Physical modification of starch by heat-moisture treatment and annealing and their applications: A review

Carbohydrate Polymers 274 (2021) 118665

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Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol

Review

Physical modification of starch by heat-moisture treatment and annealing
and their applications: A review
Laura Martins Fonseca *, Shanise Lisie Mello El Halal , Alvaro Renato Guerra Dias , Elessandra da
Rosa Zavareze
Department of Agroindustrial Science and Technology, Federal University of Pelotas, Pelotas, RS 96010-900, Brazil

A R T I C L E I N F O

A B S T R A C T

Keywords:
Annealed-starch
Combined modifications
Food
HMT-starch
Physical modification

Heat-moisture treatment (HMT) and annealing are hydrothermal starch modifications. HMT is performed using
high temperature and low moisture content range, whereas annealing uses excess of water, a long period of time,
and temperature above the glass transition and below the gelatinization temperature. This review focuses on:
research advances; the effect of HMT and annealing on starch structure and most important properties; combined
modifications; and HMT-starch and annealed-starch applications. Annealing and HMT can be performed together

or combined with other modifications. These combinations contribute to new applications in different areas. The
annealed and HMT-starches can be used for pasta, candy, bakery products, films, nanocrystals, and nano­
particles. HMT has been studied on starch digestibility and promising data have been reported, due to increased
content of slowly digestible and resistant starches. The starch industry is in constant expansion, and modification
processes increase its versatility, adapting it for different purposes in food industries.

1. Introduction
Starch is a natural, biodegradable, abundant, biocompatible, lowcost, and nontoxic polymer highly used in several industries as textile,
food, paper, packages, biomedical, and pharmaceutical. In food in­
dustries, starches are used for the production of instant foods, noodles,
baked goods, and food packages, among others. Starch presents inherent
limitations that can be overcome by its modification through methods as
chemical, enzymatic, physical, and a combination of them (Lacerda
et al., 2015; Molavi et al., 2018). There are several studies reporting the
effect of these modifications in starch properties to suit specific appli­
cations, such as: Majzoobi et al. (2015), who modified rice flour and rice
starch by HMT for application in biodegradable films; Chandla et al.
(2017), who used HMT-amaranth starch for the production of noodles;
and Choi and Koh (2017), who used annealed-starch from rice for the
same purpose.
Physical methods have gained widespread acceptance for their low
cost, safety, and effective characteristics, being a green (not requiring

chemical reagents) alternative to improve starch applicability, by
achieving specific enhanced properties for specific types of applications
(Punia, 2020). There are various physical modifications such as pregelatinization, a thermal process; heat-moisture treatment (HMT) and
annealing, two hydrothermal processes; and the non-thermal modifi­
cation includes high pressure processing, micronization, ultra­
sonication, and pulse electric field (Alc´
azar-Alay & Meireles, 2015;

Punia, 2020). Annealing and HMT are the most commonly used methods
effective in altering starch properties, such as relative crystallinity,
water absorption capacity, and pasting properties, maintaining the
molecular integrity of starch. These hydrothermal treatments also in­
fluence directly starch digestibility: this is extremely important to ach­
ieve health benefits for the consumer, by slowly digestible starch (SDS)
and resistant starch (RS) formation and reduction of rapidly digestible
starch (RDS). Thus, the application in food products can focus in in­
dividuals with chronic diseases as diabetes, among other serious health
issues (Pratiwi et al., 2018; Sudheesh et al., 2020). These changes in
starch digestibility are mainly promoted by the disruption in starch

Abbreviations: AFM, Atomic Force Microscopy; DIC, D´
etente Instantan´
ee Contrˆ
ol´
ee; DSC, Differential Scanning Calorimetry; DV-HMT, Direct vapor-heat-moisture
treatment; GRAS, Generally recognized as safe; HMT, Heat moisture treatment; NC-AFM, Non-contact Atomic Force Microscopy; RHMT, Repeated heat moisture
treatment; RP-HMT, Reduced-pressurized heat-moisture treatment; RS, Resistant starch; RDS, Rapidly digestible starch; RVA, Rapid Visco Analyzer; SEM, Scanning
Electron Microscopy; SDS, Slowly digestible starch; XRD, X-ray diffraction.
* Corresponding author.
E-mail address: (L.M. Fonseca).
/>Received 6 June 2021; Received in revised form 8 September 2021; Accepted 9 September 2021
Available online 11 September 2021
0144-8617/© 2021 Elsevier Ltd. This article is made available under the Elsevier license ( />

L.M. Fonseca et al.

Carbohydrate Polymers 274 (2021) 118665

structure, increasing accessibility of starch molecular chains to the
amylolytic enzymes, changing its crystalline structure, and thus
enhancing starch digestibility (Wang et al., 2016).
The most important structural changes achieved by HMT and
annealing are promoted by the extension of double helical lengths,
reduction of double helix content, strengthening of interactions between
amylose and amylopectin branching, and more heterogeneous semicrystalline lamellae. Thus, more mobile chains are available due to the
greater proportion of very long chains/branches. The starch structure
becomes more organized. The modification mechanism involves
increasing the interactions of starch chains, which starts by disruption of
the crystalline structure, followed by dissociation of double helix
structures and then reassociation of the disrupted crystals. The different
starch sources present distinct granule organization and behaviors when
undergoing hydrothermal processes: the high amylose starches have
potential to form thermostable molecular orders (Li et al., 2020; Pratiwi
et al., 2018).
Various food applications are cited in the literature for HMT and
annealed starches, as in baked goods, noodles, doughs, pie fillings,
flours, and whole grains or kernels. In processed foods, these modified
starches can be used as unmodified thickeners, to improve their stability
to temperature, shear, and acid conditions, also reducing retrogradation.
Other applications are in thermoplastic materials, resins, films, nano­
particles, and nanocrystals (BeMiller, 2018; BeMiller & Huber, 2015). In
addition, the HMT and annealed starches present granules more sus­
ceptible to chemical and enzymatic modifications and to acid hydrolysis
´zar-Alay & Meireles, 2015). The use of HMT and annealing pro­
(Alca
motes thermal stability for starches, being promising for the develop­
ment of products that are exposed to high temperatures during
production. In addition, they are safe and innovative methods that

improve the functional and technological properties of starch for in­
dustrial proposes (Molavi et al., 2018).
In this study, we present an updated review (2011− 2021) focused on
HMT and annealing, examining their effect on starch structure and the
properties of different types of starches, the combination with other
modifications, and recent trends in the application of modified starch,
based on reports from literature of the last 10 years.

birefringence. These changes influence starch behavior in terms of
swelling power and solubility (Singla et al., 2020). Gelatinized starch is
used in industries as a thickener, gelling agent, stabilizer, and fat sub­
stitute in foods (Oliveira et al., 2018).
Thermal properties of starch can be measured by differential scan­
ning calorimetry. It provides data of heat flow associated with gelati­
nization, showing changes in enthalpy related to the transition of
ordered and disordered crystals from low order crystalline regions of the
granule. Through this analysis, the gelatinization temperature is also
obtained. It defines the proportion of required energy for cooking
(Zavareze & Dias, 2011).
Another important property of starch is digestibility. Starch is clas­
sified according to its nutritional aspects after ingestion, by RDS, SDS,
and RS. RDS and SDS are digested and absorbed after passage through
the gastrointestinal tract and arrival in the small intestine. RS is not
digested, being fermented in the large intestine. SDS and RS are well
known for preventing diseases, showing health benefits. Therefore, their
application in food industries is growing over the years (Maior et al.,
2020; Yan et al., 2019).
Starches can be applied in food and non-food industries. For this,
specific characteristics are required, which are not often achieved by
native starches. Therefore, starch modifications are alternatives to

enhance starch properties. They broaden its industrial end-use by
providing products with higher thermal and shelf stability, as well as
mechanical, texture, and pasting properties, for instance (Falade &
Ayetigbo, 2015).
3. Physical modification
Physical modifications are low-cost, safer, and green alternatives
when compared to chemical and enzymatic processes. Their study has
been showing promising outcomes on the improvement of starch prop­
erties (Oliveira et al., 2018). Among the physical modifications are pregelatinization, ultrasonication, heat-moisture treatment, mechanical
milling, and annealing. They present variations in parameters as tem­
perature, pH, and pressure, acting by modifying the starch molecular
structure, packing arrangements, and crystallinity, for example
(BeMiller & Huber, 2015; Singla et al., 2020).
Annealing and HMT are hydrothermal processes highlighted by
achieving unique starch properties, unaltering its molecular integrity
(Obadi & Xu, 2021). In the next sections, we are going to discuss the
reported effects of HMT, annealing, and combined methods on starch
properties and starch applications.

2. Starch composition, structure and properties
Starch is a polysaccharide of plant origin formed by two macro­
molecules with glucose units linked together through glycosidic bonds.
Amylose is a long and linear macromolecule containing α-(1–4) linkages
with helical structure, with hydrogen atoms inside the helix and hy­
droxyl groups outside the helix. Amylopectin is branched, containing
α-(1–4) and α-(1–6) linkages arranged radially in the granule, double
helix as crystalline areas and branching points as amorphous areas
(Rocha et al., 2012; Sudheesh et al., 2020). The amorphous areas are
more susceptible to hydrolyses by enzymes and water absorption due to
the influence of amylose in the packing of amylopectin crystallites in the

crystalline lamellae, which influences swelling and gelatinization
(Zavareze & Dias, 2011). Starches can be found with different amylose
contents depending on the botanical source: in corn, for example, the
normal amylose content for starch is 20–30%; a high amylose content is
50–80%; and a low amylose content is 0–8% (waxy starch) (Obadi & Xu,
2021).
The functional properties of starch are related to its botanical source,
amylose/amylopectin ratio, molecular weight, and organization of the
granule chains (Sudheesh et al., 2020). The X-ray diffraction pattern can
exhibit A-type structure with medium length helices showing reduced
crystallinity, mostly reported for starches from cereal grains, and B-type
with higher length and crystallinity, mostly found for starch from tubers
(Moran, 2019). The crystallinity of starch is affected when it is heated in
excess of water. It undergoes a phenomenon named gelatinization, in
which amylose is leached, the granule is swollen and the disappearance
of the double-helical crystalline structure occurs along with the loss of

3.1. HMT
Hydrothermal processes, such as HMT, are performed by heating the
starch granules at temperatures above gelatinization temperature, with
moisture content insufficient to gelatinize starch, and submitted to a
specific period of time, maintaining granular integrity. The parameters
used for this starch modification are: high temperature, ranging from 84
to 140 ◦ C; low moisture content, ranging from 10 to 35%; and time of
exposure ranging from 1 to 16 h (Adawiyah et al., 2017; BeMiller, 2018).
The effectiveness of the treatment depends on the process parameters
(moisture content, temperature, and heating time) and the starch
characteristics, such as botanical source, structure, and amylose/
amylopectin ratio and organization (Adawiyah et al., 2017; Alc´
azarAlay & Meireles, 2015).

