Advanced Materials Research
ISSN: 1662-8985, Vol. 743, pp 223-226
doi:10.4028/www.scientific.net/AMR.743.223
© 2013 Trans Tech Publications, Switzerland
Online: 2013-08-30
Research on gelatinization process of starch
Chen Xiliang1, a, Shi Qingnan1, b
1
School of Materials Science & Engineering, Kunming University of Science and Technology,
Kunming 650093, China
a
[email protected], [email protected]
Keywords: Gelatinization, Kinetics, Mathematical model, Simulation, Starch
Abstract: Gelatinization is the main transformation of the starch dough undergoing cooking. This
process is very important both for the texture and the nutritional properties of the final product. Starch
gelatinization process has been studied by many workers, which includes the mechanism, kinetics,
and influencing factors. The kinetic models have been used by works to predict the cooking process of
starch. Finite element method (FEM) is commonly used in the simulation of starch gelatinization
process. The simulation results can predict the cooking process of starch, and are helpful for
optimizing the cooking conditions of starch dough. The theoretical and numerical simulation research
on gelatinization of starch is reviewed, and the progress and difficulties in this field are discussed.
1. Introduction
Starch is a carbohydrate consisting of a large number of glucose units joined by glycosidic bonds
[1-3]. It is the most common carbohydrate in the human diet and is contained in large amounts in such
staple foods as potatoes, wheat, maize, rice, and cassava. Studies on the starch gelatinization process
have been carried out both to answer fundamental questions and to obtain a better technological use of
this major carbohydrate in animal and human nutrition: gelatinized starch can be degraded by the gut
amylase whereas the ungelatinized fraction undergoes a much slower metabolism and can remain
almost totally undigested [4-5].
The research on starch gelatinization mainly concentrates in the following aspects.
(1) The starch gelatinization mechanism.
(2) The kinetics of starch gelatinization process.
(3) The simulation and prediction of starch gelatinization process.
Resent theoretical, experimental and numerical simulation researches on the three aspects are
discussed respectively in the following sections.
2. Gelatinization mechanism
Starch granule has the characteristic birefringent pattern [6-8]. At the temperature of
gelatinization the granules lose their birefringence and X-ray diffraction pattern, this process is known
as gelatinization [9-12]. The course of gelatinization depends on the structure of starch which is
composed of two kinds of molecules, amylose and amylopectin. The former is essentially linear
molecule, and the latter is branched molecule. Amylopection molecules are oriented perpendicular to
growth rings and to the outer surface of the granule. Portions of amylopectin molecules are in
crystallites, which are perpendicular to the growth rings. The regular orientation of the amorphous and
crystalline regions gives the granule the characteristic birefringent pattern. The non-crystalline
regions consist of the amylose molecules and sections of amylopectin molecules which are not
involved in crystallites. Small-angle neutron scattering (SANS) was used to analyze the structure of
starch, which revealed that starch granules contain three regions, namely semicrystalline regions
containing alternating crystalline and amorphous lamellae, which are embedded in a matrix of
amorphous material [13].
The gelatinization process is described by an endothermic transition, which is observed by
differential scanning calorimetry (DSC). At high water-starch ratios, water penetrates the amorphous
regions and makes the granules swell. The swelling of the amorphous regions of the granule strips
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Building Materials and Structural Engineering II
starch chains from the surface of the ordered crystallites. If sufficient water is present, all the
crystallites can be pulled apart by the swelling, the low temperature endothermic peak is the only one
observed. If water content is lower than a certain ratio, the remaining crystallites melt at significantly
higher temperatures and a second endothermic peak can be observed [13]. The damage of the
crystallites makes the granules lose their birefringence and X-ray diffraction pattern, which is known
as gelatinization.
3. Kinetic equations
In recent years, the kinetic analysis of starch gelatinization has received much attention, for the
aim of extracting the maximum relevant information from the thermal analysis data, and making
some predictions concerning extrapolated values of degree of reaction.
The rate of reaction can be described in terms of two functions, k (T ) and f (α ) , as follows
[9-13]
d(α )
= k (T ) f (α )
(1)
dt
Where α denotes the degree of gelatinization, T the temperature in degrees kelvin, f (α ) the kinetic
model, k (T ) the rate constant.
k (T ) can be expressed by the Arrhenius equation, as follows
 E 
(2)
k (T ) = A exp

 RT 
Where A denotes the pre-exponential factor, E the activation energy, R the gas constant.
