly
converted into amorphous state compared to amylopectin (Lee,
Han, Lee, Kim, & Chung, 1989). The WAI <strong>of</strong> the starches <strong>of</strong> waxy
<strong>rice</strong> <strong>cultivars</strong> (high amylopectin) were relatively low. The low WAI
values <strong>of</strong> the waxy starches were not due to their low waterbinding
capacity, but because amount <strong>of</strong> soluble fraction in the
waxy starches was relatively larger than that present in the nonglutinous
starches. The waxy starches are easily solubilized by
water so that their wet sediment weights fall <strong>of</strong>f after the centrifugation
for the WAI analysis. Herein, the amylose content does not
Table 2
Pasting and hydration properties <strong>of</strong> <strong>rice</strong> starches.
WAI WS (%) SP PV (Pa s) T (Pa s) FV (Pa s) BD (Pa s) SB (Pa s)
Rice A 7.00 e
9.19 d
7.70 c 2.19 g
1.45 cd 3.83 b
0.75 g
2.38 a
B 12.05 a
17.29 c 13.26 b 3.79 c
1.61 b
4.09 a
2.18 dc
2.47 a
C 8.80 cd
4.32 d
9.20 c 3.23 e
1.31 e
2.44 ef
1.92 e
1.13 d
D 9.31 cbd 4.60 d
9.76 cb 3.24 e
1.30 e
2.46 ef
1.95 e
1.17 d
E 12.31 a
7.42 d 13.29 b 4.25 b
1.52 cb 3.17 c
2.74 a
1.66 b
F 10.64 b
5.38 d 11.24 cb 4.31 ba
1.82 a
3.20 c
2.49 b
1.37 c
G 8.61 d
4.72 d
9.04 c 3.39 de
1.37 ed 2.48 e
2.03 de
1.12 d
H 12.27 a
6.92 d 13.18 b 4.13 b
1.35 ed 2.72 d
2.78 a
1.37 c
I 10.14 cb
6.25 d 10.83 cb 3.39 de
1.12 f
2.38 ef
2.27 c
1.26 dc
J 7.90 ed
4.37 d
8.26 c 2.51 f
1.49 c
3.09 c
1.03 f
1.61 b
K 8.16 ed 53.92 b 17.63 a 4.55 a
1.72 a
2.56 de
2.83 a
0.84 e
L 4.75 f
79.41 a 22.76 a 3.61 dc
1.52 cb 2.27 f
2.09 dce
0.75 e
WAI: water absorption index, WS: water solubility, SP: swelling power, PV: peak
viscosity, T: though viscosity, FV: final viscosity, BD: breakdown, SB: setback.
Means with the different letters in the same column are significantly different at the
5% level.
I. Lee et al. / LWT - Food Science and Technology 48 (2012) 164e168
represent properly the processability properties including WAI,
which exhibited difference among the <strong>rice</strong> starches even with
similar amylose content.
Cultivars L and K, the high amylopectin content but low amylose
varieties, showed high WS compared to others. On the contrary,
water solubility <strong>of</strong> the <strong>rice</strong> starches <strong>of</strong> <strong>cultivars</strong> A to J was less than
10%. Upon heating insoluble starch swells by penetrated water and
weakened infrastructure hydrogen bonds, and correspondingly
some fragments <strong>of</strong> the starch could be solubilized upon heating.
Thus, WS depends on amount <strong>of</strong> soluble starch, which will vary
with cultivar and processing conditions including heat treatment.
Especially, hydrogen bonds can be easily weakened in the starch
granules with high amylopectin content.
High swelling powers were observed with the <strong>rice</strong> starches <strong>of</strong>
<strong>cultivars</strong> L and K (Table 2). On the contrary, the SP <strong>of</strong> starch <strong>of</strong> cultivar
A was the lowest. The SP <strong>of</strong> a starch depends on the ratio and
molecular weights <strong>of</strong> amylose and amylopectin, and also intra- and
inter-molecular interactions. In general, amylose acts as an inhibitor
<strong>of</strong> swelling but amylopectin is likely to swell due to the weakness <strong>of</strong>
the intra- and inter-molecular coherence in starch (Morrison, Tester,
Snape, Law, & Gidley, 1993; Tester & Morrison, 1990).
3.3. Pasting properties <strong>of</strong> <strong>rice</strong> starches
Pasting properties <strong>of</strong> the <strong>rice</strong> starches are listed in Table 2.TheP
values, maximum viscosity during sol/gel transition upon heating, <strong>of</strong>
the starches with high amylose content were relatively low since they
do not swell easily or get thicker. On the other hand, waxy starches
have higher P values because they can easily swell and become pastes.
