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Food Reviews International
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/lfri20
Starch Extraction and Modification by Pulsed
Electric Fields
Luís M. G. Castro, Elisabete M. C. Alexandre, Jorge A. Saraiva & Manuela
Pintado
To cite this article: Luís M. G. Castro, Elisabete M. C. Alexandre, Jorge A. Saraiva & Manuela
Pintado (2021): Starch Extraction and Modification by Pulsed Electric Fields, Food Reviews
International, DOI: 10.1080/87559129.2021.1945620
To link to this article: https://doi.org/10.1080/87559129.2021.1945620
Published online: 10 Jul 2021.
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3. increased potential of their functionality. [3,10–13]
However, the physical modification technologies are
gaining more and more attention by the food industry since chemical reagents are not used to change
starch properties and there is no alteration of α-D-glucose residues. In this way, these new starches do
not need to be called modified and as they are intended for human consumption, physical modifica
tion techniques are preferred by consumers over chemical modification. Besides, these techniques are
simple to execute, safer, easier to operate, sustainable and environmental-friendly. [7,14–16]
Several
emergent technologies can be used for physical modification of starch, such as high pressure,
ultrasound and pulsed electric fields. [14,17]
Pulsed electric fields (PEF) technique is defined as a non-
thermal food processing technology that consists in the application of short-duration electric pulses
(nano to milliseconds) with electric fields intensities up to 80 kV/cm. It is a very versatile technique
that has shown potential to physically modify the native properties of starch from different sources.
[18–26]
In addition, when the intensity of the electric fields used is greater than 20 kV/cm, this technique
has the potential to be a substitute for the conventional thermal processing to inactivate pathogenic
and spoilage organisms at lower temperatures, while maintaining the sensorial and nutritional
characteristics of food products. [27,28]
The purpose of this review is to provide a more detailed and correct understanding of the
application of PEF technology to extract and modify starch properties. The PEF principles, funda
mentals, and working systems will be firstly explained and then the potential of PEF to extract starch
will be discussed. Next, the starch modification will be detailed and explored. After this, it will be
discussed how the properties of starch are changed by PEF. Finally, the economic feasibility of PEF will
be exploited and, the main conclusions and some future perspectives will be described.
2. Principles, fundamentals, and working systems
The essential components of a PEF system are the pulse generator and the treatment chamber
(Figure 1). High-voltage alternating current is converted into direct high-voltage energy (electrical
current that propagates in a single direction) by a pulse generator to be used by a PEF system. Once
converted, this energy is stored in the condenser from which electrical pulses are produced through
rapid discharges of electrical energy in the treatment chamber between the two electrodes. The
discharges are controlled by a switch, which is the most critical component since it must turn on/off
the circuit at high voltages and current in a fraction of microseconds. A pulse transformer is used to set
up the condenser when the voltage is insufficient. The discharges create an electric potential
Switch
Chamber
Condenser
Pulse Generator
Battery
a b
Figure 1. PEF system (A) and a simplified representation of the PEF electrical circuit (B).
2 L. M. G. CASTRO ET AL.
4. V
(A)
V
(A)
t
(μs)
t
(μs)
t
(μs)
t
(μs)
a b
c d
Figure 2. Different PEF pulses shapes: (A) Monopolar square-wave; (B) Monopolar exponential; (C) Bipolar square-wave; (B) Bipolar
exponential.
a
b
c
PRODUCT FLOW
Figure 3. Schematic representation of the electric field of the parallel (A), co-axial (B), and colinear (C) configurations.
FOOD REVIEWS INTERNATIONAL 3
5. differential, leading to the formation of the electrical pulses and, consequently, of the electrical pulse
fields. The material to be processed is also placed in the treatment chamber between the electrodes.
[29,30]
The generated pulses by the PEF system can be unipolar or bipolar if one or two pairs of electrodes
are used during treatment, respectively, but they are also classified according to the shape as square-
wave, where the applied voltage is kept constant at the maximum value for a certain time (the pulse
width) after which the voltage suddenly decreases, or as exponential, where the maximum voltage
initially applied decays exponentially over time. In this case, the pulse width is defined as the time
required for the voltage to drop to 37% (Figure 2). This difference in geometry makes square wave
pulses more advantageous, as they deliver more energy than exponential ones. For this reason, bipolar
square wave pulses are the most used in food processing. [24,31,32]
Depending on the configuration of the electrodes, the chamber will have different geometries. In
the parallel configuration, the chamber is parallelepipedal and the electrodes are on opposite sides
(Figure 3A). This allows the electric field to be uniform and the product flow has a direction
perpendicular to the electric field. To achieve an acceptable uniform electric field, the chamber length
should be superior to the one between the electrode due to the decrease of impedance (the measure
ment of the opposition that the circuit has to the current when the voltage is applied) with the chamber
length. However, the large electrode surface and low electrical resistance may lead to electrode
corrosion in the electrode-flow interface at high currents. It is advantageous to operate symmetrically
to the ground to prevent current leak. The coaxial configuration consists of two cylindrical electrodes,
being the positive pole surrounded by the negative (Figure 3B). As in the parallel configuration, the
product flow has a perpendicular direction to the electric field. Despite being easy to build and
allowing for greater homogenization, the electric field is not uniform along the column. This can be
standardized by manipulating the diameters, but this could decrease the impedance by increasing the
surface area of the electrodes, making this configuration only suitable for low-conductivity loads. In
the collinear configuration, the chamber has a tubular shape with the electrodes adjacent to each other
and separated by an insulating material (Figure 3C). This facilitates the dynamic of fluids, is very
desired for food processing, it is easy to clean and has a high resistance due to the reduced cross-
section area. When compared to the parallel configuration, multiple co-linear unities can be connected
and operated at a lower current, which limits the reaction of the electrodes. However, the electric field
and temperature are unevenly spread in the chamber.[32–34]
Treatments can be done in batch or
continuous mode. Batch treatments can be considered static and allow the use of reduced volumes of
solid and/or semi-solid samples. For this reason, they are more commonly found in experimental
studies and are more advantageous in the laboratory environment since allows to have strict control of
the parameters. However, systems that do not provide agitation can result in a certain portion of the
volume not being treated properly. In the case of continuous treatments, which are more suitable for
processing liquids and are easily integrated into industrial processes, the lack of agitation can be
avoided through multiple treatment zones inline or flow channels. Generally, the parallel chambers are
used in batch systems, whereas the coaxial and collinear chambers are more used in continuous
systems, where the sample is pumped at a known flow rate and the pulses are applied at a known
frequency. [35,36]
The phenomenon that governs PEF is called electro-pulsation, i.e., the exposure of cells to electric
pulses, which lead to alterations on the cell membranes, increasing the permeability and/or conduc
tivity. When a cell senses an external electric pulsed field, a variation in the difference between the
electric voltage of the intra and extracellular media in normal physiological conditions (basal trans
membrane potential) is induced, being its effects dependent on the duration and intensity of the
electric field. The most common effect is characterized by the formation of unstable metastable
hydrophilic pores in the bi-phospholipid membranes by water molecules, thus leading to an induced
increase permeability for molecules without mechanisms of transmembrane transport. [37]
However,
the membrane conductivity and permeability only increase considerably when a minimum value of
transmembrane potential (non-universal value and dependent on multiple factors) is reached. As long
