Abstract
Present trends towards technologies and processes that increase the use of residues make starchy vegetal biomass an important alternative material in various applications due to starch’s versatility, low cost and ease of use when its physicochemical properties are altered. Starch is increasingly used in many industrial applications and as a renewable energy resource. Starch can be modified to enhance its positive attributes and eliminate deficiencies in its native characteristics. In this article, the state of knowledge on conventional and unconventional starches and their properties, characteristics, modifications and applications are reviewed.
starch modification; starch granules; paste properties; conventional starch; unconventional starch; starch biomass; food
1 Starch
Starch is the most abundant carbohydrate reserve in plants and is found in leaves,
flowers, fruits, seeds, different types of stems and roots. Starch is used by plants
as source of carbon and energy (Smith,
2001Smith, A. M. (2001). The biosynthesis of starch granules.
Biomacromolecules, 2(2), 335-341. http://dx.doi.org/10.1021/bm000133c.
PMid:11749190.
http://dx.doi.org/10.1021/bm000133c...
). The biochemical chain responsible for starch synthesis involves
glucose molecules produced in plant cells by photosynthesis. Starch is formed in the
chloroplasts of green leaves and amyloplasts, organelles responsible for the starch
reserve synthesis of cereals and tubers (Smith,
2001Smith, A. M. (2001). The biosynthesis of starch granules.
Biomacromolecules, 2(2), 335-341. http://dx.doi.org/10.1021/bm000133c.
PMid:11749190.
http://dx.doi.org/10.1021/bm000133c...
; Tester et al., 2004Tester, R. F., Karkalas, J., & Qi, X. (2004). Starch -
Composition, fine structure and architecture. Journal of Cereal Science, 39(2),
151-165. http://dx.doi.org/10.1016/j.jcs.2003.12.001.
http://dx.doi.org/10.1016/j.jcs.2003.12....
).
Starch production in the chloroplast is diurnal and performed rapidly by the plant.
Conversely, starch reserves produced by amyloplasts are deposited over several days,
or even weeks. Starch is stored and cyclically mobilized during seed germination,
fruit maturation and the sprouting of tubers (Ellis
et al., 1998Ellis, R. P., Cochrane, M. P., Dale, M. F. B., Duffus, C. M., Lynn,
A., Morrison, I. M., Prentice, R. D. M., Swanston, J. S., & Tiller, S. A.
(1998). Starch production and industrial use. Journal of the Science of Food and
Agriculture, 77(3), 289-311.
http://dx.doi.org/10.1002/(SICI)1097-0010(199807)77:3<289::AID-JSFA38>3.0.CO;2-D.
http://dx.doi.org/10.1002/(SICI)1097-001...
). The main location of starch synthesis and storage in
cereals is the endosperm. Major starch sources are cereals (40 to 90%), roots (30 to
70%), tubers (65 to 85%), legumes (25 to 50%) and some immature fruits like bananas
or mangos, which contain approximately 70% of starch by dry weight (Santana & Meireles, 2014Santana, A. L., & Meireles, M. A. A. (2014). New starches are
the trend for industry applications: a review. Food and Public Health, 4(5),
229-241.). The
accumulation pattern of starch granules in each plant tissue, shape, size, structure
and composition is unique to each botanical species (Smith, 2001Smith, A. M. (2001). The biosynthesis of starch granules.
Biomacromolecules, 2(2), 335-341. http://dx.doi.org/10.1021/bm000133c.
PMid:11749190.
http://dx.doi.org/10.1021/bm000133c...
).
Starch synthesized by plant cells is formed by two types of polymers: amylopectin and
amylose. Amylopectin consists of linear chains of glucose units linked by α-1,4
glycosidic bonds and is highly branched at the α-1,6 positions by small glucose
chains at intervals of 10 nm along the molecule’s axis; it constitutes between 70 to
85% of common starch (Durrani & Donald,
1995Durrani, C. M., & Donald, A. M. (1995). Physical
characterisation of amylopectin gels. Polymer Gels and Networks, 3(1), 1-27.
http://dx.doi.org/10.1016/0966-7822(94)00005-R.
http://dx.doi.org/10.1016/0966-7822(94)0...
). Amylose is essentially a linear chain of α-1,4 glucans with
limited branching points at the α-1,6 positions and constitutes between 15-30% of
common starch. Starch’s structural units, amylose and amylopectin, are shown in
Figure 1. The polymodal distribution of
α-glucans chains of different sizes and the grouping of branch points in the
amylopectin molecule allow the formation of double helical chains. Amylose and
amylopectin can be arranged in a semicrystalline structure forming a matrix of
starch granules with alternating amorphous (amylose) and crystalline (amylopectin)
material, which is known as the growth rings in superior plant starch (Jenkins et al., 1993Jenkins, P. J., Cameron, R. E., & Donald, A. M. (1993). A
universal feature in the structure of starch granules from different botanical
sources. Stärke, 45(12), 417-420.
http://dx.doi.org/10.1002/star.19930451202.
http://dx.doi.org/10.1002/star.199304512...
).
Basic structural design of (a) glucose units, (b) amylose and (c) amylopectin, along with the labeling of the atoms and torsion angles. Extension of the basic units to macromolecular structures was adapted from Pérez & Bertoft (2010)Pérez, S., & Bertoft, E. (2010). The molecular structures of starch components and their contribution to the architecture of starch granules: a comprehensive review. Starch/Staerke, 62(8), 389-420. http://dx.doi.org/10.1002/star.201000013.
http://dx.doi.org/10.1002/star.201000013... .
Several types of starches are known as “waxy” starches due to the waxy appearance of
the endosperm tissue from which they are derived; these tissues contain a minimal
amount of amylose in their granule composition (<15%). Waxy starch requires high
energy for gelatinization due to its high crystallinity (Hung et al., 2007Hung, P. V., Maeda, T., & Morita, N. (2007). Study on
physicochemical characteristics of waxy and high-amylose wheat starches in
comparison with normal wheat starch. Starch/Staerke, 59(3-4), 125-131.
http://dx.doi.org/10.1002/star.200600577.
http://dx.doi.org/10.1002/star.200600577...
). Other starches have a high content of
amylose (>30%); these starches can also contain other polysaccharide molecules
and exhibit a slight deformation in granule appearance.
Cereal starches contain lipid molecules in their structures in the form of
phospholipids and free fatty acids; they are associated with the amylose fraction
(Ellis et al., 1998Ellis, R. P., Cochrane, M. P., Dale, M. F. B., Duffus, C. M., Lynn,
A., Morrison, I. M., Prentice, R. D. M., Swanston, J. S., & Tiller, S. A.
(1998). Starch production and industrial use. Journal of the Science of Food and
Agriculture, 77(3), 289-311.
http://dx.doi.org/10.1002/(SICI)1097-0010(199807)77:3<289::AID-JSFA38>3.0.CO;2-D.
http://dx.doi.org/10.1002/(SICI)1097-001...
; Tester et al., 2004Tester, R. F., Karkalas, J., & Qi, X. (2004). Starch -
Composition, fine structure and architecture. Journal of Cereal Science, 39(2),
151-165. http://dx.doi.org/10.1016/j.jcs.2003.12.001.
http://dx.doi.org/10.1016/j.jcs.2003.12....
). The presence of lipid
complexes in starch granules is observed as a hydrophobic nucleus situated within
helices formed by amylose chains. The lipid complexes vary between 0.15 to 0.55% of
the amylose fraction in cereal starches (Tester et
al., 2004Tester, R. F., Karkalas, J., & Qi, X. (2004). Starch -
Composition, fine structure and architecture. Journal of Cereal Science, 39(2),
151-165. http://dx.doi.org/10.1016/j.jcs.2003.12.001.
http://dx.doi.org/10.1016/j.jcs.2003.12....
). Lipids in starch granules, despite representing a small
fraction, can significantly reduce the swelling capacity of the starch paste (Morrison & Azudin, 1987Morrison, W. R., & Azudin, M. N. (1987). Variation in the
amylose and lipid contents and some physical properties of rice starches.
Journal of Cereal Science, 5(1), 35-44.
http://dx.doi.org/10.1016/S0733-5210(87)80007-3.
http://dx.doi.org/10.1016/S0733-5210(87)...
). Starch contains
approximately 0.6% of protein associated with the molecule. The origins of protein
and lipids on starch are situated on the granule surface. Lipids and proteins in
starch granules can raise its functionality. In wheat for example, the associated
protein in the starch granules receives a lot attention due to its association with
grain hardness. Starch also contains a relatively small quantity (<0.4%) of
minerals (calcium, magnesium, phosphorus, potassium and sodium). Among these,
phosphorus is of primary importance and is present in starch in three main forms:
monophosphate esters, phospholipids and inorganic phosphate.
The physical and chemical aspects of starch synthesis and the composition of amylose
and amylopectin have been discussed in detail in other reviews by Smith (2001)Smith, A. M. (2001). The biosynthesis of starch granules.
Biomacromolecules, 2(2), 335-341. http://dx.doi.org/10.1021/bm000133c.
PMid:11749190.
http://dx.doi.org/10.1021/bm000133c...
, Tester et al. (2004)Tester, R. F., Karkalas, J., & Qi, X. (2004). Starch -
Composition, fine structure and architecture. Journal of Cereal Science, 39(2),
151-165. http://dx.doi.org/10.1016/j.jcs.2003.12.001.
http://dx.doi.org/10.1016/j.jcs.2003.12....
, Pérez &
Bertoft (2010)Pérez, S., & Bertoft, E. (2010). The molecular structures of
starch components and their contribution to the architecture of starch granules:
a comprehensive review. Starch/Staerke, 62(8), 389-420.
http://dx.doi.org/10.1002/star.201000013.
http://dx.doi.org/10.1002/star.201000013...
and Conde-Petit et al.
(2001)Conde-Petit, B., Nuessli, J., Arrigoni, E., Escher, F., & Amadò,
R. (2001). Perspectives of starch in food science. Chimia, 55(3),
201-205..
2 Physicochemical properties of starch
The length of the α-glucan chains, amylose-amylopectin ratio and branching degree of
amylopectin define the size, structure and particular utility of starch granules in
each plant species. Other characteristics associated with the granule such as form,
surface type and phosphate groups influence the starch’s properties and uses (Smith, 2001Smith, A. M. (2001). The biosynthesis of starch granules.
Biomacromolecules, 2(2), 335-341. http://dx.doi.org/10.1021/bm000133c.
PMid:11749190.
http://dx.doi.org/10.1021/bm000133c...
).
2.1 Characteristics of starch granules: morphology, size, composition and crystallinity
Starch granules have microscopic sizes with diameters ranging from 0.1 to 200 µm,
and its morphology varies between different shapes, such as oval, ellipsoidal,
spherical, smooth, angular and lenticular, depending on the botanical source
(Buléon et al., 1998Buléon, A., Colonna, P., Planchot, V., & Ball, S. (1998). Starch
granules: structure and biosynthesis. International Journal of Biological
Macromolecules, 23(2), 85-112. http://dx.doi.org/10.1016/S0141-8130(98)00040-3.
PMid:9730163.
http://dx.doi.org/10.1016/S0141-8130(98)...
; Hoover, 2001Hoover, R. (2001). Composition, molecular structure, and
physicochemical properties of tuber and root starches: a review. Carbohydrate
Polymers, 45(3), 253-267.
http://dx.doi.org/10.1016/S0144-8617(00)00260-5.
http://dx.doi.org/10.1016/S0144-8617(00)...
; Singh et al., 2003Singh, N., Singh, J., Kaur, L., Sodhi, N. S., & Gill, B. S.
