Food Bioprocess Technol (2014) 7:212–223
DOI 10.1007/s11947-012-1037-9
ORIGINAL PAPER
Laboratory Process Development and Physicochemical
Characterization of a Low Amylose and Hydrothermally
Treated Ready-to-Eat Rice Product Requiring No Cooking
Himjyoti Dutta & Charu Lata Mahanta
Received: 19 July 2012 / Accepted: 17 December 2012 / Published online: 8 January 2013
# Springer Science+Business Media New York 2013
Abstract A low amylose and hydrothermally treated readyto-eat rice product that requires no cooking was prepared in
the laboratory. Hot soaking for 1–3 min with subsequent
variable steaming at open and under pressures remarkably
altered the kernel and flour properties. Increase in water
absorption and lowering of cooking time with extent of
steaming were prominent. Soaking of the product at 50 °C
for 20 min gave texture values more similar to cooked
samples. The viscosity parameters of hot soaking alone were
in between those of hot soaking with open steaming and
pressure steaming. Pressure steamed samples exhibited almost constantly increasing slurry viscosity throughout the
heating and cooling phases of the rapid viscosity analyzer
profile. Steaming variably altered the native A-type X-ray
diffraction pattern. Pressure steaming of samples with 3 min
hot soaking caused complete loss of the A-type conformation with feeble peaks for B- and V-type patterns. The open
steamed samples showed peaks for all A-, B-, and V-type
patterns. No endotherms for amylose-lipid complexes were
however found in the differential scanning calorimetry of
the pressure steamed samples. The raw rice flour was highly
resistant to α-amylolysis. In open steamed samples, steaming severity decreased the hydrolysis rate indicating formation of enzyme-resistant fractions, while pressure steamed
samples showed higher digestibility with treatment severity.
Keywords Rice . Texture . Cooking time . RVA .
Crystallinity . Starch digestibility . Ready-to-eat
Dr. Charu Lata Mahanta applied for an Indian patent.
H. Dutta : C. L. Mahanta (*)
Department of Food Engineering and Technology,
School of Engineering, Tezpur University, Assam, India
e-mail: charu@tezu.ernet.in
Introduction
The ease of cooking along with economy in fuel and time
consumption have made the instant cooking and quick
cooking starchy foods much popular in recent times. Instant
rice is one, such example (Prasert and Suwannaporn 2009;
Rewthong et al. 2011). Rice is principally parboiled or precooked to bring about this peculiar characteristic. Paddy is
generally not processed to give a ready-to-eat product that
looks like whole parboiled rice.
Parboiling is a unique hydrothermal technique involving
soaking of paddy in water followed by steaming, drying, and
milling. Hot soaking involving soaking in heated water is also
followed by some processors where the steaming step could
be omitted (Sareepuang et al. 2008). Parboiled rice possesses
many improved properties like higher nutrition, higher head
rice yield, lower insect infestation, improved shelling, etc.
(Bhattacharya 1985, Lin et al. 2010). Parboiled rice, however,
has a lower rate of water uptake during cooking requiring
longer time to cook and hence more energy is consumed
(Bhattacharya 1985). With increase in severity of parboiling,
the time and energy consumption of the parboiled rice is
further increased (Unnikrishnan and Bhattacharya 1987).
Parboiled rice flour shows different properties from raw rice
flour (Unnikrishnan and Bhattacharya 1987). Gelatinization
and retrogradation are the basic phenomena involved behind
all these changes. The extent of retrogradation is the principal
factor for the end product quality (Yu et al. 2010). Due to
formation of newer polymorphic structures during retrogradation, the native structure is never regained. These molecular
changes are reflected in the changed properties of the rice
kernel as well as the rice flour. Physical properties of kernel
like color, appearance, kernel dimensions, density, cooking
time, moisture absorption, etc. are very important for commercialization of the products (Shittu et al. 2009). The texture of
Food Bioprocess Technol (2014) 7:212–223
the cooked rice kernels and the viscosity of the pastes made
from their flours also are very important for the consumers’
satisfaction and food uses. Bello et al. (2006) observed harder
texture of parboiled cooked rice with lesser stickiness as compared with raw rice. The pasting curves of the flour slurry
obtained from the rapid viscosity analyzer (RVA) also give an
idea of the end product texture (Goode et al. 2005). Wide angle
X-ray diffractography (XRD) of raw rice flour shows peaks at
2 values near 15°, 17°, 18°, and 23°, which is called the typical
A-type starch diffraction pattern (Zobel 1988). However, parboiled rice flour shows altered diffraction patterns with formation of newer peaks and loss of some peaks indicating
formation of newer crystalline polymorphs as well as loss of
few native crystals. A new peak generally reported at 2 =20°
depicts formation of amylose-lipid complexes on hydrothermal
treatments, which on thermal analysis using the differential
scanning calorimeter (DSC), gives an endothermic melting
peak (Biliaderis et al. 1993; Mahanta et al. 1989). The B-type
polymorphs formed after the hydrothermal modifications are
characterized by the XRD peaks at 2 values near 17.1, 22.0,
and 24.0, resulting in a C-type (A+B) crystalline structure in
the parboiled rice. Thermal analysis gives the amount of crystalline polymorphs present in the sample based on their melting
enthalpies (Lu et al. 1994). Pregelatinized and retrograded
starches have different melting enthalpies and DSC is an
effective tool for this analysis (Zhou et al. 2010). Another
important parameter for all starchy foods is the starch digestibility as the health effects of foods has become a
primary concern of the consumers. Hydrothermal processing of starchy foods has been found to be effective
in the formation of slowly digestible starch fractions,
thereby lowering the glycemic response (Sajilata et al.
