Proceedings of the World Congress on Engineering and Computer Science 2009 Vol I

WCECS 2009, October 20-22, 2009, San Francisco, USA

Texturing by Instant Controlled Pressure Drop

DIC in the Production of Cassava Flour: Impact
on Dehydration Kinetics, Product Physical
Properties and Microbial Decontamination
Puguh Setyopratomo, Akbarningrum Fatmawati, and Karim Allaf

considered acceptable for household consumption, which

Abstract— “Swell drying” is a new drying process which is was estimated at 4-7 kg/month per household. Since cassava
coupled with dehydration itself, a stage of texturing by the flour can substitute wheat flour by as much as 30 %, the
instant controlled pressure drop technology, called the Détente entire local production of cassava flour can be absorbed,
Instantanée Contrôlée (DIC), which is inserted between pre and
especially by the food industries [3].
final drying steps. Texturing step permits to modify the
material texture, which would then affect the dehydration
The Indonesian Government is attempting to develop the
kinetics, the product physical properties, including water and potential of cassava flour as a food for domestic consumption
oil holding capacity, and the microbial decontamination. The and as a raw material for both household consumption and
results of this work showed that the cassava texturing by DIC the food industry to complement or substitute wheat flour.
implied increasing the effective moisture diffusivity, cassava The Government has recommended that the agricultural and
flour capacities vis-à-vis either the water holding and the oil industrial sectors make special efforts in promoting cassava
holding. Texturing by DIC also reduced the bacterial content of by diversifying cassava process products, improving their
cassava flour significantly. quality, and promoting their use among the different strata of
the Indonesian population.
Index Terms—cassava flour, effective diffusivity, microbial
decontamination, oil holding capacity, water holding capacity.
Cassava flour is produced from fresh cassava roots
through dehydration (drying) process. Basically, the
dehydration process is the removal of water from the cassava
I. INTRODUCTION roots to a certain level at which microbial spoilage is avoided.
Up to now, sun drying is the method mostly used to
In Indonesia, cassava is the fourth most importance food
produce cassava flour in Indonesia. Since very long time
crop after rice, maize and soybean. Whereas, most of the
exposure is needed for such method, significant deterioration
cassava product goes to starch extraction or is exported as
will occur during the drying process, which can result in very
pellet and chips. The average yield per hectare of cassava is
low quality of the cassava flour product. In this work, a new
rather low at 12 tons, but the trend has been toward a
process of a texturing by instantaneous control pressure drop,
constant increase in yields. Cassava is grown on about 1.4
called the Déetente Instantanée Contrôlée (DIC), was
million hectares throughout the country, with an average
introduced between pre and final hot air drying. The purpose
production of 16.3 million tons/year [1]. On an estate of a
of the texturing step is to modify the material texture to
tapioca plant in Lampung, a yield of 25-30 tons/ha of cassava
improve the product quality including the product physical
has been continuously attained [2], as a result of a cassava
properties [4].
intensification program started by the Government in 1975.
The DIC (Détente Instantanée Contrôlée) technology was
Cassava flour processing began in 1990 to diversify cassava
initially developed by ALLAF et al., (since 1988) [5]-[8] in
products. In the country most of cassava flour was
the University of La Rochelle. It apply instant pressure-drop
to modify the texture of the material and intensify functional
This paper was submitted on July 25, 2009, for review. behaviour. DIC treatment usually starts by creating a vacuum
Puguh Setyopratomo is Head of the Indonesian Research Team of condition, followed by injecting steam to the material
France-Indonesia Agro-industrial Laboratory (FIALab), Chemical
keeping such a contact for several seconds, proceeds then the
Engineering Department, Engineering Faculty, University of Surabaya, Raya
Kalirungkut, Surabaya, Indonesia, 60292 (Phone: 62-31-2981158; fax: sudden pressure drop toward vacuum (about 5 kPa with a rate
62-31-2981178; e-mail: puguh_sptm@yahoo.com). higher than 0.5 MPa/s). This treatment is also categorized as
Akbarningrun Fatmawati is Head of Bioprocess Technology Laboratory, a HTST (High Temperature Short Time) process. By
Chemical Engineering Department, Engineering Faculty, University of
Surabaya, Raya Kalirungkut, Surabaya, Indonesia, 60292 (email: suddenly dropping pressure, rapid autovaporisation of the
afatmawati2002@yahoo.com). moisture from the material will occur, the material will swell,
Karim Allaf is Scientific Director of France-Indonesia Agro-industrial and lead to texture change which results in higher porosity
Laboratory (FIALab); Head of Technologies for Agro-Industry of the
University of La Rochelle; Laboratory of Transfer Phenomena and
[9]. It increases the material porosity as well as the specific
Instantaneity in Agro-industry and Building LEPTIAB. Pole of Science and surface area and reduces the diffusion resistance of moisture
Technology; Avenue Michel Crepeau, 17042 La Rochelle Cedex 01 France during the final dehydration step. Such a thermo-mechanical
(email : kallaf@univ-lr.fr).

