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Optimization of instant jasmine rice process and its physicochemical properties


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Instant, or quick-cooking, rice is becoming more popular nowadays. However, it still poses problems with respect to rehydration time and quality. This study investigated the effects of processing factors: moisture content, pressure and drying temperature on physical and physicochemical properties of instant rice and its eating quality using response surface methodology (RSM). Hardness, chewiness and the whiteness index (WI) were used as responses due to their high R2 (0.927, 0.633 and 0.836, respectively) and lack-of-fit. The hardness and chewiness of rice decreased as moisture content and pressure increased. Higher drying temperatures caused increases in hardness and chewiness. Only pressure and moisture content affected density, rehydration ratio, and increase in the volume of instant rice, which was due to the porosity of the kernels. Rehydration ratio had a negative correlation with density (r = −0.886) but a positive correlation with volume increase (r = 0.637). Pressure was the main factor influencing the pasting properties of instant rice. All pasting properties of instant rice were far lower than those of milled rice, but instant rice had higher cold paste viscosity, which is typical of pregelatinized flour. This indicated rapid water absorption and shorter cooking time. Instant rice processing also caused development of amylose–lipid complexes observed as the V-type pattern in an X-ray diffractometer.
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Optimization of instant jasmine rice process and its physicochemical properties
Waraporn Prasert
, Prisana Suwannaporn
Institute of Food Research and Product Development, Kasetsart University, Bangkok 10900, Thailand
Department of Food Science and Technology, Kasetsart University, Bangkok 10900, Thailand
article info
Article history:
Received 4 February 2009
Received in revised form 7 April 2009
Accepted 14 April 2009
Available online 23 April 2009
Instant rice
Quick cooking rice
Process optimization
Eating quality
Pasting properties
Amylose–lipid complex
Instant, or quick-cooking, rice is becoming more popular nowadays. However, it still poses problems with
respect to rehydration time and quality. This study investigated the effects of processing factors: mois-
ture content, pressure and drying temperature on physical and physicochemical properties of instant rice
and its eating quality using response surface methodology (RSM). Hardness, chewiness and the whiteness
index (WI) were used as responses due to their high R
(0.927, 0.633 and 0.836, respectively) and lack-of-
fit. The hardness and chewiness of rice decreased as moisture content and pressure increased. Higher dry-
ing temperatures caused increases in hardness and chewiness. Only pressure and moisture content
affected density, rehydration ratio, and increase in the volume of instant rice, which was due to the
porosity of the kernels. Rehydration ratio had a negative correlation with density (r=0.886) but a posi-
tive correlation with volume increase (r= 0.637). Pressure was the main factor influencing the pasting
properties of instant rice. All pasting properties of instant rice were far lower than those of milled rice,
but instant rice had higher cold paste viscosity, which is typical of pregelatinized flour. This indicated
rapid water absorption and shorter cooking time. Instant rice processing also caused development of
amylose–lipid complexes observed as the V-type pattern in an X-ray diffractometer.
Ó2009 Elsevier Ltd. All rights reserved.
1. Introduction
In modern lifestyles, instant food is becoming more popular.
However, instant rice is still beset by the problems of long rehydra-
tion time and inferior quality compared to cooked milled rice. The
texture of cooked rice is related to its amylose content and the fine
structure of amylopectin. The intra- and/or intermolecular interac-
tions of starch with other components in rice such as protein, lipid
and non-starch polysaccharides results in a harder texture (Ong
and Blanshard, 1995). Moreover, processing conditions also affect
the texture of cooked rice in a way similar to the parboiling pro-
cess. The basic processes in preparing instant rice and parboiled
rice are similar, consisting of soaking, steaming and drying. These
processes have marked impacts on the organoleptic properties of
cooked rice. Derycke et al. (2005a) found that the heat-moisture
conditions during parboiling, cooling and drying had impact on
cooked parboiled rice. They observed that the texture of cooked
parboiled rice was usually firmer and less sticky than that of
non-parboiled rice. This firmer texture was related to the level of
crystalline amylose–lipid complexes formed during parboiling
which were stable during the cooking process.
According to Robert (1972), dry grains of instant rice should be
separate and should resemble milled rice in shape. Its bulk density
should be 0.4–0.42 g/cm
with a low percentage of broken kernels.
After rehydration, the volume of instant rice should increase to
1.5–3 times that of dry grains, and its color, flavor and texture
should be similar to cooked rice (Smith et al., 1985) with no hard
core or ungelatinized center (Luh et al., 1980). Previous investiga-
tors tried to propose instant rice processes which were mainly con-
cerned with three main factors: (1) the initial moisture content, (2)
the degree of gelatinization and (3) the drying or puffing method.
The initial moisture content could be manipulated by the temper-
ature of the water used in soaking and/or time. The initial moisture
content has been reported to affect the product’s homogeneity (Baz
et al., 1992), degree of gelatinization, percentage of broken kernels
(Ahromrit et al., 2006) and degree of starch leaching (Bello et al.,
2006). Degree of gelatinization was related to cooking method,
cooking time and/or temperature. Partial gelatinization (around
80%) (Smith et al., 1985) or complete gelatinization either by boil-
ing or steaming have been proposed as necessary in the instant rice
preparation process. High pressure cooking process resulted in
more homogeneous gelatinization and reduced the percentage of
broken kernels (Bhattacharya, 1985; Baz et al., 1992). Drying pro-
cesses varied from single step drying at low temperature (70 °C)
for a long time (2–3 h) to multi-step drying at high temperature
for a short time to induce case hardening followed by low temper-
ature drying for a long time to reduce moisture content (Robert,
1972; Ozai-Durrani, 1948). Other drying methods included the
use of tray dryers or centrifugal fluidized bed dryers (Baz et al.,
1992; Ramesh and Rao, 1996; Carlson et al., 1979), drum dryers
(Robert, 1972; Lewis and Lewis, 1991; Ando et al., 1980), a
0260-8774/$ - see front matter Ó2009 Elsevier Ltd. All rights reserved.
