CLASSIFICATION OF RICE CULTIVARS BY USING
PHYSICOCHEMICAL, THERMAL, HYDRATION PROPERTIES, AND
COOKING QUALITY
1
JITNAPA BOONMEEJOY, 2JETSADA WICHAPHON, 3SUDARAT JIAMYANGYUEN
1,2, 3
Department of Agro-Industry, Faculty of Agriculture, Natural Resources and Environment, Naresuan University,
MuangPhitsanulok, THAILAND 65000
E-mail: [email protected], [email protected], [email protected]
Abstract— The classification of eight different rice cultivar was conducted to classify high amylose content rice (HM 105,
RD15 and PTT1), medium amylose content rice (KTH17) and low amylose content rice (PL2, RD31, SP1 and CN1).
Physicochemical, thermal, hydration, cooking quality and effect of storage time were studied in order to classify rice cultivar
by principal component analysis. The results showed that amylose content of high amylose rice increased during storage
time but amylose content of low and medium amylose rice were consistent. Hardness value increased during storage time.
High amylose rice showed higher hardness compared to medium and low amylose. The highest and lowest hardness value
was found in SP1 (901 N) and PTT1 (431 N), respectively. This indicated that amylose content affected hardness. The result
of thermal properties showed that the gelatinization temperature positively correlated with amylose content. The highest
onset, peak and conclusion temperature showed in RD31 (72.67ºC, 77.08 ºC and 84.03 ºC, respectively). The storage time
had no effect on thermal properties. The results showed that optimum cooking time positively correlated with amylose
content. The highest optimum cooking time showed in CN1 (33.0 min) and lowest cooking time showed in HM105 (12.33
min). Hydration properties of different rice cultivar showed that high amylose content rice have capacity to absorb water
more than low and medium amylose rice. The classification of rice cultivars resected in two groups by using principal
component analysis. PC1 and PC2 contributed for 53.4% and 21.8% variance, respectively. The low and medium amylose
were classified in one group and separate from high amylose content rice. The results suggested that amylose content alone
cannot be used to classify rice cultivars. The physicochemical, thermal, hydration, and cooking quality can difference
classify rice cultivar with amylose content. This results can be a useful alternative for the food industry, especially for rice
noodle industry.
Keywords- Rice Flour, Cooking Quality, Amylose Content, Principal Component Analysis
species after selecting those by its food applicable
properties for appropriate management of rice starch
quality. Especially, there exists a significant
difference in physicochemical properties even among
the starch obtained from rice cultivars with similar
amylose content [6]-[7]. So, amylose content have
been used to distinguish the rice starch
characteristics.
Champagne et al. [8] predicted cooked rice texture
which results showed that rice with similar amylose
and protein content still had different texture quality.
Factor that affect the textural quality of cooked rice
include rice variety, amylose content, pasting
properties, protein content, postharvest practice,
moisture content, temperature, and storage period [9][11]. Another important parameters to represent
starch characteristics are water hydration properties
including water absorption index (WAI), water
solubility (WS), and swelling power (SP). The
hydration properties of starch can be correlated with
its pasting properties and physicochemical properties
which are important for the application of starch in
industry. Principal component analysis (PCA) is a
classical statistical method to extracts relevant
information from a large data set. The purpose of this
study are to classify different rice cultivars based on
physicochemical properties such as texture properties
and thermal properties, rice cooking quality and
hydration properties compare with amylose content.
I. INTRODUCTION
Rice is one of the major staple food in the world since
centuries. Rice is the most important cereal for
human consumption. Rice industry is suffering from
inefficiency in securing the uniform quality
ingredient since rice commodities that are traded
involve a wide variety of cultivars. The
physicochemical properties of freshly harvested rice
change during aging of rice [1]-[3].The most
important change that occur during the aging process
involves rheological properties, which contribute
significantly to cooking and eating properties. Rice
grain exhibits distinct physicochemical properties,
depending upon the variety, and quality of starch
especially influences its cooking properties [4]. In
rice, amylose content of starch is one of the important
characteristics determining eating and cooking
qualities [5].The changes in rice properties during
aging have been reported to depend upon variety,
storage conditions, and amylose content. Amylose
content has been long used as a parameter to predict
the texture of cooked rice. Juliano has suggested
classification of amylose content as waxy (0-5%),
very low (5-12%), low (12-20%), intermediate (2025%), and high (25-33%). The industrial standpoint,
it is approach to simplify rice cultivars categorization.