HMT influences and improves several starch properties, which are
discussed in the following sections. Changes in starch caused by HMT
include effects on morphology, swelling capacity, crystallinity, gelati­
nization, thermal stability, retrogradation, digestibility, and pasting
properties (Punia, 2020), broadening the range of starch applications in
the food industry. Table 1 summarizes several studies explored in this
review in the following sections, regarding different types of starch
modified by HMT and the treatment parameters used.
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Carbohydrate Polymers 274 (2021) 118665

starch and 63% for potato starch, both when applied the highest mois­
ture content in HMT. The authors associated this behavior to the evap­
oration of water molecules during the physical modification. The
roughness increased for sweet potato starch and decreased for potato
starch after the treatment, being the greatest changes for the HMT using
20% moisture content, increasing the roughness by 46% for sweet po­
tato starch and decreasing it by 40% for potato starch. This study pro­
vides quantitative information about changes in size and roughness of
starch granules from different botanical sources, showing that the in­
fluence of HMT depends on moisture content.
Lacerda et al. (2015) studied avocado starch modified by HMT at
120 ◦ C for 1 h, with moisture contents of 10, 20, and 30%. The
morphology was analyzed by Atomic Force Microscopy (AFM), and
native and modified avocado starches showed an oval shape. The native
starch presented protruded, flat, and smooth regions, not showing an

appropriate order after HMT, but showing a smooth region on the sur­
face. The authors attributed this change to the melting of the protruded
regions by partial gelatinization, in which the water molecules evapo­
rate, causing the amylopectin double helix chains to organize into a
denser packing structure. In the study of Lacerda et al. (2015), the
moisture content in HMT was higher than in Oliveira et al. (2018).
However, the effect of HMT on starch morphology was less pronounced,
thus showing that the botanical source of starch plays an important role
in the application of HMT.
Bartz et al. (2017)) reported the intense effect of HMT on physico­
chemical properties, morphology, swelling power, and amylose content,
by subjecting potato starch to HMT at 12, 15, 18, 21, and 24% of
moisture content for 1 h at 110 ◦ C. The effect on these properties has
been accentuated along with the increase in moisture content. The
morphology was evaluated by Scanning Electron Microscopy (SEM), and
the native potato starch granules varied in size, showing ellipsoidal
shape with some small spherical granules. HMT-starches modified with
12, 15, 21, and 24% of moisture content showed similar granule
morphology. However, the treatment using 18% of moisture presented
discrete agglomeration, as well as grooves. In their study, the differences
in moisture did not promote changes in the effect of HMT.
In another study, Wattananapakasem et al. (2021) examined the
morphology of HMT-geminated-black rice by SEM, with moisture con­
tents of 25 and 30%, treated at 90 ◦ C for 1 and 2 h. The authors reported
the presence of agglomerations and pores in the granules after applying
HMT. The increase in time of exposure to HMT from 1 to 2 h did not
change the morphology of the rice starch granules. In our point of view,
this may have happened because, at these treatment conditions, the
changes in the granule occurred in full during the shorter time of
exposure (1 h).

According to the studies presented in this review, the treatment time,
moisture, and starch source are determining factors for changes in the
morphology of granules promoted by HMT. Depending on the starch
gelatinization temperature, high moisture contents in the HMT can
promote partial gelatinization and agglomeration in the starch granules.

Table 1
Heat-moisture treatment (HMT) parameters, source of starch, and references.
Starch

HMT parameters

Reference

Temperature
(◦ C)

Time
(min)

Moisture
content
(%)

Sago and
arenga
Cassava
Grain paddy
rice and rice
starch

Potato

120

60, 90

20

120
120

60
10, 30,
60

10, 20, 30
13

110

60

Mango kernels
Potato

110
100, 120

180
120

12, 15, 18,
21, 24
20, 25, 30
30, 35

Germinated
brown rice
grain
Green Prata
banana
Black rice
Rice, cassava,
and pinh˜
ao
starches
Avocado
Corn

100

60

30

Bharti et al. (2019)
Brahma and Sit
(2020)
Chung et al. (2012)

102

60

10, 20, 25

Costa et al. (2019)

100
100, 120

960
120

30
22

Dhull et al. (2021)
Klein et al. (2013)

120
110

60
960

Lacerda et al. (2015)
Liu et al. (2016)

Potato and

sweet
potato
Sweet potato

121

60

10, 20, 30
20, 25, 30,
35
10, 15, 20

110

25

Pranoto et al. (2014))

Rice bean
Geminatedblack rice
Mung bean

110
90

180,
240,
300
960

60, 120

25
25, 30

120,
240,
360,
480,
600,
720

30

Thakur et al. (2021)
Wattananapakasem
et al. (2021)
Zhao et al. (2020)

120

Adawiyah et al.
(2017)
Andrade et al. (2014)
Arns et al. (2015)
Bartz et al. (2017))

Oliveira et al. (2018)

3.1.1. HMT influence on morphological properties

Microscopy analysis is used to characterize starch granules, showing
its different sizes and shapes (Schafranski et al., 2021). BeMiller and
Huber (2015) reviewed various studies regarding starches modified by
HMT, and found the following results: direct influence of treatment
conditions (e.g., high temperature and low moisture) on starch proper­
ties when compared with their native counterparts, showing increased
mobility of starch chains and helical structures and resulting in major
structural changes; molecular degradation of starch chains; and
morphological changes to granules as size, surface cracking, hollowing
at granule centers, decreased birefringence, and partial gelatinization or
agglomeration of granules. However, other studies (Andrade et al.,
2014; Costa et al., 2019; Lacerda et al., 2015; Pranoto et al., 2014) have
not found changes in the morphology of HMT-starches from different
sources as organic cassava, green Prata banana, avocado, and sweet
potato.
Oliveira et al. (2018) evaluated the morphology of potato and sweet
potato starches treated with moisture content of 10, 15, and 20% at
121 ◦ C for 1 h, by Non-contact Atomic Force Microscopy (NC-AFM). The
authors reported an agglutination of the granules and changes in size
and roughness, when applying HMT to the starches. The shape of the
granules was not modified by HMT: while native potato starch showed
an ellipsoidal shape, the native sweet potato starch presented a polyg­
onal shape. HMT promoted reduction in the size of the granules of po­
tato and sweet potato starches. This was accentuated by the higher
moisture content of treatment, with reductions of 17% for sweet potato

3.1.2. Influence of HMT on solubility and swelling power
The starch properties of swelling power and solubility elucidate in­
teractions between the starch chains of crystalline and amorphous
structures (Thakur et al., 2021). Repeated heat-moisture treatment

(RHMT) has been used by researchers in order to improve the effect of
HMT within the starch granules (Niu et al., 2020; Zhao et al., 2020).
According to Zhao et al. (2020), HMT provides starch with limited de­
gree of modification. Thus, repeated processing allows a redistribution
of moisture in the granules during the cooling process, providing a new
equilibrium from the new starting point (e.g., previously HMT-modified
starches). The authors have modified mung bean starch by HMT at
120 ◦ C for 2, 4, 6, 8, 10, and 12 h, and using RHMT at 120 ◦ C for 2, 3, 4,
5, and 6 h. They evaluated solubility at various temperatures ranging
from 50 to 90 ◦ C, reporting increase for all treatment times at all tem­
peratures evaluated, when compared to native starch. The swelling
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Carbohydrate Polymers 274 (2021) 118665

power presented the same trend of increased values for the analysis at
50 ◦ C and decreased values as the temperature increased from 60 to
90 ◦ C. This may have occurred by the reorganization of amylose and
amylopectin molecules, reducing the absorption of water during heat­
ing. The solubility of native starch reported by the authors was not high,
ranging from 1 to 8%, with increase in temperature from 50 to 90 ◦ C.
However, values of about 20% solubility were found for some samples
modified and analyzed using 90 ◦ C. These variations in solubility and
swelling power achieved by RHMT allow more possibilities of starch
modification by HMT, opening up a range of applications.
Klein et al. (2013) also evaluated the effect of RHMT on swelling
˜o starches (22% of

power and solubility, in rice, cassava, and pinha
moisture content, at 100 and 120 ◦ C for 2 h, and then for another 1 h at
100 and 120 ◦ C). Both parameters were decreased by HMT when
compared to their native counterparts. The swelling power of all
starches was reduced with the increase in temperature from 100 to
120 ◦ C. When comparing HMT-starch and RHMT-starch at the same
treatment temperature, only rice starch showed increased swelling
power. Thus, the rice starch was more susceptible to a new arrangement
˜o starches. The modifications of
caused by RHMT than cassava and pinha
HMT and RHMT present distinct influence according to the different
types of starches, thus providing different outcomes to starches
regarding its swelling power and solubility. Both properties are very
important for starch application, as in bakery and pasta production, in
which the starch interacts with water and other ingredients.
Pranoto et al. (2014)) studied sweet potato starches of Indonesian
varieties submitted to HMT, for future application in noodle production.
The modification was performed using moisture content of 25%, at
110 ◦ C for 3, 4, and 5 h. The data showed differences for swelling power
and solubility among the different potato starch varieties. HMT-starches
reduced swelling power and increased solubility when compared to their
respective native starches. This behavior was explained by an expansion
in the starch granule, an increase of molecular bond interaction, and the
loss of double helix formation of the starch chains when heated in water.
The treatment time did not affect swelling power or solubility in the
sweet potato starches. Costa et al. (2019) evaluated the effects of HMT
on the swelling power of green Prata banana starch, with moisture
contents of 15, 20, and 25%, treated at 102 ◦ C for 1 h. When increasing
the temperature of the analysis (70 to 90 ◦ C), there was an increase in
swelling power for native and low-HMT-starches. HMT decreased

swelling power by the molecular arrangement of starch, which reduced
the hydration of the granules. This can be related to a reduction in
crystallinity, the formation of amylose-lipid complex, and the limit
temperature of gelatinization in the starch suspension that breaks the
hydrogen bonds and releases the water molecules bound from the hy­
droxyl groups. These changes in swelling power and solubility are
important for applications in baked goods and other food products.
Properties as swelling power and amylose leaching are generally
reduced by HMT, thus presenting advantages to the production of
starch-based food products. This reduction in swelling power is pro­
moted by the restructuring of starch chains and repositioning of bonds in
them. In addition, HMT makes the granule more rigid and resistant to
heating, conferring a more hydrophobic granule (Mathobo et al., 2021).
The starches from different botanical sources of the studies presented in
this review showed distinct behavior regarding the effect of HMT on
solubility and swelling power. Increased values of these properties were
found for mung bean starch, while decreased values were found for rice,
cassava, pinh˜
ao, potato, and green Prata banana starches.

viscosity (viscosity at the end of cooling) (Schafranski et al., 2021).
The influence of HMT on pasting properties was studied by Costa
et al. (2019), Wattananapakasem et al. (2021), Thakur et al. (2021), and
Dhull et al. (2021), in starches from green Prata banana, geminatedblack rice, rice bean, and black rice, respectively. Costa et al. (2019)
treated green Prata banana starch at 102 ◦ C for 1 h, with moisture
contents of 15, 20, and 25%, finding increase in pasting temperature and
reduction in breakdown viscosity, tendency to retrogradation, and peak
and final viscosities. The changes in pasting temperature indicate that
HMT provided a swelling initiating at higher temperatures (compared to
native starch), which is related to the lower swelling power that the