2006). However, various conflicting findings have also
been reported (Rewthong et al. 2011).
The above characteristics have generally been reported in
high and intermediate amylose rice varieties and not in low
amylose rice varieties that have 7–20 % amylose according
to Juliano (1979).
In the present study, a hydrothermal technique was
developed at the laboratory scale to obtain a ready-toeat, quick cooking product from low amylose paddy
and the important properties of the product were
characterized.
Materials and Methods
Materials
Pure line Kola Chokua variety paddy from the recent harvest of 2011 was purchased from local farmers of Titabor,
Assam. The rice variety falls under low amylose type with
12.6 % (in decibels) apparent amylose content as was
213
determined by the method of Sowbhagya and
Bhattacharya (1979). The samples were kept at room temperature for 24 h and then stored at 4 °C until processing.
Methods
Sample Preparation and Coding
Initially, 400 g paddy was added to 10 l water at 100 °C in a
vessel kept over flame and the water was constantly stirred
for 1 and 3 min. The temperature instantly fell down to 92±
1 °C and thereafter increased to 100 °C in 2.5 min. The
vessel was covered with a thick gunny bag and kept at room
temperature (27± 2 °C) for 18 h to allow the paddy to
hydrate. The excess water was decanted after 18 h and the
soaked paddy was immediately steamed in an autoclave
(Equitron 7407ST, India) fitted with a pressure gauge for
10 (mild treatment), 15 (moderate treatment), and 20 min
(severe treatment) at open steaming conditions (classified as
O) of 101.32 kPa and 100 °C and pressure steaming conditions (classified as P) of 103.42 kPa and 121 °C, respectively. The nonsteamed samples were classified as N.
Drying was carried out at room temperature for 48 h followed by milling (8 %, weight basis) in a Satake huller and
polisher (Satake, Japan). A portion of each sample was
ground into flour in a laboratory grain mill (Fritsch
Pulverisette 14) and passed through a 100-μm sieve. All
the kernel and flour samples were stored in polypropylene
pouches at 4 °C for further analysis. The samples were
coded as “classification—soaking time (min) at 100 °C—
steaming time (in minutes)” (Table 1).
Table 1 Processing conditions and sample codes
Broad
classification
Soaking time at
100 °C (min)
Steaming
time (min)
Sample
codes
N
N
O
O
O
–
1
1
1
1
–
–
10
15
20
N
N-1-0
O-1-10
O-1-15
O-1-20
P
P
P
N
O
O
O
P
P
P
1
1
1
3
3
3
3
3
3
3
10
15
20
–
10
15
20
10
15
20
P-1-10
P-1-15
P-1-20
N-3-0
O-3-10
O-3-15
O-3-20
P-3-10
P-3-15
P-3-20
214
Food Bioprocess Technol (2014) 7:212–223
Grain Color
Cooking Time
The CIE L*a*b* color values of all flour samples were
obtained by a color measurement spectrophotometer
(Hunter Color-Lab Ultrascan Vis). The results for L*
(lightness), a* (red-green), and b* (yellow-blue) values
using N as reference were used to calculate the
corresponding hue angle (H*) and chroma (C*) values
(Falade and Onyeoziri 2010) using the relations
Cooking time was determined by an objective method
(Juliano 1982). Kernels weighing 20 g were cooked in
200 ml water at 98 °C on a hot plate. After 10 min of
cooking, ten kernels were brought out from the middle of
the cooked mass and pressed between two clean glass
slides. The number of translucent kernels were counted
and recorded. The pressing test was repeated after each
minute and the time at which 90 % of the kernels were
translucent was considered as the cooking time of that
sample.
H * ¼ tan
C* ¼
1
* *
b a
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ða* Þ2 þ ðb* Þ2
ð1Þ
ð2Þ
L/B Ratio
Equilibrium Moisture Content on Soaking at Room
Temperature
Equilibrium moisture content (EMCS, in percent, decibels)
of polished rice kernels soaked at room temperature for 4 h
were determined by the method of Indudhara Swamy et al.
(1971).
The length (L) and breadth at the midpoint (B) of the
polished kernels were determined using a Vernier calipers
and a screw gauge (Mitutoyo, Japan) respectively and the L/
B ratio was calculated to measure whether any dimensional
changes occurred on parboiling.
EMCð%; dbÞ¼½moisture evaporated ðgÞ=dried weight of kernels ðgÞ100
Porosity, bulk density, and true density
Sediment Volume
For porosity (ε) determination, bulk density (ρb), and true
density (ρt) were first determined. For determining ρb, an
established method (Shittu et al. 2009) was slightly modified. Briefly, polished grains were allowed to fall into a
measuring cylinder from a constant height up to a known
volume. The top level was adjusted by gentle tapping. The
weight of the filled grains was determined and ρb was
calculated from the relation
The test for SV (Bhattacharya and Ali 1976) gives an
indirect indication of degree of gelatinization of pregelatinized rice flour. Briefly, 1 g each of desiccated flour
samples was taken in a measuring cylinder and 15 ml of
0.05 N HCl was added to it with agitation after each
5 min for 1 h. The level of the flour sediment was
observed after 4 h and was reported as the SV (in milliliters)
of the sample.