4 L. M. G. CASTRO ET AL.
6. this value is maintained, the changes in permeability and conductivity are maintained. When the
electric field is removed, the value of the transmembrane potential is less than the minimum
previously reached, both conductivity and permeability decrease to a stable and detectable level
allowing diffusion of ions and small molecules. Some alterations on the physiological cellular processes
and reactions to stressors can still be exhibited after resealing of the membrane before the cell returns
to the native state. Then, the membrane recovers gradually to its native conditions if no damages were
created and the cellular viability should be preserved. [37–39]
3. Potential to obtain starches
Starch and proteins are naturally formed simultaneously in the endosperm or cotyledons, with the
starch granules involved in a continuous proteinaceous matrix. These proteins can be classified into
storage proteins, which are the proteins that are adsorbed on the surface of the starch granules after the
extraction of the granules, and in granule-associated proteins. These are biologically different from
storage proteins, have a large amount of basic and hydrophobic amino acids, and are strongly linked to
the surface and/or integral components of starch granules. However, “true” granule-associated
proteins are defined as those proteins that are found on the surface or inside the granules or in both
places and can be classified according to the molecular weight in surface or internal granule-associated
proteins. [40,41]
Because surface proteins are inefficiently removed with saline solutions and the
extraction of internal proteins requires gelatinization of starch granules. However, to guarantee that
extracted starch maintain economic value, it must be isolated without significant alterations of the
starch granule. Prabhu et al. [42]
studied the use of PEF to extract starch from the macroalga Ulva ohnoi
coupled with biomass fractionation into protein and ash. An alga suspension was treated by PEF and
then the thalli were resuspended in water, agitated, and filtered to collect the starch-containing
biomass. The starch was further collected and dried. The conductivity of the PEF supernatant was
69.84% higher than the control, indicating that treatment affected membrane permeability allowing
the removal of salts and ions from the algae cytosol (p<0.05). After PEF treatment, more protein and
ash (14.94 and 68.52%, respectively) was effectively extracted out of the initial biomass to the super
natant in relation to the control (3.16 and 46.67%, respectively) (p<0.05). Duque et al. [20]
studied the
effect of PEF treatment on the physical and functional properties of oat flour. The raw oat flour used
consisted of milled intact raw oat groats, while the thermally processed oat flour was composed of
kilned (115ºC for 30 min), steam-cooked (18 min at 100-104ºC), rolled, and milled raw oat groats as
performed in the industry. It was verified that the PEF treatment altered the secondary structure of
proteins by converting the α-helixes into β-sheets, promoting the unfolding and/or re-assembly of the
proteins. The absence of starch in the supernatant of all samples could be explained by the size of the
pores created, witch difficulted the release of starch from the matrix but allowed the passage of other
components such as protein, minerals, and ions. The PEF treated biomass had less ash than the
control, while the protein and starch contents were significantly higher than the control and original
biomass. Furthermore, the starch extraction yield and starch purity on PEF-treated biomass were
59.54 and 53.05%, respectively, while in the control were 52.31 and 59.40%, respectively. Therefore, the
usage of PEF can lead to the increase of starch yield by removing other cellular constituents such as
proteins and ash. Such a decrease in purity could have been caused by damages induced to the
cellulose of cell walls and cytoskeleton. These results show a new potential to use PEF as an emerging
pre-treatment technique to improve starch extraction. However, more research needs to be carried out
to evaluate its potential applied to other matrices such as vegetables, fruits, roots and tubers, and
cereals rich in starch and optimize the treatment conditions to obtain starches with higher purity.
4. Ability to modify starch properties
The native starch properties can be modified by PEF. Initially, a starch suspension is prepared with
deionized water at 25ºC and the electric conductivity is adjusted between 50 and 200 μS usually with
FOOD REVIEWS INTERNATIONAL 5
7. Table 1. Treatment conditions by pulsed electric fields.
Suspension (w/
w) PEF system
EFI (kV/
cm)
SEI (kJ/
kg)
σ (μS/
cm)
τ
(μs) P (nº) t (μs) f (Hz) T (ºC) Reference
Wheat starch
(-)
Potato
starch (-)
Pea starch (-)
— 2.86-
8.57
2.86-
8.57
2.86-
8.57
— — 6
6
6
— — 600
600
600
— Li et al. [25]
Li et al.
[25]
Li et al.
[25]
Rice starch (40
g)
- 2.86-
8.57
- - 6 - - 600 - Wu et al.
[19]
Potato starch
(8%)
Bench-scale continuous
Unipolar square-wave
pulse
Two parallel copper
electrodes
Pumping flow: 60 mL/
min
30-50 - 200 40 20.16 806 1008 <50 Han et al.
[22]
Corn starch
(8%)
Bench-scale continuous
Bipolar square-wave
pulse
Two parallel copper
electrodes
Pumping flow: 60 mL/
min
30-50 - 200 40 - - 1008 <50 Han et al.
[24]
Tapioca starch
(8%)
Bench-scale continuous
Bipolar square-wave
pulse
Two parallel copper
electrodes
Pumping flow: 60 mL/
min
30-50 - 150 10 21.37 214 1000 <50 Han et al.
[21]
Waxy rice
starch (10%)
Bench-scale continuous
Bipolar square-wave
pulse
Two parallel copper
electrodes
Pumping flow: 60 mL/
min
30-50 - 50 40 - - 1000 40-
45
Zeng et al.
[26]
Maize starch
(8%)
Bench-scale continuous
Bipolar square-wave
pulse
Pumping flow: 60 mL/
min
30-50 - 150 10 20.16 424- 1272
1000 <50 Han
et al.