ISBN:978-988-17012-6-8 WCECS 2009

Proceedings of the World Congress on Engineering and Computer Science 2009 Vol I
WCECS 2009, October 20-22, 2009, San Francisco, USA

treatment also induces microbiological decontamination

[10].
This research was aimed to apply the DIC technology in
the production of cassava flour. The variation of the process
variables i.e. steam pressure/temperature and time of
treatment in DIC reactor will be studied in accordance with
the kinetics of dehydration, the physical properties which
include water and oil holding capacity, and the microbial
decontamination.

II. MATERIALS AND METHODS

A. Raw Material
Freshly harvested cassava roots (Manihot esculenta) were
purchased locally and used in all experiments. After washing
and peeling, the cassava roots were cut into pieces of
16x16x2 mm3.
B. Dehydration Method
Raw and processed cassava pieces were subjected to a   Figure 2. Schematic diagram of global processing
stream of hot air at 50 oC in a hot air dryer (Venticell Dryer).
The cassava pieces were dried until the residual water content
of about 20-25 %wb. was reached before DIC treatment. The
same hot air dryer and conditions were used for initial as well
as for final dehydration.
C. The DIC Reactor
The DIC reactor is shown schematically in Fig. 1. The
reactor consisted of four major components, i.e. (a) the
processing vessel (1.5x10-3 m3 volume), where samples were
placed and treated, (b) the vacuum system, which consisted
mainly of a vacuum tank with a volume 60-fold greater than
the processing vessel, (c) the adequate vacuum pump, and (d)
the pressure-dropping system, which is a pneumatic valve,  
separated the processing vessel from the vacuum tank and
Figure 3. DIC temperature and pressure history: PA and TA are the
could be operated after a high steam pressure treatment and if
steam pressure and temperature respectively in the processing
required before the injection of steam in order to establish an vessel, PV the vacuum tank pressure, TP temperature of product: (a)
initial vacuum in the processing vessel. sample at atmospheric pressure; (b) initial vacuum; (c) saturated
D. The Experiment Procedure steam injection to reach the selected pressure; (d) constant
temperature corresponding to saturated steam pressure; (e) abrupt
The general experimental protocol is detailed in Fig. 2. pressure drop towards vacuum; (f and g) releasing to the
After preparing the raw material, initial partial dehydration atmospheric pressure.
was carried out. This is required pre-treatment before the DIC
processing. The food sample was then treated in the processing vessel
in which a vacuum of 5 kPa was established by a brief
connection with the vacuum tank (Fig. 3-b). The initial
vacuum treatment facilitated the diffusion of steam into the
sample. Consequently, the time necessary for the temperature
of the sample to reach the steam temperature was reduced.
Saturated steam was then introduced into the vessel at a
fixed pressure level (Fig. 3-c) and maintained for a
predetermined time (Fig. 3-d). This step was followed by a
sudden pressure drop (Fig. 3-e). The rapid pressure drop
inside the processing vessel induced a rapid cooling of the
sample which passed in less than one second from 100–144
°C (depending on the steam pressure conditions) to about 30
°C. Treatment ended by a releasing to the atmospheric
Figure 1. Schematic diagram of the DIC reactor: (a) treatment pressure (Figure 3-f & g); as the atmospheric air injection
vessel with heating jacket; (b) vacuum tank with cooling liquid then occurs under vacuum, the air expansion decreased
jacket; (c) vacuum pump; (d) instant pressure-drop valve. further the treated food temperature.