(2003). Morphological, thermal and rheological properties of starches from
different botanical sources. Food Chemistry, 81(2), 219-231.
http://dx.doi.org/10.1016/S0308-8146(02)00416-8.
http://dx.doi.org/10.1016/S0308-8146(02)...
). Size distribution can be uni-, bi-,
or polymodal. In amyloplasts, starch granules are present individually or in
groups (Jane et al., 1994Jane, J., Kasemsuwan, T., Leas, S., Zobel, H., & Robyt, J. F.
(1994). Anthology of starch granule morphology by scanning electron microscopy.
Stärke, 46(4), 121-129.
http://dx.doi.org/10.1002/star.19940460402.
http://dx.doi.org/10.1002/star.199404604...
; Pérez & Bertoft, 2010Pérez, S., & Bertoft, E. (2010). The molecular structures of
starch components and their contribution to the architecture of starch granules:
a comprehensive review. Starch/Staerke, 62(8), 389-420.
http://dx.doi.org/10.1002/star.201000013.
http://dx.doi.org/10.1002/star.201000013...
). Common cereals
such as wheat, barley and rye contain two types of starch granules: (i) A-type,
lenticular shape and large size and (ii) B-type, spherical shape and small size
(Tester et al., 2006Tester, R. F., Qi, X., & Karkalas, J. (2006). Hydrolysis of
native starches with amylases. Animal Feed Science and Technology, 130(1-2),
39-54. http://dx.doi.org/10.1016/j.anifeedsci.2006.01.016.
http://dx.doi.org/10.1016/j.anifeedsci.2...
; Vamadevan & Bertoft, 2015Vamadevan, V., & Bertoft, E. (2015). Structure-function
relationships of starch components. Starch/Staerke, 67(1-2), 55-68.
http://dx.doi.org/10.1002/star.201400188.
http://dx.doi.org/10.1002/star.201400188...
). The
physicochemical properties of certain native starches are listed in Table 1. Starch granules are typically
isolated before microscopic observation, and the isolation method is important
because it can potentially affect the starch’s original size (Gao et al., 2014Gao, H., Cai, J., Han, W., Huai, H., Chen, Y., & Wei, C. (2014).
Comparison of starches isolated from three different . Trapa
speciesFood Hydrocolloids, 37, 174-181.
http://dx.doi.org/10.1016/j.foodhyd.2013.11.001.
http://dx.doi.org/10.1016/j.foodhyd.2013...
; Lawal et al., 2011Lawal, O. S., Lapasin, R., Bellich, B., Olayiwola, T. O., Cesàro,
A., Yoshimura, M., & Nishinari, K. (2011). Rheology and functional
properties of starches isolated from five improved rice varieties from West
Africa. Food Hydrocolloids, 25(7), 1785-1792.
http://dx.doi.org/10.1016/j.foodhyd.2011.04.010.
http://dx.doi.org/10.1016/j.foodhyd.2011...
). Granule morphology typically contains
a central line known as the hilum or “Maltese cross”. Each starch granule may
contain one or more Maltese crosses, and this characteristic reduces the
birefringence ability of the starch granule (Jiang et al., 2010Jiang, H., Jane, J. L., Acevedo, D., Green, A., Shinn, G.,
Schrenker, D., Srichuwong, S., Campbell, M., & Wu, Y. (2010). Variations in
starch physicochemical properties from a generation-means analysis study using
amylomaize V and VII parents. Journal of Agricultural and Food Chemistry, 58(9),
5633-5639. http://dx.doi.org/10.1021/jf904531d. PMid:20394425.
http://dx.doi.org/10.1021/jf904531d...
).
The amount of amylose present in the granule significantly affects the
physicochemical and functional properties of starch. The amylose content can
vary within the same botanical variety because of differences in geographic
origin and culture conditions (Gao et al.,
2014Gao, H., Cai, J., Han, W., Huai, H., Chen, Y., & Wei, C. (2014).
Comparison of starches isolated from three different . Trapa
speciesFood Hydrocolloids, 37, 174-181.
http://dx.doi.org/10.1016/j.foodhyd.2013.11.001.
http://dx.doi.org/10.1016/j.foodhyd.2013...
). Researchers have highlighted the role of amylose in the
initial resistance of granules to swelling and solubility, as swelling proceeds
rapidly after leaching of amylose molecules. The capacity of amylose molecules
of form lipid complexes prevents their leaching and consequently the swelling
capacity (Singh et al., 2003Singh, N., Singh, J., Kaur, L., Sodhi, N. S., & Gill, B. S.
(2003). Morphological, thermal and rheological properties of starches from
different botanical sources. Food Chemistry, 81(2), 219-231.
http://dx.doi.org/10.1016/S0308-8146(02)00416-8.
http://dx.doi.org/10.1016/S0308-8146(02)...
). Amylose
is anhydrous and can form excellent films, which are important characteristics
for industrial applications. Films formed by amylose are very strong, colorless,
odorless and tasteless (Campos et al.,
2011Campos, C. A., Gerschenson, L. N., & Flores, S. K. (2011).
Development of edible films and coatings with antimicrobial activity. Food and
Bioprocess Technology, 4(6), 849-875.
http://dx.doi.org/10.1007/s11947-010-0434-1.
http://dx.doi.org/10.1007/s11947-010-043...
).
Phosphorus is one of the non-carbohydrate components present in the starch
granule and significantly affects its functional characteristics. Phosphorus is
present as monoester phosphates or phospholipids in various types of starches.
Monoester phosphates are associated with the amylopectin fraction by covalent
bonds, increasing the clarity and viscosity of the paste, whereas the presence
of phospholipids results in opaque and low viscosity pastes (Craig et al., 1989Craig, S. A. S., Maningat, C. C., Seib, P. A., & Hoseney, R. C.
(1989). Starch paste clarity. Cereal Chemistry, 66(3), 173-182.). The phospholipid
content in starch granules is proportionally related to amylose. Phospholipids
tend to form complexes with amylose and long branches of amylopectin, resulting
in starch granules with limited solubility (Morrison et al., 1993Morrison, W. R., Tester, R. F., Snape, C. E., Law, R., & Gidley,
M. J. (1993). Swelling and gelatinization of cereal starches. IV. Some effects
of lipid-complexed. Cereal Chemistry, 70(4), 385-391.; Singh et
al., 2003Singh, N., Singh, J., Kaur, L., Sodhi, N. S., & Gill, B. S.
(2003). Morphological, thermal and rheological properties of starches from
different botanical sources. Food Chemistry, 81(2), 219-231.
http://dx.doi.org/10.1016/S0308-8146(02)00416-8.
http://dx.doi.org/10.1016/S0308-8146(02)...
). The nature of the phosphorus in starch granules has an
important influence on the transmittance of the paste. Starches such as wheat
and rice with high phospholipid contents produce pastes with low transmittance
power compared to potato or corn starch pastes because the latter starches
contain less phospholipids. Potato starch demonstrates high transmittance due to
its phosphate monoester content (Singh et al.,
2003Singh, N., Singh, J., Kaur, L., Sodhi, N. S., & Gill, B. S.
(2003). Morphological, thermal and rheological properties of starches from
different botanical sources. Food Chemistry, 81(2), 219-231.
http://dx.doi.org/10.1016/S0308-8146(02)00416-8.
http://dx.doi.org/10.1016/S0308-8146(02)...
).
Starch granules have very complex structures. The complexity is built around
variations in their composition (α-glucans, moisture, lipids, proteins and
phosphorylation), component structure and variation between amorphous and
crystalline regions. Amylose associated with large branches of amylopectin
molecules comprise the amorphous region of granules, and amylopectin molecules
with short branches comprise the crystalline region; therefore, a higher
proportion of amylopectin in starch granules results in greater crystallinity
(Cheetham & Tao, 1998Cheetham, N. W. H., & Tao, L. (1998). Variation in crystalline
type with amylose content in maize starch granules: an X-ray powder diffraction
study. Carbohydrate Polymers, 36(4), 277-284.
http://dx.doi.org/10.1016/S0144-8617(98)00007-1.
http://dx.doi.org/10.1016/S0144-8617(98)...
). There
are three types of crystalline structures: A-type characteristics from cereal
starches, B-type found in tubers and C-type present in legumes (Singh et al., 2003Singh, N., Singh, J., Kaur, L., Sodhi, N. S., & Gill, B. S.
(2003). Morphological, thermal and rheological properties of starches from
different botanical sources. Food Chemistry, 81(2), 219-231.
http://dx.doi.org/10.1016/S0308-8146(02)00416-8.
http://dx.doi.org/10.1016/S0308-8146(02)...
). Crystalline
structures are based on the double helix formed by the amylopectin molecule. In
A-type structures, the amylopectin branches are short (polymerization degree of
6-15) and linked by α-1,6 bonds. A-type is characteristic of amylopectin
ramifications. In B-type, the glucose chains are more polymerized and can act as
bases where the branches are A-type or form branched amylopectin molecules.
B-type chains are subdivided into B1, B2, B3 and B4. B1 chains have a
polymerization degree between 15 and 25, and B2 chains are typically between 40
and 50; B3 and B4 are the highest. C-type crystallinity is a combination of the
A- and B-types and consists of amylopectin molecules with non-reduced ends
(Cheetham & Tao, 1998Cheetham, N. W. H., & Tao, L. (1998). Variation in crystalline
type with amylose content in maize starch granules: an X-ray powder diffraction
study. Carbohydrate Polymers, 36(4), 277-284.
http://dx.doi.org/10.1016/S0144-8617(98)00007-1.
http://dx.doi.org/10.1016/S0144-8617(98)...
).
2.2 Birefringence and glass transition temperature (Tg)
Birefringence is the ability to doubly refract polarized light. All starch
granules in their native form exhibit birefringence that is proportional to
their crystalline structure. Birefringence patterns in starch granules represent
the radial arrangement of amylopectin molecules, and their chains form 90°
angles with the reduced ends in the direction of the hilum or starch granule
center. Weak birefringence patterns are indicative of disorganization of the
crystalline region (BeMiller & Whistler,
2009BeMiller, J. N., & Whistler, R. L. (2009). Starch: chemistry and
technology. Oxford: Academic Press.). Loss of birefringence in starch granules is associated with
deformation due to its modification (Liu et
al., 1991Liu, H., Lelievre, J., & Ayoung-Chee, W. (1991). A study of
starch gelatinization using differential scanning calorimetry, X-ray, and
birefringence measurements. Carbohydrate Research, 210(C), 79-87.
http://dx.doi.org/10.1016/0008-6215(91)80114-3.
http://dx.doi.org/10.1016/0008-6215(91)8...
).
Tg is an important parameter affecting the physical properties of
polymers. Glass transition occurs similar to a thermodynamic second order
transition, where the specific volume and enthalpy are functions of temperature
(Biliaderis et al., 1999Biliaderis, C. G., Lazaridou, A., & Arvanitoyannis, I. (1999).
Glass transition and physical properties of polyol-plasticized pullulan-starch
blends at low moisture. Carbohydrate Polymers, 40(1), 29-47.
http://dx.doi.org/10.1016/S0144-8617(99)00026-0.
http://dx.doi.org/10.1016/S0144-8617(99)...
).
Tg describes the induction temperature of the progressive
transition from an amorphous state to a rubbery state as the material is heated,
generally in the presence of a solvent or plasticizer when referring to
polysaccharides (Tester & Debon,
2000Tester, R. F., & Debon, S. J. J. (2000). Annealing of starch - a
review. International Journal of Biological Macromolecules, 27(1), 1-12.
http://dx.doi.org/10.1016/S0141-8130(99)00121-X. PMid:10704980.
http://dx.doi.org/10.1016/S0141-8130(99)...