ρb ¼ mass of grain=volume occupied
ð3Þ
True volume was determined by the toluene displacement
method. Briefly, to a known volume of toluene (Merck,
India) in a measuring cylinder, polished kernels of known
weight were immersed and the volume displaced by the
kernels was recorded and the density (ρt) was calculated
by the relation
ρt ¼ mass of grain = volume of toluene occupied
ð4Þ
The porosity (ε) was determined from Eqs. (3) and (4) by
the relation (Jain and Bal 1997)
"ð%Þ ¼ ½ðρt
ρb Þ=ρt 100
ð5Þ
ð6Þ
Cooked Rice Texture
Briefly, 20 g samples from both raw and processed rice
kernels were cooked for their cooking times and texture
profile analysis (TPA) of the cooked grains was performed using a Texture Analyzer (TA.HD.plus, Stable
Micro Systems, UK). A 5-kg load cell fitted with a
cylindrical probe of 2 cm diameter was used for
performing the two-cycle compression test (Suzuki
1979). A single kernel was collected from the middle
of the cooked rice mass and compressed to 70 % at
0.5 mm/s. The time between two chews was 3 s. All
the TPA parameters, namely hardness, fracturability,
adhesiveness, springiness, and chewiness were determined by the inbuilt software (Exponent Lite). Ten
replicates for each sample were run and the mean
values for each parameter taken. In addition to this,
Food Bioprocess Technol (2014) 7:212–223
215
looking at the quick cooking nature of the product, the
samples were soaked in excess water at 20 and 50 °C
for 60 and 20 min respectively in a hot water bath
(Labtech, India) and the TPA parameter values were
compared.
Pasting Properties
The pasting profiles of flour suspensions (12 %, w/w;
28 g total weight) were recorded using a Rapid Visco
Analyzer (RVA Starchmaster2, Newport Scientific
Instruments). The Rice1 profile of Newport Scientific
was used, where the samples were held at 50 °C for
1 min, heated from 50 °C to 95 °C at 12 °C/min, held
at 95 °C for 2.40 min followed by cooling to 50 °C at
11.25 °C/min, and finally holding at 50 °C for 1 min.
The pasting curves obtained were compared and the
pasting parameters, namely peak viscosity (PV), hot
paste viscosity (HPV), cold paste viscosity (CPV),
breakdown (BD), and total setback (SBt) were recorded.
PV=maximum viscosity during heating, HPV=minimum
viscosity at 95 °C, CPV=final viscosity at 50 °C, BD=
PV-HPV, and SBt=CPV-PV.
X-Ray Diffraction
Wide angle X-ray diffractograms were obtained using a Xray diffractometer (Rigaku Miniflex, Japan) with a Cu Kα
value of 1.5404 A° operating at 30 kV acceleration potential
and 15 mA current with a copper target. The scanning range
was 10–40° of 2θ values in steps of 0.05°. The total area
under the curve and the area under each prominent peak
were determined and the percentage crystallinity was calculated (Singh et al. 2006)
% crystallinity ¼ ðarea under peaks=total areaÞ 100
ð7Þ
Starch Digestibility Rate
The extent of enzymatic hydrolysis leading to release of
glucose from starch gives an indication of digestibility
of starchy foods. The amount of glucose liberated on
hydrolysis gives a measure of digestible starch fractions
present in it. The in vitro starch hydrolysis rates (Goni
et al. 1996) of the rice flour samples were estimated.
For this, 50 mg of flour samples were first deproteinized using 0.2 ml of a solution containing 1 g of
Pepsin in 10 ml of HCI-KCI buffer (pH 1.5) by keeping
in a shaking water bath at 40 °C for 1 h. The volume
was then made up to 25 ml with Tris-maleate buffer
(pH 6.9). To this, 5 ml of a solution of in Tris-maleate
buffer containing 2.6 IU pancreatic α-amylase (SigmaAldrich) were then added to each sample and incubated
at 37 °C. One milliliter aliquot was taken out from each
tube after each 30 min from 0 up to 180 min to
determine the hydrolysis rate at different times. The
aliquots were boiled to inactivate the enzymes and
stored under refrigeration for further analysis. Then
3 ml of 0.4 M sodium acetate buffer (pH 4.75) containing 60 μl of amyloglucosidase (Sigma-Aldrich) was
added to each aliquot and incubated at 60 °C for
45 min to hydrolyse the digested starch into glucose.
The glucose liberated was estimated by the 3,5-dinitrosalicylic acid method and was converted to starch by
multiplying by a factor of 0.9. The degree of hydrolysis
was calculated as the percentage of starch degraded
from the total starch content.
Statistical Analysis
All the experiments were carried out in three or more replicates and the means are reported. Significant differences
between the means by Duncan’s multiple range test at a
significance level of 0.05 were performed using SPSS 11.5
(SPSS Inc., USA).