ISBN:978-988-17012-6-8 WCECS 2009

Proceedings of the World Congress on Engineering and Computer Science 2009 Vol I
WCECS 2009, October 20-22, 2009, San Francisco, USA

The equilibrium after the drop in pressure depended on ∂ρ w ⎡ ∂2ρw ⎤

operating conditions: the higher the steam pressure level, the = ⎢ Deff ⎥ (2)
∂t ⎢⎣ ∂r 2 ⎦⎥
higher the equilibrium pressure. The steam generated by
flash vaporization after the decompression produced
micro-texturation, which was closely linked to a complex The effective diffusivity Deff is considered as constant
process of micro-alveolation. This process depended on the because of the constant temperature and homogeneous
difference in temperature between the two thermodynamic structure of the material during drying. Different
equilibrium states, before and after decompression. After mathematical solutions have been proposed for this equation,
treatment the sample was air-dried at 50 °C in convective hot depending on the initial and boundary conditions [15]; in our
air dryer to around 7% wb (7.5% db) moisture content. study, we can adopt the solution given by Crank, according to
Afterward the dried cassava pieces were grounded using a the geometry of the solid matrix [16]; by expressing the
commercial grinder (Philip Grinder) to pass a 200 mesh sieve amount X of water in the solid, equation (2) becomes:
and stored at 25 °C in sealed plastic containers prior to further
analyses. ∞
X − Xe
E. Fundamentals
MR =
X0 − Xe
= ∑ A exp(−q t )
=1
i
2
i

There are four transfer mechanisms which usually (3)

intervene during the drying process [11]; they are: 1). Heat
transfer from outside towards the product surface; the energy where X is the water content dry basis at t, Xe, the amount of
can be generally brought by contact, convection, or radiation. X at equilibrium (tÎ∞) and X0 the value of X at t = 0. For a
2).Heat transfer within the product; the energy is transmitted slab geometry form, Eq. (3) becomes:
by conduction. 3). Water transfer within the product; it is
carried out either in liquid (by various process including ∞ ⎛ (2n + 1)2 π 2 Deff t ⎞
8 1
capillarity and molecular diffusivity; the driving force is the
gradient of water content) and / or vapour phase (the driving
MR = ∑
π n=0 (2n + 1)
2 2
exp⎜−
⎜ 2
4 L0
⎟
⎟
(4)
⎝ ⎠
force is the gradient of the partial pressure of vapour). 4).
Vapour transport from the surface towards outside. Where Deff is the effective diffusivity (m2/s); L0 is the
Energy exchange to the product surface result in constant thickness of slab (m). For long drying period, Eq. (4) can be
rate drying period and proceed in very short time. Then, further simplified to only the first term of series [17]-[18].
especially for biomaterials, during almost overall drying Thus Eq. (4) is written in logarithmic form as follows:
process the water transfer take place within the product that
result in falling rate of drying.
By assuming that external heat and mass transfers do not 8 π 2 Deff t
ln MR = ln − (5)
limit the overall rate operation thanks to adequate air flow π2 4 L20
temperature and velocity, only internal transfers are
considered as controlling the processes [12]. Mounir & Allaf Diffusivities are typically determined by plotting
[13] assumed that, when mass transfer is much slower than experimental drying data in term of ln MR versus drying time
conduction heat transfer within the product, the drying t in Eq. (5), because the plot gives a straight line with a slope
kinetics is controlled by mass transport of water within the as follows:
granule; this is the case of numerous biopolymers. The
process is then described by a first stage of superficial
π 2 Deff
interaction followed by a diffusion Fick-type’s law within the Slope = (6)
material; Allaf’s formulation [14] is generally used: 4L20