Thus it is plausible to classify the rice starch
categorized by similarity on the processability of their
Proceedings of The IRES 30th International Conference, Tokyo, Japan, 18th February 2016, ISBN: 978-93-85973-35-2
66
Classification of Rice Cultivars by Using Physicochemical, Thermal, Hydration Properties, and Cooking Quality
Brookfield viscometers Ltd., USA). The rice samples
were prepared by the modified method of Juliano et
al. [13]. Rice samples 10 g cooked in 100 ml distilled
water at 95±1°C till white core disappeared. The
cooked rice was drained of water completely using a
strainer and surface moisture of the samples was
blotted out. A 250 mm diameter probe was used to
compress sample, with pre-test and post-test speeds
of 1 mm/s and test speed of 0.5 mm/s. Parameters
recorded from the test curves was hardness
II. MATERIALS AND METHODS
2.1. Materials
Eight different cultivars of rice were used in the
study. The cultivars of HM105, RD15, and PTT1were
low amylose content rice. The KTH17 was medium
amylose rice and CN1, RD31, SP1, and PL2 were
high amylose content rice. The moisture content of all
milled rice was 10-13%. All the sample were stored
at room temperature (27-37ºC) in wood box for six
months.
2.2. Preparation of rice flour
The paddy samples were de-husked and polished with
Rice polishing machine (NW 1000 TURBO,
Natrawee Technology Co., ltd., Chachoengsao,
Thailand). Polished rice grains were ground into flour
using a blender (MX-900M, Panasonic, Johor,
Malaysia) and passed through a 100 mesh sieve
screen. The obtained rice flour was kept in a zip-lock
plastic bag and stored in freezer at -20oC before
analysis.
2.6. Functional properties
Water absorption index (WAI) was measured
according to the method of Medcalf and Gilles [14].
Starch suspension was heated at 80C. The result were
calculated using the following equation
Water absorption index
= (wet sediment weigh)/ (sample weigh)
2.7. Cooking quality
Optimum cooking time was determined by the
modified method reported by Juliano [4]. In a 250 ml
beaker, about 100 ml-distilled water was boiled
(95±1ºC) and 5 g of head rice samples dropped into
it. Measurement of cooking duration was started
immediately. After 10 min and every minute
thereafter, 10 grains of rice were removed and
pressed between two clean glass plates. Cooking time
was recorded when at least 90% of the grains no
longer had opaque core or uncooked centers. The rice
was then allowed to simmer for about another 2 min
to ensure that the core of all grains had been
gelatinized. Optimum cooking time was taken as the
established cooking time plus 2 additional minutes.
2.3. Amylose content analysis
Amylose content was determined by the modified
simplified assay method reported by Juliano [12]
using the Starch-iodine blue method. Milled rice flour
0.1 g was weighed in 100 mL volumetric flasks. Then
added 1 mL of 95% ethanol and 9 mL of 1 N NaOH.
The suspension was heated in a boiling water bath for
10 min. The samples were diluted to 100 mL with
distilled water and mixed well. The Samples solution
5 mL of each sample was made up to 100 mL with
distilled water, 1 mL of 1 M acetic acid and 2 mL of
iodine solution (0.2 g iodine and 2.0 g Potassium
iodide in 100 mL distilled water). The test mixture
was left for 20 min. Then the intensity of color
developed was measured in spectrophotometer (DR
4000U, UV Visible Spectrophotometer, Hach,
Loveland, Colorado, USA) at 620 nm against the
reagent blank. Amylose content (%) was calculated
from a standard curve prepared using amylose
standard.
2.8. Statistical analyses
Data were analyzed by one way analysis of variance
(ANOVA) and Duncan’s multiple range test at 5%
probability level (SPSS 17.0). A multivariate analysis
software MINITAB version 17 were used to perform
principal component analysis (PCA).