*Corresponding author. Tel.: +662 5625038; fax: +662 5625021.
E-mail address: (P. Suwannaporn).
Journal of Food Engineering 95 (2009) 54–61
Contents lists available at ScienceDirect
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freezethaw process (Robert, 1972) and high pressure cooking
(Leelayuthsoontorn and Thipayarat, 2006; Bhattacharya, 1985;
Baz et al., 1992).
In this study, response surface methodology (RSM), an empirical
modeling technique used to estimate the relationship between a
set of controllable experimental factors (Myers and Montgomery,
2002), was applied to optimize the instant rice preparation pro-
cess. The process factors with the greatest effect on instant rice
product quality were investigated together with their interactions.
Moreover, the changes in physical and physicochemical properties
during the instant rice preparation process were also studied in or-
der to understand their relationships with the product and its eat-
ing quality.
2. Materials and methods
2.1. Raw materials
A sample of the inbred KDML 105 rice variety was obtained as
paddy from the Thailand Rice Research Institute. The paddy sam-
ples were dehusked using a McGill sample sheller (dehusker),
and the rice bran was removed using a McGill No. 2 mill. Samples
were milled to a constant degree of milling (DOM = 90). The DOM
was measured using a Satake Milling Meter MM-1B. The white rice
was packed in plastic bags and kept at 4 °C.
2.2. Experimental design
A five-level, three-variable central composite design (CCD) was
applied to estimate the relationship between variables concerning
texture and the whiteness index (WI) of instant rice. CCD consisted
of eight factorial points, six axial points (two axial points on the
axis of each design variable at a distance of 1.68 from the design
center) and six center points, leading to 20 sets of experiments.
The experiments were run in random order to minimize the effects
of unexpected variability in the observed responses due to extrane-
ous factors.
Milled KDML 105 rice was soaked in water for various soaking
times to obtain moisture contents of 35–60% wet basis
;1.68 to +1.68 level). After soaking, the rice grains were
cooked under pressures of from 11.6 to 28.4 lb/in
(or 8.00 10
to 19.58 10
Pa) (X
;1.68 to +1.68 level) for 5 min. Then, the
cooked rice was dried using a tray dryer at temperatures from
166.4 to 233.6 °C(X
;1.68 to +1.68 level) to obtain a product
with a moisture content of less than 12%. The variables and their
process levels are shown in Tables 1 and 2.
Regression analysis was performed based on the experimental
data and was fitted to an empirical second order polynomial model
as shown in the following equation:
where Ywas the response variable, B
were the regression
coefficients of variables for intercept, linear, quadratic and interac-
tion terms, respectively, and x
and x
were independent variables.
For optimization and validation; cooked rice prepared from
electric cooker was used as control sample. The model with no sig-
nificant lack-of-fit and high R
was selected. The optimum condi-
tions were those which gave no significant differences from
control sample. Validation was obtained by comparison the attri-
butes that gave no significant lack-of-fit and high R
between real
value and prediction value using t-test at 95% level of confidence.
2.3. Density, rehydration ration and volume increase
2.3.1. Density
Dry instant rice was put in 100-ml cylinder and tapped 25–30
times to allow uniform compacking of grain, then recorded the vol-
ume and weighted the instant rice in the cylinder. Density was cal-
culated by:
Density ¼weight of instant rice ðgÞ
volume of instant rice ðmlÞ:
2.3.2. Rehydration ratio
Rehydration ratio was determined using 10 g of dry instant rice
added with 100 ml water heated by microwave for 6 min, drain the
excess water for 5 min, and then weighed. The rehydration ratio
was calculated as weight of rice before and after cooking:
Rehydration ratio ¼weight of instant rice after cooking ðgÞ
weight of instant rice before cooking ðgÞ:
2.3.3. Volume increase
Volume increase was determined by measuring the volume of
20 g of instant rice before and after cooking by microwave 6 min
using graduated cylinders tapped 25–30 times to allow uniform
compacking of grain. The volume increase calculated as the volume
of rice before and after cooking as:
Volume increase ¼volume of rice after cooking ðmlÞ
volume of rice before cooking ðmlÞ:
2.4. Scanning electron micrographs (SEM)
SEMs of instant rice samples were taken with a Hitachi Table-
Top/Tischmikroskop model TM-1000 at magnitude x 80. The sam-
ples were prepared by breaking a rice kernel at the center and
sticking it on the stub without gold film coating.
2.5. Texture profile analysis (TPA)
Thirty grams of instant Jasmine rice was rehydrated with
110 ml water and microwaved for 6 min. TPA was performed using
a texture analyzer (, Stable Micro System, UK). Follow-
ing Park et al. (2001), 10 g of rehydrated rice was molded into a
block using a cylindrical container. It was compressed to 60% with
a rod-type probe (2.5 diameters) at a speed of 1.7 mm/s. Hardness,
adhesiveness, springiness, cohesiveness, gumminess and chewi-
ness were determined.
2.6. Whiteness index (WI)
The whiteness of rehydrated rice was measured using a color-
imeter (Chromameter model CR-300, Japan). Measurement was
based on the Hunter system with color values of L,aand b. The
measurements were performed in two replications and were re-
peated three times per replicate. The whiteness index (WI) was
calculated as follows:
Table 1
Coded levels for independent variables used in developing experimental data.