Thermal Analysis
Results and Discussion
A Differential Scanning Calorimeter (model DSC-60;
Shimadzu, Tokyo, Japan), periodically calibrated with
pure indium for heat flow and temperature was used
for thermal profile analysis of the flour samples; 1:2
flour-to-moisture ratio was taken in an aluminum pan
and saturated for 12 h at 4 °C. The pan was then
hermetically sealed and heated against an empty reference pan from 25–150 °C at a heating rate of 5 °C/min
under N2 atmosphere. The onset (To), peak (Tp), and
conclusion (Tc) temperatures and enthalpy of gelatinization (ΔH, in joules per gram) were obtained from the
thermograms using TA-60WS software.
Color Values
It was observed that the lightness values (L*) decreased
on hot soaking alone compared to raw and further with
extent of steaming (Table 2). The hue angle (H*) value
also exhibited a similar fall indicating increased redness
in the samples. These values indicating loss of whiteness and significant rise in the redness may be attributed to the migration of husk and bran pigments into the
endosperm (Bhattacharya 2004) as the husk of the paddy LK was highly pigmented (Fig. 1). Additionally,
216
Table 2 Color values, L/B ratio, density, porosity, and cooking time of the raw and processed rice kernels
Samples
Color
L*
L/B ratio
a*
b*
H*
C*
L
B
Bulk density
True density
Porosity
Cooking time
L/B
ρβ
ρt
ε (%)
T (min)
79.3±0.3 o
78.1±0.4 n
75.1±0.3 m
69.1±0.3 i
63.3±0.2 e
0.6±0.1 a
2.0±0.1 b
3.2±0.2 d
5.4±0.1 h
8.0±0.4 l
14.2±0.1
15.2±0.3
19.1±0.4
22.1±0.8
24.3±0.7
a
b
d
h
k
87.4±0.4 o
82.3±0.3 n
80.3±0.4 l
76.2±0.3 h
71.8±0.6 d
14.2±0.6
15.3±0.4
19.4±0.2
22.7±0.3
25.6±0.3
a
b
d
h
k
6.0±0.3
6.0±0.3
6.0±0.2
6.0±0.4
6.1±0.1
2.7±0.2
2.7±0.4
2.7±0.7
2.7±0.4
2.7±0.4
a
a
a
b
b
2.1±0.2
2.2±0.1
2.2±0.1
2.2±0.1
2.2±0.1
0.7±0.3
0.7±0.5
0.7±0.4
0.7±0.5
0.8±0.7
a
b
b, c
b, c
c, d
1.4±0.2
1.4±0.1
1.4±0.2
1.4±0.1
1.4±0.1
a
a
a, b
b, c
b, c
48.6±0.3
46.5±0.4
46.2±0.4
46.6±0.7
45.9±0.6
j
e
d
f
b
18.1±0.4
17.1±0.3
16.1±0.4
14.2±0.1
13.6±0.2
o
n
l
j
f
P-1-10
P-1-15
P-1-20
N-3-0
O-3-10
O-3-15
O-3-20
P-3-10
P-3-15
P-3-20
71.2±0.4 k
66.9±0.4 g
57.8±0.4 b
73.0±0.3 l
71.0±0.3 j
64.4±0.6 f
60.0±0.5 c
67.7±0.3 h
61.2±0.2 d
54.1±0.7 a
4.3±0.4 g
6.4±0.5 j
9.6±0.6 n
2.4±0.4 c
3.8±0.3 e
5.8±0.2 i
9.2±0.7 m
4.0±0.3 f
7.6±0.1 k
12.7±0.3 o
21.1±0.4
22.4±0.5
25.1±0.6
15.7±0.6
20.2±0.3
23.6±0.3
24.9±0.4
20.8±0.3
24.7±0.3
29.8±0.4
g
i
n
c
e
j
m
f
l
o
78.4±0.6 i
73.9±0.6 f
68.9±0.5 b
81.1±0.6 m
79.1±0.3 k
76.1±0.4 g
69.7±0.5 c
78.8±0.3 j
72.7±0.2 e
66.9±0.3 a
21.5±0.4
23.3±0.1
26.9±0.2
15.9±0.4
20.5±0.8
24.3±0.3
26.6±0.7
21.2±0.4
25.9±0.3
32.4±0.5
g
i
n
c
e
j
m
f
l
o
6.0±0.3
6.1±0.2
6.1±0.2
6.0±0.5
6.0±0.5
6.0±0.3
6.1±0.3
6.0±0.3
6.1±0.3
6.1±0.1
2.7±0.3
2.7±0.1
2.6±0.4
2.6±0.2
2.6±0.2
2.6±0.3
2.6±0.3
2.6±0.7
2.6±0.2
2.5±0.2
b
b
b, c
a
b
b, c
c
b, c
c
c
2.2±0.3
2.2±0.3
2.2±0.3
2.2±0.1
2.2±0.1
2.2±0.1
2.3±0.2
2.3±0.3
2.3±0.2
2.3±0.1
0.7±0.3
0.8±0.4
0.8±0.3
0.7±0.1
0.7±0.1
0.7±0.1
0.8±0.2
0.7±0.1
0.8±0.2
0.8±0.1
b, c
c, d
e
b, c
b, c
b, c
c, d
b, c
c, d
e
1.4±0.2
1.4±0.3
1.4±0.1
1.4±0.1
1.4±0.1
1.4±0.2
1.5±0.1
1.4±0.2
1.5±0.1
1.5±0.1
b, c
b, c
c, d
a
b, c
c, d
e
c, d
e
e
46.6±0.4 f
45.9±0.3 b
45.6±0.3 a
46.8±0.2 h
46.6±0.2 f
46.9±0.3 i
46.6±0.1 g
46.9±0.3i
46.6±0.3 g
46.0±0.1 c
14.2±0.4
12.8±0.4
11.6±0.3
16.9±0.5
14.1±0.4
13.3±0.4
14.1±0.2
13.9±0.3
11.8±0.4
9.3±0.5
k
d
a
m
h
e
i
g
b
c
The means followed by a common letter are not significantly different by Duncan’s multiple range test at p<0.05
Food Bioprocess Technol (2014) 7:212–223
N
N-1-0
O-1-10
O-1-15
O-1-20
Food Bioprocess Technol (2014) 7:212–223
217
accordance with that reported by Bhattacharya et al.