ρw G G G ρ
(ν w − ν m ) = − Deff gr ad w (1) F. Water and Oil –Holding Capacity Determination
ρm ρm
Method proposed by J.A. Larrauri [19] was used with
slight modification. Five milliliters of distilled water or
where: commercial
ρw : apparent density of water in the material (kg.m-3), olive oil were added to 0,2 g of dry sample, incubated at 40
ρm : apparent density of dry material (kg.m-3), o
C for 1 h. After centrifugation, the liquid phase was
vw : absolute velocity of water flow within the porous separated
medium (m.s-1). and the residue was weighed. WHC and OHC were
vm : absolute velocity of solid medium (m.s-1). calculated as g water or oil absorbed per g of dry sample,
Deff : effective diffusivity of water within the solid medium respectively.
(m².s-1).
G. Determination of Microbial Content
Mounir & Allaf [11] assumed neglecting effects of The microbial content of the cassava samples were
possible shrinkage, and with the hypothesis of constant analyzed using total plate count method. A ten gram sample
effective diffusivity during drying, Fick’s second law was aseptically blended and serially diluted using peptone
becomes for 1-D: saline water (0.85% NaCl and 0.1% peptone) in test

ISBN:978-988-17012-6-8 WCECS 2009

Proceedings of the World Congress on Engineering and Computer Science 2009 Vol I
WCECS 2009, October 20-22, 2009, San Francisco, USA

tubes. As much as 1 ml of diluted samples in the test tubes model:

was transferred into plate count agar and incubated for 48
hours at 35oC. The colonies formed were counted afterward. 2 2
η = β 0 + ∑ β i x i + ∑ β ii x i2 + β12 x 12
Table 1. Experiment trials with steam pressure P and thermal i =1 i =1
treatment time t expressed in coded and real values.
(8)
Saturated steam High temperature
Trial
pressure processing time
where βo, βi, βii and β12 are regression coefficients and xi are
Coded Real values Coded Real the coded variables linearly related to ξi. The coding of ξi into
No.
levels (MPa) levels values (s) xi is expressed by the following equation:
1 +α 0.54 0 30
2 0 0.40 +α 47.7 ( )
xi = 2 ξ i − ξ i* / d i
3 0 0.40 0 30 (9)
4 +1 0.50 +1 42.5
where ξi = actual value in original units; ξi* mean of high and
5 +1 0.50 -1 17.5 low levels of ξi; and di = difference between the low and high
6 0 0.40 0 30 levels of ξi.
7 -1 0.30 -1 17.5
8 -1 0.30 +1 42.5 III. RESULTS AND DISCUSSION
9 -α 0.26 0 30
A. Moisture Effective Diffusivity ( Deff )
10 0 0.40 -α 12.3
The observed profile of the moisture content change is
11 0 0.40 0 30 presented on Fig. 4. It showed that the experimental data lied
α= 4
2 N , N is the number of independent variables. In the present on curvature profile, which indicated that falling rate drying
case: N=2 and α = 1.4142 mechanism had occurred during the whole drying period. In
such case, water diffusion mechanism would control the
process.
H. Experimental Design and Statistical Analysis To investigate the impact of DIC texturing on the drying
A two variable central composite rotatable design was kinetics, the main parameter had been the water diffusivity
used. Such design needs 13 experiments including 4 within material. Taking the prerequisite assumption, then the
repetition runs at the centre point. The experiments were run effective diffusivity (Deff) was calculated using Eq. (5). For
in random in order to minimize the effects of unexpected the DIC treated cassava, the surface plot of Deff is presented
variability in the observed responses due to extraneous on Fig. 5 and the regression coefficients are showed on Table
factors. For each factor, the experimental range and the 2. Even though the obtained regression coefficients were
central point are based on the results of other preliminary very low, the results showed that the DIC treatment increased
trials. Table 1 lists the independent variables, their symbol, the water effective diffusivity. The reference Deff obtained
and the coded and real factor level. Regression coefficients with conventional drying (drying without inserting DIC
and analysis of variance (ANOVA) are computed using treatment) had been 1.13 x 10-10 m2/s, whereas the Deff values
Minitab-11.12 (Mini Tab Inc., USA) software. in all DIC treated cassava were somewhere higher (1.37 -
The objective is to observe the influence of the process 3.26) x 10-10 m2/s. It indicated that the change in cassava
variables i.e. steam pressure/temperature and time of physical properties, such as capillary and molecular
treatment in DIC reactor on the dependent responses which diffusivity, had occurred during texturing by DIC treatment.
consisted of kinetic of dehydration (effective moisture The higher Deff value due to the texture change is one among
diffusivity) and cassava flour physical properties, including other advantages of DIC treatment application, especially for
water holding capacity (WHC) and oil holding capacity biomaterial products.
(OHC). Since the processing pressure (ξ1) and the treatment
time (ξ2) were set as the design variables, the responses were B. The Water and the Oil Holding Capacity
assumed to be affected by the two independent variables ξi. It The water holding capacity (WHC) and the oil holding
was also assumed that the dependent variables (referred to as capacity (OHC) are the physical properties that indicate the
responses), η, which were experimentally measured, defined capacity of a material to hold water and oil, respectively.
the system, and was formulated as: Both physical properties were very important to be known for
flour or powder food material, as some different food
η = f (ξ1 ,ξ 2 )
powders usually should be blended together to produce a
certain final food product. Then appropriate WHC or OHC of
(7) food raw material becomes an important property.
In this work the effect of DIC treatment on WHC and OHC
The obtained experimental data were analyzed by RSM of the cassava flour was studied. Surface plots were
to fit to the following second-order polynomial presented in Fig. 6 for WHC and Fig. 7 for OHC. The