Factor Code Level
(1.68) 1 0 +1 +
Moisture Content (% wb) X
34.90 40 47.5 55 60.10
Pressure (lb/in
11.60 15 20 25 28.40
Drying Temperature (°C) X
166.36 180 200 220 233.64
W. Prasert, P. Suwannaporn /Journal of Food Engineering 95 (2009) 54–61 55
WI ¼100 ð100 LÞ
2.7. Pasting properties
Pasting properties of instant rice were determined using a Rapid
Visco Analyzer (Rapid Visco Analyzer model RVA3D Newport Sci-
entific Instruments and Engineering, Australia) according to AACC
standard method No. 61–02 (AACC, 1995). A programmed heating
and cooling cycle was used at constant shear rate. The sample was
equilibrated at 50 °C for 1 min, heated to 95 °C for 3.48 min, held at
95 °C for 2.70 min, cooled to 50 °C for 3.88 min, and finally, held at
50 °C for 1.24 min. Total time was 12.30 min. These tests were
done in triplicate. Paste viscosity plotted in arbitrary RVA units
(RVU) versus time was used to determine the peak viscosity (PV),
trough viscosity, final viscosity (FV), breakdown viscosity
(BKD = PV trough), and setback viscosity (SB = FV trough).
2.8. X-ray diffraction measurements
One gram of milled rice flour and 1 g of instant rice flour were
packed tightly in rectangular silicon cells. Samples were spread
evenly to obtain a smooth surface. The sample cell was then placed
in sample holder. X-ray diffraction patterns were obtained with a
diffractometer (JEOL, model JDX-3530, Japan) using monochro-
matic Cu-K
radiation 1.542 ÅA
. The diffractometer was operated
at 40 kV, 45 mA and the spectra scanned over a diffraction angle
(2h) range of 5–40°at a step size of 0.02°2hper second. Percentage
of crystallinity was calculated as the percentage of peak area to the
total diffraction area using this equation (Cheetam and Tao, 1998):
%Relative crystallinity ¼area above the smooth curve 100
total diffraction area above the baseline :
3. Result and discussion
3.1. Process optimization
The responses modeled as linear, quadratic and cubic functions
of the three independent variables were tested for adequacy and
model fitness using ANOVA. The selections of adequate models
were determined using model analysis, lack-of-fit test and R-
square analysis (Chen et al., 2005). The ‘‘lack-of-fit” test compared
the residual error to the pure error from replicated design points.
The model with no significant lack-of-fit and high R
was selected
(Table 3).
The results showed that hardness, chewiness, and whiteness in-
dex had high coefficient of determination (R
) which equaled
0.927, 0.633 and 0.836, respectively, and no significant lack-of-fit
(Table 3). Park et al. (2001) reported a high correlation between
the instrumental texture parameters hardness and chewiness and
the sensory attributes of cooked rice. Likewise, Prakash et al.
(2005) found positive correlation between instrumental hardness
and sensory hardness and chewiness in thermal processed rice.
As a consequence, hardness and chewiness were used as the main
responses in RSM for the texture of instant rice.
3.2. Effect on texture
Estimation of texture in terms of hardness and chewiness over
independent variables X
and X
was shown in Figs. 1 and 2.
3.2.1. Effect on hardness
Fig. 1 showed that the hardness of rice decreased as pressure in-
creased at lower moisture content but the reverse result was ob-
tained for higher moisture content. But an increase in drying
temperature caused a harder texture. The statistical analysis in
Table 3 indicated that all variables had a significant effect on hard-
ness, especially moisture content in linear, quadratic and interac-
tion terms. At higher moisture content, thinner case hardening
and bigger pore size were noticeable in the SEM images (Fig. 4).
High pressure induced high gelatinization, which also resulted in
a softer texture in the rehydrated rice.
The hardness of cooked instant rice had positive correlation with
density (Table 4). Density was related to the porosity of the struc-
ture of processed rice seen in the SEM images. The cracks and pores
in instant rice permitted rapid entry of water and heat transfer dur-
ing cooking, resulting in a softer texture rehydrated rice.
3.2.2. Effect on chewiness
Chewiness refers to number of chews required to masticate
cooked rice before it was suitable for swallowing or the amount
of work required to chew the sample for sensory evaluation. It
was observed that pressure and drying temperature had main ef-
fects on chewiness (Table 3). If pressure was fixed at the same
moisture content, chewiness also increased with the increase in
drying temperature. Initial moisture content affected chewiness
in the interaction term and with pressure in the quadratic term
(P< 0.05) (Table 3). At low moisture content (mc < 48% wt), chew-
iness was decreased with increased pressure while at high mois-
ture content (mc > 48% wt) the result was contrast, chewiness
trend to increase when increased pressure (Fig. 2).
Table 2
Variables and their levels employed in a central composite design.
Experiment Moisture content (X
) Pressure (X
) Drying temperature (X
Code value Real value (%) Code value Real value (lb/in
) Code value Real value (°C)
11.68 34.9 0 20.0 0 200.0
2 1.68 60.1 0 20.0 0 200.0
3 0 47.5 1.68 11.6 0 200.0
4 0 47.5 1.68 28.4 0 200.0
5 0 47.5 0 20.0 1.68 166.4
6 0 47.5 0 20.0 1.68 233.6
71 40.0 1 15.0 1 180.0
81 40.0 1 15.0 1 220.0
91 40.0 1 25.0 1 180.0
10 1 40.0 1 25.0 1 220.0
11 1 55.0 1 15.0 1 180.0
12 1 55.0 1 15.0 1 220.0
13 1 55.0 1 25.0 1 180.0
14 1 55.0 1 25.0 1 220.0
15–20 0 47.5 0 20.0 0 200.0
56 W. Prasert, P. Suwannaporn / Journal of Food Engineering 95 (2009) 54–61
3.3. Effect on the whiteness index (WI)
All factors influenced the whiteness index, especially pressure.