). Because starch consists of an amorphous and a crystalline
region, the exact Tg is detected with difficultly.
2.3 Swelling capacity and solubility of starch granules
One of the most important structural characteristics of starch is that it passes
through several different stages from water absorption to granule
disintegration. Water absorption and consequent swelling of the starch granule
contribute to amylopectin-amylose phase separation and crystallinity loss, which
in turn promotes the leaching of amylose to the inter-granular space (Conde-Petit et al., 2001Conde-Petit, B., Nuessli, J., Arrigoni, E., Escher, F., & Amadò,
R. (2001). Perspectives of starch in food science. Chimia, 55(3),
201-205.). When starch
molecules are heated in water excess, the semi-crystalline structure is broken,
and water molecules associate by hydrogen bonding to hydroxyl groups exposed on
the amylose and amylopectin molecules. This association causes swelling and
increases granule size and solubility (Singh et
al., 2003Singh, N., Singh, J., Kaur, L., Sodhi, N. S., & Gill, B. S.
(2003). Morphological, thermal and rheological properties of starches from
different botanical sources. Food Chemistry, 81(2), 219-231.
http://dx.doi.org/10.1016/S0308-8146(02)00416-8.
http://dx.doi.org/10.1016/S0308-8146(02)...
). The swelling capacity and solubility of starch illustrate
the interactions of the polymeric chains comprising the amorphous and
crystalline granule fractions (Zhang et al.,
2005Zhang, P., Whistler, R. L., BeMiller, J. N., & Hamaker, B. R.
(2005). Banana starch: production, physicochemical properties, and digestibility
— a review. Carbohydrate Polymers, 59(4), 443-458.
http://dx.doi.org/10.1016/j.carbpol.2004.10.014.
http://dx.doi.org/10.1016/j.carbpol.2004...
). The extent of this interaction is influenced by the
amylose-amylopectin proportion and is characteristic of each molecule depending
on the polymerization degree, length and grade of chain branching, molecular
weight and molecular conformation (Hoover,
2001Hoover, R. (2001). Composition, molecular structure, and
physicochemical properties of tuber and root starches: a review. Carbohydrate
Polymers, 45(3), 253-267.
http://dx.doi.org/10.1016/S0144-8617(00)00260-5.
http://dx.doi.org/10.1016/S0144-8617(00)...
; Ratnayake et al.,
2002Ratnayake, W. S., Hoover, R., & Warkentin, T. (2002). Pea
starch: composition, structure and properties - a review. Starch/Staerke, 54(6),
217-234.
http://dx.doi.org/10.1002/1521-379X(200206)54:6<217::AID-STAR217>3.0.CO;2-R.
http://dx.doi.org/10.1002/1521-379X(2002...
). The swelling capacity of starch is directly associated with the
amylopectin content because the amylose acts as a diluent and inhibitor of
swelling (Singh et al., 2003Singh, N., Singh, J., Kaur, L., Sodhi, N. S., & Gill, B. S.
(2003). Morphological, thermal and rheological properties of starches from
different botanical sources. Food Chemistry, 81(2), 219-231.
http://dx.doi.org/10.1016/S0308-8146(02)00416-8.
http://dx.doi.org/10.1016/S0308-8146(02)...
). Some
species of starch that contain amylose-lipid complexes exhibit swelling capacity
and solubility restrictions (Morrison et al.,
1993Morrison, W. R., Tester, R. F., Snape, C. E., Law, R., & Gidley,
M. J. (1993). Swelling and gelatinization of cereal starches. IV. Some effects
of lipid-complexed. Cereal Chemistry, 70(4), 385-391.).
The swelling stage of starch granules is the initial step of all other paste
characteristics. Initially, granule swelling is reversible, increasing its
volume up to 30% (Gryszkin et al.,
2014Gryszkin, A., Zieba, T., Kapelko, M., & Buczek, A. (2014).
Effect of thermal modifications of potato starch on its selected properties.
Food Hydrocolloids, 40, 122-127.
http://dx.doi.org/10.1016/j.foodhyd.2014.02.010.
http://dx.doi.org/10.1016/j.foodhyd.2014...
). Water absorption and heating of the starch dispersion breaks the
hydrogen bonds responsible for granule cohesion, partially solubilizing the
starch (Hoover, 2001Hoover, R. (2001). Composition, molecular structure, and
physicochemical properties of tuber and root starches: a review. Carbohydrate
Polymers, 45(3), 253-267.
http://dx.doi.org/10.1016/S0144-8617(00)00260-5.
http://dx.doi.org/10.1016/S0144-8617(00)...
). Water penetrates
the interior of the starch granule, hydrating the linear fragments of
amylopectin (Xie et al., 2008Xie, F., Yu, L., Chen, L., & Li, L. (2008). A new study of
starch gelatinization under shear stress using dynamic mechanical analysis.
Carbohydrate Polymers, 72(2), 229-234.
http://dx.doi.org/10.1016/j.carbpol.2007.08.007.
http://dx.doi.org/10.1016/j.carbpol.2007...
). This
process leads to irreversible swelling, increasing the granule size several fold
and the paste viscosity. Paste viscosity is essentially the principal measure of
the potential application of starch in industry (Gryszkin et al., 2014Gryszkin, A., Zieba, T., Kapelko, M., & Buczek, A. (2014).
Effect of thermal modifications of potato starch on its selected properties.
Food Hydrocolloids, 40, 122-127.
http://dx.doi.org/10.1016/j.foodhyd.2014.02.010.
http://dx.doi.org/10.1016/j.foodhyd.2014...
; Sarker et al., 2013Sarker, M. Z. I., Elgadir, M. A., Ferdosh, S., Akanda, M. J. H.,
Aditiawati, P., & Noda, T. (2013). Rheological behavior of starch-based
biopolymer mixtures in selected processed foods. Starch/Staerke, 65(1-2), 73-81.
http://dx.doi.org/10.1002/star.201200072.
http://dx.doi.org/10.1002/star.201200072...
).
2.4 Gelatinization and retrogradation properties of starch
Starch, when heated in the presence of excess water, undergoes a transition phase
known as gelatinization, and there is a characteristic temperature interval for
gelatinization corresponding to each starch species. Gelatinization occurs when
water diffuses into the granule, which then swells substantially due to
hydration of the amorphous phase causing loss of crystallinity and molecular
order (Donovan, 1979Donovan, J. W. (1979). Phase transitions of the starch–water system.
Biopolymers, 18(2), 263-275.
http://dx.doi.org/10.1002/bip.1979.360180204.
http://dx.doi.org/10.1002/bip.1979.36018...
; Jenkins et al., 1993Jenkins, P. J., Cameron, R. E., & Donald, A. M. (1993). A
universal feature in the structure of starch granules from different botanical
sources. Stärke, 45(12), 417-420.
http://dx.doi.org/10.1002/star.19930451202.
http://dx.doi.org/10.1002/star.199304512...
; Jiménez et al., 2012Jiménez, A., Fabra, M. J., Talens, P., & Chiralt, A. (2012).
Edible and biodegradable starch films: a review. Food and Bioprocess Technology,
5(6), 2058-2076. http://dx.doi.org/10.1007/s11947-012-0835-4.
http://dx.doi.org/10.1007/s11947-012-083...
). The gelatinization
process starts at the hilum and quickly spreads throughout the periphery.
Gelatinization occurs initially in the amorphous region, favored by the weak
hydrogen bonds present in this area. The process then extends to the crystalline
region. Amylose presence reduces the fusion point in the crystalline region and
the amount of energy necessary to initiate gelatinization (Sasaki et al., 2000Sasaki, M., Fang, Z., Fukushima, Y., Adschiri, T., & Arai, K.
(2000). Dissolution and hydrolysis of cellulose in subcritical and supercritical
water. Industrial & Engineering Chemistry Research, 39(8), 2883-2890.
http://dx.doi.org/10.1021/ie990690j.
http://dx.doi.org/10.1021/ie990690j...
). The gelatinization process is
represented by transition temperatures and gelatinization enthalpies in the
paste, and these measures are characteristic for each species. High transition
temperatures correspond to a high degree of crystallinity, high stability and
resistance of the granule structure to gelatinization (Tester et al., 2004Tester, R. F., Karkalas, J., & Qi, X. (2004). Starch -
Composition, fine structure and architecture. Journal of Cereal Science, 39(2),
151-165. http://dx.doi.org/10.1016/j.jcs.2003.12.001.
http://dx.doi.org/10.1016/j.jcs.2003.12....
). Gelatinization of starch granules is
associated with a loss of birefringence and crystalline order due to the
breaking of the double helix in the crystalline region and the leaching of
amylose (Donovan, 1979Donovan, J. W. (1979). Phase transitions of the starch–water system.
Biopolymers, 18(2), 263-275.
http://dx.doi.org/10.1002/bip.1979.360180204.
http://dx.doi.org/10.1002/bip.1979.36018...
; Evans & Haisman, 1982Evans, I. D., & Haisman, D. R. (1982). The effect of solutes on
the gelatinization temperature range of potato starch. Stärke, 34(7), 224-231.
http://dx.doi.org/10.1002/star.19820340704.
http://dx.doi.org/10.1002/star.198203407...
). This
transitions starch from a semi-crystalline form (relatively indigestible) to an
amorphous form that is easily digestible (Tester & Debon, 2000Tester, R. F., & Debon, S. J. J. (2000). Annealing of starch - a
review. International Journal of Biological Macromolecules, 27(1), 1-12.
http://dx.doi.org/10.1016/S0141-8130(99)00121-X. PMid:10704980.
http://dx.doi.org/10.1016/S0141-8130(99)...
). Similar to water, other solvents are also
used to promote gelatinization. The principal consideration with solvents is
their capacity to form hydrogen bonds with the molecules in the starch granules
(i.e., liquid ammonia, formamide, formic acid, chloroacetic acid and dimethyl
sulfoxide). The gelatinization process is affected by solvent type and
starch/solvent proportions (Jiménez et al.,
2012Jiménez, A., Fabra, M. J., Talens, P., & Chiralt, A. (2012).
Edible and biodegradable starch films: a review. Food and Bioprocess Technology,
5(6), 2058-2076. http://dx.doi.org/10.1007/s11947-012-0835-4.
http://dx.doi.org/10.1007/s11947-012-083...
). Gelatinization is necessary for particular processes, e.g.,
textile and hydrolyzed starch industries. Gelatinization affects the rheological
properties and viscosity of the paste, making the starch granule more accessible
to enzymatic action. When starch granules swell and its components are in
solution, the medium properties change from a simple starch granules suspension
to a starch paste. Amylose and amylopectin form separate phases because of
thermodynamic immiscibility. In food, starch is typically in combination with
other polymeric ingredients, such as proteins and other polysaccharides, forming
different phases (Conde-Petit et al.,
2001Conde-Petit, B., Nuessli, J., Arrigoni, E., Escher, F., & Amadò,
R. (2001). Perspectives of starch in food science. Chimia, 55(3),
201-205.). Gelatinization of granules is caused by many processes or the
manufacturing of products from raw materials based on starch, especially
cereals. Gelatinization progress along the granule is determined by the
physicochemical properties of the starch, the presence of other ingredients, the
availability of water and process parameters applied (i.e., temperature, time
and mechanical energy) (Schirmer et al.,
2015Schirmer, M., Jekle, M., & Becker, T. (2015). Starch
gelatinization and its complexity for analysis. Starch/Staerke, 67(1-2), 30-41.
http://dx.doi.org/10.1002/star.201400071.
http://dx.doi.org/10.1002/star.201400071...
