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

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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.