The highest P value was observed with cultivar K while the lowest
value was with cultivar A. The P values <strong>of</strong> the <strong>rice</strong> starches <strong>of</strong> the
<strong>cultivars</strong> D and E were significantly different but their amylose
contents were similar. On the contrary, the P values <strong>of</strong> starches <strong>of</strong> the
<strong>cultivars</strong> C and J were similar though their amylose contents were
varied considerably. In conclusion, amylose content is not correlated
closely with the P value which is one <strong>of</strong> important parameters that
need to be considered for the starch processability. It is advantageous
to characterize starches <strong>of</strong> different <strong>cultivars</strong> <strong>based</strong> on the processing
parameters including P value, instead <strong>of</strong> amylose content.
T values, which represent the lowest viscosity upon heating, <strong>of</strong>
the <strong>rice</strong> starches were presumably observed at the end <strong>of</strong> heating at
95 C. The highest T value observed with cultivar F while cultivar I
exhibited the lowest among the <strong>cultivars</strong> studied.
F values represent the viscosity <strong>of</strong> starch paste after cooling to
50 C. The F values <strong>of</strong> <strong>cultivars</strong> A and B were the highest. The high
amylose <strong>rice</strong> starches showed relatively high F values since starch
pastes formed after heating likely to become harder dramatically
upon cooling. On the contrary, amylopectin-rich starch (cultivar L)
developed into a clear paste with low viscosity. The F values <strong>of</strong> the
<strong>rice</strong> starches <strong>of</strong> the <strong>cultivars</strong> I and J were differed significantly but
their amylose contents are similar. However, the F values <strong>of</strong>
starches <strong>of</strong> the <strong>cultivars</strong> D and G exhibited close similarity but their
amylose contents are varied considerably.
Breakdown values reflect the heat stability at 95 C. After initial
gelatinization, continuous exposure <strong>of</strong> starch paste to high
temperature lowers its viscosity. In general, hardness <strong>of</strong> starch
paste is high at low temperature, vice versa, as temperature and
texture are mutually dependent and in reversible manner. Hence
a high breakdown value may be considered as a relatively low heat
stability point because low value indicates thermal stability (Karim,
Norziah, & Seow, 2000). Breakdown values <strong>of</strong> the <strong>rice</strong> starches <strong>of</strong>
the <strong>cultivars</strong> D and E were differed significantly but their amylose
contents are similar. On the contrary, the breakdown values <strong>of</strong> the
<strong>rice</strong> starches in the <strong>cultivars</strong> E and H present similar breakdown
values but their amylose contents are varied considerably.

Setback values indicate the hardness <strong>of</strong> gel paste upon cooling.
Setback values <strong>of</strong> high amylose starches from <strong>cultivars</strong> A and B were
higher than that <strong>of</strong> others. Strangely, high setback value was
observed in the starch <strong>of</strong> cultivar J which was categorized under
a low amylose starch group or variety, <strong>based</strong> on amylose content.
These results provide another example that actual pasting property
is more important than amylose content for industry considerations.
The starch from cultivar L showed the lowest setback value
indicating a lower tendency to retrograde and is correspondingly
more viscosity-stable. It is known that setback value is an important
parameter for presumption <strong>of</strong> starch retrogradation which
occurs severely in case <strong>of</strong> high amylose starches (Karim et al., 2000;
Miles, Morris, Orford, & Ring, 1985).
3.4. <strong>Classification</strong> <strong>of</strong> <strong>rice</strong> starches
Rice <strong>cultivars</strong> are classified according to previously determined
amylose content <strong>of</strong> their starches, as shown in Table 3, into 3
groups. The present categorization is different from the conventional
system <strong>of</strong> categorization <strong>based</strong> on amylose content <strong>of</strong> starch.
As aforementioned, <strong>based</strong> on processability characteristics the <strong>rice</strong>
<strong>cultivars</strong> are categorized into four groups (Table 4). As a result,
medium and low amylose groups are merged into single Group ii
since statistical difference was not significant.