).
The molecular interaction produced after gelatinization and cooling of the paste
is known as retrogradation (Hoover,
2000Hoover, R. (2000). Acid-treated starches. Food Reviews
International, 16(3), 369-392.
http://dx.doi.org/10.1081/FRI-100100292.
http://dx.doi.org/10.1081/FRI-100100292...
). During retrogradation, amylose molecules associate with other
glucose units to form a double helix, while amylopectin molecules re-crystallize
through association of its small chains (Singh
et al., 2003Singh, N., Singh, J., Kaur, L., Sodhi, N. S., & Gill, B. S.
(2003). Morphological, thermal and rheological properties of starches from
different botanical sources. Food Chemistry, 81(2), 219-231.
http://dx.doi.org/10.1016/S0308-8146(02)00416-8.
http://dx.doi.org/10.1016/S0308-8146(02)...
). After retrogradation, starch exhibits lower
gelatinization and enthalpy compared to native starch because its crystalline
structure has been weakened (Sasaki et al.,
2000Sasaki, M., Fang, Z., Fukushima, Y., Adschiri, T., & Arai, K.
(2000). Dissolution and hydrolysis of cellulose in subcritical and supercritical
water. Industrial & Engineering Chemistry Research, 39(8), 2883-2890.
http://dx.doi.org/10.1021/ie990690j.
http://dx.doi.org/10.1021/ie990690j...
). Initially, the amylose content exercises a strong influence
over the retrogradation process; a large amount of amylose is associated with a
strong tendency for retrogradation. Amylopectin and intermediate materials
influence the retrogradation process during storage under refrigeration; each
polymer has a different recrystallization rate (BeMiller, 2011BeMiller, J. N. (2011). Pasting, paste, and gel properties of
starch–hydrocolloid combinations. Carbohydrate Polymers, 86(2), 386-423.
http://dx.doi.org/10.1016/j.carbpol.2011.05.064.
http://dx.doi.org/10.1016/j.carbpol.2011...
; Conde-Petit et al.,
2001Conde-Petit, B., Nuessli, J., Arrigoni, E., Escher, F., & Amadò,
R. (2001). Perspectives of starch in food science. Chimia, 55(3),
201-205.). Recrystallization of starch easily occurs at temperatures
under 0 °C, but also occurs above 100 °C. Starch retrogradation is intensified
by repeated freezing and thawing of paste (Leszczyñski, 2004Leszczyñski, W. (2004). Resistant starch – classification,
structure, production. Polish Journal of Food and Nutrition
Sciences, 13(54), 37-50.). Some research has shown that paste components
such as proteins influence the retrogradation properties of paste through
emulsification. Proteins form complexes with starch that retards the
retrogradation process during refrigerated storage (Wu et al., 2010Wu, Y., Chen, Z., Li, X., & Wang, Z. (2010). Retrogradation
properties of high amylose rice flour and rice starch by physical modification.
LWT - Food Science and Technology (Campinas.), 43(3), 492-497.). The presence of other components in
addition to proteins and lipids, such as other carbohydrates, salts and
polyphenols, significantly affects retrogradation (Fu et al., 2015Fu, Z., Chen, J., Luo, S. J., Liu, C. M., & Liu, W. (2015).
Effect of food additives on starch retrogradation: a review. Starch/Staerke,
67(1-2), 69-78. http://dx.doi.org/10.1002/star.201300278.
http://dx.doi.org/10.1002/star.201300278...
). In general, retrogradation in starch
pastes, as well as foods containing starch, is unfavorable in terms of food
quality, causing syneresis of gels or hardness. Currently, retrograded starch is
classified as a form of resistant starch (RS) (Zięba et al., 2011Zięba, T., Szumny, A., & Kapelko, M. (2011). Properties of
retrograded and acetylated starch preparations: Part 1. Structure,
susceptibility to amylase, and pasting characteristics. LWT - Food Science and
Technology (Campinas.), 44(5), 1314-1320.) and is used in industry for different purposes
described in other sections of this review.
2.5 Rheological and thermal properties
Starch paste forms immediately after gelatinization, and starch granules are
increasingly susceptible to disintegration by shearing because they are swollen.
The paste obtained is a viscous mass consisting of one continuous phase of
solubilized amylose and/or amylopectin and one discontinuous phase of the
remaining starch granules (Ambigaipalan et al.,
2011Ambigaipalan, P., Hoover, R., Donner, E., Liu, Q., Jaiswal, S.,
Chibbar, R., Nantanga, K. K. M., & Seetharaman, K. (2011). Structure of faba
bean, black bean and pinto bean starches at different levels of granule
organization and their physicochemical properties. Food Research International,
44(9), 2962-2974.
http://dx.doi.org/10.1016/j.foodres.2011.07.006.
http://dx.doi.org/10.1016/j.foodres.2011...
). Starch functionality is directly related to gelatinization and
the properties of the paste. All of these properties affect the stability of
products, consumer acceptance and production reliability (Šubarić et al., 2012 Šubarić, D., Ačkar, D., Babić, J., Sakač, N., & Jozinović, A.
(2012). Modification of wheat starch with succinic acid/acetic anhydride and
azelaic acid/acetic anhydride mixtures I. Thermophysical and pasting properties.
Journal of Food Science and Technology, 51(10), 2616-2623.
http://dx.doi.org/10.1007/s13197-012-0790-0. PMid:25328203.
http://dx.doi.org/10.1007/s13197-012-079...
). The characteristics of the native
starch, the effects of the physical or chemical modifications of the granules,
the process parameters and the botanical sources of the starch are all critical
factors governing the behavior and characteristics of the starch paste. The
transformation of starch during manufacturing depends on the
temperature-time-mixture ratio and the modification ratio during processing
(Conde-Petit et al., 2001Conde-Petit, B., Nuessli, J., Arrigoni, E., Escher, F., & Amadò,
R. (2001). Perspectives of starch in food science. Chimia, 55(3),
201-205.).
Starch granules are insoluble in cold water due to the hydrogen bonds and
crystallinity of the molecule. When starch is dispersed in hot water below its
Tg, the starch granules swell and increase several times in size,
breaking the molecules and consequently leaching amylose to form a
three-dimensional network and increase the paste’s viscosity (Sarker et al., 2013Sarker, M. Z. I., Elgadir, M. A., Ferdosh, S., Akanda, M. J. H.,
Aditiawati, P., & Noda, T. (2013). Rheological behavior of starch-based
biopolymer mixtures in selected processed foods. Starch/Staerke, 65(1-2), 73-81.
http://dx.doi.org/10.1002/star.201200072.
http://dx.doi.org/10.1002/star.201200072...
). Starch paste can
contain un-swollen granules, partially swollen granules, aggregates of swollen
starch granules, fragments and molecules of retrograded starch and starch that
has dissolved or precipitated (BeMiller &
Whistler, 2009BeMiller, J. N., & Whistler, R. L. (2009). Starch: chemistry and
technology. Oxford: Academic Press.).
The presence of relatively short chains of amylose and amylopectin adds opacity
to starch suspensions and foods containing them. In products such as sources,
dressings and puddings, this opacity is not a disadvantage; however, jellies and
fruit fillings require starch suspensions with high clarity (Eliasson, 2004Eliasson, A. C. (2004). Starch in food: structure, function and
applications. Boca Raton: CRC Press.). Paste clarity is commonly
determined by the percent transmittance from a dilute solution of starch (1%
w/w) at a wavelength of 650 nm (Bello-Pérez
& Paredes-López, 1996Bello-Pérez, L. A., & Paredes-López, O. (1996). Starch and
amylopectin - effects of solutes on clarity of pastes. Starch/Staerke, 48(6),
205-207. http://dx.doi.org/10.1002/star.19960480602.
http://dx.doi.org/10.1002/star.199604806...
; Ulbrich
et al., 2015Ulbrich, M., Wiesner, I., & Flöter, E. (2015). Molecular
characterization of acid-thinned wheat, potato and pea starches and correlation
to gel properties. Starch/Staerke. 66, 1-14.). Products like potato starch have transmittances
between 42 to 96% and are considered high clarity pastes, followed by cassava
starch at 51-81%. Common cereals generally present transmittances of 13 to 62%
(Craig et al., 1989Craig, S. A. S., Maningat, C. C., Seib, P. A., & Hoseney, R. C.
(1989). Starch paste clarity. Cereal Chemistry, 66(3), 173-182.; Nuwamanya et al., 2013Nuwamanya, E., Baguma, Y., Wembabazi, E., & Rubaihayo, P.
(2013). A comparative study of the physicochemical properties of starches from
root, tuber and cereal crops. African Journal of Biotechnology, 10(56),
12018-12030.). Low clarity in
common cereals (non-waxy) is due to the presence of traces of swollen starch
granules (Craig et al., 1989Craig, S. A. S., Maningat, C. C., Seib, P. A., & Hoseney, R. C.
(1989). Starch paste clarity. Cereal Chemistry, 66(3), 173-182.) and
amylose-lipid complexes (Bello-Pérez &
Paredes-López, 1996Bello-Pérez, L. A., & Paredes-López, O. (1996). Starch and
amylopectin - effects of solutes on clarity of pastes. Starch/Staerke, 48(6),
205-207. http://dx.doi.org/10.1002/star.19960480602.
http://dx.doi.org/10.1002/star.199604806...
). Clarity in starch suspensions is modified
during storage, decreasing due to amylose and/or amylopectin molecules (Jacobson et al., 1997Jacobson, M. R., Obanni, M., & Bemiller, J. N. (1997).
Retrogradation of starches from different botanical sources. Cereal Chemistry,
74(5), 511-518. http://dx.doi.org/10.1094/CCHEM.1997.74.5.511.
http://dx.doi.org/10.1094/CCHEM.1997.74....
; Waterschoot et al., 2015aWaterschoot, J., Gomand, S. V., Fierens, E., & Delcour, J. A.
(2015a). Production, structure, physicochemical and functional properties of
maize, cassava, wheat, potato and rice starches. Starch/Staerke, 67(1-2), 14-29.
http://dx.doi.org/10.1002/star.201300238.
http://dx.doi.org/10.1002/star.201300238...
).
Rheological properties describe the behavior of materials subjected to shearing
forces and deformation, which are considered viscoelastic complexes. The basic
feature of starch rheology is its viscosity. Other rheological characteristics
involve texture, transparency or clarity, shear strength and the tendency for
retrogradation. All of these features play important roles in the commercial
applications of starch (BeMiller &
Whistler, 2009BeMiller, J. N., & Whistler, R. L. (2009). Starch: chemistry and
technology. Oxford: Academic Press.; Berski et al.,
2011Berski, W., Ptaszek, A., Ptaszek, P., Ziobro, R., Kowalski, G.,
Grzesik, M., & Achremowicz, B. (2011). Pasting and rheological properties of
oat starch and its derivatives. Carbohydrate Polymers, 83(2), 665-671.
http://dx.doi.org/10.1016/j.carbpol.2010.08.036.
http://dx.doi.org/10.1016/j.carbpol.2010...
). Rheological starch properties are studied through the behavior
of viscosity curves, which are influenced by temperature, concentration and
shear stress (Singh et al., 2003Singh, N., Singh, J., Kaur, L., Sodhi, N. S., & Gill, B. S.