[23]
Potato (1:1) Batch treatment
Two parallel stainless-
steal electrodes
0.5
0.7
0.9
1.1
0.7
0.9
58.48
49.25
49.63
50.10
151.81
153.09
1610 20 900-
6250
- 100 - Abduh
et al. [18]
Oat flour (8%)
(Raw)
Batch treatment
Two parallel stainless-
steel electrodes
Bipolar square-wave
pulse
2.2
2.1
2.1
4.4
4.3
4.1
53
249
484
51
220
441
305
303
309
308
305
307
20 1458
5000
7778
307
1029
1628
- 100 - Duque
et al. [20]
Oat flour (8%)
(Thermally
treated)
Batch treatment
Two parallel stainless-
steel electrodes
Bipolar square-wave
pulse
2.2
2.1
2.1
4.4
4.3
4.1
49
233
434
48
200
418
348.25
355.70
355.30
355.10
358.22
358.00
20 1250
4118
6364
261
854
1400
- 100 - Duque
et al. [20]
Abbreviations: EFI: Electric field intensity; SEI: Specific energy input; σ: conductivity; τ: Pulse width; P: pulse number; t: treatment
time; f: frequency; T: Temperature.
6 L. M. G. CASTRO ET AL.
8. a KCl solution. Next, the suspension is mixed and pumped into the PEF chamber to be treated at the
desired conditions (Table 1). Despite the treatment conditions change significantly according to the
starch modification property desired and according the starch source, the intensity of the electric field
usually range between 2.86 and 50 kV/cm, the treatment time range between 214 and 1272 μs and the
frequency used varies between 600 and 1008 Hz. The pulse duration ranges change between 6 and 40
μs and the pulses applied are usually between 20.16 and 21.37 μs. After treatment, the suspensions are
cooled to the room temperature, vacuum filtered, dried at 40ºC and stored. According to the Joule
effect, the passage of an electric current through a conductive material generates heat, which is directly
proportional to the square of the intensity of the electric current, causing the temperature to increase
during the treatment.[32,43,44]
When the temperature reaches 60ºC or more, the starch may gelatinize
and a water bath is usually used to keep the temperature below 50ºC preventing gelatinization
process.[22–24,45]
On the other hand, the increase in temperature leads to an increase in conductivity,
which is influenced by the ionic strength of the suspension. If the conductivity is very low (non-
conductive suspension medium), the induced transmembrane potential will be too low. However, high
conductivities are not desirable for PEF treatment since only small electric fields can be created.
[32,46,47]
According to the literature, conductivity is maintained between 50 and 200 μS/cm. If the
conductivity is too low, it must be corrected with a KCl solution, a reference certificate material in the
conductivity calibration. [47]
If the conductivity is too high, sludge can be washed and centrifuged. [26]
4.1. Granule morphology and particle size
The different arrangements of the amylopectin chains in the granule cause starch to have different
polymorphisms. The type A polymorphism is formed by six double amylopectin chains, while type
B has seven chains. Type C is a mix between type A and B. [48]
Li et al. [25]
evaluated the effect of PEF on
the granular morphology of starches with different polymorphisms and reported that the morphology
of wheat (type A), potato (type B), and pea (type C) starch granules were not damaged by PEF
treatment from 2.86 to 8.57 kV/cm. However, Wu et al. [19]
observed sunken areas on the PEF-treated
rice starch granules (type-A) subjected to the same electric field intensities, and fractures were also
seen at the highest intensity used (8.57 kV/cm). These results may indicate that the damage caused by
using low electric field strengths may be dependent on the botanical origin of the starch. The damages
on granular morphology appear to be more evident when a higher electric field intensity order is used
independently of the starch polymorphism. Zeng et al. [26]
treated waxy rice (type A) starch using
intensities from 30 to 50 kV/cm and verified that the damages to the granules increased with the field’s
intensity. Native starch granules had an irregular shape and the surface of some granules was rough
when treated at 30 kV/cm. At 40 kV/cm, some pits were observed, as well as aggregation due to surface
adhesion between the starch granules. After the 50 kV/cm treatment, some starch granules were
twisted and flocked. Similar results were reported for corn (type A), potato (type B), and tapioca (type
A) starches.[21,22,24]
Such alterations of morphology suggest that the granules structure was altered
after the PEF treatment.
Regarding the particle size (Table 2), Han et al. [24]
evaluated the effect of PEF on the particle size
distribution of corn starch granules and observed an increase of the mean volume diameter of the PEF
treated granules, when compared to the native. However, the granular particle size at which 90% of
granules were smaller by volume (D90) increased significantly at 40 and 50 kV/cm, i.e., the granular
size increased. These results indicate that the treatment damaged the granule outer part and the inner
part could have absorbed more water and swells after treatment. Consequently, occurs granular
aggregation due to the strengthening of the van der Waal’s and electrostatic forces between the
granules. Similar results were reported for potato starch. [22]
Recently, Duque et al. [20]
also verified
a significant increase on the particle size of the raw oat flour at D10 and D50 and for the thermally
processed flour at a D10 due to the aggregation of the starch granules regardless the electric field
intensity used (~2 or ~4 kV/cm) at the highest specific energy input, indicating that the thermally
processed flour was less susceptible than raw flour due to the thermal pretreatment. It was also verified
FOOD REVIEWS INTERNATIONAL 7
9. that the secondary structure of the protein associated with the oat starch granules was altered during
the PEF treatment, indicating that the changes on these proteins during the treatment could have been
partially responsible for such aggregation.[49]
4.2. Birefringence and X-ray diffractometry
The amylopectin present in the crystalline regions have a radial arrangement from the helium of the
starch granule to its surface. The Maltese crosses appear when polarized light crosses this arrangement,
being this phenomenon named birefringence. [50]
Li et al. [25]
evaluated the effect of the electric field
intensity from 2.86 to 8.57 kV/cm on wheat, pea, and potato starches with different polymorphisms.
Under polarized light, the birefringence did not vary significantly at lower electric fields (2.86 to 5.71
kV/cm), indicating that the arrangement of amylose and amylopectin was not significantly disturbed.
Abduh et al. [18]
also did not report changes on the birefringence of potato starch granules treated in
the range of 0.5 to 1.1 kV/cm at the specific energy input of 50 and 150 kJ/kg. However, when Li et al.
[25]
applied higher electric field intensities (7.14 and 8.57 kV/cm), the Maltese crosses of the wheat
Table 2. Particle size distribution results of the PEF-treated starches.