HMT-starch presented (data shown in Section 3.1.2). The reduction in
breakdown indicates improvement in shear stability and tendency to
retrogradation: this is related to the amylopectin chains that may inhibit
amylopectin retrogradation due to the lower formation of double heli­
ces. Wattananapakasem et al. (2021) modified the geminated-black rice
starch using moisture contents of 25 and 30%, at 90 ◦ C for 1 and 2 h. The
authors reported improved pasting properties promoted by HMT, as well
as higher pasting temperature when compared to native starch. They
also attributed the improvements in starch pasting properties to the
molecular rearrangement in the starch granule. The viscosity and
pasting temperature were higher for the HMT-starch when compared to
native starch. The authors did not report changes in pasting properties
regarding the time of exposure to HMT, which varied at 1 and 2 h. The
reorganization of molecular structure is promoted by HMT without
breaking the amylose and amylopectin chains, but promotes intense
changes in starches, significantly altering the paste profile.
Thakur et al. (2021) modified the rice bean using 25% of moisture
content at 110 ◦ C for 16 h, and reported that HMT reduced the peak,
breakdown, and final viscosities, and improved the mechanical and
thermal stabilities of starch. This modified starch did not present setback
viscosity, which was associated to reduction in amylose leaching,
resulting in a decrease for this parameter. Dhull et al. (2021) modified
black rice starch by HMT, using 30% of moisture content at 100 ◦ C for
16 h, and reported that HMT reduced the peak and final viscosities and
increased the breakdown viscosity and pasting temperature. These au­
thors attributed the changes on the pasting properties to a protective
shell promoted around the exterior of partially gelatinized starch gran­
ules after HMT, acting as a barrier to the penetration of water and
inhibiting gelatinization and pasting. In the studies of Thakur et al.
(2021) and Dhull et al. (2021), the time of HMT applied (16 h) was

higher than in other studies: Costa et al. (2019) used 1 h and Wattana­
napakasem et al. (2021) used 1 and 2 h of treatment exposure. This can
also explain the different effect on pasting properties.
This physical modification can be performed directly in grains:
Chung et al. (2012) modified germinated brown rice grains, whereas
Arns et al. (2015) modified paddy rice grains and rice starch. Chung
et al. (2012) found increase in pasting viscosity after HMT. This was due
to improvement of starch chain interactions, promoting a granular ri­
gidity that is attributed to the increased volume occupied by the swollen
granules in the continuous phase. Arns et al. (2015) used HMT at 120 ◦ C,
with 13% of moisture content and 10, 30, and 60 min of treatment,
showing reduced pasting temperature, breakdown and setback, and
increased peak viscosity, when comparing the grain and starch in their
native and modified forms. In our point of view, these changes in pasting
properties are related to the effect of HMT on the following starch
granule characteristics: the strengthening of bonds between adjacent
amylopectin chains; increased crystalline lamella; enhanced thermal
and mechanical stability; and greater resistance to swelling due to a
rearrangement of the internal forces. The exterior layers of the grains
protected the starch structure; however, HMT had effect even when
applied directly in the grains. Also, it can be a cost-effective option, since
no starch extraction is performed and HMT provides changes and im­
provements to the granule properties.

3.1.3. Influence of HMT on pasting properties
The pasting properties of starches are most commonly measured by
Rapid Visco Analyzer (RVA), which obtains the following parameters of
starch pastes: pasting temperature (temperature that starts the increase
in viscosity); peak viscosity (maximum viscosity); breakdown viscosity
(difference between peak and minimum viscosity); setback (tendency to

retrograde, difference between final and minimum viscosity); and final
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3.1.4. Influence of HMT on crystallinity
The different types of crystallinities (diffraction pattern) of starch
granules are characterized by X-ray diffraction (XRD) analysis. The
diffraction patterns are produced by the packages of hexagonal chains of
amylopectin (Schafranski et al., 2021). Basically, the diffraction patterns
found in starches are A-, B-, and C-types. The A- and B-types differ in
their compactness and both show a double helical structure. The C-type
is considered a mixture of A- and B-types. XRD measures the relative
crystallinity of starches, which present a semi-crystalline structure with
crystalline and amorphous lamellae in its granule. Overall, this param­
eter is reduced by HMT (Khatun et al., 2019).
Changes in crystallinity and X-ray pattern promoted by HMT were
found in potato and sweet potato starches treated with moisture con­
tents of 10, 15, and 20% (Oliveira et al., 2018). The native sweet potato
starch showed A-type diffraction pattern (with diffraction peaks at (2θ)
15, 17, and 23◦ ) that did not change after HMT. However, the diffraction
pattern for potato starch changed in intensity from B-type (diffraction
peaks at (2θ) 5.6, 17, 22, and 24◦ ) to A-type (diffraction peaks at (2θ) 15
and 23◦ ). These authors also reported changes in the crystalline region
of the granules after HMT. A decrease in relative crystallinity for both
starches was found with gradual increase in the moisture of the HMT
applied. The most pronounced effect in crystallinity was for the highest

moisture contents used in HMT for both starches, decreasing 11% for
potato starch and 36% for sweet potato starch, when compared to the
native starches. HMT promotes dehydration and movement of double
helices into the central channel that can induce changes in the diffrac­
tion pattern and relative crystallinity of starches. This movement
occurred during the HMT, being likely to disrupt starch crystallites and/
or change the crystalline orientation.
Other studies also found changes in X-ray pattern when applying
HMT in potato starch. Brahma and Sit (2020) modified potato starch
using HMT at different treatment conditions, applying moisture contents
of 30 and 35% for 24 h, then heating at 100 and 120 ◦ C for 2 h. They also
found changes in X-ray pattern that changed from B-type (native) to A +
B type (HMT-starch). The native starch showed peaks at 17.3, 22, and
24◦ (2θ). Changes were found in the intensity of the peak at 17◦ , as well
as a merge obtained for the peaks at 22◦ and 24◦ . The relative crystal­
linity was lower for the HMT-starches than for their native counterpart.
Bartz et al. (2017)) treated potato starch using HMT with various
moisture contents (12, 15, 18, 21, and 24%). The X-ray pattern pre­
sented changes varying along with the moisture content of the treat­
ment. The native potato starch showed a B-type pattern (5.6, 15, 17, 20,
22, and 24◦ ), then changing to a mixture of A- and B-types. For the
starches modified with 12, 15, 18, and 21% of moisture contents, the
diffractograms showed changes in the intensity of the pattern (mostly in
peaks of 5.6, 17, 22, and 24◦ ). On the other hand, the starch modified
using the highest moisture content (24%) presented A-type (15, 20, and
23◦ ) pattern. The changes in intensity by using HMT occur due to the
disappearance of the double helices among the chains within the starch
crystals, resulting in a matrix that is more orderly than in native starch.
Relative crystallinity decreased with moisture contents of 12 and 15%,
and it increased with 21% and 24% contents. The changes found in X-ray

pattern and crystallinity can be attributed to a partial gelatinization of
starch granules, which had influence on other parameters as reported
here.
Depending on the starch source, the diffraction pattern may not
change by HMT, as reported by Lacerda et al. (2015) in avocado starch.
The increase in moisture content of HMT from 10 to 20 and then to 30%
influenced crystallinity with a reduction of 15% in relative crystallinity
for the modified samples (not differing statistically among different
moisture content applied) when compared to untreated starch. This may
be due to the breaking of starch granules that was proportional to the
extent in moisture content which promoted partial gelatinization at high
moisture content. The authors related this behavior to the increase in
amorphous area in the semi-crystalline lamella, reducing crystallinity
with the excessive heat during HMT. Bharti et al. (2019) examined

mango kernel starches from Indian cultivars modified by HMT, using 25,
30, and 35% of moisture content, at 110 ◦ C for 3 h. The different cul­
tivars presented A-type diffraction pattern with diffraction peaks at (2θ)
15 and 23◦ , which remained the same after HMT. For all mango culti­
vars, relative crystallinity decreased. However, the authors did not
report the values of crystallinity for all samples, which makes difficult
the evaluation of the influence of HMT at different moisture content
exposure.
Andrade et al. (2014) modified organic cassava starch using HMT in
an autoclave, at 120 ◦ C for 60 min, with 10, 20, and 30% of moisture
content. The authors reported that the intensity of the treatment
(different moisture content) reduced relative crystallinity by 11% for the
starch modified using 10 and 20% of moisture content, and by 50% for
the starch modified using 30% moisture content, when compared to
native starch. Thus, relative crystallinity data has been inversely pro­

portional to the moisture content of the HMT.
Starches modified by HMT are used for the production of nano­
crystals. This is explored in Section 5, which presents recent trends and
applications of starch. The changes in crystallinity of HMT starches
promote improved properties of the nanocrystals, such as higher ther­
mal stability than the nanocrystals produced with native starch. Thus,
the changes in crystallinity broaden the applications of HMT-starch.
3.1.5. Influence of HMT on thermal properties
Differential Scanning Calorimetry (DSC) evaluates the gelatinization
properties of starches when heated in excess of water. This endothermic
phenomenon can be evaluated by DSC through parameters as gelatini­
zation, transition temperatures (onset, peak, gelatinization, and final
temperatures), and gelatinization enthalpy (Schafranski et al., 2021).
Overall, HMT promotes increase in the thermal stability of starches
by a shift in the onset, peak, and final gelatinization temperatures to
higher values. Oliveira et al. (2018) analyzed potato and sweet potato
starches modified by HMT, reporting an increase in gelatinization
temperatures and a decrease in the gelatinization enthalpy. This trend
was more accentuated for the sweet potato starch than for the potato
starch. The increase in gelatinization temperatures was attributed to a
strengthening of interactions between amylose and amylopectin
branching. Gelatinization enthalpy is related to the stability of the
crystalline domains of starch. Thus, we believe that the reduced
enthalpy can be explained by the collapse in the crystal structure of
starch granules, which were evaluated by XRD (reported in Section
3.1.4). The authors also evaluated HMT with different moisture contents
(10, 15, and 20%) and found increase in thermal stability with the in­
crease in moisture content, when compared to the native starch. This is
seen by the higher initial temperatures and lower gelatinization
enthalpy parameters, which represent the thermal stability of starch

granules. This outcome could be due to the disruption of the amorphous
regions of partially gelatinized amylose and amylopectin, and the
structural changes induced.
The changes in thermal properties promoted by HMT can be attrib­
uted to the formation of a stable configuration. This is due to a
realignment of polymer chains with the non-crystalline regions of starch
after HMT. Reductions in gelatinization enthalpy can be attributed to
the disruption of hydrogen bonding in the crystalline region of starch,
throughout the exposure to high temperature (Adawiyah et al., 2017).
Differences in thermal properties were reported by Lacerda et al. (2015),
who modified avocado starch by HMT (moisture contents of 10, 20, and
30%). There was an increase in gelatinization temperature and a
decrease of approximately 50% for gelatinization enthalpy, only for the
sample modified using 20% moisture content. A large endothermic
event was observed for the starch treated with moisture content of 30%,
which made it impossible to measure thermal properties. Adawiyah
et al. (2017) used HMT to modify different starches at 120 ◦ C and 20%
moisture content. For sago (Metroxylon sago) starch, the HMT exposure
time was 60 min and for arenga (Arenga pinnata), 90 min. They reported
a shift in gelatinization temperature and reduced gelatinization
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Carbohydrate Polymers 274 (2021) 118665

enthalpy, with 39% reduction for sago starch and 28% for arenga starch.
The gelatinization temperatures as onset, conclusion and peak, all
shifted to higher values when comparing HMT and native starches. The

increase in gelatinization temperatures indicates an increase in thermal
stability rendered by HMT. However, the treatment had more influence
on some of the starches, as sago. This can be explained by the different
chain arrangement, the amylose/amylopectin ratio, and other charac­
teristics that vary for each type of starch.
Costa et al. (2019) modified green Prata banana starch by HMT (at
102 ◦ C for 1 h, with moisture contents of 15, 20, and 25%). The treat­
ment showed decrease in gelatinization enthalpy by 32% for the HMTstarches when compared to their native counterparts, regardless of
moisture content. The physical modification also influenced the gelati­
nization temperatures, decreasing the onset temperature and increasing
peak and final temperatures, thus indicating improved thermostability
for the starch modified by HMT. The effect of HMT on thermal properties
can be explained by the perfection of the crystalline areas after in­
teractions of amylose–amylose and amylose–amylopectin. The effect of
HMT on gelatinization temperatures is in agreement with the changes in
pasting properties found by the authors, shown in Section 3.1.3.