At high moisture content, the whiteness index decreased when
pressure increased (Fig. 3). This result is in accord with the study
on parboiled rice by Bhattacharya (1996), who found that pressure
and steaming time had marked effects on product’s Hunter color.
Yellowish color was prominent when paddy was parboiled for
longer times. Islam et al. (2002) showed that brightness of par-
boiled rice decreased with the increase in steaming temperature.
The deterioration of the whiteness of parboiled rice was more pro-
nounced at higher temperatures. Leelayuthsoontorn and Thipaya-
rat (2006) found that the WI of cooked rice decreased as the
cooking temperature increased. The cooking temperature was
clearly an important factor influencing WI. However, at low mois-
ture content, the whiteness index also increased with increased in
3.4. Validation
The instant rice preparation processes were carried out in tripli-
cate to confirm the results. The predicted and observed values are
shown in Table 5. The observed values were not statistically differ-
ent at the 95% confidence level. The results showed that the equa-
tion was able to predict the texture and color of rehydrated
instant rice.
3.5. Effect on rice grain structure
The SEM images showed that instant rice grains had a hollow
structure and were case hardened (Fig. 4). In the soaking step,
the increase in grain dimensions has been attributed to the swell-
ing of starch granules and subsequent widening of cracks in the
grain by water diffusion (Ahromrit et al., 2006). Puffed kernels, in
which could be seen larger hollow centers, occurred noticeably
Table 3
Regression coefficients of the polynomial function and the coefficients of determination (R
Coefficient Hardness Adhesive Springiness Cohesive Gumminess Chewiness WI
943.6 0.97 0.41 2,439.98 2,355.99
38.71 0.013 0.0219 32.55 61.67
30.8 0.005 0.0018 97.81 82.90
38.35 0.002 0.003 94.64 97.82
41.34 0.002 0.0024 155.07 157.06
53.95 0.004 0.0133 35.74 46.41
32.79 0.008 0.0029 11.29 7.86
52.59 0.001 0.005 108.86 106.56
9.1 0.0006 0.001 7.49 8.76
26.86 5E05 0.002 17.15 19.00
0.927 0.377 0.274 0.462 0.553 0.633 0.836
0.072 0.425 0.113 0.043 0.032 0.062 0.054
Fig. 1. Contour plot of hardness of rehydrated instant rice as a function of instant
rice process conditions.
Fig. 2. Contour plot of chewiness of rehydrated instant rice as a function of instant
rice process conditions.
W. Prasert, P. Suwannaporn / Journal of Food Engineering 95 (2009) 54–61 57
when both pressure and drying temperature increased altogether.
The puffing phenomenon resulted from the sudden expansion of
water vapor in the granule. In the drying step, moisture was re-
moved from the surface of the rice grains faster than from the inte-
rior (Baz et al., 1992). The surface of rice became slightly harder
than the center during drying (Lin and Jacobs, 2002). This caused
case hardening, which blocked water vapor leaching during the
drying process and resulted in puffing of the grain, giving it a lar-
ger, hollow structure in the center that allows easy rehydration.
3.6. Effect on density, rehydration ratio and volume increase
The results in Table 6 show that only pressure and moisture
content affected density, rehydration ratio and volume increase.
Leelayuthsoontorn and Thipayarat (2006) also found that high
pressure caused larger pore size and thickness with a sponge-like
texture. As a consequence, low density rice was obtained under
conditions of high moisture and high pressure. The rehydration ra-
tio had a negative correlation with density (r=0.546) and a posi-
tive correlation with volume increase (r= 0.542) (Table 4). Rice
was rehydrated more rapidly because of the increase in its surface
area as its volume increased.
3.7. Effect on pasting properties
The integrity of the starch granule and its hydration properties
can be investigated easily by measuring the pasting behavior of
rice flour before and after treatment. All pasting properties of in-
stant rice were far lower than those of milled rice (Fig. 5), but in-
stant rice showed higher cold paste viscosity, which is the typical
hydration property of pregelatinized flour (Lai, 2001).
The disruption of molecular order within starch granules during
steaming caused loss of starch granule integrity and the destruc-
tion of crystallinity, resulting in cold soluble starch (Lai, 2001)
and a decrease in the magnitude of all pasting properties. A similar
observation was previously reported (Hagenimana et al., 2006).
Unlike pregelatinized starch, peak viscosity was still observed in
instant rice flour, which indicated the presence of partially ungel-
atinized starch polymers.
Increase in pressure caused degradation and gelatinization of
starch. The RVA profile of instant rice indicated that instant rice
could absorb water more rapidly and required a shorter cooking
time than milled rice. It indicated granule rigidity and molecular
re-association, which were significantly enhanced by the hydro-
thermal treatment. The change in pasting properties depended
mainly on the combined effects of moisture, pressure and drying
temperature. However, the formation of disulphide bonds in the
protein fraction and the complexation of lipid with amylose also
Table 4
Correlation coefficients between texture and physical properties of instant rice.