Suspension
EFI
(kV/
cm)
SEI
(kJ/
kg)
D4,3 (μm)
PEF/Native
D3,2 (μm)
PEF/
Native
D10 (μm)
PEF/Native
D50 (μm)
PEF/Native
D90 (μm)
PEF/Native
SSA (m2
/
g)
PEF/
Native Reference
Corn 30
40
50
— 23.65/15.22
27.74/
15.22
29.68/
15.22
9.46/7.37
10.15/
7.37
10.47/
7.37
8.18/7.40
9.28/
7.40
10.47/
7.40
18.54/14.89
22.77/
14.89
23.60/
14.89
44.29/24.22
53.80/24.22
58.81/24.22
0.63/0.81
0.59/
0.81
0.57/
0.81
Han et al.
[24]
Potato 30
40
50
— 56.11/37.93
85.16/
37.93
113.8/4/
37.93
16.80/
16.67
22.95/
16.67
24.91/
16.67
16.93/
16.12
19.16/
16.12
21.79/
16.12
38.14/35.76
46.17/
35.76
51.14/
35.76
89.74/63.68
231.41/
63.68
341.96/
63.68
0.36/0.36
0.26/
0.36
0.24/
0.36
Han et al.
[22]
Oat flour
(Raw)
2.2
2.1
2.1
4.4
4.3
4.1
53
249
484
51
220
441
———— ———— 6-7/7-8
7-8/7-8
24-30/
7-8
7-8/7-8
7-8/7-8
22-27/
7-8
23-30/23-33
22-31/23-
33
93-108/23-
33
29-34/23-
33
32-34/23-
33
85-123/23-
33
64-298/331-
451
43-370/331-
451
244-403/
331-451
234-365/
331-451
341-358/
331-451
295-412/
331-451
———— Duque
et al. [20]
Oat flour
(Thermal
treated)
2.2
2.1
2.1
4.4
4.3
4.1
49
233
434
48
200
418
———— ———— 14-15/12-
14
16-20/
12-14
33-46/
12-14
13-15/
12-14
11-18/
12-14
30-57/
12-14
150-192/82-
257
106-238/
82-257
146-213/
82-257
151-213/
82-257
91-206/82-
257
102-255/
82-257
889-914/565-
1299
871-955/
565-1299
213-931/
565-1299
904-939/
565-1299
639-918/
565-1299
226-925/
565-1299
———— Duque
et al. [20]
Abbreviations: EFI: Electric field intensity; SEI: Specific energy input; D4,3: Volume mean diameter (De Brouckere diameter); D3,2: Area
mean diameter (Sauter diameter); D10: size of the particle below which 10% of the sample lies; D50: size of the particle which 50% of
the sample is smaller and 50% is larger; D90: he size of the particle below which 90% of the sample lies; SSA: Special surface area;
PEF/native: PEF treated vs native starch.
8 L. M. G. CASTRO ET AL.
11. (type A) and potato (type B) starch granules faded, while no alterations were observed on pea starch
(type C). This suggests that starches from type A and B can be more susceptible to PEF treatment than
type C. PEF treatment can cause changes in the radial arrangement of amylopectin in the crystalline
zones, leading to losses of the Maltese crosses and consequently birefringence, depending on the
polymorphism of the starch but also on the intensity of the applied electric fields. Wu et al. [19]
used
intensities from 2.86 to 8.57 kV/cm to treat rice starch (type A) granules, but possible changes on the
Maltese crosses were not possible to observe due to the very small diameter of rice granules (3-8 μm).
The diffraction methods such as X-ray diffractometry (XRD) are the only method available to
quantify the long-range crystalline order,[51,52,53]
and some studies have been applied on starch as
depicted in Table 3. Li et al. [25]
evaluated the effect of PEF treatment from 2.86 to 8.57 kV/cm on
starches with different polymorphisms, namely wheat (type A), potato (type B), and pea (type C)
starches. No significant changes were observed on the diffraction peaks, indicating that crystalline
morphology variations caused by PEF treatment were small. In general, the relative crystallinity values
of starches treated with lower electric field intensities (2.86 to 5.71 kV/cm) appear to be slightly higher
than those treated at higher intensities (7.14 and 8.57 kV/cm) when compared to the native starch,
which correlates with the differences in birefringence observed previously. These results indicate that
during treatment the amylose chains could have been reorganized at lower field intensities, leading to
an increase of relative crystallinity. At higher field intensities, the treatment could have disrupted the
starch chain arrangements, namely hydrogen bonds between the amylopectin chains in the crystalline
regions. Once these bonds are disrupted, the relative crystallinity decreases and consequently occurs
a loss of birefringence (Maltese crosses) under polarized light. [50]
These results are similar to the
findings obtained by Wu et al. [19]
for rice starch treated from 2.86 to 8.57 kV/cm. For higher electric
field intensities, Zeng et al. [26]
treated native waxy rice starch verifying that the relative crystallinity
decreased with the increase of the electric field intensity from 30 to 50 kV/cm. Additionally, the
diffraction peaks intensity at 15.3, 17.1, 18.2, and 23.5° also decreased with the increase of the field
intensity. These results are in agreement with the findings reported for tapioca, corn, and potato
starches. [21,22,24]
The higher the electric field intensity is, the more energy is provided during the PEF
treatment to disrupt the non-covalent bonds between the starch chains and, at the same time, promote
the interaction between the water molecules and the hydroxyl groups of the starch molecular chains.
This leads to a transformation of starch granules from crystal into non-crystal. [23]
The decrease of
crystallinity can be a consequence of the disruption of the amylopectin crystallites that form it. [53]
During the literature revision, it was noticed that the percentage of amylose of the analyzed starches
was never reported. Knowing that the amylose content can have a significant effect on starch
polymorphism,[54]
it is suggested that such information should be included and reported from now
on. [50]
4.3. Small-angle X-ray scattering, Fourier transform infrared spectra, and nuclear magnetic
resonance
The lamellar architecture of starch can be characterized and studied by small-angle X-ray scattering
(SAXS) (Table 3). Starch granules are formed by amorphous rings alternating with semi-crystalline
rings. While the amorphous rings are made up of disorganized amylose and amylopectin, the semi-
crystalline rings are formed by an alternating lamellar structure of crystalline regions and amorphous
regions with a regular repetition distance between 9 and 10 nm. [48]
Li et al. [25]
studied the effect of the
PEF treatment on the semi-crystalline lamellae thickness of starches with different polymorphism,
namely wheat (type A), potato (type B), and pea (type C) starches. No significant differences were
found for wheat, indicating that no changes were induced in the semi-crystalline lamellae thickness.