(1972) mentioning positive interrelation of porosity with
kernel length. This might be due to the simultaneous
decrease of the kernel breadths (B) causing more grains
to be accommodated within a unit volume, resulting in
increased ρt value than the raw rice kernels (Table 2).
This increase was higher for the pressure parboiled
samples indicating better packing properties, hence also
exhibiting lower ε values.
Cooking Time
Fig. 1 The Kola Chokua paddy
there might have also occurred Maillard browning due
to the high heat applied during soaking and steaming.
The chroma (C*) value indicative of color purity and
clarity increased markedly with extent of processing
indicating more uniform product appearance. More drastic changes in the color values were observed in a
different study where similar steaming conditions were
employed with the same paddy variety after the same
soaking duration but without the short-term boiling step
(Dutta and Mahanta 2012). An explanation for this may
be that the hot soaking causes surface gelatinization of
the rice starch accompanied by pigment migration. On
cooling, the gelatinized surface starch retrogrades. The
retrograded layer has a harder texture as reported by
Kadan et al. (2001) and Yu et al. (2010) and hence
might have served as a partial barrier resulting in lower
migration of pigments during the steaming step.
L/B Ratio
Physical dimensions of L, B, L/B were almost similar in
the raw rice, open steam parboiled rice and pressure
parboiled rice contrary to the observations of Saeed et
al. (2011), Saif et al. (2004), Siddiquee et al. (2002),
Sowbhagya et al. (1993), and Igathinathane et al. (2008)
in parboiled rice.
Table 2 shows the values of the cooking times of the
different samples. T (cooking time) was highest for the
raw N kernels. N required around 18 min to cook. Hot
soaking only marginally lowered the T values, which
was further reduced on both open and pressure steaming
which reflected the effect of gelatinization of starch. P3-10 exhibited the fastest cooking, with almost half the
T value of N. The very low cooking time of severely
parboiled rice reflected the effect of both gelatinization
and thermal degradation. Although, parboiling is said to
increase the cooking time of rice kernels, reduction in
cooking time in heat moisture treated starches have also
been reported (Kulp and Lorenz 1983; Adebowale et al.
2005). Furthermore, the low cooking time of Chokua
parboiled rice may be attributed to the low amylase
content of the rice. As amylose content is low, the
extent of retrogradation of the gelatinized starch during
drying was restricted.
Equilibrium Moisture Content at Soaking at Room
Temperature
Marked increases in EMC-S (in percent, decibels) were
observed on processing (Fig. 2a). Although N-1-0 and
N-3-0 did not vary much in the EMC-S, both open and
pressure steaming resulted in higher water uptake by the
kernels. This increase was higher in the pressure steaming of 3 min hot-soaked samples than 1 min hot-soaked
samples. EMC-S was highest for P-3-20 followed by P1-20 with values of 259.9 and 236.6 %, respectively.
The increased EMC-S was probably due to the thermally degraded starch in the samples.
Porosity
Sediment Volume
The pattern of change in porosity on parboiling is
dependent on the rice variety and also on the final
moisture content of the paddy (Kachru et al. 1994;
Reddy and Chakraverty 2004). The changes in bulk
and true density were marginal; both properties increased with parboiling. The marginal decrease in porosity with increasing L/B ratio, however, was not in
SV also showed a similar pattern as EMC-S, with higher
volume increase by the rice flour in acidic solution with
increasing severity of processing (Fig. 2b). It was
indicative of increased degree of starch gelatinization and
subsequent thermal degradation with severity of processing
(Bhattacharya and Ali 1976).