content provides different outcomes to starch, which could enable
various applications.
Liu et al. (2016) modified corn starch using HMT, with moisture
contents of 20, 25, 30, and 35%, at 110 ◦ C for 16 h. The modification
efficiently increased SDS and RS contents and decreased RDS. At the
highest moisture content (35%) used in HMT, the RDS presented its
lowest value, while SDS and RS had their highest value. The degree of
hydrolysis decreased with the increase in the moisture content used in
HMT. We believe that the outcome of their study could suggest the
effective application of this physically modified starch in the prevention
of chorionic disease. Chung et al. (2012) used HMT to modify germi­
nated brown rice grains (moisture content of 30%, at 100 ◦ C for 1 h), in
order to evaluate its effect on digestibility. The contents of RDS and SDS

decreased and RS increased, which is explained by the extended
perfection of the crystalline structure of the granule and the retrogra­
dation of amylose. In contrast, Zhao et al. (2020) reported reduction in
RS and enhanced SDS and RDS of mung bean starch after HMT (30%
moisture content, at 120 ◦ C for 2, 4, 6, 8, 10, and 12 h) or RHMT (30%
moisture content, at 120 ◦ C for 2, 3, 4, 5, and 6 h). In general, HMT
increases RS; thus, the authors explain that the different trend found in
their study is due to RS being possibly transformed into SDS by enhanced
enzyme susceptibility, and this would be caused by the disruption of
starch granules and changes in crystalline structures when the associa­
tions between starch molecule chains are weakened. The SDS and RDS
values were higher when comparing the RHMT and HMT modifications,
which could be related to the higher relative crystallinity of starches
after RHMT. Thus, RHMT promoted a starch with greater digestibility,
which can be applied in foods with faster energy supply.
Amylose content in starches can diversify the digestibility and the
effect of HMT on this property. Wang et al. (2016) modified regular corn
starch and high-amylose corn starch using HMT, with moisture contents
of 20, 25, or 30%, at 120 ◦ C for 2 h. The RDS values decreased with the
increase in moisture content used in the modification. The greater re­
ductions were found using 30% of moisture content for both starches,
with 24% reduction for regular corn starch and 43% for high-amylose
corn starch, when compared to their native counterparts. The SDS
content increased and RS increased drastically when compared with
native starches: RS increased by about 1000%, for high-amylose content
modified at 30% moisture content. Therefore, this study shows that
HMT is a great alternative to modify high amylose content starch and
produce resistant starch.
The HMT parameters, such as temperature, moisture content, and
the botanical source of starch, promote distinct effect on SDS, RDS, and

RS. Thus, in order to efficiently apply HMT-starches in applications that
require high levels of RS, for example, a thorough study must be
performed.

3.1.6. Influence of HMT on enzymatic digestibility
HMT-starch has potential for the prevention of chronic diseases, due
to changes in native starch digestibility. Digestion of starch is an enzy­
matic hydrolysis in which starch is broken down into glucose, which is
converted to energy for the human body (Khatun et al., 2019). Studies
reporting in vitro methods for measuring starch digestibility are per­
formed by simulating in vivo conditions (Iuga & Mironeasa, 2020).
HMT is widely reported for changes in starch digestibility, enhancing
the nutritional value of starch-based products by increasing the SDS and
RS contents (Iuga & Mironeasa, 2020). There are specific factors directly
related to the effect of HMT in digestibility, such as the starch botanical
source, starch properties as crystallinity, granule size, amylose, and
amylopectin content, interactions and organization between those two
macromolecules, and the process parameters (Pratiwi et al., 2018).
According to Khatun et al. (2019)), the alteration of starch digestibility
by HMT is very important for consumers, since starch digestion is linked
with population health, especially for individuals with diabetes. These
authors reviewed the digestibility of HMT-rice starches and state that
the rice starch morphology presents very small, medium, and large
granules (comparing to other starch sources), being the last related to
the reduced in vitro rice starch digestibility. Other starch botanical
sources were cited for HMT modification, providing effect in α-amylase
susceptibility that was increased for rice, wheat, and potato starches.
Also, Khatun et al. (2019) reported decrease in RDS and increase in SDS
and RS in corn, pea, and lentil starches. The RS content relies on the
processing and storage conditions of food, such as temperature. It is also

related to several starch properties as gelatinization and retrogradation,
crystalline structure, and amylose and amylopectin ratio. These factors
are crucial for the enzymatic susceptibility of starch (Liu et al., 2016).
Normally, reduced digestibility is reported in the literature,
confirmed by decreased content of RDS and increased content of SDS
and RS. This occurs due to structural changes in starch granules, which
become more rigid and make it difficult for enzymes to attack during
digestion (Chung et al., 2012). Brahma and Sit (2020) performed HMT
in potato starched at 100 and 110 ◦ C for 2 h using 30 and 35% of
moisture content. HMT promoted an increase in SDS and RS, and
reduction in the RDS of potato starches. When comparing the HMTstarches, the RS values were higher with 35% moisture content,
increasing by 95% in the treatment at 100 ◦ C and by 88% in the treat­
ment at 120 ◦ C. This outcome suggests the formation of a rigid structure
that reduced the accessibility of the enzymes in the analysis to disrupt
starch molecules. In the highest moisture content (35%) exposure and
the lowest temperature (100 ◦ C), a greater effect on RDS and SDS was
obtained. The different data reported by the authors regarding distinct
parameters elucidate that the influence of temperature and moisture

3.2. Annealing
Annealing is a hydrothermal process that subject starch with exces­
sive (~70%, v/v) or intermediate (~40%, v/v) water content to tem­
peratures above the glass transition temperature and below the
gelatinization temperature of starch, under a period of time that varies
from minutes to days. The process parameters and starch characteristics
define the effect of annealing treatment, as previously discussed for
HMT. However, in annealing the moisture content does not vary, since
the treatment is held in excess of water (BeMiller, 2018; BeMiller &
Huber, 2015; Punia, 2020).
Table 2 shows the studies here reported on annealing applied to

different types of starch, as well as their treatment parameters. The
following sections explore these studies.
The effects of annealing on starch properties include: increase in
crystallinity, thermal stability, gelatinization temperature, starch gran­
ular size, and molecular mobility, due to an increase in the mobility of
the amorphous regions to a crystalline state. It also promotes the reor­
´zar-Alay & Meireles, 2015). This
ganization of molecular chains (Alca
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Carbohydrate Polymers 274 (2021) 118665

(2021), who assessed Castanopsis fruit starch treated in two steps, first
at 40 ◦ C for 24 h and then at 55 ◦ C for more 24 h, totalizing 48 h. The
authors reported that the granules presented rough surfaces with
irregular, polygonal, and spherical shapes, unaltered by annealing,
regardless of the number of steps in the treatment. Another study re­
ported no changes in morphology: Song et al. (2013) performed
annealing in potato and sweet potato starches (at 55 ◦ C for 72 h). Both
native and modified starches presented granules without pores and with
different morphologies among the cultivars (irregular, polygonal,
spherical, oval, round, and bell-shaped). Therefore, we can conclude
that the shape of starch granules is not affected by annealing, regardless
of the starch botanical source or the annealing treatment parameters.
Annealing is well known for modifying several properties of starch.
Morphology is affected when evaluating the size of starch granules; in
contrast, its shape and structure are not significantly affected. This was

confirmed by the studies showed in this review in which starches from
different botanical sources were modified by annealing.

Table 2
Annealing parameters, types of starch, and references.
Starch

Annealing parameters

Reference

Temperature ( C)

Time (min)

Germinated brown
rice grain
Yam

50

1440

50

1440

Sweet potato

50

Corn and wheat
Corn
Oca

55, 60, 65, 70, 80
50
42, 50

1440, 2880,
4320
30
1440
1440

Corn

63

1440

Waxy starches from
corn, potato, rice
and barley

10 ◦ C below the
temperature of
gelatinization

Castanopsis fruit

Sweet potato and
potato
Corn

40, 55
55

120, 180,
480, 960,
1440, 2880,
4320
1440, 2880
4320

45

1440, 4320

Oat

50

1440

◦

Chung et al.
(2012)
Falade and
Ayetigbo (2015)

Hu et al. (2020)
Li et al. (2020)
Liu et al. (2016)
Puelles-Rom´
an
et al. (2021)
Rocha et al.
(2012)
Samarakoon
et al. (2020)

3.2.2. Influence of annealing on solubility and swelling power
The swelling power and amylose leaching of starch granules are
reduced by annealing, which improves the quality of starch paste and gel
for application in food products (Mathobo et al., 2021). Shi et al. (2021)
modified Castanopsis fruit starch using a two-step annealing process
(step one at 40 ◦ C for 24 h, then step two at 55 ◦ C for more 24 h). The
authors reported substantial decrease in swelling power and solubility
after modification; both parameters decreased along with the increase in
annealing treatment from step one to two. In addition, as temperature
increased from 60 to 90 ◦ C, swelling power also increased for native and
annealed starches. The decrease in swelling power after annealing can
be attributed to the increase in crystallinity (see Section 3.2.4). The
reduction in solubility indicates that there was a strengthening of the
bonds, with an increase in the interactions between amylose and
amylopectin molecules, forming a more stable structure and reducing
the leaching of amylose.
Wang et al. (2014) performed a comparative study of annealing in
waxy, normal, and high-amylose corn starches, using parameters as
water excess, at 45 ◦ C for 24 and 72 h. The swelling power increased

prominently with the increase in amylose content of the starches. When
comparing native and annealed starches, the modification did not
change the swelling power for waxy starch. However, swelling power
decreased for normal and high-amylose starches, by 7 and 18%,
respectively. The distinct changes in solubility and swelling power of the
starches reported can be attributed to interactions between the starch
chains and the amylose-lipid complexes.