Clustering analysis <strong>of</strong> pasting parameters, hydration parameters,
and a combination <strong>of</strong> both parameters (the combined parameters)
<strong>of</strong> the starches was performed to classify <strong>rice</strong> <strong>cultivars</strong>. The <strong>rice</strong>
<strong>cultivars</strong> classification <strong>based</strong> on pasting parameters listed in
Table 3. Interestingly, cultivar J was grouped with A in spite <strong>of</strong> huge
difference in amylose content where J possess concentration
similar to that <strong>of</strong> the levels present in <strong>cultivars</strong> H and I. The peculiarity
<strong>of</strong> cultivar J regarding the pasting properties is an example
that the amylose content is <strong>of</strong>ten not disparate from the pasting
properties. The seven studied <strong>cultivars</strong> having medium and low
amylose starches were distributed in Groups iii and iv; they are not
in order with respect to amylose content and correspondingly
<strong>cultivars</strong> E and F, <strong>rice</strong> <strong>cultivars</strong> with medium amylose starch
content, were swapped with <strong>cultivars</strong> G and I but grouped with
cultivar H. Cultivars C and D were categorically placed under Group
iii, separated from <strong>cultivars</strong> E and F despite having a similar amount
<strong>of</strong> amylose (about 21 g/100 g). On the other hand, cultivar G was
clustered with <strong>cultivars</strong> C and D due to similar pasting characteristics
though there is a difference in their amylose contents. We
assumed that proccesability <strong>of</strong> <strong>rice</strong> starches was affected not only
amylose content but other factors such as soluble amylose content,
amylopectin chain length, crystallinity, residue protein content, and
amyloseelipid complex.
Rice <strong>cultivars</strong> were classified <strong>based</strong> on hydration parameters <strong>of</strong>
their starches into 4 groups. Interestingly, <strong>cultivars</strong> A and J were
classified into one group and <strong>cultivars</strong> C and D were separated from
<strong>cultivars</strong> E and F; these results are in good agreement with the
classification <strong>based</strong> on the pasting property parameters. Cultivars A
and B were distributed between two different groups. The classification
<strong>of</strong> cultivar I <strong>based</strong> on the hydration parameters was not in
agreement with the previous classification; cultivar I was grouped
Table 3
Cluster analysis classification <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong> <strong>based</strong> on processability parameters.
with <strong>cultivars</strong> C, D, and G in the cluster analysis <strong>based</strong> on the
pasting parameters. Cultivar I showed relatively higher values <strong>of</strong>
WAI and SP similar to <strong>cultivars</strong> B, E, F, and H. Cultivars K and L, the
glutinous <strong>rice</strong> <strong>cultivars</strong>, are classified into two different groups.
Both <strong>cultivars</strong> showed excessively high values <strong>of</strong> WS and SP
compared to those <strong>of</strong> non-glutinous <strong>cultivars</strong>, but they are
considered statistically as different categories due to significant
difference in the hydration properties. This result indicates that the
hydration properties <strong>of</strong> the <strong>rice</strong> starches are different even if their
amylose contents are similar. The classification <strong>based</strong> on combined
parameters was different from the cluster analysis <strong>based</strong> classification
which, in turn, <strong>based</strong> on pasting property parameters; but
was similar to the results obtained by the cluster analysis using the
hydration parameter.
3.5. Validation <strong>of</strong> cluster analysis classification <strong>of</strong> <strong>rice</strong> starches
Texture pr<strong>of</strong>ile analysis parameters <strong>of</strong> <strong>rice</strong> starch gels are listed
in Table 4. The gel texture pr<strong>of</strong>iles are indicated by hardness,
cohesiveness, and gumminess dependent on physicochemical
properties <strong>of</strong> individual starches used. The overall, hardness and
gumminess increased but cohesiveness decreased as amylose
content increases. However, hardness and gumminess <strong>of</strong> <strong>cultivars</strong>
D and E were exceptional compared to other <strong>cultivars</strong> having
similar amylose starches. This result shows that the texture pr<strong>of</strong>iles
<strong>of</strong> the starch gels could be different even if their amylose contents
are similar as observed with hydration and pasting properties
studied previously. It is an example to show that the amylose
content is not disparate from starch texture pr<strong>of</strong>iles which are
important parameters to determine functionality and sensory
properties <strong>of</strong> the starch-<strong>based</strong> foods.
The classification <strong>of</strong> the <strong>rice</strong> <strong>cultivars</strong> <strong>based</strong> on the texture
pr<strong>of</strong>iles <strong>of</strong> the prepared gels is shown in Table 5. It has been performed
to validate the cluster analysis classification established by
the hydration and pasting parameters. Cultivars A and B containing
high amylose were placed into two separate groups; they are
categorically placed into different groups by the clustering analyses
<strong>based</strong> on pasting properties, hydration, and their combination, but
Based on Group i Group ii Group iii Group iv Group v Group vi
amylose content A, B C, D, E, F, G, H, I, J K, L
pasting viscosity A, J B C, D, G, I E, F, H K L
hydration A, C, D, G, J B, E, F, H, I K L
combined a
A, C, D, G, J B, E, F, H, I K L
a Combined with hydration and pasting parameters.
I. Lee et al. / LWT - Food Science and Technology 48 (2012) 164e168 167
Table 4
Texture pr<strong>of</strong>ile analysis <strong>of</strong> <strong>rice</strong> starch gels.