2.4. Thermal properties
Thermal properties of rice flour were determined by
using differential scanning calorimetry (DSC) (DSC
1, METTLER TOLEDO, Columbus, USA). Rice
flour samples (10 mg) and distilled water were added
to the DSC pan in a 1:2 ratio (w/w). The pan was
hermitically sealed and allowed to equilibrate at 25 C
for 1 h. The samples were then heated from 10 C to
110 C at 10 C/min. An empty DSC pan was used as a
reference. Onset, peak, conclusion temperatures and
gelatinization enthalpy were determined. (Shivananda
K. GarimellaPurna a, Rebecca A. Miller a, Paul A.
Seib a, Robert A. Graybosch b, Yong-Cheng Shi)
III. RESULTS AND DISCUSSION
3.1. Chemical analysis
2.5. Texture profiles analysis
Textural profile analysis (TPA) of the cooked rice
was performed using a texture analyzer (QTS 25,
Fig.1. Amylose content of rice flour stored for 6 months
Proceedings of The IRES 30th International Conference, Tokyo, Japan, 18th February 2016, ISBN: 978-93-85973-35-2
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Classification of Rice Cultivars by Using Physicochemical, Thermal, Hydration Properties, and Cooking Quality
They found that cooked rice increased hardness value
during storage and Meullenet et al. [18] reported that
hardness value of ageing rice was higher than that of
freshly rice. From Fig. 2, the hardness of cooked rice
shows a positive correlation with amylose content.
This suggests that hardness of cooked rice was
mainly influenced amylose content. Rice with high
amylose content is liable to leach more into the
cooking water [19]. The hardness of freshly cooked
rice is less than aged cooked rice because amylose
and amylopectin reaction occurs contributing to the
increase of cooked rice hardness. The long
amylopectin chains may crystallize with an amylose
molecule, which might extend through several
adjacent ‘clusters’, thereby contributing to double
helices in several crystallites [20].
3.3. Functional properties
Fig. 3 shows water absorption index (WAI) of
different rice cultivars during six months storage. For
the first three months, the WAI of highamylose rice
was higher than that low and medium amylose rice.
The WAI increased during three months of storage
and after that it decreased and consistent. The highest
and lowest WAI was found in RD31 (14.16) and PL2
(8.02), respectively. This results were different from
the previous report [13] showed that the low amylose
content rice can absorb water more than high amylose
rice, which could be explain that amylose content
contains more crystalline region, resulting in the
difficulty of water molecules to migrate inside the
grains. However, the finding of this study was in
accordance with Lee et al. [21], which reported that
the WAI of high amylose rice was higher than that of
low and medium amylose rice. These disagreed
results indicated that amylose content and WAI of
aged rice can bedifferently classified depending on
rice cultivars.
Amylose content of the sample rice cultivars during
six months is shown in Fig. 1. The results showed
that PL2 rice had the highest amylose
content(36.77%) and PTTT1 show the lowest
amylose content (18.42%). During storage, amylose
content of low and medium amylose rice were
consistent but that of high amylose rice increased
after 4 months of storage. Villareal [15] and Chrastil
[2], [3] and Sermsirisopon [16] reported that amylose
content slightly increased during storageshowed that
PL2 rice had the highest amylose content(36.77%)
and PTTT1 show the lowest amylose content
(18.42%). During storage, amylose content of low
and medium amylose rice were consistent but that of
high amylose rice increased after 4 months of storage.
Villareal [15] and Chrastil [2], [3] and
Sermsirisopon[16] reported that amylose content
slightly increased during storage.
3.2. Texture Profiles Analysis (TPA)
The hardness of cooked rice is shown in Fig. 2. The
highest and lowest hardness belonged toSP1 (901 N)
and PTT1 (431 N), respectively. The results show
that hardness value of high amylose rice was higher
than that of low and medium amylose, except RD31.