However, significant differences were found for pea and potato starches at 2.86 and 5.71 kV/cm
treatments, respectively. The scattering peak position for pea decreased from 0.912 to 0.597 nm−1
and
for potato increased from 0.669 to 0.683 nm−1
. These alterations led to an increase of 0.285 nm of pea
lamella repeating distance and a decrease of 0.193 nm of potato when compared to the corresponding
10 L. M. G. CASTRO ET AL.
12. native starches. For waxy rice starch (type A), Zeng et al. [26]
reported that the lamella repeating
distance of starches treated by PEF increased with the PEF intensity. The native starch had a lamella
repeating distance of 8.89 nm, but when the 30, 40, and 50 kV/cm electric field intensities were applied,
the distance increased to 8.93, 9.56, and 9.63 nm, respectively. Contrarily, Wu et al. [19]
verified that the
treated lamella repeating distance of the PEF treated rice starches (type A) decreased significantly with
the increased PEF intensity from 2.86 to 8.57 kV/cm. These results indicate that the PEF treatment can
differently affect the lamella repeating distance of starches from different botanical origins.
The bands of the Fourier transform infrared spectra (FTIR) spectra at ~1047 and ~1022 cm−1
can
be used to detect changes in the crystallinity and amorphous regions of starch granules. For this
reason, the intensity ratio A1047/1022 has been extensively used to acquire information on the crystal
linity of short-range molecular order and the double-helix packing within the inner granule structure.
Nuclear magnetic resonance (NMR) has been used for direct quantification of the proportion of
double-helices of the short-range order based on the C1 and C4 positions. [52]
In Table 3 are presented
the studies about the measurement of the short-range double-helical order of native and PEF treated
starches using FTIR spectra and NMR analysis. Han et al. [23]
reported no significant effects on the
maize starch chemical structure when treated at 50 kV/cm using 1
H and 13
C NMR spectra. Li et al. [25]
analyzed the infrared spectra of the wheat, potato, and pea starches treated from 2.86 to 8.75 kV/cm
and verified that the A1047/1022 intensity of the potato starch had a bigger variation than the pea and
wheat starches. The 13
C NMR spectra revealed that the order structure of the wheat (type A) and
potato (type B) starches decreased 0.7 and 1.6%, respectively, when treated at 8.75 kV/cm compared to
the native starch, while an increase of 4.5% was observed for pea starch (type C). Such a decrease
indicates that the ordered (crystalline) structures were disrupted, which may have been due to the
break of hydrogen bonds. Wu et al. [19]
also reported a significant decrease in the A1047/1022 intensity of
the waxy rice (type A) treated at 8.75 kV/cm. It can be inferred that PEF treatment changes the order
structure of all starch polymorphisms, but the changes are more severe for the type B. Duque et al. [20]
treated raw and thermally processed oat flour with PEF and reported that the A1047/1022 intensity of the
oat raw flour decreased significantly when compared to the control after being treated at 4.1 kV/cm
and 441 kJ/kg. These results indicate that PEF induced disruption of the short-range crystallinity, thus
altering the starch structure. In the case of the thermally processed oat flour, no significant changes on
the A1047/1022 intensity were found after PEF treatment.
It can be seen that the relative crystallinity values determined by X-ray diffraction are substantially
lower than the proportion of double-helices determined by RMN analysis (RMN structure order).
These differences indicate that there is a percentage of double chains of amylopectin that is not
quantified by the X-ray diffraction. [55]
4.4. In-vitro digestibility and molecular weight
In-vitro digestibility starch studies have great importance since they can predict the glycemic response
in in-vivo systems. The most used and reliable technique is still the Englyst method. [56]
In Table 4 are
presented the studies about the in-vitro digestibility of native and PEF treated starches. Li et al. [25]
evaluated the effect of PEF treatment from 2.86 to 8.57 kV/cm on the digestibility of starch with
different polymorphisms, namely wheat (type A), potato (type B) and pea (type C) starches. In general,
the treated starches had a significant increase in rapidly digestible starch and a decrease in slowly
digestible starch, while the resistant starch content remained unchanged when compared to the native
starches. These results are in agreement with those reported by Wu et al. ,[19]
who treated rice (type A)
starch from 2.86 to 8.57 kV/cm. Zeng et al. [26]
also documented similar results for waxy rice starch,
despite the decrease in the resistant starch content. The different types of polymorphism do not appear
to be a possible explanation for such results. However, it remains plausible to think that due to the
damage and morphological changes that PEF can cause in starch granules, the digestible enzyme will
have easier access to new and/or greater number of glycosidic linkages in regions that initially would
be inaccessible. As previously observed, the PEF treatment can lead to a decrease of the starch relative
FOOD REVIEWS INTERNATIONAL 11
14. crystallinity and alter the starch granules morphology, which indicated that the starch structure can be
more susceptible to enzymatic activity. Thus, a greater number of degraded glycosidic bonds should
translate into greater hydrolysis of the starch, i.e., an increase in the rapidly hydrolyzed starch, and
consequently less will be the slowly digestible starch content. These results indicate that the molecular
weight of starch chains’ could have been altered after the PEF treatment (Table 4). Han et al. [23]
reported that the molecular weight of maize treated starch decreased significantly with the increase of
the electric field intensity from 30 to 50 kV/cm and with the treatment time from 424 to 1272 μs
(r2
>0.95). The decrease in molecular weight increased with the increase of the electric field intensity.
Additionally, the electric field intensity had more effect on the decrease of molecular weight than time.