Texture Density (g/cm
) Rehydration ratio Volume increase (ml)
Hardness .564* .291 .127
Adhesiveness .123 .133 .020
Springiness .169 .284 .249
Cohesiveness .758** .756** .481
Gumminess .102 .194 .202
Chewiness .152 .125 .144
*, ** significant at P< 0.05 and 0.01, respectively.
Fig. 3. Contour plot of whiteness index of rehydrated instant rice as a function of
instant rice process conditions.
Table 5
Predicted and observed values for the response variables.
Response variables Predicted value Observed value
Hardness 5958.30 5929.77
± 305.81
Chewiness 2392.74 2348.53
± 171.84
Whiteness index (WI) 77.88 77.89
± 0.69
Not significant for t-test at 95% level confidence.
Table 6
Analysis of variance showing the effect of variable as a linear terms and interaction
(cross product) on response parameters (P< 0.05).
Source Density (g/cm
) Rehydration ratio Volume Increase (ml)
0.619 2.778
0.444 1.457 2.707
0.022 2.322 11.185
2.319 0.160 0.953
3.641 0.017 1.509
3.572 0.906 1.124
Significantly different at the 95% confidence level.
58 W. Prasert, P. Suwannaporn / Journal of Food Engineering 95 (2009) 54–61
had effects. Derycke et al. (2005b) suggested that the formation of
disulphide bonds during the parboiling process restricted starch
granule swelling capacity. Moreover, the formation of starch lipid
complexes also restricted the swelling capacity, hence lowering
the pasting properties.
3.8. Amylose–lipid complexes
Amylose–lipid complex formation depended on both heat and
moisture applied during the instant rice preparation process. A-
type crystallinity was either greatly reduced or completely
Fig. 4. Scanning electron micrographs transverse of instant rice (dry grain) at different pressure and drying temperature treatment at (a) 40% moisture content (b) 55%
moisture content.
W. Prasert, P. Suwannaporn / Journal of Food Engineering 95 (2009) 54–61 59
destroyed. The effect of process conditions on the formation of
crystalline amylose–lipid complexes was investigated using XRD
as shown in Fig. 6.
The X-ray patterns of milled rice showed the A pattern which dis-
appeared in instant rice. Instant rice showed the V-type pattern, or
the intensity of the reflections at 2h= 13 and 20°. This result indi-
cated that the instant rice preparation process destroyed the crystal-
line structure of the starch granules. This result agrees well with
Miyoshi (2002) and Shih et al. (2007) found that the formation of
amylose–lipid complexes occurred during heat-moisture treatment
of starch, as indicated by the occurrence of the V-type pattern. Before
gelatinization, starch had limited binding capacity with lipid be-
cause most of the lipid in the system was unable to come into con-
tacted with starch (Pilli et al., 2008). After gelatinization, the
V-type pattern was detected either because more complexes were
formed during heating or the crystalline regions had increased in
size. The V-type crystal pattern was greatest when the highest pres-
sure was used in the process. A similar result was also observed in the
parboiling process, in which amylose–lipid complexes were created
during the heating step. The diffraction lines of amylose–lipid com-
plexes increased progressively with the degree of parboiling. (Priest-
ley, 1976; Biliaderis et al., 1993; Derycke et al., 2005a).
4. Conclusions
Processing conditions affected the physical and physicochemi-
cal properties of instant rice. The hardness and chewiness of rehy-
drated rice was decreased as moisture content and pressure
increased. At high moisture content, the whiteness index de-
creased when pressure increased. Only pressure and moisture con-
tent affected density, rehydration ratio, and volume increase
because they increased the kernel’s porosity, as demonstrated by
the SEM image. The cracking and puffing in the structure of instant
rice were important to the texture of the rehydrated rice. Pressure
was the main factor influencing the pasting properties of instant
rice. All pasting properties of instant rice were far lower than those
of milled rice. But instant rice showed higher cold paste viscosity,
which is the typical hydration property of pregelatinized flour. The
instant rice preparation process caused development of amylose–
lipid complexes observed as the V-type pattern in the X-ray
This research was funded by Kasetsart University Research and
Development Institute year 2007–2008 and partially student fund-
ing from the Graduate School Kasetsart University. Additional
thanks to the Thailand Rice Research Institute, Department of Agri-
culture for their information and support.
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... The longer the freezing time the higher the porosity of instant corn rice (figure 2). The gaps or pores that form in instant rice will facilitate the transfer of water and heat during cooking so as to produce softer rice [17]. Types of corn varieties had no effect on porosity but freezing time had a significant effect on porosity of instant corn rice (p < 0.05). ...
... According to Husain et al., (2006) porosity has an important role in the instantization of a material because the opening of the pores of a material will facilitate rehydration and speed up rehydration time [5]. Prasert and Suwannaporn (2009) stated that the value of the rehydration ratio has a negative correlation with its density [17]. The rehydration process occurs faster due to the increase in surface area which coincides with the increase in volume. ...
... According to Husain et al., (2006) porosity has an important role in the instantization of a material because the opening of the pores of a material will facilitate rehydration and speed up rehydration time [5]. Prasert and Suwannaporn (2009) stated that the value of the rehydration ratio has a negative correlation with its density [17]. The rehydration process occurs faster due to the increase in surface area which coincides with the increase in volume. ...
... During the drying process, case hardening can occur, which blocks the release of water vapor. It results in an expanding grain structure that is larger in the middle, allowing the rehydration process easier (Prasert & Suwannaporn, 2009). According to Fernandes et al. (2010), it also affects the nutritional value of grains, namely reducing the protein content of grains but increasing bioavailability and reducing the queuing content of nutrients. ...