218
b
10
9
8
SV (mL)
7
6
5
4
3
2
Samples
Samples
Samples
5
0
Samples
P-3-20
P-3-20
P-3-10
P-3-15
O-3-20
O-3-15
O-3-10
N-3-0
P-1-20
P-1-15
O-1-20
P-1-10
O-1-15
N-1-0
O-1-10
0.05
10
O-3-20
0.10
O-3-10
0.15
15
N-3-0
0.20
P-1-15
P-1-20
0.25
20
P-1-10
0.30
O-1-20
0.35
25
O-1-15
0.40
30
O-1-10
0.45
N
Springiness
0.50
35
N-1-0
Chewiness (g)
0.55
N
d
0.60
0.00
P-3-20
-15
P-3-15
-14
Samples
c
N-3-0
-13
P-3-15
P-3-20
P-3-15
P-3-10
O-3-20
N-3-10
O-3-10
O-3-15
P-1-15
P-1-20
P-1-10
O-1-20
O-1-15
N-1-10
O-1-10
N
0
-12
O-3-20
P-3-10
200
-11
P-3-10
400
O-3-15
600
-9
-10
O-3-15
800
-8
N-3-0
1000
-7
O-3-10
1200
-6
P-1-15
P-1-20
1400
-5
O-1-20
P-1-10
Hardness(g)
1600
-4
O-1-10
O-1-15
Adhesiveness (g/s)
1800
N-1-0
b
2000
N
The textural properties of open pan cooked (100 °C) samples and samples soaked at 20 and 50 °C for 60 and 20 min
respectively were studied (Fig. 3). ). Hardness decreased
progressively with extent of processing. Adhesiveness of
the cooked kernels increased on open steaming which might
be attributed to formation of hot water soluble fractions
while pressure steaming exhibited decrease with severity
of pressure steaming possibly due to thermally degraded
starch. Springiness values, however, showed marked
a
Samples
increase for both the processing types. The presence
and type of amylose and amylopectin fine structures in
the starch plays important role in the rice TPA parameters (Ong and Blanshard 1995) creating scope for further research in this area.
Soaking at 50 °C for 20 min gave texture parameter
values nearer to that of the open cooked samples as compared with soaking in water at 20 °C for 60 min. This
similarity was more prominent for the pressure processed
samples. From the TPA results, it is evident that just soaking
at 50 °C for 20 min of the hot-water-soaked and pressure
Cooked Rice Texture
Fig. 3 The TPA parameter values namely a harness (in grams),
b adhesiveness (in grams per
second), c springiness, and d
chewiness (in grams) of the parboiled samples cooked at 100 °C
till done ( ), 50 °C for 20 min
( ), and 20 °C for 60 min ( )
O-3-10
O-3-15
O-3-20
P-3-10
P-3-15
P-3-20
N-1-0
O-1-10
O-1-15
O-1-20
P-1-10
P-1-15
P-1-20
N
N-3-0
0
O-3-10
O-3-15
O-3-20
P-3-10
P-3-15
P-3-20
O-1-10
O-1-15
O-1-20
P-1-10
P-1-15
P-1-20
1
N-1-0
260
240
220
200
180
160
140
120
100
80
60
40
20
0
N
a
EMC-S % (db)
Fig. 2 a Equilibrium moisture
contents on soaking (in percent,
dry weight basis) and b
sediment volumes (in
milliliters) of the raw and
processed samples
Food Bioprocess Technol (2014) 7:212–223
Food Bioprocess Technol (2014) 7:212–223
80
70
60
50
00:03:18
00:06:38
Viscosity (Pa.s)
90
100
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
90
80
70
60
50
40
00:09:58
00:03:18
Pasting Properties
Hot-soaked samples (both 1 and 3 min hot soaked) had
pasting profile similar to the corresponding raw, however,
the viscosity at PV, HPV, and CPV were considerably higher
(Fig. 4). PV for N-1-0 was 4.558 Pas and for N-3-0 was
3.932 Pas. On open steaming, while PV remained almost
constant for the LK1 samples (3.577–4.646 Pas), minor
drop was observed for the processed LK3 samples (4.109–
3.375 Pas), and suggestive of lower thermal stability of the
polymeric pattern developed on hot soaking. The CPV for
the open steamed samples, O-3-10 (6.924 Pas), O-3-15
(7.092 Pas), and O-3-20 (6.682 Pas) were however higher
than O-1-10 (6.246 Pas), O-1-15′ (6.191 Pas), and O-1-20
(6.446 Pas). SBt values were similarly higher. This may be
explained as to the formation of short linear molecular
chains on thermal degradation which probably was able to
300
25
X-Ray Diffraction
The native A-type diffraction pattern of N with characteristic peaks near 15.1, 17.1, 18.3, and 23.2 remained unaltered
on hot soaking (Fig. 5a). While both open and pressure
steamed samples from 1-min boiled category and only open
30
35
b
24
22
20
200
150
100
P-1-20
P-1-15
P-1-10
O-1-20
O-1-15
O-1-10
N-1-0
50
15.1
17.1
1 8 .3
23.2
0
-50
-100
18
% Crystallinity
P-3-20
P-3-15
P-3-10
O-3-20
O-3-15
O-3-10
N-3-0
250
16
14
12
10
8
6
4
2
-150
P-3-15
P-3-20
P-3-10
O-3-15
O-3-20
N-3-0
Samples
O-3-10
P-1-20
P-1-10
P-1-15
2θ (Bragg angle)
40
O-1-20
30
O-1-15
20
O-1-10
0
10
N-1-0
N
N
Intensity (a.u.)