(2003). Morphological, thermal and rheological properties of starches from
different botanical sources. Food Chemistry, 81(2), 219-231.
http://dx.doi.org/10.1016/S0308-8146(02)00416-8.
http://dx.doi.org/10.1016/S0308-8146(02)...
).
“Paste properties” is the term used to describe the changes that occur in starch
after gelatinization in excess water. Instruments like the Rapid Visco Analyzer
(RVA) describe the viscosity parameter as functions of temperature and time. The
RVA describes paste behavior in three periods: (i) a controlled heating period,
increasing the temperature of the suspension from room temperature to a maximum
that is generally determined at 95 °C; (ii) an isothermal period, maintaining
the suspension at the maximum temperature for analysis; and (iii) a cooling
period, decreasing the temperature to approximately 50 °C. Throughout the
analysis, the suspension is subjected to shear forces. Suspensions typically
exhibit a peak in viscosity that starts after gelatinization and increases as
the granules swell, followed by a decrease in viscosity due to granule
disintegration and polymer realignment. A “Breakdown” is defined by a difference
between the viscosity peak and the minimum viscosity at the maximum analysis
temperature. During the cooling period, amylose leaching forms a gel or
three-dimensional network. Gel formation further increases the viscosity, called
the “cold paste viscosity”. The difference between the paste viscosity at the
end of the cooling period and the minimum viscosity at 95 °C is termed the
“setback” (Saunders et al., 2011Saunders, J., Levin, D. B., & Izydorczyk, M. (2011). Limitations
and challenges for wheat-based bioethanol production. InTech. Retrieved from.
http://cdn.intechopen.com/pdfs/17894/InTech-Limitations_and_challenges_for_wheat_based_bioethanol_production.pdf
http://cdn.intechopen.com/pdfs/17894/InT...
; Wang & Weller, 2006Wang, L., & Weller, C. L. (2006). Recent advances in extraction
of nutraceuticals from plants. Trends in Food Science & Technology, 17(6),
300-312. http://dx.doi.org/10.1016/j.tifs.2005.12.004.
http://dx.doi.org/10.1016/j.tifs.2005.12...
).
Starch gels are composed of amylose chains and intermediate materials dispersed
in a starch suspension after granule disintegration in a three-dimensional
network structure. The level and nature of the leached material and molecular
interactions determine the viscoelastic properties. Methods used to describe the
viscoelastic parameters of the paste include equipment such as a dynamic
rheometer, an amylograph or a viscoamylograph (Schirmer et al., 2015Schirmer, M., Jekle, M., & Becker, T. (2015). Starch
gelatinization and its complexity for analysis. Starch/Staerke, 67(1-2), 30-41.
http://dx.doi.org/10.1002/star.201400071.
http://dx.doi.org/10.1002/star.201400071...
). Several parameters describe the viscoelastic
behavior of pastes: (G’), the measure of recovered or accumulated energy in each
deformation cycle and an indicator of the elastic behavior of the paste; the
dissipated energy (G’’), the loss of energy in each deformation cycle that
describes the viscosity behavior of the material; and the modulus or tangent
(G’’/G’), describing the material’s behavior (high values (›1) indicate
liquid-like behavior, and low values indicate solid-like (<1) behavior)
(BeMiller & Whistler, 2009BeMiller, J. N., & Whistler, R. L. (2009). Starch: chemistry and
technology. Oxford: Academic Press.;
Waterschoot et al., 2015bWaterschoot, J., Gomand, S. V., Fierens, E., & Delcour, J. A.
(2015b). Starch blends and their physicochemical properties. Starch/Staerke,
67(1-2), 1-13. http://dx.doi.org/10.1002/star.201300214.
http://dx.doi.org/10.1002/star.201300214...
). Gel
resistance is determined using a texture analyzer, in which parameters such as
peak force [N] define the resistance of the three-dimensional network (Ulbrich et al., 2015Ulbrich, M., Wiesner, I., & Flöter, E. (2015). Molecular
characterization of acid-thinned wheat, potato and pea starches and correlation
to gel properties. Starch/Staerke. 66, 1-14.).
The main factors affecting the rheological properties of starches are their
source and the presence of other polymers (Sarker et al., 2013Sarker, M. Z. I., Elgadir, M. A., Ferdosh, S., Akanda, M. J. H.,
Aditiawati, P., & Noda, T. (2013). Rheological behavior of starch-based
biopolymer mixtures in selected processed foods. Starch/Staerke, 65(1-2), 73-81.
http://dx.doi.org/10.1002/star.201200072.
http://dx.doi.org/10.1002/star.201200072...
; Schirmer et
al., 2015Schirmer, M., Jekle, M., & Becker, T. (2015). Starch
gelatinization and its complexity for analysis. Starch/Staerke, 67(1-2), 30-41.
http://dx.doi.org/10.1002/star.201400071.
http://dx.doi.org/10.1002/star.201400071...
). Many polymers coexist with starch in aqueous mixtures and
interact in different ways to produce several attributes influencing the
stability, texture and quality of food products. Starch paste viscosity is
associated with lipids, mainly phospholipids, that complex with amylose and
hinder or reduce the granule’s swelling capacity. Other effects associated with
paste viscosity are decreased amylose solubility, increased formation time and
limited gelling properties. Amylose-lipid complexes require high temperatures
for dissociation (Singh et al., 2003Singh, N., Singh, J., Kaur, L., Sodhi, N. S., & Gill, B. S.
(2003). Morphological, thermal and rheological properties of starches from
different botanical sources. Food Chemistry, 81(2), 219-231.
http://dx.doi.org/10.1016/S0308-8146(02)00416-8.
http://dx.doi.org/10.1016/S0308-8146(02)...
).
Rheology is widely recognized for its effect on the quality of food and its
sensory characteristics. The rheological properties of starch determine its
potential application as a thickener or gelling agent (Berski et al., 2011Berski, W., Ptaszek, A., Ptaszek, P., Ziobro, R., Kowalski, G.,
Grzesik, M., & Achremowicz, B. (2011). Pasting and rheological properties of
oat starch and its derivatives. Carbohydrate Polymers, 83(2), 665-671.
http://dx.doi.org/10.1016/j.carbpol.2010.08.036.
http://dx.doi.org/10.1016/j.carbpol.2010...
). Determining the thermal properties
of starch involves terms such as the onset temperature (To), peak
temperature (Tp), conclusion temperature (Tc), difference
between Tc and To, and enthalpy of fusion, all of which
can be measured using equipment like a differential scanning calorimeter (DSC)
(Kong et al., 2012Kong, X., Kasapis, S., Bao, J., & Corke, H. (2012). Influence of
acid hydrolysis on thermal and rheological properties of amaranth starches
varying in amylose content. Journal of the Science of Food and Agriculture,
92(8), 1800-1807. http://dx.doi.org/10.1002/jsfa.5549.
PMid:22318856.
http://dx.doi.org/10.1002/jsfa.5549...
) and depend on
the starch concentration (Waterschoot et al.,
2015bWaterschoot, J., Gomand, S. V., Fierens, E., & Delcour, J. A.
(2015b). Starch blends and their physicochemical properties. Starch/Staerke,
67(1-2), 1-13. http://dx.doi.org/10.1002/star.201300214.
http://dx.doi.org/10.1002/star.201300214...
). During heating, To is the temperature at which the
paste viscosity starts to increase; Tp is the maximum viscosity
temperature; and Tc is the final temperature of the viscosity
increment. (Tc-To) is a comparative measure, and an
increase in this value indicates a high amount of granule modification in the
amorphous and crystalline regions (Jenkins et
al., 1993Jenkins, P. J., Cameron, R. E., & Donald, A. M. (1993). A
universal feature in the structure of starch granules from different botanical
sources. Stärke, 45(12), 417-420.
http://dx.doi.org/10.1002/star.19930451202.
http://dx.doi.org/10.1002/star.199304512...
; Kong et al.,
2012Kong, X., Kasapis, S., Bao, J., & Corke, H. (2012). Influence of
acid hydrolysis on thermal and rheological properties of amaranth starches
varying in amylose content. Journal of the Science of Food and Agriculture,
92(8), 1800-1807. http://dx.doi.org/10.1002/jsfa.5549.
PMid:22318856.
http://dx.doi.org/10.1002/jsfa.5549...
). Some researchers include retrogradation among the thermal
properties of starch. This paste property typically begins 20 °C lower than its
gelatinization temperature (Tgel), and retrogradation is proportional
to the presence of amylopectin (Tan et al.,
2006Tan, H. Z., Gu, W. Y., Zhou, J. P., Wu, W. G., & Xie, Y. L.
(2006). Comparative study on the starch noodle structure of sweet potato and
mung bean. Journal of Food Science, 71(8), C447-C455.
http://dx.doi.org/10.1111/j.1750-3841.2006.00150.x.
http://dx.doi.org/10.1111/j.1750-3841.20...
; Yuan et al., 1993Yuan, R. C., Thompson, D. B., & Boyer, C. D. (1993). Fine
structure of amylopectin in relation to gelatinization and retrogradation
behavior of maize starches from three wx-containing genotypes in two inbred
lines. Cereal Chemistry, 70, 81-81.).
Variations in a starch’s thermal properties after gelatinization and throughout
refrigerated storage can be attributed to variations in the amylose/amylopectin
ratio, the size and shape of the granule, and the presence or absence of lipids
and proteins (Singh et al., 2003Singh, N., Singh, J., Kaur, L., Sodhi, N. S., & Gill, B. S.
(2003). Morphological, thermal and rheological properties of starches from
different botanical sources. Food Chemistry, 81(2), 219-231.
http://dx.doi.org/10.1016/S0308-8146(02)00416-8.
http://dx.doi.org/10.1016/S0308-8146(02)...
; Tan et al., 2006Tan, H. Z., Gu, W. Y., Zhou, J. P., Wu, W. G., & Xie, Y. L.
(2006). Comparative study on the starch noodle structure of sweet potato and
mung bean. Journal of Food Science, 71(8), C447-C455.
http://dx.doi.org/10.1111/j.1750-3841.2006.00150.x.
http://dx.doi.org/10.1111/j.1750-3841.20...
).
3 Starch modification
Starch is rarely consumed in its intact form and frequently used by industry in its
native form. Most native starches are limited in their direct application because
they are unstable with respect to changes in temperature, pH and shear forces.
Native starches show a strong tendency for decomposition and retrogradation (Berski et al., 2011Berski, W., Ptaszek, A., Ptaszek, P., Ziobro, R., Kowalski, G.,
Grzesik, M., & Achremowicz, B. (2011). Pasting and rheological properties of
oat starch and its derivatives. Carbohydrate Polymers, 83(2), 665-671.
http://dx.doi.org/10.1016/j.carbpol.2010.08.036.
http://dx.doi.org/10.1016/j.carbpol.2010...
). Additionally, some
starch granules are inert, insoluble in water at room temperature, highly resistant
to enzymatic hydrolysis and consequently lacking in functional properties. Native
starches are often modified to develop specific properties such as solubility,
texture, adhesion and tolerance to the heating temperatures used in industrial
processes (Singh et al., 2007Singh, J., Kaur, L., & McCarthy, O. J. (2007). Factors
influencing the physico-chemical, morphological, thermal and rheological
properties of some chemically modified starches for food applications - a
review. Food Hydrocolloids, 21(1), 1-22.
http://dx.doi.org/10.1016/j.foodhyd.2006.02.006.
http://dx.doi.org/10.1016/j.foodhyd.2006...
; Sweedman et al., 2013Sweedman, M. C., Tizzotti, M. J., Schäfer, C., & Gilbert, R. G.