Shi et al. (2021)
Song et al.
(2013)
Wang et al.
(2014)
Werlang et al.
(2021)

occurs due to the hydration of the granule improving the arrangement of
double helices, causing a reversible swelling of the granule and
rendering an ordered structure with higher granule stability (Rocha
et al., 2012).
3.2.1. Influence of annealing on morphological properties
Annealing has been used recently on the modification of different
botanical sources of starch, such as yam starch, in which Falade and
Ayetigbo (2015) used annealing at 50 ◦ C for 24 h. The authors modified
the starch of various yam cultivars (water, white, yellow, and bitter).
Different outcomes were obtained among the samples, which influenced
the functional properties of starch. Regarding morphology, the evalua­
tion was performed in light microscope and for each cultivar, the
granules showed different shapes, but annealing did not affect the
shapes of any cultivar. When compared to the morphology of native yam

starches, the differences were the following: the modification changed
the size of the water cultivar granules; for the yellow cultivar, annealing
promoted reduced mean, modal, and median dimensions of the gran­
ules; and bitter and white cultivar showed no change in size. In this
study, the authors reported that not only the botanical source of starch,
but also the cultivar influenced the annealed starch properties, due to
amylose content, molecular rearrangement and size of amylose and
amylopectin chains, among other parameters.
´n et al. (2021) studied oca starch physically modified
Puelles-Roma
by annealing at 42 and 50 ◦ C for 24 h. The structure of starch granules
was not affected by annealing, due to the low temperature used in the
process of modification, which is below gelatinization temperature. The
shape of starch (evaluated by SEM analysis) was not affected either.
However, the granule size of annealed starch was higher than the size of
native starch. The same result was observed by Rocha et al. (2012), who
modified normal and waxy corn starches by annealing in excess of
water, for 24 h at 63 and 62 ◦ C, respectively. The morphology was
evaluated by SEM, showing no changes in granule shape: all granules
were round and polyhedral. The annealed normal and waxy starches
showed more pores and increased pore size in the granule surface, when
compared to their respective native starches. These changes can be due
to a spread of proteins over the starch granule surface, along with
annealing application and the weakening in tissue structure under
heating, forming a compact shape.
Again, annealing did not change morphology in the study of Shi et al.

3.2.3. Influence of annealing on pasting properties
The effect of annealing on starch pasting properties depends on
factors as amylose leaching, branch chain length distribution of

amylopectin, granule swelling, and relative crystallinity. This physical
modification promotes more resistance of the granules to deformation
by strengthening its intragranular binding forces (Song et al., 2013). Hu
et al. (2020) evaluated the effect of annealing at different time periods of
treatment on sweet potato starch, at 50 ◦ C for 1, 3, and 5 days. The
authors reported that according to the increase in annealing time, there
was an increase in the pasting temperature and a decrease in break­
down, peak, and final viscosities, as well as in setback (compared with
native starch). As annealing time elapsed, these changes in pasting
properties became more prominent. From the data reported by the au­
thors, we can see that annealing promoted more resistance to high
temperatures and weakened retrogradation, thus improving the pasting
properties of sweet potato starch. We can attribute the changes in
pasting properties of starches treated with annealing to the associations
among the chains within the amorphous region of the granule and the
changes in crystallinity promoted during this treatment.
In general, annealing does not change the shape of viscoamylograph
curves by RVA. Its effect on pasting properties is widely reported, as
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Carbohydrate Polymers 274 (2021) 118665

these are strongly influenced by treatment parameters as exposure time.
Song et al. (2013) modified potato and sweet potato starches using
annealing (55 ◦ C for 72 h). The annealed-starches presented reduction in
peak viscosity, breakdown, and setback, and increase in pasting tem­
perature. In our point of view, the changes mentioned for pasting

properties can be related to improved crystallinity (data can be found in
Section 3.2.4) and to the enhancement of the packing arrangement of
starch through annealing. The decrease in breakdown shows that the
starch is more stable during heating and continuous shear. This opens up
new applications that require starch stability in high temperature.
Werlang et al. (2021) modified oat starch (50 ◦ C for 24 h) using
annealing, and it had effect only on setback, which presented a lower
value when comparing annealed-starch to its native counterpart. In this
study, the other pasting properties of oat starch gels remained the same
after the modification. This outcome showed that in oat starch the effect
of annealing did not present the same influence on the pasting properties
as for other starches showed here, such as potato and sweet potato
starches. This elucidates the distinction of treatment response to
different types of starch with various structures and characteristics.
Amylose content is an important factor for obtaining the pasting
properties of starches by RVA. High-amylose starches did not present a
viscoamylograph curve under the conditions used by RVA, due to their
low viscosity. Therefore, the pasting parameters of high-amylose
starches cannot be measured by this analysis. Wang et al. (2014)
annealed corn starches containing different amylose contents (waxy,
normal, and high-amylose) at 45 ◦ C for 24 and 72 h. In the three
starches, annealing had no effect on pasting temperature, decreased
peak temperature and final viscosity, and increased final viscosity and
setback. The time of annealing had effect on these properties, which
increased or decreased gradually, as annealing time elapsed. The
breakdown viscosity decreased after 24 h of annealing and increased
after 72 h. The studies of Werlang et al. (2021), Hu et al. (2020), Song
et al. (2013), and Wang et al. (2014) showed the effect of annealing on
pasting properties of starches from oat, sweet potato, potato and sweet
potato, and corn, respectively. The data obtained did not show any

trends of increase or decrease in pasting parameters, and the effect of
annealing was different for each type of starch cited. Nevertheless, when
comparing native and annealed starch, changes were observed for all
botanical sources evaluated, which can be attributed to the disruption of
intra and intermolecular hydrogen bonds of the starch grain in the
presence of heat and water.

58% and 82% of amylose content, using annealing (at 55, 60, 65, 70, and
80 ◦ C for 30 min). The normal amylose content of starches showed Atype diffraction pattern, while the starch with high amylose content
presented B-type pattern. These patterns were not changed after
annealing, but the relative crystallinity decreased as the annealing
temperature increased. This study is important for showing that
different types of botanical sources, as well as amylose content and
modification parameters, can modify starch properties and structure
with different outcomes.
Samarakoon et al. (2020) investigated the effect of annealing on the
properties of waxy starches from different botanical sources (corn, po­
tato, rice, and barley). It can be observed in this study that annealing
affects the properties and the structure of starches from different
botanical sources differently. The diffraction patterns were not changed
by annealing. Native waxy starches from corn, rice, and barley presented
A-type pattern and potato starch showed B-type pattern. Relative crys­
tallinity was not changed for barley, rice and potato starch; however, for
corn starch it increased by 9% after annealing. Another study (Rocha
et al., 2012) reported the effect of annealing on normal and waxy corn
starches (water excess for 24 h at 63 and 62 ◦ C, respectively). Regarding
the amylose content, annealing showed no influence. The relative
crystallinity of normal amylose content did not change; however, there
was an increase of 7% for waxy starch. The decreased relative crystal­
linity found for some studies can be explained by partial gelatinization

and helix changes, leading to the destruction and reorientation of starch
crystallites. For each type of starch and the different amylose content,
the effect of annealing was distinct, which occurred for all the studies
shown in this review. This reinforces that the botanical source of starch
is able to change the effect of physical modification. When a starch is
chosen for application, this needs to be taken into consideration, since
the modifications can promote specific outcomes for each starch.
3.2.5. Influence of annealing on thermal properties
Overall, annealing led to increased onset, peak, and final tempera­
tures and gelatinization temperature range, and decreased gelatiniza­
tion enthalpy. This improved the thermal properties of starches,
broadening their application in food products that are exposed to high
temperatures during production. Different cultivars of potato and sweet
potato starches were modified by Song et al. (2013). The gelatinization
enthalpy decreased for all cultivars, except for one that also showed
increased relative crystallinity (see Section 3.2.4). The onset, peak, and
final temperatures decreased, and gelatinization temperature increased
upon annealing.
Modification parameters, such as time of exposure to high temper­
ature, provide greater influence on the thermal properties of starch.
According to the increase in days of treatment, annealing provided
starches with greater onset, peak, and final temperatures and reduced
gelatinization temperature, as reported by Hu et al. (2020). The authors
performed annealing in sweet potato starch (50 ◦ C for 1, 3 and 5 days).
Only in the 5-day treatment did the gelatinization enthalpy of starch
increase. In 1- and 3-day treatments, this property decreased slightly.
We believe that this occurs probably due to partial gelatinization during
annealing.
Variations in annealing temperature are also reported to present
greater effect. Thermal properties improve with the increase in tem­

perature, as reported by Puelles-Rom´
an et al. (2021), who modified oca
starch using annealing at 42 and 50 ◦ C for 24 h, using different water
ratios (1:2 w/v, being 35 g starch/70 ml distilled water, and 1:6 w/v,
being 15 g starch/90 ml distilled water). Annealing led to increase in
onset, peak, and final temperatures and gelatinization temperature
range, becoming more accentuated as annealing temperature increased.
The higher temperatures are related to a partial gelatinization of starch
during annealing. The changes in water ratio did not have effect on the
thermal properties, not differing among the samples at the same treat­
ment temperature. Gelatinization enthalpy was not changed by any of
the annealing conditions. Therefore, we can state that oca starch is more

3.2.4. Influence of annealing on crystallinity
The diffraction pattern of starch is mostly not affected by annealing.
In contrast, HMT-starches show shifts in the diffraction pattern, as
shown in Section 3.1.4. The different effect on starch properties among
the treatments is directly related to the parameters used in both modi­
fications, e.g., moisture content, temperature, and exposure time.
Recently, starches from different botanical sources were evaluated
for their diffraction pattern, which did not present any changes (Li et al.,
2020; Samarakoon et al., 2020; Shi et al., 2021). Annealing was applied
by Shi et al. (2021) to modify Castanopsis fruit starch (step one at 40 ◦ C
for 24 h and step two at 55 ◦ C for more 24 h). Native starch showed
diffraction peaks at (2θ) 5.7, 15.1, 17.2, 22.3, and 23.9◦ . This represents
a C-type pattern, which was not changed by annealing, regardless of
treatment step. Relative crystallinity decreased for starch treated with
two-step annealing (total of 48 h) when compared to native starch.
However, the starch modified after only one step (24 h at 40 ◦ C) kept the
same relative crystallinity. Thus, the addition of a second step in

annealing using a higher temperature (55 ◦ C) for additional 24 h
increased crystallinity by 19%. We believe that this behavior can be
attributed to the greater effect of heat, which affects the structure of the
starch granule in the second step.
Amylose content is known to influence the relative crystallinity of
starches. Li et al. (2020) modified three types of wheat starches with 37,
85, and 93% of amylose content, and two types of corn starches with
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resistant than other types of starch, since the changes in thermal prop­
erties were achieved using the highest temperatures tested and, even so,
there were no changes in gelatinization enthalpy.
The improvements in thermal properties indicate that annealing
enhances the crystal quality of starch by amylopectin aggregation
through the rearrangement of amylose, which needs less energy to break
the crystal structure due to the weakening of the network. Oat starch
was annealed by Werlang et al. (2021) (50 ◦ C for 24 h). The onset, peak,
and final temperatures and gelatinization temperature range increased
for the annealed oat starch, when compared to its native counterpart.
Gelatinization enthalpy reduced by 13% from native to annealed starch,
which can be associated to the destruction of the semi-crystalline
structure and the melting of imperfect amylopectin crystals.
The reported studies about the use of annealing on potato, sweet
potato, oca, and oat starches showed increased thermal stability. All
´n et al., 2021; Song et al., 2013;

studies (Hu et al., 2020; Puelles-Roma
Werlang et al., 2021) showed reduced onset, peak, and final tempera­
tures, regardless of the botanical source of starch. On the other hand, the
gelatinization temperature and enthalpy presented different trends with
the application of annealing, when compared to native counterparts.