This indicated that hardness is affected by amylose
content of rice. The cooked rice with low amylose
exhibited soft texture, while that of high amylose is
harder. High amylose rice shows higher hardness
value compared to that of low and medium. This is
due to the fact that amylose contains more crystalline
region, which in turn, shows more compact starch
granule and exhibits harder gel trends. In addition, the
storage time influenced the texture of cooked rice in
which high amylose rice is more affected compared
to low and medium amylose rice. This finding was
similar to that has been reported by Juliano [4] and
Charstil [17].
3.4. Thermal properties
Table 1: Thermal properties of different rice flour during 6
months storage
Several concepts have been proposed to explain the
gelatinization process. Starch gelatinization is an
endothermic process that corresponds to the loss of
starch crystalline in the starch granules under
particular
heat
and
moisture
conditions.
Gelatinization describes the range of irreversible
changes when starch is heated in excess water [22].
Thermal properties of difference rice flour during six
months storage is shown in Table 1. The result
Proceedings of The IRES 30th International Conference, Tokyo, Japan, 18th February 2016, ISBN: 978-93-85973-35-2
68
Classification of Rice Cultivars by Using Physicochemical, Thermal, Hydration Properties, and Cooking Quality
showed that low and medium amylose rice was not
different in terms of onset, peak and conclusion
temperatures as well as gelatinization enthalpy during
storage. This result indicated that onset, peak and
conclusion temperature of rice flour are not affected
by storage time. This result was agreeable with the
studies of Karlsson and Eliasson [23] who reported
that no changes in the onset, peak and conclusion
temperatures of starch were observed with storage
time. The initiation of gelatinization is called the
onset.
Peak
is
the
position
where
theendothermicreaction occurs at the maximum.
Conclusion is when all the starch granules are fully
gelatinized, and the curve remains stable [24].
high amylose rice also requires more cooking time.
From the results of all samples, it was noticed that
cooking time increased in accordance with storage
time. This finding was agreeable with results of
Villareal et al. [15], who reported that the storage
time affected gelatinization of rice flour, in which
they were positively correlated. This increase was due
to the greater mobility and subsequent restructuring
of starch and changes in the protein bodies present in
the grain.
3.6. Principal component analysis (PCA)
The results of physicochemical properties, cooking
quality and hydration properties data were used to
classify rice cultivar by using principal component
analysis as shown as score plot in Fig. 5.
From the results showed that amylose content
exhibited positive correlation with physicochemical
properties, cooking quality and hydration properties
(data not shown). The PC1 and PC2 contributed for
53.4% and 21.8% variance, respectively. The results
showed distinctive two groups from classification,
including (1) low and medium amylose rice and (2)
high amylose group. This finding suggested that
classification of rice using other parameters
(physicochemical, hydration, and cooking quality)
can yield different results compared to a conventional
method using amylose content.
CONCLUSIONS
Using solely amylose content may not provide the
true results in classifying different rice cultivars. This
study suggested alternative way of rice grouping by
incorporating physical, thermal, hydration, as well as
cooking quality. The results obtained were more
appropriate and accurate to apply for rice industry in
which combination of these attributes can reflect
complete aspects for rice classification.
The highest onset, peak and conclusion temperature
was found in RD31 (72.67ºC, 77.08 ºC and 84.03 ºC,
respectively) and the lowest was found in PL2
(64.41ºC, 67.38 ºC and 73.04 ºC, respectively).
Comparing of onset, peak, conclusion and ∆ Hgel
among rice varieties with different amylose content, it
was found that, in general, high amylose rice showed
higher values than those of low and medium amylose
rice, which could be affected by starch structure
properties. The starch with low amylose contains
more amorphous and less crystalline regions, leading
to lower gelatinization temperature. The lower
gelatinization temperatures for rice flours indicated
that less energy is required to starch gelatinization.
ACKNOWLEDGMENTS
This research was funded by Thailand Research Fund
(TRF) under the grant number MSD57I0041. Rice
samples and part of financial were provided by the
rice milling factory (Rong See Fai Thai Songserm
Ltd.) located in NakornSawan Province, Thailand.
The authors greatly appreciated
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3.5. Cooking quality
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amylose rice have high cooking time compared to
low and medium amylose rice. According to
gelatinization temperature, high amylose rice
requireshigh temperature and energy, resulting that
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