(2013). Structure and physicochemical properties of octenyl succinic anhydride
modified starches: a review. Carbohydrate Polymers, 92(1), 905-920.
http://dx.doi.org/10.1016/j.carbpol.2012.09.040. PMid:23218383.
http://dx.doi.org/10.1016/j.carbpol.2012...
).
Several methods have been developed to produce modified starches with a variety of
characteristics and applications. All of these techniques alter the starch polymer,
making it highly flexible and changing its physicochemical properties and structural
attributes to increase its value for food and non-food industries (López et al., 2010López, O. V., Zaritzky, N. E., & García, M. A. (2010).
Physicochemical characterization of chemically modified corn starches related to
rheological behavior, retrogradation and film forming capacity. Journal of Food
Engineering, 100(1), 160-168.
http://dx.doi.org/10.1016/j.jfoodeng.2010.03.041.
http://dx.doi.org/10.1016/j.jfoodeng.201...
). The starch modification
industry is constantly evolving. Modifications of starch include physical, chemical
and enzymatic methods (Yadav et al., 2013Yadav, B. S., Guleria, P., & Yadav, R. B. (2013). Hydrothermal
modification of Indian water chestnut starch: Influence of heat-moisture
treatment and annealing on the physicochemical, gelatinization and pasting
characteristics. LWT - Food Science and Technology (Campinas.), 53(1),
211-217.).
Physical methods involve the use of heat and moisture, and chemical modifications
introduce functional groups into the starch molecule using derivatization reactions
(e.g., etherification, esterification, crosslinking) or involve breakdown reactions
(e.g., hydrolysis and oxidation) (Singh et al.,
2007Singh, J., Kaur, L., & McCarthy, O. J. (2007). Factors
influencing the physico-chemical, morphological, thermal and rheological
properties of some chemically modified starches for food applications - a
review. Food Hydrocolloids, 21(1), 1-22.
http://dx.doi.org/10.1016/j.foodhyd.2006.02.006.
http://dx.doi.org/10.1016/j.foodhyd.2006...
; Wurzburg, 1986Wurzburg, O. B. (1986). Modified starches-properties and uses. Boca
Raton: CRC Press.).
3.1 Physical modification of starch
Physical modifications of starch can improve its water solubility and reduce the
size of the starch granules. Physical methods to treat the native granules
include: different combinations of temperature, moisture, pressure, shear and
irradiation. Physical modification of starch granules is simple, cheap and safe.
These techniques do not require chemical or biological agents, and are therefore
preferred when the product is intended for human consumption (Ashogbon & Akintayo, 2014Ashogbon, A. O., & Akintayo, E. T. (2014). Recent trend in the
physical and chemical modification of starches from different botanical sources:
a review. Starch/Staerke, 66(1-2), 41-57.
http://dx.doi.org/10.1002/star.201300106.
http://dx.doi.org/10.1002/star.201300106...
). Table 2 gives examples of different
research on the physical modification of starch.
Pre-gelatinized starch (PGS)
Pre-gelatinized starch (PGS) is starch that has undergone a cooking process
until complete gelatinization and a simultaneous (or subsequent) drying
process. Drying methods include drum drying, spray drying and extrusion. The
main consequence of this treatment is the destruction of the granular
structure, resulting in complete granular fragmentation, and the absence of
birefringence properties. The principal properties of PGS are an increase in
swelling capacity, solubility and cold water dispersion. PGS functionality
depends on the cooking conditions, drying and the starch source (Ashogbon & Akintayo, 2014Ashogbon, A. O., & Akintayo, E. T. (2014). Recent trend in the
physical and chemical modification of starches from different botanical sources:
a review. Starch/Staerke, 66(1-2), 41-57.
http://dx.doi.org/10.1002/star.201300106.
http://dx.doi.org/10.1002/star.201300106...
). Of the
physically modified starches, PGS is primarily used as a thickener in many
instantaneous products, such as baby food, soups and desserts, due to its
ability to form pastes and dissolve in cold water. The use of PGS is
preferred in sensible foods because it does not require heating to form a
paste (Majzoobi et al., 2011Majzoobi, M., Radi, M., Farahnaky, A., Jamalian, J., Tongdang, T.,
& Mesbahi, G. (2011). Physicochemical properties of pre-gelatinized wheat
starch produced by a twin drum drier. Journal of Agricultural Science and
Technology, 13(2), 193-202.).
Hydrothermal modification
This physical modification involves changes in the physical and chemical
properties of the starch without destroying the granule structure (Zavareze & Dias, 2011Zavareze, E. D. R., & Dias, A. R. G. (2011). Impact of
heat-moisture treatment and annealing in starches: a review. Carbohydrate
Polymers, 83(2), 317-328.
http://dx.doi.org/10.1016/j.carbpol.2010.08.064.
http://dx.doi.org/10.1016/j.carbpol.2010...
). Physical
modifications occur at temperatures above the Tg and below the
Tgel of the starch granules (Tester & Debon, 2000Tester, R. F., & Debon, S. J. J. (2000). Annealing of starch - a
review. International Journal of Biological Macromolecules, 27(1), 1-12.
http://dx.doi.org/10.1016/S0141-8130(99)00121-X. PMid:10704980.
http://dx.doi.org/10.1016/S0141-8130(99)...
). Essentially, hydrothermal
modification can only occur when starch polymers transition from the
amorphous region to the semicrystalline region. Starch in its native form
exhibits amylopectin ramifications by forming a double helix chain, and this
behavior imparts a crystalline structure to the starch molecule. Heat
treatment involving temperatures between the Tg and melting
temperature (Tm) may not alter the double helix conformation or
degree of starch crystallinity; these conditions are present when starch
pastes are drying. Physical modification of starch performance improves
starch paste characteristics such as texture and plasticity by reducing
Tg and consequently relaxing the hydrogen bonds and
polymer-polymer interactions. The presence of water reduces the
Tm (Conde-Petit et al.,
2001Conde-Petit, B., Nuessli, J., Arrigoni, E., Escher, F., & Amadò,
R. (2001). Perspectives of starch in food science. Chimia, 55(3),
201-205.). Hydrothermal modification is differentiated into annealing
and hydrothermal treatments (Collado &
Corke, 1999Collado, L. S., & Corke, H. (1999). Heat-moisture treatment
effects on sweetpotato starches differing in amylose content. Food Chemistry,
65(3), 339-346.
http://dx.doi.org/10.1016/S0308-8146(98)00228-3.
http://dx.doi.org/10.1016/S0308-8146(98)...
).
-
a
Annealing (ANN) is a physical treatment of starch granules in which the parameters of moisture, temperature and heating time determine the results obtained (Tester & Debon, 2000Tester, R. F., & Debon, S. J. J. (2000). Annealing of starch - a review. International Journal of Biological Macromolecules, 27(1), 1-12. http://dx.doi.org/10.1016/S0141-8130(99)00121-X. PMid:10704980.
http://dx.doi.org/10.1016/S0141-8130(99)... ). The ANN process requires an excess of water (76% w/w) or an intermediate containing water (40% w/w) (Jacobs & Delcour, 1998Jacobs, H., & Delcour, J. A. (1998). Hydrothermal modifications of granular starch, with retention of the granular structure: a review. Journal of Agricultural and Food Chemistry, 46(8), 2895-2905. http://dx.doi.org/10.1021/jf980169k.
http://dx.doi.org/10.1021/jf980169k... ). The objective of this treatment is to improve the molecular mobility. ANN is associated with a physical reorganization of the starch granule in the presence of water (Tester & Debon, 2000Tester, R. F., & Debon, S. J. J. (2000). Annealing of starch - a review. International Journal of Biological Macromolecules, 27(1), 1-12. http://dx.doi.org/10.1016/S0141-8130(99)00121-X. PMid:10704980.
http://dx.doi.org/10.1016/S0141-8130(99)... ). Water is a suitable plasticizer for starch. Starch granule hydration causes a transition from a glassy to a static state, increasing the mobility of the amorphous regions to a crystalline state. These changes generate tangential and radial movements in the crystalline and amorphous regions, and physicochemical modifications increase chain interaction in the crystallinity region (Chen et al., 2014Chen, X., He, X., & Huang, Q. (2014). Effects of hydrothermal pretreatment on subsequent octenylsuccinic anhydride (OSA) modification of cornstarch. Carbohydrate Polymers, 101(0), 493-498. http://dx.doi.org/10.1016/j.carbpol.2013.09.079. PMid:24299803.
http://dx.doi.org/10.1016/j.carbpol.2013... ). The ANN process is associated with partial gelatinization of starch Tester & Debon (2000)Tester, R. F., & Debon, S. J. J. (2000). Annealing of starch - a review. International Journal of Biological Macromolecules, 27(1), 1-12. http://dx.doi.org/10.1016/S0141-8130(99)00121-X. PMid:10704980.
http://dx.doi.org/10.1016/S0141-8130(99)... state that the ANN term can only be used when the temperature of the process does not reach Tgel and therefore gelatinization does not occur. In ANN starch, the Tgel after modification is not less than the Tgel of the native starch. The ANN process has important industrial applications, imparting different characteristics to products due to an increase in starch granule size, thermal stability, Tgel and the availability of starch to digestion by enzymes such as α-amylase. However, there is no justification for its use in terms of energy and time because many cheaper chemical processes can modify starch properties rapidly and selectively, making them more competitive than ANN. -
b
Hydrothermal treatment (HMT). This treatment includes a thermal application in the presence of a limited amount of water (typically less than 35% w/w) and a process time between 15 min to 16 h (Jacobs & Delcour, 1998Jacobs, H., & Delcour, J. A. (1998). Hydrothermal modifications of granular starch, with retention of the granular structure: a review. Journal of Agricultural and Food Chemistry, 46(8), 2895-2905. http://dx.doi.org/10.1021/jf980169k.
http://dx.doi.org/10.1021/jf980169k... ). The effects of this treatment on the morphological and physicochemical properties of starch granules include important changes in crystalline structure, swelling capacity, gelatinization, paste properties and retrogradation (Hoover, 2010Hoover, R. (2010). The impact of heat-moisture treatment on molecular structures and properties of starches isolated from different botanical sources. Critical Reviews in Food Science and Nutrition, 50(9), 835-847. http://dx.doi.org/10.1080/10408390903001735. PMid:20924866.
http://dx.doi.org/10.1080/10408390903001... ; Hormdok & Noomhorm, 2007Hormdok, R., & Noomhorm, A. (2007). Hydrothermal treatments of rice starch for improvement of rice noodle quality. LWT - Food Science and Technology (Campinas.), 40(10), 1723-1731.; Jyothi et al., 2010Jyothi, A. N., Sajeev, M. S., & Sreekumar, J. N. (2010). Hydrothermal modifications of tropical tuber starches. 1. Effect of heat-moisture treatment on the physicochemical, rheological and gelatinization characteristics. Starch/Staerke, 62(1), 28-40. http://dx.doi.org/10.1002/star.200900191.
http://dx.doi.org/10.1002/star.200900191... ). Structural and physicochemical changes generated by HMT are directly influenced by the botanical source of the starch granule with respect to its composition and organization of amylose and amylopectin. HMT is also used as a pre-treatment because of the structural modification into amorphous and crystalline regions on the granules. These alterations make the granule susceptible to chemical and enzymatic modifications and acid hydrolysis (Zavareze & Dias, 2011Zavareze, E. D. R., & Dias, A. R. G. (2011). Impact of heat-moisture treatment and annealing in starches: a review. Carbohydrate Polymers, 83(2), 317-328. http://dx.doi.org/10.1016/j.carbpol.2010.08.064.
http://dx.doi.org/10.1016/j.carbpol.2010... ).