40
24.1
20
17.3
350
15
20.0
10
00:09:58
reassociate forming retrograded starch. Pressure steaming
resulted in gradual yet extensive drop in the PV as was also
evident in some earlier works (Himmelsbach et al. 2008;
Swasdisevi et al. 2010). This drop is similar to that of acidthinned starch used in paper and textile industries (Dutta et
al. 2011). This was accompanied by very low BD (12–
28 cP) with higher CPV. Severe processing causes thermal
degradation of starch polymer structure (Mahanta and
Bhattacharya 1989). Increase in the final slurry viscosity,
hence may be attributed to leaching of the degraded simpler
chains causing rise in slurry densities. The almost continuous rise in the slurry viscosity with minor BD
throughout the RVA cycle indicated the thickening property of the pressure steamed samples, suggesting its
suitability for specific uses.
steamed low amylose Chokua rice gave similar textural as
open pan cooking of such treated rice. Such processing
conditions hence obviate the need of cooking and convert
the processed Chokua rice into ready-to-eat cereal.
a
00:06:38
Time (h:min:s)
Time (h:min:s)
Fig. 5 a The XRD patterns of
raw and processed flour
samples with peaks indicated
and b percent crystallinity of
the samples with processing
Temperature (oC)
b
100
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Temperature (oC)
a
Viscosity (Pa.s)
Fig. 4 RVA pasting curves of
parboiled samples hot soaked
for a 1 and b 3 min. The
representations of the symbolic
curves are as follows: Native
( ), hot soaked and nonsteamed
), open steamed O-10
(
), O-15 (
), O-20
(
), and pressure steamed
(
), P-15 (
),
P-10 (
)
and P-20 (
219
220
Food Bioprocess Technol (2014) 7:212–223
P-1-20
P-1-15
P-1-10
O-1-20
O-1-15
O-1-10
b
P-3-20
P-3-15
P-3-10
Endothermic heat flow
a
Endothermic heat flow
Fig. 6 DSC thermographs of
parboiled samples hot soaked
for (a) 1 min and (b) 3 min
O-3-20
O-3-15
O-3-10
N-1-0
N
30 40 50 60 70 80 90 100110120130140150160170
Temperature (oC)
steamed samples from 3-min boiled category gave mixed
patterns with peaks corresponding to all A- (2Ɵ=15.1°,
23.2°), B- (2Ɵ =17.3°), and V-type (2Ɵ =20°), the high
pressure processed LK(3) samples exhibited almost amorphous diffractographs with feeble peaks indicating mixed
pattern of B- (2Ɵ=17.3° and 24.1°) and V-type (2Ɵ=20°).
Mahanta et al. (1989) and Xiao et al. (2011) also reported
similar diffraction peaks in their parboiled samples. Percent
crystallinity was maximum in raw rice. Hot soaking reduced
crystallinity. In both 1 and 3 min series of processed samples, open steaming showed gradual increase in percent
crystallinity, while for pressure steamed samples, the
Table 3 DSC thermal parameter values of the raw and processed rice
flour samples
ΔΗ (J/g)
Sample
To (°C)
Tp (°C)
Tc (°C)
N
N-1-0
O-1-10
O-1-15
O-1-20
P-1-10
P-1-15
P-1-20
63.4±1.2 m
50.0±2.1 c
68.1±1.4 n
69.2±1.3 o
59.8±1.2 j
61.1±2.3 l
57.8±1.4 g
53.3±2.1 f
75.1±0.8
68.6±1.9
83.1±1.4
78.9±2.2
70.6±1.2
72.0±2.1
69.4±1.2
67.8±1.3
k
e
o
m
h
j
f
d
82.3±1.2
75.2±2.1
90.1±1.4
83.3±1.4
80.0±1.3
80.0±2.2
74.9±1.2
76.2±2.3
i
d
m
j
f
f
b
e
10.6±0.7i
8.6±1.4 f
45.4±1.3 o
20.4±1.3 m
12.8±1.6 j
9.4±1.4 h
8.2±1.1 e
7.2±0.8 d
N-3-0
O-3-10
O-3-15
O-3-20
P-3-10
P-3-15
P-3-20
50.1±1.2 d
60.0±2.1 k
59.3±1.2 i
51.8±2.3 e
58.3±1.4 h
47.7±2.2 a
49.1±1.2 b
69.8±1.2
78.2±0.4
71.9±1.1
62.0±2.1
79.9±2.0
66.3±1.6
66.2±1.3
g
l
i
a
n
c
b
84.2±1.0
89.2±2.1
80.2±1.2
70.1±1.3
95.2±2.2
75.0±1.1
82.2±1.2
k
l
g
a
n
c
h
9.2±1.1
26.8±0.7
17.2±0.9
17.2±1.3
7.1±1.2
6.3±1.6
6.3±0.6
g
n
l
k
c
a
b
The means followed by a common letter are not significantly different
by Duncan’s multiple range test at p<0.05
To onset temperature, Tp peak temperature, Tc conclusion temperature,
ΔH enthalpy of the crystallite melting endotherm
N-0-3
N
30 40 50 60 70 80 90 100110120130140150160170
Temperature (oC)
percent crystallinity was less in 15 min steaming time than
10 and 20 min steaming. Such changes in crystallinity were
also reported by Manful et al. (2008) and Yu et al. (2010).
Probably the new polymorphic forms (B- and V-type) have
increased the percent crystallinity (Fig. 5b).