new perspectives for science and technologies of starch modification.
Table 3 summarizes the studies reported for combined modifications
using HMT or annealing.
Combined methods with HMT, such as infrared heating, can be
performed in order to achieve the same improved properties in a shorter
time and with less energy. These combined methods for modification
were performed by Ismailoglu and Basman (2015) in corn starch and by
Ismailoglu and Basman (2016) in wheat starch. In both studies, the
authors used microwave with powers of 550 or 730 W, exposure times of
30, 60, or 90 min, and moisture content of 20 and 30%. The two studies
also had results regarding the botanical source of starch. The authors
found a retained A-type diffraction pattern; changes in thermal prop­
erties as increased onset, conclusion and gelatinization temperatures
were reported by the realignment of the polymer chain and formation of
a stable configuration; the pasting properties were affected by a decrease
in viscosity only for the samples treated using 550 W and 730 W and
30% of moisture content. We believe that the changes in pasting tem­
peratures are attributed to changes in crystallinity and the chains in the
amorphous region association. The authors showed a slight increase in
relative crystallinity.
The effect of heating methods with different impact of vacuum
pressure on corn starch properties was investigated by Bahrani et al.
(2013) using DV-HMT (direct vapor-heat-moisture treatment), RP-HMT
(reduced-pressurized heat-moisture treatment) and DIC (D´etente

Instantan´
ee Contrˆ
ol´ee). An improvement in the swelling capacity of the
granules was induced by the intensification of the hydrothermal process.
DIC promoted larger decrease of about 85% in viscosity when compared
to the other modifications, in which a decrease of 58% was found for DVHMT and 53% for RP-HMT. In this study, the intensification in hydro­
thermal process provides significant changes in rheological properties,
which can directly affect the functionality and application of starch. The

3.2.6. Influence of annealing on enzymatic digestibility
The degrading enzymes of enzymatic digestibility initially attack the
amorphous regions of starch molecules and then the crystalline regions
if they are exposed (Song et al., 2013). After annealing, RDS and SDS
contents increased, and RS content decreased when Song et al. (2013)
modified potato and sweet potato starches. The increase in RDS is
attributed to the easy and rapid attack of the enzymes of digestion on the
amorphous region and melted crystalline defects. The loss of the α-he­
lical structure upon partial gelatinization of annealed starches can
explain the increase in SDS and the decrease in RS.
Shi et al. (2021) determined the digestibility of Castanopsis fruit
starch after a two-step annealing process (step one at 40 ◦ C for 24 h and
step two at 55 ◦ C for additional 24 h). After annealing, RDS content
decreased and SDS content increased. Interestingly, RS was not changed
by annealing, even for the starch that showed increased crystallinity (see
Section 3.2.4). Following the same trend, annealing (at 50 ◦ C for 24 h) in
corn starch increased SDS and RS contents and decreased RDS, when
compared to native starch (Liu et al., 2016). In contrast, Wang et al.
(2014) annealed corn starches with different amylose contents (waxy,
normal, and high-amylose), but found no effect on digestibility.
Annealing can be promising for the modification of grains such as

germinated brown rice, which was modified using HMT (moisture
content of 30%, at 100 ◦ C for 1 h) (Chung et al., 2012). When comparing
germinated brown rice grains to their modified form, RDS content
decreased, RS increased, and SDS remained the same. The higher RS
content can be attributed to improved interactions in starch chains
formed during annealing. Therefore, this modification is an effective
alternative for controlling the digestibility of grains, which needs to be
the subject for future studies.
Annealing does not gelatinize starch; thus, the increase in RS is due
to structural changes as its increased crystallinity and molecular reor­
ganization. Throughout the studies reported to explore the effect of
annealing on digestibility (Chung et al., 2012; Liu et al., 2016; Shi et al.,
2021; Song et al., 2013; Wang et al., 2014), it could be seen that
annealing does not affect the digestibility of the starches. Thus, for ap­
plications that require decreased digestibility, with higher SDS and RS
content, annealing must be applied correctly according to each type of
starch.

Table 3
Combined modifications of HMT and/or annealing with other modifications in
starches from different sources.
Starches

Modifications

Important outcome

References

Corn

DV-HMT/RP-HMT/
and DIC
Annealing/dry heating

Decreased swelling
capacity and viscosity
Decreased SDS and RS
after treatment for corn
starch, increased for
potato starch
Improved freeze-thaw
stability, final viscosity,
rheological properties,
and solubility
Decreased viscosity,
thermal and pasting
properties
Decreased viscosity,
thermal and pasting
properties
Increased thermal
properties, SDS and RS
Increased SDS, RS,
viscoelasticity and
thermal stability
Decreased swelling power
and solubility, increased
RS
Decreased swelling power

and solubility, increased
SDS and RS
Reduced retrogradation,
improved thermal
properties and granule
stability

Bahrani et al.
(2013)
Chi et al.
(2019)

Corn and
potato

4. Combined modifications
Annealing and HMT can also be performed together or combined
with other modifications, such as chemical, physical, and enzymatic.
Combinations are an asset due to their improvement of properties,
opening up new applications in different fields. In addition, there are

Barley

Annealing/
hydroxypropylation

Corn

HMT/infrared heating

Wheat

HMT/infrared heating

Corn

HMT/organic acids

Corn

HMT/lactic acid

Kithul

HMT/annealing/crosslinking

Corn

HMT/extrusion

Potato

HMT/Amylose‑sodium
stearate complexes

Devi and Sit
(2019)
Ismailoglu
and Basman
(2015)

Ismailoglu
and Basman
(2016)
Maior et al.
(2020)
Reyes et al.
(2021)
Sudheesh
et al. (2020)
Yan et al.
(2019)
Yassaroh
et al. (2021)

HMT: Heat-moisture treatment; DV-HMT: direct vapor-heat-moisture treatment;
RP-HMT: reduced-pressurized heat-moisture treatment; DIC: D´etente
Instantan´
ee Contrˆ
ol´ee.
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modified starches showed the same size and shape as native starch with
some agglomerations, which is aligned with the reported studies using
only HMT: Bartz et al. (2017)) and Wattananapakasem et al. (2021),
who modified potato and rice starches, respectively. These studies are

shown in Section 3.1.1.
Chemical modification along with HMT was also reported to have
impact on the digestibility and thermal, structural, and pasting prop­
erties of corn starch, as evaluated by Maior et al. (2020), who combined
organic acids (lactic, citric, and acetic) and HMT. The authors found no
changes in diffraction pattern and a slight reduction in relative crys­
tallinity for all samples. This trend was also found by Ismailoglu and
Basman (2015) and Ismailoglu and Basman (2016), who combined HMT
and microwave modifications. The samples treated with HMT combined
with citric acid and lactic acid did not show gelatinization curves; the
sample treated with HMT and acetic acid showed a reduction of 15% in
gelatinization enthalpy; and the sample treated only with HMT showed
no difference for this property. The surface of the granules showed in its
morphology an increase in pores and some irregularities. Regarding
digestibility, there was increase in SDS and RS: we can suggest a
promising use for the production of low-carbohydrate foods for con­
sumers with chronic diseases such as diabetes, for example. The changes
in SDS and RS can be attributed to changes in starch structure as the
rupture of the double helices, which is proven by the reduction reported
in gelatinization enthalpy. Thus, we conclude that these modifications
performed together allow the possibility of applying modified starch in
functional food, producing higher levels of RS.
The combined modification of HMT and lactic acid was also evalu­
ated by other authors (Reyes et al., 2021), presenting changes in corn
starch such as reduced relative crystallinity of about 62% for the starch
modified only with HMT and about 33% for the starch modified by HMT
and lactic acid combined. The gelatinization enthalpy presented a
similar reduction for the starch modified by HMT and HMT combined
with lactic acid, reducing about 62%. In addition, increased solubility,
viscoelasticity and thermal stability were found. Regarding in vitro di­

gestibility, the modifications combined decreased RDS and increased
SDS and RS. We can see that combining the modification promoted more
accentuated influence on the enzymatic hydrolysis of starch granules by
acting more effectively on the enzymatic fractionation of starch chains.
The combined effects of extrusion and HMT on the physicochemical
properties and digestibility of corn starch were studied by Yan et al.
(2019). The modifications showed decreased swelling power and solu­
bility, and changed X-ray diffraction pattern from V- to V + A-type. The
pasting properties improved, with higher enthalpy values of about
133%. SDS and RS increased, with a 12% rise for RS: this shows that
combined modifications make the granules less susceptible to enzymatic
hydrolysis, due to more crystal perfection that leads to a resistance to
enzyme digestibility. In this study, starch structure, physicochemical
properties and digestibility were modified by combining HMT with
extrusion, allowing more applications of starch. Sudheesh et al. (2020)
combined different types of modification, performing annealing, HMT,
and cross-linking on underutilized kithul (Caryota urens) starch. In all
combinations performed, no changes were reported for the A-type dif­
fractogram pattern. The authors found a decrease in swelling power and
solubility, an increase in gelatinization enthalpy, and increase in hard­
ness of modified starch gel when compared to native starch. The dual
modification of cross-linking and HMT promoted the highest relative
crystallinity among the other combinations, and these modifications
combined also showed higher RS content, with an 18% increase when
compared to native starch. The RS was higher for all the combined
modifications when compared to the modifications performed alone.
The RS content is generally increased when HMT is combined with other
modifications, showing promising applications. Thus, changes in starch
elucidate improved granular stability and we believe that the confec­
tionery industry is one of the areas interested in good gel forming

capacity.
The improvement in the modification of starch is related to the

possible untangling in the entanglements among starch chains, which
induces strong movement of the chains, thus facilitating molecular
rearrangement during annealing (Zhong et al., 2020). It should be noted
that the effects of annealing or HMT on starch properties are enhanced
when these modifications are combined with each other or with other
types of modifications. The effectiveness of annealing was improved
when combined with microwave pretreatment, intensifying starch
properties as gelatinization enthalpy, particle size, peak viscosity, and
breakdown viscosity.
Devi and Sit (2019) performed annealing in one and two steps fol­
lowed by hydroxypropylation on barley starch. Relative crystallinity
and paste clarity increased, whereas swelling power, solubility, freezethaw stability, and paste viscosities decreased when performing
annealing alone. When the modifications were combined, they
enhanced freeze-thaw stability, final viscosity, paste clarity and tem­
perature, rheological properties, swelling power, and solubility. The use
of both physical and chemical modifications improves particular starch
properties that can be explored by food industries. Dry heating and
annealing combined to modify starch are a green alternative for
improving starch properties: the synergistic effect of both methods alter
starch lamellar thickness, increase double helical orders and improve
digestibility (Ashogbon, 2020). These modifications synergistically
modulate the starch structure, increasing thermostability and homoge­
neity and presenting direct influence on digestibility. This was reported
by Chi et al. (2019), who modified corn and potato starches using
annealing combined with dry heating, focusing on improvements in
starch digestibility. SDS and RS decreased after combined modification
for corn starch and increased for potato starch. This can be attributed to