Therefore, the decrease of the molecular weight could have been due destabilization of the amylo
pectin. However, Zeng et al. [26]
found that PEF treatment did not cause significant variations in the
molecular weight of waxy rice starch chain. Li et al. [25]
hypothesized that changes in the molecular
weight of starch molecules could have been responsible for the starch digestible capacity. More
recently, Wu et al. [19]
noticed an increase in the relative molecular weight of short amylopectin
chains and an increase of the relative molecular weight of long amylopectin chains when the intensity
of the electric field was superior to 5.71 kV/cm after treatment, despite did not found significant
changes in the molecular weight. Such a result indicates a breakdown of the molecular chain as
supposed by Li et al. [25]
Furthermore, the ratio of the chain length ratio of amylose to amylopectin was
less than one and the amylose content did not vary significantly when compared to the control. [19]
These results point in the direction of changes in the amylopectin chains during PEF treatment. Future
analyzes of the detailed structure of amylopectin may provide new data to explain the variations in
starch digestibility. Another relevant question is the behavior of these modified starches in in-vitro
simulation systems of the human digestive tract and their impacts on human health as well as the
potential benefits. Abduh et al. [18]
evaluated the glucose release per volume digest of the in-vitro
human intestine digestion and observed that the digestibility of the starch leached from the potato
shreds into the processing medium after PEF treatment was reduced (lower amount of glucose
released) after 120 min of digestion when compared to the earlier digestion times. Such reduction
was prevalent in the starch treated at 1.1 kV/cm and 50 kJ/kg in relation to the untreated starch
(p<0.05), which could have been due to starch disruption as indicated by the changes in the
gelatinization range temperature. This result is an initial evidence of the health benefits that the
starches treated by PEF starch treatment can have, since a reduction of starch digestibility is normally
associated to resistant starch, which has several benefits such as the diabetes management and decrease
the glycemic indexes. [57]
4.5. Differential scanning calorimetry and pasting properties
Table 5 depicts the most recent studies about the effect of PEF on the gelatinization temperatures and
enthalpy of the modified starches. Han et al. [23]
reported that for maize starch, gelatinization
temperatures and enthalpy decreased with the increase of the electrical field strength from 30 to 50
kV/cm and treatment time from 424 to 1272 μs due to the breaking of amylopectin chains, decreasing
the molecular weight and consequently leading to their degradation. But this result also shows that
there is an interactive effect between the electrical field strength and the treatment time. Zeng et al. [26]
reported that the gelatinization temperatures and enthalpies also decreased significantly for waxy rice
starch for the same range of electric field strength. The PEF-treated starches had lower gelatinization
temperatures and enthalpies when compared to the native ones (p<0.05). These results are similar to
the ones found for tapioca, corn and potato starches. [21,22,24]
PEF treatment leads to the breaking of
hydrogen bonds and therefore less energy is needed to disrupt the remaining ones, as evidenced by the
decrease in the gelatinization temperatures and enthalpies, especially the onset temperature, which
corresponds to the temperature at which the starch gelatinizes. The onset temperature can also be
found through the pasting property graphs when there is an initial increase in the viscosity, i.e., the
pasting temperature. [6,45]
The difference can rely on the fact that differential scanning calorimetry is
FOOD REVIEWS INTERNATIONAL 13
17. based on temperature sweeps and heat flow variations, whereas its determination by the graphs of
pasting properties is based on the measurement of viscosity changes. [58]
Abduh et al. [18]
processed
shredded potato using electric field intensities from 0.5 to 1.1 kV/cm and specific energy inputs at 50
and 150 kJ/kg and reported that the leached granules leached during the treatment and using higher
specific energy inputs had a narrower gelatinization range than those performed at a lower total
specific energy, which indicates that the crystallites had a stronger cohesion. The gelatinization
temperatures were inferior to those reported for potato starch treated between 30 to 50 kV/cm, but
Table 6. Pasting properties results of the PEF-treated starches.
Suspension
EFI
(kV/
cm)
SEI
(kJ/
kg)
PT
(ºC)
PEF/
Native
Peak
(BU)
PEF/
Native
SH (BU)
PEF/
Native
SC (BU)
PEF/
Native
EC (BU)
PEF/
Native
FV (BU)
PEF/
Native
BD (BU)
PEF/
Native
SB (BU)
PEF/
Native Reference
Tapioca 30
40
50
— — 921/982
889/
982
820/
982
517/496
505/
496
469/
496
295/279
281/
279
260/
279
572/557
546/
557
493/
557
512/505
489/
505
444/
505
626/703
608/
703
560/
703
— Han et al.
[21]
Corn 30
40
50
— — 291/335
282/
335
250/
335
280/320
271/
320
243/
320
220/253
215/
253
201/
253
528/568
469/
568
470/
568
482/537
442/
537
426/
537
71/82
67/82
49/82
— Han et al.
[24]
Potato 30
40
50
— — 2771/
2961
2705/
2961
2641/
2961
1074/
1060
1063/
1060
1022/
1060
555/524
535/
524
523/
524
955/913
917/
913
910/
913
922/907
862/
907
877/
907
2216/
2437
2170/
2437
2119/
2437
— Han et al.
[22]
Rice 2.86
5.71
8.57
— — 637.0/
632.2a
639.0/
632.2a
629.3/
632.2a
— — 587.0/
583.0ab
589.0/
583.0ab
581.0/
583.0ab
803.3/
805.0a
805.7/
805.0a
799.7/
805.0a
50.0/
49.2a
50.0/
49.2a
48.3/
49.2a
216.3/
222.0a
216.7/
222.0a
218.7/
222.0a
Wu et al.
[19]
Oat flour
(Raw)
2.2
2.1
2.1
4.4
4.3
4.1
53
249
484
51
220
441
83/84
84/
84
75/
84
83/
84
83/
84
72/
84
3334/
3451a
3154/
3451a
2081/
3451a
3122/
3451a
3135/
3451a
1761/
3451a
———— ———— 1592/
1624ab
1518/
1624ab
909/
1624ab
1378/
1624ab
1432/
1624ab
761/
1624ab
3692/
3711a
3297/
3711a
2439/
3711a
3403/
3711a
3395/
3711a
2223/
3711a
1742/
1826a
1636/
1826a
1172/
1826a
1744/
1826a
1703/
1826a
999/
1826a
2100/
2086a
1779/
2086a
1529/
2086a
2025/
2086a
1963/
2086a
1461/
2086a
Duque
et al.
[20]
Oat flour
(Thermal
treated)
2.2
2.1
2.1
4.4
4.3
4.1
49
233
434
48
200
418
67/68
66/
68
67/
68
68/
68
66/
68
73/
68
4268/
4385a
4148/
4385a
3923/
4385a
4159/
4385a
4070/
4385a
4087/
4385a
———— ———— 3094/
3075ab
3075/
3075ab
3029/
3075ab
3021/
3075ab
3053/
3075ab
3213/
3075ab
5227/
5292a
5223/
5292a
5156/
5292a
5149/
5292a
5219/
5292a
5310/
5292a
1173/
1235a
1073/
1235a
893/
1235a
1138/
1235a
1017/
1235a
873/
1235a
2133/
2142a
2148/
2142a
2127/
2142a
2127/
2142a
2166/
2142a
2097/
2142a
Duque
et al.
[20]
Notes: a) Results reported in cp; b) Trough viscosity.
Abbreviations: EFI: Electric field intensity; SEI: Specific energy input; SH: Start holding; SC: Start of cooling; EC: End of cooling; FV: Final
viscosity; BD: Breakdown; SB: Setback; PEF/native: PEF treated vs native starch.