By substitution Eq. 2, Eq. 1 is expressed as follows
d (α )
 E 
(3)
= A exp
 f (α )
dt
 RT 
The f (α ) in Eq. 3 represents the mathematical expression of the kinetic model, some of the
most cited basic kinetic models are listed in Table 1 [13].
Table 1. Comonly used basic kinetic models [13]
Model
f (α )
(1-α)
Random nucleation. Unimolecular decay law
Reaction nth order
(1-α)n
Sestak-Berggren
αm(1-α)n
Johnson-Mehl-Avrami
n(1-α)[ln(1-α)1-1/n]
Two-dimensional growth of nuclei (Avrami equation)
2(ln(1-α)1/2)(1-α)
3(ln(1-α)2/3)(1-α)
Three-dimensional growth of nuclei (Avrami equation)
One-dimensional diffusion
1/2α
Two-dimensional diffusion
1/(ln(1-α))
Three-dimensional diffusion (Jander equation)
(3(1-α)2/3)/(2(1-(1-α)1/3))
Three-dimensional diffusion (Ginstling-Brounshtein)
3/2((1-α)-1/3-1)
There are many different views on the starch gelatinization kinetic models.
(1) Some researchers considered that the kinetic model f (α ) is first order, f (α ) = 1 − α ,
especially in the earlier research [14]. Then Eq. 3 can be transformed as
d (α )
 E 
(4)
= A exp
(1 − α )
dt
 RT 
In Eq. 4, the values of A and E vary with the water content in starch granules. However, the
value of E is a constant even if the heating rate changes.
Advanced Materials Research Vol. 743
225
(2) Some researchers consider that the kinetic model f (α ) is nth order [15], then Eq.3 can be
considered as
d (α )
 E 
n
(5)
= A exp
(1 − α )
dt
 RT 
In Eq. 5, the values of of n and E vary with the water content in starch granules and heating
rate.
(3) Another view is that the kinetic model f (α ) is not invariable, the reaction is two-step,
corresponding to two different kinetic models. The first step is the nth order reaction, f (α ) = (1 − α ) ;
the
second
step
is
the
three-dimensional
diffusion
of
Jander’s
type,
13
23
f (α ) = 3 1 − α
2 1 − (1 − α )
[13].
On the basis of these kinetic models, the gelatinization process of starch can be numerically
analyzed.
n
(
)((
))
4. Simulation research
Gelatinization is the main transformation of starch dough undergoing cooking. This process is
very important both for the texture and the nutritional properties of the final product. Hence, the
prediction of gelatinization degree is important for the cooking process.
Finite element method (FEM) is a commonly used numerical method to simulate the temperature
field during the gelatinization process of gelatin [16-20]. Computational fluid dynamics (CFD) is
used to model the entire bread baking process [18-20]. Chhanwal et al. [20] used the FEM to simulate
the baking process of starch dough by commercial software COMSOL Multiphysics. The
gelatinization kinetic model used in their simulation is the first order, i.e. f (α ) = 1 − α .
The gelatinization process of starch can be simulated by FEM. It is helpful for predicting the
gelatinization degree at any time and any position in the starch. However, more works should be
undertaken listed as follows.
(1) Improvement of the models. More modeling work should be down including mass transport
and volume expansion during starch cooking process.
(2) Optimization of gelatinization process. FEM has been used in predicting the gelatinization
process of starch, and provides an effective method to optimize the cooking conditions.
5. Conclusions
The experimental, theoretical and numerical simulation research on starch gelatinization process
is reviewed, mainly focus on three aspects: the gelatinization mechanism, the kinetic models, and the
simulation of starch gelatinization process by FEM.
Numerical simulation is used in the study of starch gelatinization process from a different aspect,
which is helpful for controlling and optimizing starch cooking process according to certain
requirements.
Improvement of mathematical models of cooking process of starch is necessary. More modeling
work should be down including mass transport and volume expansion during starch cooking process.
Acknowledgements
This work is supported by the Natural Science Foundation of Yunnan Province, China
(KKSA201151077) Program.
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Building Materials and Structural Engineering II
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