... Physical analysis carried out included bulk density, dehydration ratio, and expansion volume, which refers to Kumalasari et al. (2018), rehydration time (Bui & Coad, 2015), and hardness (Prasert & Suwannaporn, 2009) with modifications. A total of 10 grams of rehydrated Bose samples were molded in the form of a tube with a size of 1 cm of height and 1.5 cm of diameter. ...
... Rehydration ratio of instant Bose (Table 2) ranged from 3.13 to 3.82 g/g. Rehydration ratio is negatively correlated with bulk density (Prasert & Suwannaporn, 2009). The longer soaking time, the higher the rehydration ratio of instant Bose was. ...
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Abstract Bose is a traditional Indonesian food made from a mixture of corn grits and beans that are cooked for a long time. Bose has the potential to be processed into instant food. This study aims to examine the effect of adding several types of beans (soybeans, mungbeans, and peanuts) and the length of soaking time (2, 9, and 16 hours) on the physicochemical and sensory properties of instant Bose. A completely randomized design was used in this study. Instant Bose with the addition of soybeans had the highest protein and iron content, while instant Bose with the mungbeans addition had the highest carbohydrate content. The addition of peanuts in instant Bose resulted the highest fat content, the longest rehydration time and the highest hardness compared to the other treatments. The longer soaking time decreased the nutritional value of instant Bose, speeded up rehydration time, increased swelling volume, and decreased hardness. Based on the sensory analysis, instant Bose made from a mixture of soybeans with the soaking time of 16 hours showed the highest preference. This kind of Bose contained 15.32% protein, 4.85% fat, and 1.85% iron with a rehydration time of 8.38 minutes and a hardness of 664.24 N.
... Instant rice is gaining popularity due to people's fast-paced lifestyle (Batista et al., 2019). The industrial methods for producing instant rice are as follows: (a) pre-cooking of rice grain and then sterilization (Meng et al., 2018); (b) pre-cooking of rice grain and then drying (Prasert & Suwannaporn, 2009); (c) extruding of rice flour and then drying (Mishra, Mishra, & Srinivasa Rao, 2012). The extrusion-cooked instant rice (EIR) uses rice flour as raw material, which is beneficial to the highvalue utilization of broken rice and the reconstitution of nutrients (Johns et al., 2013;Na-Nakorn, Kulrattanarak, Hamaker, & Tongta, 2019). ...
Extruded instant rice (EIR) could not maintain an intact grain morphology during cooking, which seriously affected its cooking quality. The problem was solved by pre-fermentation of rice flour for 5-10 days. Consequently, the cooking loss was significantly reduced, while the hardness, stickiness and water absorption of EIR were significantly increased. The mechanism was that the gel network of EIR was strengthened by the following ways: (1) pre-fermentation significantly increased the total starch and amylose contents of rice flour due to the dissolution or leaching of lipids, ash and soluble proteins into the fermentation broth; (2) pre-fermentation degraded the amorphous region of starch granules by enzymes and organic acids, resulting in a molecular structure with lower polydispersity index and molecular weight, and higher proportion of long- and ultra-long branched chains of amylopectin. This kind of molecular structure was conducive to the formation of ordered double helix structures and strong gel network.
People usually cook rice in various methods, such as using steamer, rice pot and rice cooker. The Inpari IR Nutrizinc variety is claimed to be Zn-rich rice. The quality needs to be traced after it is cooked into steamed rice. This research aim was to study the effect of cooking methods on physicochemical and organoleptic properties of Inpari IR Nutrizinc and Inpari 45 rice varieties. The research design used was factorial randomized block design with 2 treatments i.e., cooking methods (steamer, rice pot and rice cooker) and rice varieties (Inpari IR Nutrizinc and Inpari 45), repeated three times. Results showed that the cooking method by using rice cooker was able to maintain the nutrition better than other treatments. Steamed rice from Inpari IR Nutrizinc has higher nutritional value than steamed rice from Inpari 45 variety, it contained of 54.88% moisture, 0.19% ash, 0.07% fat, 6.03% protein, 38.83% carbohydrate and 14.89 ppm zinc. Consumption of rice with high protein and Zinc content can support government programs in reducing stunting prevalence in Indonesia
Infrared radiation heating (IRH) was used in this study as a new technique for generating fissures in rice grains subjected to temperatures of 100, 125, and 150 °C for 2, 6, and 10 min, for the production of polished and brown quick-cooking rice (QCR). According to the increase in temperature and exposure time, there was an increase in the fissures, reducing the cooking time. IRH at 150 °C/6 min proved to be a promising technique for the production of polished-QCR with a cooking time of 5.79 min, even though the raw grains were opaque and slightly yellow appearance and the cooked rice was stickier. The IRH technique for the production of brown-QCR reduced the cooking time, reaching a time of 16.16 min. The production of brown-QCR by IRH still needs to be combined with another technique that eliminates the effects of the pericarp and aleurone in delaying water absorption.
The uniformity of rice milling is of vital significance in the rice processing industry. Unfortunately, the reasons for non-uniform milling of grains in friction rice mills still remain poorly understood. In this paper, the motion of rice in the mill is numerically simulated based on the discrete element method. The removal mechanism for the bran layer in the friction mill is discussed and verified by experiment. A method of quantifying milling uniformity was introduced. The results showed that for successful milling, the intact bran layer must experience abrasion caused by sieve-rice contact then be completely removed by rice–rice friction. Non-uniform milling occurs due to the existence of “milling blind zones”, where the bran layer cannot be removed. Milling uniformity is closely related to the ability of rice to move from blind zones to the outer ring of the mill. The use of alternating rate to quantify this ability is proposed. The higher alternating rate the better milling uniformity. Alternation rate is affected by the tumbling movement of rice in the milling cavity. The research helps clarify the milling process of rice and provides guidance for the design of rice friction mills.