Non-thermal physical modification
Some processes in food production are applied to extend the life of a product
using thermic treatments at boiling temperatures (or even higher) for
seconds or minutes. Traditional treatments cause a loss of some vitamins and
nutrients and alter their organoleptic properties. Non-thermal modification
is an alternative to traditional processes that also eliminates pathogenic
microorganisms and spores. Non-thermal techniques involve the use of high
pressure, ultrasound, microwaves (Anderson
& Guraya, 2006Anderson, A. K., & Guraya, H. S. (2006). Effects of microwave
heat-moisture treatment on properties of waxy and non-waxy rice starches. Food
Chemistry, 97(2), 318-323.
http://dx.doi.org/10.1016/j.foodchem.2005.04.025.
http://dx.doi.org/10.1016/j.foodchem.200...
; Braşoveanu
& Nemtanu, 2014Braşoveanu, M., & Nemtanu, M. R. (2014). Behaviour of starch
exposed to microwave radiation treatment. Starch/Staerke, 66(1-2), 3-14.
http://dx.doi.org/10.1002/star.201200191.
http://dx.doi.org/10.1002/star.201200191...
; Hódsági et
al., 2012Hódsági, M., Jámbor, É., Juhász, E., Gergely, S., Gelencsér, T.,
& Salgó, A. (2012). Effects of microwave heating on native and resistant
starches. Acta Alimentaria, 41(2), 233-247.
http://dx.doi.org/10.1556/AAlim.41.2012.2.10.
http://dx.doi.org/10.1556/AAlim.41.2012....
; Mollekopf et al.,
2011Mollekopf, N., Treppe, K., Fiala, P., & Dixit, O. (2011). Vacuum
microwave treatment of potato starch and the resultant modification of
properties. Chemieingenieurtechnik (Weinheim), 83(3), 262-272.
http://dx.doi.org/10.1002/cite.201000105.
http://dx.doi.org/10.1002/cite.201000105...
) and electric pulses. The high pressure technology in
industry uses pressure from 400 to 900 MPa. High pressure generally
restricts the swelling capacity and consequently decreases paste viscosity.
Other technologies use pressure several times bellow atmospheric pressure
(vacuum pressures); this technology uses gas in a plasma state and is the
most recent technology used for starch granule modification (Deeyai et al., 2013Deeyai, P., Suphantharika, M., Wongsagonsup, R., & Dangtip, S.
(2013). Characterization of modified tapioca starch in atmospheric argon plasma
under diverse humidity by FTIR spectroscopy. Chinese Physics Letters, 30(1),
181031-181034. http://dx.doi.org/10.1088/0256-307X/30/1/018103.
http://dx.doi.org/10.1088/0256-307X/30/1...
; Wongsagonsup et al., 2014Wongsagonsup, R., Deeyai, P., Chaiwat, W., Horrungsiwat, S.,
Leejariensuk, K., Suphantharika, M., Fuongfuchat, A., & Dangtip, S. (2014).
Modification of tapioca starch by non-chemical route using jet atmospheric argon
plasma. Carbohydrate Polymers, 102, 790-798.
http://dx.doi.org/10.1016/j.carbpol.2013.10.089. PMid:24507348.
http://dx.doi.org/10.1016/j.carbpol.2013...
). Plasma is
an ionized gas composed of several types of active ionic species: electrons,
ions, excited atoms and protons (Bogaerts
et al., 2002Bogaerts, A., Neyts, E., Gijbels, R., & Van der Mullen, J.
(2002). Gas discharge plasmas and their applications. Spectrochimica Acta. Part
B: Atomic Spectroscopy, 57(4), 609-658.
http://dx.doi.org/10.1016/S0584-8547(01)00406-2.
http://dx.doi.org/10.1016/S0584-8547(01)...
). For this treatment, the gases used include
ethylene, hydrogen, oxygen, ammonia, air, methane or argon in a plasma
state. This treatment modifies the starch in different ways, including its
hygroscopicity, degree of polymerization and oxidation (Wongsagonsup et al., 2014Wongsagonsup, R., Deeyai, P., Chaiwat, W., Horrungsiwat, S.,
Leejariensuk, K., Suphantharika, M., Fuongfuchat, A., & Dangtip, S. (2014).
Modification of tapioca starch by non-chemical route using jet atmospheric argon
plasma. Carbohydrate Polymers, 102, 790-798.
http://dx.doi.org/10.1016/j.carbpol.2013.10.089. PMid:24507348.
http://dx.doi.org/10.1016/j.carbpol.2013...
).
Modification of starch using microwaves involves several interacting
mechanisms, such as irradiation, furnace dimensions and the characteristics
of the starch. In the microwave irradiation process, the most important
parameters are moisture and temperature, which influence the dielectric
properties of the starch (Braşoveanu &
Nemtanu, 2014Braşoveanu, M., & Nemtanu, M. R. (2014). Behaviour of starch
exposed to microwave radiation treatment. Starch/Staerke, 66(1-2), 3-14.
http://dx.doi.org/10.1002/star.201200191.
http://dx.doi.org/10.1002/star.201200191...
). Starch modification by microwaves results from
the rearrangement of starch molecules that generates changes in solubility,
swelling capacity, rheological behavior, Tgel and enthalpies
(Iida et al., 2008Iida, Y., Tuziuti, T., Yasui, K., Towata, A., & Kozuka, T.
(2008). Control of viscosity in starch and polysaccharide solutions with
ultrasound after gelatinization. Innovative Food Science & Emerging
Technologies, 9(2), 140-146.
http://dx.doi.org/10.1016/j.ifset.2007.03.029.
http://dx.doi.org/10.1016/j.ifset.2007.0...
; Yu et al., 2013Yu, S., Zhang, Y., Ge, Y., Zhang, Y., Sun, T., Jiao, Y., &
Zheng, X. Q. (2013). Effects of ultrasound processing on the thermal and
retrogradation properties of nonwaxy rice starch. Journal of Food Process
Engineering, 36(6), 793-802.
http://dx.doi.org/10.1111/jfpe.12048.
http://dx.doi.org/10.1111/jfpe.12048...
; Zuo et al., 2012Zuo, Y. Y. J., Hébraud, P., Hemar, Y., & Ashokkumar, M. (2012).
Quantification of high-power ultrasound induced damage on potato starch granules
using light microscopy. Ultrasonics Sonochemistry, 19(3), 421-426.
http://dx.doi.org/10.1016/j.ultsonch.2011.08.006.
PMid:21962479.
http://dx.doi.org/10.1016/j.ultsonch.201...
). Depending on the starch source and
moisture, modification by microwave also produces variations in morphology
and crystallinity in the granule (Braşoveanu & Nemtanu, 2014Braşoveanu, M., & Nemtanu, M. R. (2014). Behaviour of starch
exposed to microwave radiation treatment. Starch/Staerke, 66(1-2), 3-14.
http://dx.doi.org/10.1002/star.201200191.
http://dx.doi.org/10.1002/star.201200191...
).
The use of ultrasound is also considered a physical modification treatment.
This treatment is applied to starches in suspension and starches that have
undergone previous gelatinization (Iida et
al., 2008Iida, Y., Tuziuti, T., Yasui, K., Towata, A., & Kozuka, T.
(2008). Control of viscosity in starch and polysaccharide solutions with
ultrasound after gelatinization. Innovative Food Science & Emerging
Technologies, 9(2), 140-146.
http://dx.doi.org/10.1016/j.ifset.2007.03.029.
http://dx.doi.org/10.1016/j.ifset.2007.0...
; Yu et al.,
2013Yu, S., Zhang, Y., Ge, Y., Zhang, Y., Sun, T., Jiao, Y., &
Zheng, X. Q. (2013). Effects of ultrasound processing on the thermal and
retrogradation properties of nonwaxy rice starch. Journal of Food Process
Engineering, 36(6), 793-802.
http://dx.doi.org/10.1111/jfpe.12048.
http://dx.doi.org/10.1111/jfpe.12048...
; Zuo et al., 2012Zuo, Y. Y. J., Hébraud, P., Hemar, Y., & Ashokkumar, M. (2012).
Quantification of high-power ultrasound induced damage on potato starch granules
using light microscopy. Ultrasonics Sonochemistry, 19(3), 421-426.
http://dx.doi.org/10.1016/j.ultsonch.2011.08.006.
PMid:21962479.
http://dx.doi.org/10.1016/j.ultsonch.201...
).
Ultrasound primarily affects the amorphous region, while maintaining the
granule’s shape and size. The starch surface becomes porous, and properties
such as the swelling capacity, solubility and viscosity of the paste are
modified (Luo et al., 2008Luo, Z., Fu, X., He, X., Luo, F., Gao, Q., & Yu, S. (2008).
Effect of ultrasonic treatment on the physicochemical properties of maize
starches differing in amylose content. Starch/Staerke, 60(11), 646-653.
http://dx.doi.org/10.1002/star.200800014.
http://dx.doi.org/10.1002/star.200800014...
).
Ultrasonic modification depends on the sound, frequency, temperature,
process time and the starch suspension properties (i.e., concentration and
botanical source of starch) (Zuo et al.,
2009Zuo, J. Y., Knoerzer, K., Mawson, R., Kentish, S., & Ashokkumar,
M. (2009). The pasting properties of sonicated waxy rice starch suspensions.
Ultrasonics Sonochemistry, 16(4), 462-468.
http://dx.doi.org/10.1016/j.ultsonch.2009.01.002.
PMid:19201242.
http://dx.doi.org/10.1016/j.ultsonch.200...
).
Other physical modification methods: grinding and extrusion
Large-scale extraction of starch from cereals such as wheat require grinding. Substantial granule damage occurs during grinding, and shear forces that compress the granule structure are generated. Damage to the starch granule is visible as cracks in the starch surface. Grinding reduces the crystallinity of the amylopectin molecule and its double helix conformation severely. Fragmentation of the amylopectin molecule eliminates restrictions on the swelling capacity, thereby facilitating subsequent gelatinization. The easy gelatinization of the starch granules after grinding decreases parameters such as T0 and enthalpies in the final starch product.
Extrusion is defined as a process at high temperatures and in short amounts
of time (HTST), wherein starch granules are subjected to mechanical shearing
forces in a relatively low moisture environment (Camire et al., 1990Camire, M. E., Camire, A., & Krumhar, K. (1990). Chemical and
nutritional changes in foods during extrusion. Critical Reviews in Food Science
and Nutrition, 29(1), 35-57. http://dx.doi.org/10.1080/10408399009527513.
PMid:2184829.
http://dx.doi.org/10.1080/10408399009527...
). Extrusion increases the
Tgel of starch, changing the molecular extension and its
associations, such as the amylose-lipid complex structure. The extrusion
process also affects starch digestibility and can reduce the RS content
(Martínez et al., 2014Martínez, M. M., Rosell, C. M., & Gomez, M. (2014). Modification
of wheat flour functionality and digestibility through different extrusion
conditions. Journal of Food Engineering, 143, 74-79.
http://dx.doi.org/10.1016/j.jfoodeng.2014.06.035.
http://dx.doi.org/10.1016/j.jfoodeng.201...
).
3.2 Chemical modification of starch
Chemical modification involves the introduction of functional groups on the
starch molecule without affecting the morphology or size distribution of the
granules. Chemical modifications generate significant changes in starch
behavior, gelatinization capacity, retrogradation and paste properties (López et al., 2010López, O. V., Zaritzky, N. E., & García, M. A. (2010).