the different molecular structure of those two starches, shown in their
diffraction patterns (A-type for corn and B-type for potato). The inter­
esting data present by Chi et al. (2019) showed an increase in efficiency
of annealing when combined with dry heating and a significant
improvement in digestibility for potato starch. It is worth mentioning
that the two physical modifications used are green and low-cost. For
targeting applications as in the prevention of chronic diseases, the in
vitro enzymatic digestibility of starch must be further investigated in
order to efficiently control the effect of dry heating and annealing per­
formed together.
The physicochemical properties of amylose‑sodium stearate com­
plexes (at concentrations of 2, 5, and 8%) in HMT-potato starch were
evaluated by Yassaroh et al. (2021). The amylose inclusion complexes
were used with sodium stearate as guest molecules. The addition of
amylose‑sodium stearate complexes reduced starch retrogradation and
improved thermal properties, which are promising results for cookingrelated applications. Throughout changes in X-ray pattern to V6- type
amylose crystallite, the formation of amylose inclusion complexes was
proven. The combined modifications increased relative crystallinity,
pasting temperature and granule stability, and decreased the swelling
ability, which was more accentuated than in HMT performed alone. The
authors explored different applications for the modified potato starch as
filler, emulsifier, and thermally stable thickener. For future studies, it
would be interesting that the digestibility of the starches modified by
amylose‑sodium stearate complexes and HMT could be evaluated, since
due to the properties obtained it is possible that SDS and RS contents are
improved.
The changes upon starch when using HMT or annealing alone can be
insufficient depending on the applications requested. Thus, using these
physical modifications together or with other modifications promotes
more efficient outcomes, as shown in this review by expressive changes

in thermal, pasting, and swelling properties, as well as in digestibility.
Therefore, performing combined modifications can enhance starch
functionality, broadening its spectrum of applications.
5. Recent trends and applications
Starch application has been expanding over the years and
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researchers have been studying its use for producing several materials as
biodegradable films, which are used as food packages (Schafranski et al.,
2021). Starch modification is performed to improve specific properties
of the films, enhancing mechanical properties and reducing water vapor
permeability, an important factor for food package industries. The
application of starch in food packaging is an increasing trend, exploring
the production of biodegradable and/or edible packages, as well as the
possibility of active and intelligent packaging. The modification of
starch meets the need for improved properties, which are required for
the applications cited.
The production of biodegradable films is a promising application for
physically modified starches. Zavareze et al. (2012) developed biode­
gradable films based on potato starch modified by HMT (110 ◦ C for 1 h),
using different starch concentrations (3, 4, and 5%, w/v). The modifi­
cation provided lower viscosity, solubility and swelling power to the
starches, when compared to its native form. The mechanical properties
of the films were improved by the higher values of tensile strength,
young modulus, and elongation at break, when comparing the films

based on native and HMT-starches. However, the water vapor perme­
ability increased after HMT. It is well known that this is not desired for
the application of films as food packaging, since the moisture transfer
between food and atmosphere must be avoided. Thus, we can state that
the biodegradable films based on HMT-starch can be used for packaging,
depending on the food characteristics and the desired characteristic for
the package.
Higher water vapor permeability was also found in biodegradable
films based on rice flour and rice starch, both modified by HMT, using
20% of moisture content at 120 ◦ C for 5 h (Majzoobi et al., 2015). The
authors reported changes in other properties of the films when HMT was
performed, such as reduced lightness, transparency, tensile strength,
and water solubility. Thus, they suggest that the biodegradable films
may be suitable for packaging of frigid products, or with less sensitivity
to moisture content. Indrianti et al. (2018)) modified sweet potato starch
using HMT (25% of moisture content, at 110 ◦ C for 1, 2, and 3 h) and
applied it in the production of edible films. The authors found increase
in thickness, tensile strength, and elongation at break and decrease in
solubility and water vapor permeability of the films produced with
modified starch. The time of exposure did not have influence on the
edible films. The great data found by the authors provide quantitative
and qualitative information about edible films, being the improved
properties of the films an indication that they can be applied in food
products in future studies. The production of biodegradable films using
HMT-starches from different botanical sources as potato, rice and sweet
potato (Indrianti et al., 2018; Majzoobi et al., 2015; Zavareze et al.,
2012) was reported in this review. From these studies we can observe
that for sweet potato, the water vapor permeability of the films has
decreased, while for potato and rice starches, this parameter has
increased. The solubility has decreased for all the starches modified by

the different studies. This distinct data obtained for some properties can
be attributed mostly to the variations on starch structure among the
botanical sources, but also to the different parameters used in the
modifications.
Different approaches for starch modifications and applications as
raw material for production of nanoparticles were revised by Kumari
et al. (2020)), who showed a wide range of applications for modified
starch nanoparticles in food systems, such as encapsulating agents,
reinforcement materials, and emulsion stabilizers. The authors reported
that modifications as HMT improve the thermal properties and relative
crystallinity of nanoparticles. Interestingly, HMT is being widely applied
to modify starch nanoparticles, due to its capacity of increasing the
thermal properties and the crystallinity of nanoparticles (Ji et al., 2019;
Kumari et al., 2020). Annealing is also used to modify the structure of
nanoparticles: Ji et al. (2019) modified waxy corn starch nanoparticles
by annealing at 55 ◦ C for 6, 12, 24, and 48 h. They reported that
annealing changed the spherical morphology of the nanoparticles, but
maintained their nanoscale size. The relative crystallinity of

nanoparticles was enhanced according to the increase in treatment time,
achieving 19% higher values when compared to native starch nano­
particles. The melting temperature increased, suggesting an effective
packing of double helices. Physical modifications as HMT, when applied
on starch before the production of nanocrystals, are proven to be
effective in increasing the yield, decreasing preparation time and
increasing relative crystallinity. Nanocrystals are the most common
application of starch in nanotechnology. They are crystalline structures
produced mostly by acid hydrolysis of starch and are widely applied in
various industries as food, cosmetics, paper, among others (Niu et al.,
2020; Zhou et al., 2020). Dai et al. (2019) produced HMT-waxy corn

starch nanocrystals by acid hydrolysis and reported a higher yield and a
shorter period of time to produce the nanocrystals when HMT was used.
The authors reported that the HMT increased the relative crystallinity of
the starch and the starch-nanocrystals and showed pores in the granule
structure surface. Hence, we can state that the main objective of using
HMT in the production of nanocrystals was achieved, since higher yield,
short production time, and higher crystallinity were obtained when
compared to native starch-based nanocrystals.
Nanocrystals based on RHMT-waxy corn starch presented higher
thermal stability, lower molecular order, and double-helix content when
evaluated by Niu et al. (2020). Changes in crystalline pattern from Atype to B-type were found, as relative crystallinity increased according
to the increase in HMT. This property achieved an increase of 15% when
compared to native starch. Pinto et al. (2021) modified pinh˜
ao starch
using HMT or annealing, in order to produce starch nanocrystals with
improved properties. Annealing promoted higher thermal stability and
HMT promoted higher yields of nanocrystals and higher relative crys­
tallinity, when compared to nanocrystals from native starch. Dai et al.
(2019), Niu et al. (2020) and Pinto et al. (2021) reported similar changes
in nanocrystals as the increase in relative crystallinity and yields when
comparing starches, native and modified by annealing and HMT. We can
see that the improvements in properties are directly linked with the
nanocrystal applications. This indicates that physical modifications can
be performed in starch before the production of nanocrystals, so as to
improve characteristics and enable applications as raw material in
nanotechnology.
The interest from industries in biodegradable materials (films,
nanoparticles, and nanocrystals) is growing. They reduce environmental
pollution, as less material is disposed in the environment, and they
replace synthetic polymers in food packages. It can be seen that most of

the starch materials mentioned were produced using modified starches.
Starch is applicable to several sectors of food industries. It can be
used: as a modifier of texture and viscosity; for gel formation and
moisture retention; in baking flour; in pasta; and in instant and fried
foods (Alc´
azar-Alay & Meireles, 2015). The demand from consumers for
healthier baked goods has been growing over the years. Therefore, we
can find studies on the partial or total replacement of wheat flour for
more nutritional flours, such as barley.
The modification by HMT can treat starch for undesired properties,
enabling its application in gluten-free food products (Iuga & Mironeasa,
2020). Flours can be modified by HMT, being applied in bread matrices
and having effect on the techno-functional and nutritional parameters of
breads. A study performed by Collar and Armero (2018) showed the
impact of HMT (15% moisture content, 120 ◦ C and 1 h) on bread, based
on a mixture of wheat and whole barley flours. The authors aimed at
partial substitution of wheat flour by using barley flour as a strategy to
create an added value to baked goods. When analyzing the breads, a
superior functional profile was found in whole barley flour exposed to
HMT: it exhibited similar properties to wheat-based bread, such as cell
uniformity, smoothness, and taste, being all the properties evaluated
dependent on the availability of water in the HMT process of dough
making. In our point of view, this is an important outcome, since the
substitution of wheat flour in breads is known for yielding products with
inferior technological properties. A similar trend was observed by Collar
and Armero (2018) for polyphenol bioaccessibility and anti-radical
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DPPH activity, regardless of the HMT and the hydration of flours in
blended matrices. These results show promising applications of the
HMT-barley flour in baked goods. We can observe that the modifications
reported in this review make the starches fit for applications in the
production of baked goods for people with chronic diseases (as celiac
disease and diabetes) and restrictions on consuming bakery products.
In the rice industries, microorganisms can be developed during
parboiling in the soaking step. An alternative for this issue can be the
application of HMT in the grain, which presents the advantage of
reducing microorganisms at this step of rice processing. Another
advantage is the inactivation of enzymes that release compounds as
sugar, phosphorus and nitrogen in the soaking water. Arns et al. (2014)
have modified paddy rice grains by HMT (13% moisture content, 120 ◦ C
and 10, 30, and 60 min), which had effect on rice grain before par­
boiling. Before parboiling the grains, the authors quantified the meta­
bolic defects, which increased by 23% for the paddy rice grain modified
for 60 min (the longest treatment time), when compared to the native
grain. We can explain this behavior by the longer period of exposure to
high temperature that increased the chemical reactions, causing the
appearance of stains and other changes in the grains. Regarding the
parameters evaluated after rice grain parboiling, Arns et al. (2014)
evaluated cooking time and volumetric and gravimetric yields after
cooking. Cooking time increased by 73% when comparing the native
grain to the one treated for 60 min. This parameter increased gradually
with the increase in HMT time. However, the parameters of volumetric
and gravimetric yield after cooking have shown no difference between
the native grain and the ones treated for 10 and 60 min, only increasing