16 L. M. G. CASTRO ET AL.
18. the gelatinization enthalpies were superior. [22]
These differences could have been due to differences in
potato variety and/or differences in the electric field intensity conditions. Furthermore, no effects were
observed on the unleached starch granules, indicating that these granules were less subjected to
treatment than those that were leached since they were protected in the original matrix. According
to Duque et al.,[20]
who treated raw and thermally processed oat flour using electric field strengths
from 2.1 to 2.2 kV/cm at 53-484 kJ/kg and from 4.1 to 4.4 kV/cm at 51-441 kJ/kg, the narrowing of the
range of the gelatinization temperature indicated that fusion of the crystallites of less cohesion was
favored and may have been strengthened, thus leading to the increase of the gelatinization
temperatures.
In Table 6 are presented the studies concerning the effect of PEF on the pasting temperature and
viscosity of starch when compared to the native starches. Wu et al. [19]
treated rice (type A) starch
using electric field intensities from 2.86 to 8.57 kV/cm and reported that treatment did not have
a significant impact on rice starch peak, trough, breakdown viscosities, and pasting temperature with
a small decrease in the setback viscosity. At higher intensities, Han et al. [21]
studied the effect of PEF
processing on tapioca (type C) starch and observed that the viscosity peak decreased when the electric
field increment from 30 to 50 kV/cm, indicating that granules swell less before they burst. After
treatment, both granules’ surface and crystalline structure were destroyed, leading to a decrease in
peak viscosity. Breakdown viscosity also decreased with increasing electric field strength, indicating
that the stability of the hot paste increased. Setback and final viscosities also decreased with increasing
electric field strength, thus indicating less retrogradation tendency. These results were similar to the
findings for corn (type A) and potato starches (type B). [22,24]
Duque et al [20]
recently treated raw and
thermally treated oat flour at 2.1-2.2 kV/cm at 53-484 kJ/kg and 4.1-4.4 kV/cm at 51-441 kJ/kg.
Overall, the PEF treatment caused a significant decrease in the viscosity and pasting temperatures
treated at higher specific energy inputs. The decrease in pasting temperatures relative to the control
indicated that the starch granules of the oat flour started swelling earlier than the control flour. The
peak viscosity of the raw oat flour decreased when compared to the control, but the treatment did not
cause significant changes in the case of the thermally processed flour. These results indicate that raw
oat flour had higher susceptibility than thermally processed flour due to the effect of thermal pre-
treatment, which may have led to aggregation and partial gelatinization before treatment. The break
down viscosity decreased in both flours compared to the control and the lowest values were seen for
the thermally treated flour. The decrease in breakdown viscosity indicated an improvement in the
paste stability, i.e., the swollen starch granules may have a lower degree of collapse and less extension
of the solubilized starch capable of retrograding. Additionally, only the raw oat flour had significantly
lower setback viscosity when compared to the control, indicating a decreased tendency to retrograde.
However, no analysis was made of how swelling and solubility were affected by the treatment, nor were
tests carried out to understand the impact of PEF treatment on starch retrogradation despite evidence
of lower retrogradation of treated starches.
5. Benefits and limitations
Besides being used to physically modify starch, the PEF technique has also been recently used to
chemically modify starches and further compared with the traditional chemical acetylation methods.
[55,59,60–63]
Results show that the traditional acetylation of starch by PEF reduces costs, saves reagent,
reduces the modification time, and promotes reaction efficiency (higher degrees of acetylation. [60–
62,64]
Figure 4 compares step by step both traditional acetylation and starch physical modification by
PEF. According to the literature, traditional acetylation requires the use of acetic anhydride as an
acetylating agent, which leads to increased costs and entails additional risks for the environment.
Regarding the modification step itself, this procedure requires extra care that does not occur in
physical modification such as pH adjustment (so that acetylation conditions are promoted). This
adjustment is made with NaOH, which implies the use of a second chemical reagent. In addition,
FOOD REVIEWS INTERNATIONAL 17
19. traditional acetylation is a time-consuming process, much more than physical modification. After
modification, it is necessary to use ethanol to stop the acetylation reaction and wash the starches to
remove unused acetic anhydride during acetylation. Until this stage, chemical acetylation requires the
use of different chemical solvents, whereas physical modification only requires the use of water as
a solvent. Then the starches are dried, sieved and stored. Thus, PEF technology is much faster, safer,
greener, and more environmentally friendly. In the physical modification, it is only necessary to filter
the cooled starches after modification and then dry, sieve, and store.
Overall, the physical modification has several advantages over the chemical methods, namely: 1)
simplification/reduction of the number of steps and consequently a reduction of the time spent from
the preparation of the starch suspension to the storage of the modified starch; 2) a significant reduction
in modification time; 3) non-usage of chemical solvents and the exclusive use of water, which leads to
a decrease in waste produced (greener and more environmentally friendly); 4) more ease of use; 5)
easier control of experimental conditions, having already created guidelines for the application of PEF
in food and biotechnological processes with the parameters that are necessary to control; and 6) the
possibility to carry out in batch or continuous mode (automation).
Some of the major disadvantages of PEF are 1) the high initial cost of the PEF equipment, 2) the
maintenance costs and 3) the need for specialized workers. [30,65]
However, the initial investment
becomes more advantageous in the long run and with the equipment full depreciation after five years.
Using orange juice as a case study it was estimated that the cost per PEF would be around $0.037/L
using a commercial equipment worth $988,000. The total capital cost of $2,100,000 with an annual
Suspension (35%)
Acetic anhydride addition
(dropwise within 30 min)
Modification
(30 ºC at 300 rpm for 60 min and pH
8.0-8.5 adjusted with NaOH 3%)
Ethanol addition
(stop reaction)
Washing (with ethanol)
Drying (45 ºC)
Sieving and storage
Suspension (8%)
Conductivity adjustment
(50-200 μS/cm)
Stirring
Modification
(< 50 ºC at 2.86-50 kV/cm for 214-
1272 μs and 600-1008 Hz)
Sample cooling
(water bath)
Filtration
Drying (45 ºC)
Sieving and storage
Chemical modification
Physical modification
Conductivity adjustment
(11 mS/cm)
Figure 4. Flowcharts of the physical and starch modification.