A new process for the production of instant red jasmine rice was investigated using fluidized bed drying with the aid of swirling compressed air. Drying characteristics were evaluated using the operating parameters of fluidizing air temperature (90–120 °C) and pressure of swirling compressed air (4–6 bar). Appropriate air pressure was determined based on the highest value of model parameters from the semi-empirical Page equation and effective diffusivity. Influences of supply time of swirling compressed air (2–10 min) and drying temperature of 90–120 °C were investigated and optimized based on the quality attributes using response surface methodology. Drying at 120 °C and compressed air pressure of 6 bar gave the highest rate constant and effective diffusion coefficient. Drying at 120 °C combined with injecting swirling air for 2 min was the most suitable approach, while drying at 90 °C and supplying compressed air for 10 min was the best choice to preserve antioxidant properties. Air temperature of 98.5 °C with 2 min supply of swirling compressed air suitably provided high physical and rehydration properties and retained high health benefits of antioxidant compounds. Finally, after rehydration in warm water at 70 °C for 10 min, the textural properties of the rehydrated rice sample were comparable to conventionally cooked rice.
The effects of cooking methods (pressure cooking, microwave cooking, and atmospheric pressure cooking) and infrared-assisted freeze drying (IRFD) on drying characteristic, crystalline structure, pasting property, rehydration behavior, microstructure, texture, and flavor of instant quinoa samples were investigated. Results showed that IRFD significantly reduced the drying time needed for freeze drying (FD). The crystalline structure of starch in raw quinoa was destroyed in cooking process, IRFD process well maintained the gelatinized state of quinoa samples. The pressure cooked samples owned the highest porosity and best rehydration ability. Pressure cooking and microwave cooking caused the softer and thicker texture of rehydrated instant quinoa samples. As for the flavor of quinoa sample, IRFD possessed the stronger retention ability compared with FD. In summary, pressure cooking and IRFD could be the applicable processing methods for the production of instant quinoa product or other dehydrated instant product with high quality.
The present research aimed to evaluate the effect of microwave-assisted conventional drying (hybrid drying) on the physico-chemical and functional characteristics of formulated instant banana-milk powders (IBSPs), and organoleptic attributes of banana-milk shakes during storage. The instant powders were prepared from ripe (IBSP1 (control) and IBSP2) and overripe (IBSP3) bananas using hot-air drying (control) and hybrid (microwave assisted hot-air) drying. The water holding capacity, water solubility index, and viscosity of fresh samples, IBSP1, IBSP2, and IBSP3 were 1.97, 1.53 and 0.60 g/g dry sample, 69.48, 75.21 and 76.62 g/mL and 82.29, 86.29 and 72.55 mPas, respectively. A significant (p < 0.05) increase in moisture content, water activity (aw), acidity, and non-enzymatic browning was observed in all the variants/samples during storage. Among various treatments, the shakes prepared by reconstitution (IBSP: water ratio, 1:4) of IBSP2 formulation rated highest organoleptically (significant, p < 0.05).
Quick cooking germinated brown rice (QCGBR) is a novel convenient food product with valuable health benefits. Different cooking and conditioning methods were studied for standardisation of its preparation process. Freshly harvested paddy of Prativa variety was milled in rubber roll sheller to get brown rice which was soaked in demineralised water at 30±2°C for 12 h followed by 24 h of germination in an incubator maintained at 27±1° C temperature and 85-90 % relative humidity to obtain germinated brown rice. The germinated brown rice was immediately cooked using three different cooking methods such as atmospheric cooking at normal ambient pressure, pressure cooking with water in a domestic pressure cooker at 1 bar gauge pressure and pressure steaming (without water) with steam at 1 bar gauge pressure to predetermined cooking time. The cooked samples after washing were then conditioned by keeping them at 4°C for 24 h (refrigerated storage) or -10°C for 24 h (frozen storage) in a house hold refrigerator. The stored samples were taken out after 24 h and tempered for 1 h followed by drying in a tray dryer at 90°C to obtain the quick cooking germinated brown rice. The samples obtained from different cooking and conditioning methods were analysed for cooking quality, physico-chemical parameters, damaged grain percentage, GABA content and sensory attributes to standardise the cooking and conditioning methods. Cooking time, water uptake ratio, solid loss and volume expansion ratio of quick cooking germinated brown rice varied significantly with cooking and conditioning methods of its preparation (p<0.05). Though frozen conditioning resulted in lowest cooking time, it was not accepted by the sensory panel due to high damaged grain percentage, distorted shape and softness after cooking. The QCGBR obtained by pressure cooking method followed by refrigerated conditioning resulted in highest sensory score.
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The role of proteins in the pasting and cooking properties of non-parboiled (npb) and parboiled (pb) rice was tested by means of a reducing agent dithiothreitol (DTT) and a protease (trypsin). DTT increased the swelling power and carbohydrate leaching of flour from npb rice flour but decreased its amylose leaching. Although DTT slightly increased the Rapid Visco Analyser (RVA) viscosity at the initial stages of the pasting process, it decreased RVA viscosity in the further phases of the experiment. Preincubation of flour with a trypsin decreased RVA viscosity along the whole temperature profile. Addition of DTT to the cooking water decreased water absorption and rice hardness and increased leaching of solids during cooking and stickiness of the cooked npb rice. Addition of DTT to the cooking water of flour from pb rice increased swelling power, carbohydrate leaching, and amylose leaching. Addition of DTT also increased RVA viscosity. Preincubation with trypsin had a similar effect but the changes were less pronounced. Addition of DTT increased stickiness of cooked pb rice and increased water absorption and leaching of solids during cooking. Taken together, the results provide evidence for the existence of a protein barrier affecting starch swelling, rheological, and cooking properties of both npb and pb rice.