for the treatment time of 30 min. The increased cooking time can be
related to a greater internal restructuring in the grain, which would
enhance resistance to water absorption, being in accordance with other
parameters evaluated, such as pasting properties (i.e., lower values of
peak viscosity and final viscosity).
According to Obadi and Xu (2021), the quality of noodles is directly
linked to starch properties. The starch must have high tensile strength,
low stick after cooking, and low cooking loss during cooking, and these
can be achieved by using modified starches. Noodles based on amaranth
starch modified by HMT (110 ◦ C for 2.5 h) were produced by Chandla
et al. (2017)). The authors compare the noodles from HMT-amaranth
starch with noodles from native amaranth and corn starches, finding
firmer texture, improved taste, and distinct flavor for HMT-starch noo­
dles. Annealing widens the range of applications of starch, since
annealed starches can improve food qualities as appearance, shelf sta­
bility, and emulsification materials (Ji et al., 2019). The use of annealed
starches in food products is more often found in the preparation of
noodles. In poor-quality rice flour, it has been reported that annealing
provided soft texture in fresh noodles (BeMiller, 2018). Wang et al.
(2018) studied the effect of annealing (55 ◦ C for 16 h) on the physico­
chemical properties of rice starch and the quality of rice noodles.
Annealing did not change the granule morphology or crystalline pattern
of rice starch; however, relative crystallinity increased, and there was
decrease in solubility, swelling power, pasting viscosity, breakdown,
and setback. The application of annealed rice starch in the production of
noodles was improved by changes in the gel texture of rice starch.
Increasing annealed rice starch content in the blends for noodles
improved sensory evaluation scores, cooking qualities, and texture
properties. Therefore, annealing is a promising alternative to be inserted
in the industries, in order to obtain rice starch with improved properties

for the production of gluten-free baked goods.
Annealing (50 ◦ C for 3 h) was combined with water-soluble fraction
removal to modify flours from different varieties of rice, for the pro­
duction of noodles. Choi and Koh (2017) reported that the treatments in
flours reduced cooking losses and improved the textural properties of
cooked rice noodles. Mouthfeel firmness increased for all varieties. It is
worth mentioning that this study showed that using this combined
modification in noodles improved its functional characteristics without
using chemical additives. The studies of Chandla et al. (2017)), Wang

et al. (2018) and Choi and Koh (2017) evaluated the effect of HMT on
amaranth starch, annealing on rice starch, and annealing combined with
water-soluble fraction removal on rice flours, respectively. They have in
common the application of modified starches in the production of
noodles, which was improved regardless of the modification applied.
Thus, we can state that HMT, annealing and combined modifications
produce starches with techno-functional properties that can be applied
in noodles.
Ji (2020) evaluated the effect of annealing (55 ◦ C for 24 h) on the
functional properties of corn starch/corn oil/lysine blends and reported
that the modified starch had decrease in enthalpy and gelatinization
temperature, and maintained A-type crystalline structure. Regarding the
blend analysis, the gelatinization temperature also increased, suggesting
that amylose-lipid interactions restrict water penetration, thus needing
higher temperatures for dissociation. The blends with annealed starch in
its composition showed improvement of its pasting properties and the
digestibility assays showed increased content of slowly digestible starch
content, showing a good prospect for the efficient modification of the in
vitro digestibility of starch. The changes in digestibility upon annealing
are also obtained in starch food products, which enable the application

of annealed starches in food industries.
Poly(lactic acid)/corn starch blends were produced by extrusion
molding (Lv et al., 2015). The blend was annealed, remaining for 1 week
at room temperature with moisture content of 60%, and then heated at
various temperatures (50, 60, 80, 100, and 120 ◦ C). Increase in thermal
stability was reported with the increase in enthalpy, achieving 14% for
the most severe treatment (120 ◦ C) compared to the untreated sample.
There was also improvement in mechanical properties of blends. It was
concluded that annealing is effective in reorganizing molecular chains,
weakening structural relaxation and increasing the crystallinity of ma­
terials. The studies of Ji (2020) and Lv et al. (2015) exploit the pro­
duction of blends using annealed-starches. This improved the properties
of blends, showing a promising field of applications.
Currently, the encapsulation of compounds and their incorporation
in polymer matrices for application in food packaging are some of the
most cited research subjects. Regarding this matter, starch is widely used
for being a great matrix: it is biocompatible, biodegradable, low-cost,
widespread, and non-toxic. Ethylene gas was encapsulated into inclu­
sion complexes based on V-type crystalline starches by Shi et al. (2019),
which were modified by annealing at temperatures of 30–70 ◦ C and
heated in aqueous ethanol solutions of 45–100% (v/v) for 10 min. In the
results for morphology, light microscopy and X-ray diffraction, the au­
thors could observe an increase in single helices content by annealing.
When using annealing at 70 ◦ C with 50% (v/v), the ethylene concen­
tration in the inclusion complexes increased from 8.0–31.8% (w/w) to
18.1–49.6% (w/w), and the inclusion complexes prepared with
annealed V-starches showed to be more stable in different storage en­
vironments. This study provides great results regarding technologies for
the encapsulation of gas in a renewable and biodegradable matrix, also
showing the importance of annealing and its role in the application of

starch. However, studies using HMT and annealed-starch for encapsu­
lation of active compounds are scarce in literature, being a great topic to
be approached by scientists and technologists.
Table 4 presents studies regarding the applications of starches
modified by HMT and annealing, as well as the effect of these modifi­
cations on properties of the final products. The physical modifications of
HMT and annealing showed in Table 4 were performed on starches from
different botanical sources and presented distinct and specific influence
on starch properties. The modifications were chosen by the studies in
order to improve determined characteristics for specific applications of
the starches in food products and food packages. The authors studied
applications for noodle and bread production, biodegradable and edible
films, nanocrystals, and nanoparticles. Each application focused on
improving different properties: for noodle production, firmer texture;
for HMT-starch noodles, improved taste and distinct flavor; for pro­
duction of biodegradable films, decreased water vapor permeability and
12


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Carbohydrate Polymers 274 (2021) 118665

Table 4
Applications of starches, flours or grain modified by heat-moisture treatment
(HMT) and annealing.
Starch/
Flour/
Grain

Modification

Paddy rice
grain

HMT

Parboiled rice

Amaranth

HMT

Noodles

Rice

Application

Annealing/
Watersoluble
fraction
removal

Noodles

Wheat
and
whole
barley

flours

HMT

Bread

Waxy corn
starch

HMT

Nanocrystals

Waxy corn
starch

Annealing

Nanoparticles

Corn
starch

Annealing

Corn starch/
corn oil/lysine
blends

Sweet

potato
starch

HMT

Edible films

Corn
starch

Annealing

Rice
starch
and
flour

HMT

Waxy corn
starch

Repeated
heatmoisture
treatments
Annealing
and HMT

Pinh˜
ao

starch

Poly(lactic
acid)/corn
starch blends
Biodegradable
films

Nanocrystals

Nanocrystals

V-type
starch

Annealing

Inclusion
complexes for
ethylene gas
encapsulation

Rice
starch

Annealing

Noodles

Important

outcome

Reference

Increased cooking
time and
volumetric and
gravimetric yield
Firmer texture,
improved taste
and distinct flavor
for HMT-starch
noodles
Reduced the
cooking losses
and improved the
textural
properties of
cooked rice
noodles; increase
in mouthfeel
firmness
Similarity in
bread properties;
maintained
bioaccessibility
and anti-radical
DPPH activity
Higher yield;
shorter period of

time in
production; and
higher relative
crystallinity
Higher
crystallinity;
higher melting
temperature
Improved pasting
properties;
increased content
of slowly
digestible starch
Higher thickness,
tensile strength
and elongation;
lower solubility

Arns et al.
(2014)

Higher thermal
and mechanical
properties
Higher tensile
strength, stretch
resistance; greater
rigidity and
extensibility
Higher

crystallinity;
higher thermal
stability
Increased
production yields
and thermal
stability;
decreased
crystallinity
Higher ethylene
gas
concentration;
higher stability
during storage
Increased sensory
evaluation scores,
cooking qualities

Lv et al.
(2015)

Table 4 (continued )
Starch/
Flour/
Grain

Potato
starch

Chandla

et al.
(2017))

Modification

HMT/
oxidation

Application

Biodegradable
films

Important
outcome
and texture
properties
Decreased water
vapor
permeability;
increased tensile
strength

Reference

Zavareze
et al.
(2012)

increased tensile strength.

Choi and
Koh
(2017)

6. Conclusions
The modification of starch by HMT and/or annealing affects the
structural parameters and physical and functional properties of starch,
including crystallinity, morphology, solubility, viscosity, swelling abil­
ity, pasting, and gelatinization properties, as well as thermal and
freeze–thaw stability. Improvements in the characteristics of HMTstarch and annealed-starch associated with their possible applications
are: (i) reduced solubility and increased gel hardness of starch for use in
noodles; (ii) reduction in swelling power for application in biodegrad­
able films; (iii) increase in SDS and RS for functional food products; (iv)
reduction in retrogradation and breakdown viscosity for bakery goods;
and (v) increase in thermal stability for frozen food products.
Annealed-starch and HMT-starch are used in a variety of materials in
the food sector, as food packages (e.g., biodegradable films, edible films,
nanocrystals, and others), and in food products as pasta, pastry, baked
goods, and others. These applications are possible because these phys­
ical methods do not generate environmental pollutants. Thus, these
starches can be added to food products in higher amounts than chemi­
cally modified starches.
Promising data regarding starch digestibility was widely reported for
HMT, due to enhanced SDS and RS contents, which promote the use of
starch in functional food products. Future studies on the in vivo di­
gestibility of modified starch products are needed, as well as an
expansion of their applications, so that they reach industrial level more
effectively.

Collar and
Armero
(2018)

Dai et al.
(2019)

Ji et al.
(2019)
Ji (2020)

Indrianti
et al.
(2018))

CRediT authorship contribution statement
Laura Martins Fonseca: Writing – original draft, Data curation,
Investigation, Conceptualization, Writing – review & editing, Visuali­
zation. Shanise Lisie Mello El Halal: Investigation, Visualization,
Writing – review & editing. Alvaro Renato Guerra Dias: Writing –
review & editing, Conceptualization, Funding acquisition. Elessandra
da Rosa Zavareze: Writing – review & editing, Conceptualization,
Funding acquisition, Supervision.

Majzoobi
et al.
(2015)
Niu et al.
(2020)

Declaration of competing interest
Pinto
et al.
(2021)

The authors report no declarations of interest.
Acknowledgements
o de Aperfeiỗoamento de
This study was financed by Coordenaỗa
Pessoal de Nớvel Superior - CAPES (Finance Code 001), Conselho
´gico - CNPQ
Nacional de Desenvolvimento Científico e Tecnolo
` Pesquisa do Estado do Rio
(306378/2015-9) and Fundaỗ
ao de Amparo a
Grande do Sul (BR) - FAPERGS (17/255100009126).

Shi et al.
(2019)

Wang
et al.
(2018)

13


L.M. Fonseca et al.

Carbohydrate Polymers 274 (2021) 118665

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