Thermal Properties
The DSC thermographs of the samples are shown in Fig. 6
and the thermal parameter values presented in Table 3. Hotsoaked sample with no steaming showed marked decrease in
melting enthalpy of the rice flour. However, mildly parboiled samples showed higher transition enthalpies with a
shift of the melting peak towards higher temperatures.
Similar findings in parboiled rice were reported earlier by
Lai et al. (2001). Further higher treatment lowered the
enthalpy values with a shift of the peak towards lower
temperature again as was also evident in the RVA patterns
of the samples. This indicates differences in the thermal
properties of the different polymorphs formed with different
extents of processing and lowering of the thermal stability
with processing severity (Ong and Blanshard 1995).
Furthermore, hot-soaked N-1-0 and N-3-0, mildly processed
O-1-10, and the pressure steamed P-1-15, P-1-20, P-3-10, P3-15, and P-3-20 did not exhibit any endotherm for
amylose-lipid complex melting. The endotherms were observed primarily in the moderately processed samples and
all were of type I (melting temperature, <100 °C) as reported
by Biliaderis and Galloway (1989). The absence it in the
severely processed samples indicates that these complexes
formed at higher processing conditions, as were observed in
the XRD patterns, melted throughout the period of the DSC
profile used, without showing any distinct endotherm.
Another probable reason might be that these polymorphs had similar temperature sensitivity and hence
have merged with the main peak responsible for the
retrograded starch fractions.
Food Bioprocess Technol (2014) 7:212–223
b 100
100
90
80
70
60
50
N
N-1-0
O-1-10
O-1-15
O-1-20
P-1-10
P-1-15
P-1-20
40
30
20
10
0
0
20
40
60
80
100
120
140
160
180
Hydrolysis time (min)
Degree of hydrolysis (%)
a
Degree of hydrolysis (%)
Fig. 7 Starch hydrolysis rates
of flours of the parboiled
samples hot soaked for a 1 and
b 3 min
221
90
80
70
60
50
N
N-3-0
O-3-10
O-3-15
O-3-20
P-3-10
P-3-15
P-3-20
40
30
20
10
0
0
20
40
60
80
100
120
140
160
180
Hydrolysis time (min)
Starch Digestibility Rate
Conclusions
Starch digestibility rapidly increased till 90 min of incubation
for all flour samples (Fig. 7), thereafter remained almost
constant till 180 min. The raw rice flour showed comparatively lower hydrolysis rate than the rest (69.3 % after 180 min).
Hot-soaked samples did not differ in starch digestibility from
raw samples in line with the similarity in crystallinity and
thermal properties. Probably, hot-soaked samples did not undergo much alteration at the molecular level. Mild open
steaming gave higher digestibility than moderate and severe
steaming indicating formation of newer indigestible fractions
on retrogradation of gelatinized starch as also observed in
previous works (Sajilata et al. 2006). Increasing severity of
open steaming hence might result in the formation of newer
enzyme resistant fractions. The trend was however reversed in
pressure steamed samples after 1 and 3 min hot soaking times.
Steaming severity increased the digestibility markedly and
was highest (93.8 % after 180 min) for P-3-20, also observed
by Takahashi et al. (1994) and Niba (2003). Hence, the results
were indicative of clear nutritional differences between the
products of the two processes.
The pressure steaming of Kola Chokua paddy after hot
soaking treatment gave a quick cooking, ready-to-eat
product similar in texture to cooked rice kernels. Such
parboiled rice had different physicochemical properties
than those obtained from open steaming technique. The
changes in properties can be attributed to the effect of
gelatinization and thermal degradation of starch which
may explain their higher rate of starch digestibility.
Thus, pressure steaming of hot-soaked Kola Chokua
paddy gives ready-to-eat rice product. On the other
hand, the product processed by open steaming of hotsoaked paddy gave enzyme resistant starch. Such samples also recorded high pasting and cooling viscosities.
These specific properties can be exploited for specific
end uses. The thermal degradation of starch can be
further studied at the molecular level.
Parboiling steps
Soaking
The Ready-to-Eat Product
The flowchart of the process developed in this study is given
in Fig. 8. In order to hasten the water absorption by the
kernels, the kernels were given a hot soaking treatment that
involved cooking the low amylose Kola Chokua paddy in
water for 1–3 min and then allowing the paddy to hydrate
overnight in that water at room temperature. The soaked
paddy was then steamed at the different conditions mentioned. Pressure steaming gave a better quality product as
judged by the texture of the kernels soaked in water. The
textural properties of such pressure steamed rice gave soft
textured rice kernels on soaking in water for 20 min at 50 °
C. Thus, the above processing conditions gave a ready-toeat rice product that softened easily when soaked in warm
water and was suitable for consumption.
The method
Low amylose paddy
Soak in boiling water for 1-3 min
Wrap the boiling vessel with gunny bag
Keep for soaking at room temperature for 18 h
Drain excess water
Boiling/
Steaming
Drying
Open/pressure steam for 10-20 min
Dry in shade for 48 h
Mill
Fig. 8 Flowchart showing different steps of parboiling in the developed process (patent applied for)
222
Acknowledgment The authors acknowledge Department of Science
and Technology, New Delhi for providing financial assistance for
carrying out this research work.
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