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Differential scanning calorimetry (DSC) was used to determine the thermal properties of parboiled rice, and these properties, i.e. gelatinization parameters, namely, peak temperature (T-p) and residual gelatinization enthalpy (DeltaH) were evaluated. The T-p increased and DeltaH decreased with increase in the severity of heat treatment during the parboiling process. The physical property of color value correlated positively with the T-p and the degree of starch gelatinization correlated positively with the hardness of the parboiled rice. The T-p, which represents half the conversion temperature of the sample melting, is believed to be a suitable indicator to identify the severity of heat treatment in the parboiling process. The quantitative T-p values of 77.4 to 79.2degreesC corresponding to the processing conditions of 90degreesC-30 min and 100degreesC-15 min are viewed as an index for better quality of the rice. The thermal properties thus can be utilized to understand the cooking behavior of parboiled rice.
Drying studies of cooked rice were carried out at temperatures from 160 °C to 240 °C. The moisture ratio (MR) was found to follow the same pattern as grain drying. The drying parameters of Page's equation was determined to predict the course of moisture ratio with time. The empirical model predicted the behaviour of the drying system consistently.
This paper reports the pasting, gelatinisation and leaching behaviour of 11 cultivars of rice, the starch structural properties of which were determined in the preceding paper. The results show that the contents of leached amylose in the cooking water, as determined by both size exclusion–high performance liquid chromatography (SE–HPLC) and iodine colorimetry, were correlated positively with the texture of cooked rices, which possessed total amylose contents in the range 18·4–29·5%. The amount of leached amylose depended on the total amylose content of the rice. A similar correlation between the conventional «setback» value, measured using the Viscoamylograph, and the texture of cooked rice may be a result of the leached starch content. The gelatinisation temperatures of rice starches determined by differential scanning calorimetry (DSC) were not correlated with the texture of cooked rice, but were significantly related to the crystallinity of the rice starch. The longest chain population (92–98 DPn), which had been detected previously in the hard rice samples, was not found in their corresponding leached starches. This observation may well support the suggestion in the preceding paper that the longest amylopectin chains could interact with other components in rice, the resultant complexes being retained in the cooked grain and inhibiting softening.
The effects of cooking at elevated temperatures (80, 100, 120 and 140°C) and pressure levels (0, 0.1, 0.3 and 0.5MPa) on the textural and morphological properties of cooked Jasmine rice were investigated. The developed high pressure cooker was utilized to process Jasmine rice in excess water under isothermal conditions. Rice cooking at higher temperature produced softer and stickier grain texture as well as more off-white colour. Using scanning electron microscopy technique, the microstructure revealed that the soft texture at high cooking temperature corresponded well to the increase of pore size and thickness of the sponge-like texture of inner layer endosperm. As the temperature increased, the outer layer of cooked rice became less porous. Boiling significantly altered the external appearance (namely colour and exterior integrity) and texture of cooked rice while cooking pressure had a little or no effect.
Various properties of raw and parboiled rice were compared in an effort to elucidate the factors responsible for the changes induced by parboiling.The parboiled rice was less prone to disintegration on cooking, the kernels remaining well separated and less sticky than the non-parboiled sample. The solids leached into the cooking water and the extent of solubilisation of the kernels on cooking were both considerably lowered by parboiling. Amylograms of flour prepared from the rice revealed that this was due to the resistance of the starch in the parboiled rice to swelling and solubilisation in hot water.From the results of X-ray diffraction spectra it was concluded that the behaviour of parboiled rice is influenced by the presence of an insoluble helical amylose complex and not, as is generally assumed, by retrogradation.
The purpose of this research was to create response surface models through regression on experimental data and to apply the Sequential Quadratic Programming (SQP) and Genetic Algorithms (GAs) on the models to obtain optimal processing conditions for dairy tofu. The two-stage effort of obtaining a surface model using response surface methodology (RSM), and optimizing this model using GAs or SQP techniques was demonstrated to be an effective approach. Both SQP and GAs techniques were able to determine the optimal conditions for manufacturing the probiotic dairy tofu. The conditions were 1% of glucono-delta-lactone (GDL), 0% of peptides level, 3% of isomaltooligosaccharides (IMO) and 18% of milk concentrations, and they were confirmed by verification experiments. Among the SQP and two GAs employed, the SQP, modified with the multi-start capability, is the most efficient one.
Rice is the staple food of many countries and its sensory quality is of great concern to the consumers. Its preservation through thermal processing in retort pouches for ready-to-eat purposes was carried out by different time–temperature schedules with and without oil to achieve a minimum Foof 3 min. The sensory analysis of the cooked rice carried out using quantitative descriptive analysis showed that a process schedule of 118C, 8 min was optimum to have the optimal sensory characteristics. The same rice samples were subjected to instrumental texture measurements by texture analyzer using a crosshead speed of 0.5 mm/s with 90% compression for hardness and stickiness parameters. The instrumental hardness showed high correlation with sensory hardness, chewiness and overall quality (r = 0.72; r = 0.73; r = 0.79) and a negative correlation with sensory stickiness (r = −0.75). Applying principal component analysis, thermally processed rice samples were further classified based on the sensory and instrumental texture attributes.