Hardness (N) Cohesiveness Gumminess
A 1.64 a
0.63 e
1.04 a
B 1.15 b
0.76 d
0.88 ba
C 0.79 c
0.79 dc
0.63 bcd
D 0.91 cb
0.81 bdc
0.74 bc
E 0.48 ed
0.86 bdac
0.41 efd
F 0.50 ed
0.77 d
0.38 efd
G 0.65 cd
0.89 bdac
0.57 ecd
H 0.51 ed
0.92 bac
0.46 efcd
I 0.42 edf
0.88 bdac
0.37 efd
J 0.36 ef
0.93 ba
0.33 ef
K 0.18 f
0.98 a
0.17 f
L 0.19 f
0.99 a
0.19 f
Means with the different letters in the same column are significantly different at the
5% level.

168
Table 5
Cluster analysis classification <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong> <strong>based</strong> on textural parameters.
Group i Group ii Group iii Group iv Group v
A B C E K
D F L
G H
I
J
not by the classification <strong>based</strong> on amylose contents (Table 3). The
most important advantage with the new classification system is
that <strong>cultivars</strong> C, D, and G and <strong>cultivars</strong> E, F, and H have been categorically
placed under two different groups, which belong to
a single group in the case <strong>of</strong> amylose-<strong>based</strong> classification (Table 3).
In the classification <strong>based</strong> on pasting parameters, Group iv (<strong>cultivars</strong>
E, F, and H) showed higher values <strong>of</strong> peak, trough, final,
breakdown, and setback viscosities than Group iii (<strong>cultivars</strong> C, D,
and G). In the proposed classification <strong>based</strong> on the hydration
parameters and their combination with pasting properties data,
Group i (<strong>cultivars</strong> C, D, and G) showed lower values <strong>of</strong> WAI and SP
than Group ii (<strong>cultivars</strong> E, F, and H). This cluster analysis was
successful to classify the <strong>cultivars</strong> C, D, and G and the <strong>cultivars</strong> E, F,
and, H which differ in terms <strong>of</strong> processability. In our previous study
(unpublished report), the protein content in <strong>rice</strong> flour <strong>of</strong> cultivar E, F
(6.64 g/100 g), and H (6.12 g/100 g) was found lower than cultivar C
(6.38 g/100 g), D (6.68 g/100 g), and G (6.77 g/100 g). Protein
content can be correlated with pasting properties. Therefore, there
are differences in physical characteristics because residue protein
content may be lower in starch isolated from <strong>cultivars</strong> E, F, and H
than one <strong>of</strong> <strong>cultivars</strong> G, C, and D. In conclusion, the classification
system <strong>based</strong> on pasting and hydration parameters representing
practical processability is better compared to the conventional
method <strong>based</strong> on amylose content.
4. Conclusions
In this study, classification <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong> was performed <strong>based</strong>
on the hydration and the pasting properties <strong>of</strong> their starches. The
<strong>cultivars</strong> having similar amylose content are categorized into
different groups under proposed new classification because their
starches showed different hydration and pasting properties.
However, some <strong>cultivars</strong> with different amylose contents are
grouped together into a single category due to the similarity <strong>of</strong>
hydration and pasting properties <strong>of</strong> their starches. Thus, the classification
<strong>of</strong> <strong>rice</strong> starches, in turn, <strong>cultivars</strong> <strong>based</strong> on the practical
processability is more appropriate and useful system than the
classical classification considering the amylose content only. This
study provides a resolution to standardize purpose-specific classification
<strong>of</strong> starches from a variety <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong>. Rice <strong>cultivars</strong>
classified within a category <strong>based</strong> on practical processability can be
considered as uniform even if their chemical compositions
including amylose content are different. Thus, mixture <strong>of</strong> the
starches from different <strong>rice</strong> <strong>cultivars</strong> but possessing similar processing
characteristics can be used for different food applications.
In conclusion, <strong>rice</strong> starches categorization can be simplified and
standardized by using processability parameters despite a variety
<strong>of</strong> <strong>rice</strong> <strong>cultivars</strong>. This classification strategy can be expanded to
categorize <strong>rice</strong> <strong>cultivars</strong> suited for properties <strong>of</strong> precooked dried
<strong>rice</strong>, <strong>rice</strong> noodle, and bakery products when the classification is
I. Lee et al. / LWT - Food Science and Technology 48 (2012) 164e168
carried out <strong>based</strong> on the parameters that represent practical
processabilities.
Acknowledgments
This study was supported by “Cooperative Research Program for
Agricultural science and technology development (Project No.
PJ007172)” Rural Department Administration, Republic <strong>of</strong> Korea.
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