ISBN:978-988-17012-6-8 WCECS 2009

Proceedings of the World Congress on Engineering and Computer Science 2009 Vol I
WCECS 2009, October 20-22, 2009, San Francisco, USA

increase of the treatment time up to around 30 s resulted in

lower WHC, whereas lengthening the treatment time from 30
s resulted in higher WHC. Increasing the steam pressure did
not affect the WHC significantly. At low steam pressure,
which is less than
4 x 105 Pa, increasing the treatment time up to 30 s resulted in
lower OHC, whereas lengthening the treatment time from 30
s resulted in higher OHC. At high steam pressure, more than
4 x 105 Pa, lengthening the treatment time resulted in higher
OHC.

Pre-Drying Final Drying Figure 6. Surface plot of the water holding capacity

Pre-drying

Final drying
at t = 110 minutes

Conventional
DIC Treatment

Drying

Figure 7. Surface plot of the oil holding capacity

It was also found that texturing by DIC resulted in the

increase of WHC from 1.2 g water/g dry cassava (drying
without DIC treatment) to 2.0-8.0 g water/g dry cassava.
Texturing by DIC also resulted in the increase of the OHC
from 0.4 g oil/g dry cassava (drying without DIC treatment)
to 0.8-2.0 g oil/g dry cassava. The increase of both WHC and
OHC indicated that the texturing by DIC might change the
micro structure of cassava, such as the total pore volume and
the specific surface.

Figure 4. The profile of the moisture content change during pre- Table 2. The regression coefficients
and final-drying.
The The Responses
coefficients Deff WHC OHC
β0 - 1.831 16.067 4.960
β1 1.360 - 2.546 - 1.372
β2 0.097 - 0.473 - 0.076
β11 - 0.173 0.394 0.138
β22 - 0.001 0.008 0.001
β12 - 0.003 0.014 0.007
R2 17.67% 34.53 % 21.81 %

C. The Microbial Decontamination

The observation of the microbial content of treated
cassava showed that no fungi growth was detected in the final
Figure 5. Surface plot of the effective diffusivity product, both for process without DIC treatment and for
process with DIC treatment. This showed that drying at 50 oC
for 4–5 hours has effectively inhibited the fungi growth on
cassava. It would be one advantage compared to producing
cassava flour by sun drying, where fungi growth was usually
found due to the very low rate of drying.
The result of the bacterial content of treated cassava is

ISBN:978-988-17012-6-8 WCECS 2009

Proceedings of the World Congress on Engineering and Computer Science 2009 Vol I
WCECS 2009, October 20-22, 2009, San Francisco, USA

shown in Table 3. In this case DIC treatment was conducted REFERENCES

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ACKNOWLEDGMENT
The authors wish to thank THE ABCAR-DIC PROCESS
SAS, La Rochelle France for providing a set of DIC
equipment.

ISBN:978-988-17012-6-8 WCECS 2009