18 L. M. G. CASTRO ET AL.
20. depreciation of $210,000/year. Utility and labor costs were estimated to be around $69,000/year and
$220,000/year, respectively. [65]
6. Conclusions
PEF has shown the potential to aid the extraction of starch from algae, but more studies are needed
to evaluate its potential in other matrices such as vegetables, fruits, roots and tubers, and cereals rich
in starch and to optimize the operating conditions to increase protein removal and increase starch
purity. The PEF treatment induces significant changes in granular morphology and the changes on
the Maltese crosses do not seem to be affected at lower intensity fields, but the crosses seem to
disappear according to the starch polymorphism at higher electric fields, being the type A and
B starches more susceptible than the type C. The PEF treatment also leads to the decrease of relative
crystallinity, can change the starches lamellar repeating distance depending on the botanical origin
of starch, decrease the gelatinization temperatures and enthalpies, viscosity, and pasting tempera
ture. Regarding the in-vitro digestibility, it seems to lead to an increase of the rapidly digestible
starch content and a consequent decrease in the slowly digestible starch, while maintaining the
resistant starch content. These can be related to changes in the starch chains and future analyzes of
the detailed structure of amylopectin may provide new data to explain the variations in starch
digestibility. The lower digestibility of starch treated by PEF in in-vitro human simulated digestion
conditions seems promising for the incorporation of these starches in the human diet. The PEF
modification technology is a safer technique as it does not require the use of chemical solvents,
therefore it is a more environmentally friendly technique, presenting a lower processing cost
compared to traditional acetylation.
Acknowledgments
Thanks are due to the Universidade Católica Portuguesa by the financial support of the CBQF Associate Laboratory
under the FCT project UID/Multi/50016/2019 and to the University of Aveiro and FCT/MCT for the financial support
for the QOPNA research Unit (FCT UID/QUI/00062/2019) and to Laboratório Associado LAQV-REQUIMTE (UIDB/
50006/2020) through national funds and, where applicable, co-financed by the FEDER, within the PT2020 Partnership
Agreement. Author Luís M. G. Castro is also grateful for the financial support of this work from FCT through the
Doctoral Grant SFRH/BD/136882/2018.
Funding
This work was supported by the Fundação para a Ciência e a Tecnologia [SFRH/BD/136882/2018,UID/Multi/50016/
2019,UID/QUI/00062/2019,UIDB/50006/2020].
ORCID
Luís M. G. Castro http://orcid.org/0000-0002-4082-9679
Elisabete M. C. Alexandre http://orcid.org/0000-0003-4175-2498
Jorge A. Saraiva http://orcid.org/0000-0002-5536-6056
Manuela Pintado http://orcid.org/0000-0002-0760-3184
Author contributions
Luís M. G. Castro searched, reviewed the available literature, and created the first version of the manuscript. Elisabete
M. C. Alexandre, Jorge A. Saraiva, and Manuela Pintado conceptualize the idea, provided scientific supervision,
performed a critical revision, and provided the necessary conditions to produce the paper.
FOOD REVIEWS INTERNATIONAL 19
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22 L. M. G. CASTRO ET AL.
![Starch Extraction and Modification by Pulsed Electric Fields
Luís M. G. Castro a,b
, Elisabete M. C. Alexandre a,b
, Jorge A. Saraiva b
,
and Manuela Pintado a
a
CBQF - Centro de Biotecnologia e Química Fina – Laboratório Associado, Escola Superior de Biotecnologia,
Universidade Católica Portuguesa, Rua Diogo Botelho 1327, Porto 4169-005, Portugal; b
University of Aveiro, LAQV-
REQUIMTE, Laboratório Associado, Department of Chemistry, Aveiro 3810-193, Portugal
ABSTRACT
Starch modification arises from the need to obtain starches with the desir
able properties, being the physical modification techniques preferred over
the chemical ones. Pulsed electric fields (PEF) can improve starch extraction
and alter starch properties by decreasing the relative crystallinity, gelatiniza
tion temperatures and enthalpies, viscosity and pasting temperature. The
lamellar repeating distance can be altered depending on the starch botanical
origin. PEF can alter the digestible starch content, while maintaining the
resistant one. Future research of the amylopectin structure may provide
reasoning for these variations in starch digestibility behavior. The in-vitro
human simulated digestion points to a decrease in digestibility.
Keywords
Pulsed electric fields;
extraction yields; starch
modification; pasting and
thermal properties;
polymorphism and in-vitro
digestion
1. Introduction
Starch occurs naturally as water-insoluble complex granules. Its properties are dependent on different
external and internal factors such as the botanical origin, climate conditions, and the plant cultivation
area. Granules also have various shapes, sizes and diameters depending on the botanical origin. [1–3]
Starch is formed by amylose and amylopectin, which compose 98 to 99% of the dried weight of
granules, and both are homopolysaccharides formed by α-D-glucose residues linked by α1→4
linkages. While amylose has a linear structure, the amylopectin is highly branched due to the α1→6
linkages. [4,5]
These structural differences lead to two homopolysaccharides with different properties.
Amylose has lower viscosity, gelatinization and melting temperatures, higher retrogradation rate and
increased capacity to complex with lipids when compared to amylopectin, whilst amylopectin has
a better thickener ability, more stable freeze-thawing properties, stronger adhesive forces and form
softer gels. [6]
Because native starches have a low solubility in water, strong tendency to retrograde,
high instability in gels and pastes, poor thermal stability, some starch granules are inert and are very
resistant to enzymes, they are rarely used in the original form, since they do not have the functional
properties to be successfully employed by the food industry. [3,7]
Thus, starch modification has been
done for several years to improve its characteristics such as clarity and sheen, texture, film formation,
adhesion, increase freeze-thaw stability, and decrease retrogradation, gelling tendencies and syneresis,
so that starches can be used. [8–10]
Native starches can be modified by cchemical (like oxidation,
phosphorylation, succinylation, and acetylation), enzymatical (by using enzymes such as cellulase,
xylanase, papain, and pronase) or physical methods (pre-gelatinization, hydrothermal, and non-
thermal technologies). The chemical modification of starch consists in the incorporation of new
functional groups into a starch backbone so that the modified starch has the desired characteristics.
These are the most used methods due to the non-destructive nature of the processes that leads to an
CONTACT Elisabete M. C. Alexandre elisabete.alexandre.pt@gmail.com Universidade Católica Portuguesa, CBQF - Centro de
Biotecnologia e Química Fina – Laboratório Associado, Escola Superior de Biotecnologia, Rua Diogo Botelho 1327, Porto 4169-005,
Portugal.
FOOD REVIEWS INTERNATIONAL
https://doi.org/10.1080/87559129.2021.1945620
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