Physicochemical characterization of chemically modified corn starches related to
rheological behavior, retrogradation and film forming capacity. Journal of Food
Engineering, 100(1), 160-168.
http://dx.doi.org/10.1016/j.jfoodeng.2010.03.041.
http://dx.doi.org/10.1016/j.jfoodeng.201...
). Food and non-food
industries expand starch properties and improve them through chemical
modifications. Table 3 shows examples of
different chemical modifications of starch.
Cationic starch
Cationic starches are generally produced by reacting starch with compounds
containing tertiary or quaternary ammonium, imino, amino, sulfuric or
phosphate groups. Free hydroxyl ions present in the native starch molecule
are commonly altered using cationic monomers such as 2,3-epoxypropyl
trimethyl ammonium chloride (ETMAC) or 3-chloro-2-hydroxypropyl trimethyl
ammonium chloride (CTA) in dry or wet processes. In dry cationic
modification, in the absence of a liquid phase, the reactive is sprayed onto
the dry starch during extrusion. The semi-dry method for cationization
involves a mixture of starch and spray reagent prior to the thermal
treatment. Wet cationization includes a homogeneous reaction with dimethyl
sulfoxide (DMSO) or a heterogeneous reaction in alkaline solution. The
physicochemical properties of the starch and granular structure are altered
after the cationic process, particularly when the process involves a high
degree of substitution. The cationic reaction reduces the paste temperature,
increases the viscosity peak and results in various changes in starches from
different sources. Among modified starches, cationic starch materials are
preferred by the textile industry because the positive charge introduced in
the molecular chains conform to the electrostatic bonds between the negative
charges of the cellulose fibers (Hubbe,
2007Hubbe, M. A. (2007). Bonding between cellulosic fibers in the
absence and presence of dry-strength agents – a review. BioResources, 1(2),
281-318.). There are several applications for cationic starches
(i.e., in water treatment as flocculants and as additives in textile
products, paper and cosmetics), preferred for their low cost, excellent fit,
biocompatibility and rapid degradation (Zhang, 2001Zhang, L. M. (2001). A review of starches and their derivatives for
oilfield applications in China. Stärke, 53(9), 401-407.
http://dx.doi.org/10.1002/1521-379X(200109)53:9<401::AID-STAR401>3.0.CO;2-2.
http://dx.doi.org/10.1002/1521-379X(2001...
).
Cross-linked starch
Crosslinking of a polymer occurs when linear or branched chains are
covalently interconnected and is known as cross-linking or cross-ligation.
The reagents used form ether or ester bonds with hydroxyl groups in the
starch molecules (Singh et al.,
2007Singh, J., Kaur, L., & McCarthy, O. J. (2007). Factors
influencing the physico-chemical, morphological, thermal and rheological
properties of some chemically modified starches for food applications - a
review. Food Hydrocolloids, 21(1), 1-22.
http://dx.doi.org/10.1016/j.foodhyd.2006.02.006.
http://dx.doi.org/10.1016/j.foodhyd.2006...
). This modification increases the polymer’s rigidity by forming
a three-dimensional network. Crosslinking in starch increases the degree of
polymerization and molecular mass; starch molecules lose water solubility
and become soluble in organic solvents. Several agents are used to crosslink
native starch: sodium trimetaphosphate (STMP), sodium tripolyphosphate
(STPP), epichlorohydrin (ECH) and phosphoryl chloride (POCl3),
among others (Woo & Seib,
2002Woo, K. S., & Seib, P. A. (2002). Cross-linked resistant starch:
preparation and properties 1. Cereal Chemistry, 79(6), 819-825.
http://dx.doi.org/10.1094/CCHEM.2002.79.6.819.
http://dx.doi.org/10.1094/CCHEM.2002.79....
).
Depending on the reagent used for crosslinking, the final product is
classified in one of three types: i) monostarch phosphate produced by starch
esterification with orthophosphoric acid, potassium or sodium
orthophosphoric or STPP; ii) distarch phosphate produced when native starch
reacts with STMP or POCl3; or iii) phosphated distarch phosphate,
resulting from combined treatments of monostarch and distarch phosphates
(Gunaratne & Corke, 2007Gunaratne, A., & Corke, H. (2007). Functional properties of
hydroxypropylated, cross-linked, and hydroxypropylated cross-linked tuber and
root starches. Cereal Chemistry, 84(1), 30-37.
http://dx.doi.org/10.1094/CCHEM-84-1-0030.
http://dx.doi.org/10.1094/CCHEM-84-1-003...
;
Jyothi et al., 2006Jyothi, A. N., Moorthy, S. N., & Rajasekharan, K. N. (2006).
Effect of cross-linking with epichlorohydrin on the properties of cassava (
Crantz) starch. Manihot esculentaStarch/Staerke, 58(6),
292-299. http://dx.doi.org/10.1002/star.200500468.
http://dx.doi.org/10.1002/star.200500468...
).
The source of starch granule, methods and parameters used for crosslinking
modification has an important influence on the properties of the final
product. Starch properties affected by crosslinking modification include the
paste clarity and swelling capacity. Some authors suggest that both
properties are linked, and a reduction in swelling is responsible for the
decrease in paste clarity (Kaur et al.,
2006Kaur, L., Singh, J., & Singh, N. (2006). Effect of cross-linking
on some properties of potato ( L.) starches. Solanum
tuberosumJournal of the Science of Food and Agriculture, 86(12),
1945-1954. http://dx.doi.org/10.1002/jsfa.2568.
http://dx.doi.org/10.1002/jsfa.2568...
; Koo et al., 2010Koo, S. H., Lee, K. Y., & Lee, H. G. (2010). Effect of
cross-linking on the physicochemical and physiological properties of corn
starch. Food Hydrocolloids, 24(6-7), 619-625.
http://dx.doi.org/10.1016/j.foodhyd.2010.02.009.
http://dx.doi.org/10.1016/j.foodhyd.2010...
).
The degree of crosslinking also reduces the moisture, lipids and proteins
associated with the native starch granule; these changes are produced by all
of the aforementioned crosslinking agents in different proportions (Carmona-Garcia et al., 2009Carmona-Garcia, R., Sanchez-Rivera, M. M., Méndez-Montealvo, G.,
Garza-Montoya, B., & Bello-Pérez, L. A. (2009). Effect of the cross-linked
reagent type on some morphological, physicochemical and functional
characteristics of banana starch (Musa paradisiaca). Carbohydrate Polymers,
76(1), 117-122.
http://dx.doi.org/10.1016/j.carbpol.2008.09.029.
http://dx.doi.org/10.1016/j.carbpol.2008...
). In the
food industry, cross-linked starch is associated with formulations of frozen
products due to its stabilizing, thickening, clarity and retrogradation
resistance properties of the pastes formed. Its uses also extend to other
industries such as plastics (López et al.,
2010López, O. V., Zaritzky, N. E., & García, M. A. (2010).
Physicochemical characterization of chemically modified corn starches related to
rheological behavior, retrogradation and film forming capacity. Journal of Food
Engineering, 100(1), 160-168.
http://dx.doi.org/10.1016/j.jfoodeng.2010.03.041.
http://dx.doi.org/10.1016/j.jfoodeng.201...
).
Acetylated starch
Acetylation is a modification of polymeric starch molecules through the
introduction of functional acetylated groups (CH3CO) that react
with free hydroxyl groups present in the branched chains of the starch
polymer to produce a specific ester (Sweedman et al., 2013Sweedman, M. C., Tizzotti, M. J., Schäfer, C., & Gilbert, R. G.
(2013). Structure and physicochemical properties of octenyl succinic anhydride
modified starches: a review. Carbohydrate Polymers, 92(1), 905-920.
http://dx.doi.org/10.1016/j.carbpol.2012.09.040. PMid:23218383.
http://dx.doi.org/10.1016/j.carbpol.2012...
). Acetylation is the more common chemical
modification method, resulting in native starch esterification using
reactive reagents such as anhydrous acetic acid, vinyl acetate or OSA in the
presence of an alkaline catalyst (NaOH, KOH, Ca(OH)2,
Na2CO3) (Wang
& Wang, 2002Wang, Y. J., & Wang, L. (2002). Characterization of acetylated
waxy maize starches prepared under catalysis by different alkali and
alkaline-earth hydroxides. Starch/Staerke, 54(1), 25-30.
http://dx.doi.org/10.1002/1521-379X(200201)54:1<25::AID-STAR25>3.0.CO;2-T.
http://dx.doi.org/10.1002/1521-379X(2002...
). Starch modified with OSA is an effective
emulsifier used in the food, pharmaceutical and cosmetic industries; in this
modification, OSA adds hydrophobic chains to the hydrophilic structure of
starch (Chen et al., 2014Chen, X., He, X., & Huang, Q. (2014). Effects of hydrothermal
pretreatment on subsequent octenylsuccinic anhydride (OSA) modification of
cornstarch. Carbohydrate Polymers, 101(0), 493-498.
http://dx.doi.org/10.1016/j.carbpol.2013.09.079. PMid:24299803.
http://dx.doi.org/10.1016/j.carbpol.2013...
). The
introduction of acetyl groups reduces the resistance of bonds between the
starch molecules. Acetylated starch increases the swelling capacity and
solubility compared to native starch (Berski et al., 2011Berski, W., Ptaszek, A., Ptaszek, P., Ziobro, R., Kowalski, G.,
Grzesik, M., & Achremowicz, B. (2011). Pasting and rheological properties of
oat starch and its derivatives. Carbohydrate Polymers, 83(2), 665-671.
http://dx.doi.org/10.1016/j.carbpol.2010.08.036.
http://dx.doi.org/10.1016/j.carbpol.2010...
). The presence of hydrogen bonds in
acetylated starch is restricted due to electrostatic repulsion forces on the
starch molecule (Lawal & Adebowale,
2005Lawal, O. S., & Adebowale, K. O. (2005). Physicochemical
characteristics and thermal properties of chemically modified jack bean (.
Canavalia ensiformis) starchCarbohydrate Polymers, 60(3),
331-341. http://dx.doi.org/10.1016/j.carbpol.2005.01.011.
http://dx.doi.org/10.1016/j.carbpol.2005...
). In acetylated starch, hydroxyl groups and anhydrous
glucose have been converted to acetylated groups (Huang et al., 2010Huang, Q., Fu, X., He, X., Luo, F., Yu, S., & Li, L. (2010). The
effect of enzymatic pretreatments on subsequent octenyl succinic anhydride
modifications of cornstarch. Food Hydrocolloids, 24(1), 60-65.
http://dx.doi.org/10.1016/j.foodhyd.2009.08.005.
http://dx.doi.org/10.1016/j.foodhyd.2009...
). Acetylated starch with a low
degree of substitution (0.01-0.2) has several applications in conforming
films, adherents, thickeners, stabilizers, texturizers and encapsulation
agents (Elomaa et al., 2004Elomaa, M., Asplund, T., Soininen, P., Laatikainen, R., Peltonen,
S., Hyvärinen, S., & Urtti, A. (2004). Determination of the degree of
substitution of acetylated starch by hydrolysis, 1H NMR and TGA/IR. Carbohydrate
Polymers, 57(3), 261-267.
http://dx.doi.org/10.1016/j.carbpol.2004.05.003.
http://dx.doi.org/10.1016/j.carbpol.2004...
). Bello-Pérez et al. (2000)Bello-Pérez, L. A., Contreras-Ramos, S. M., Jìmenez-Aparicio, A.,
& Paredes-López, O. (2000). Acetylation and characterization of banana (Musa
paradisiaca) starch. Acta Cientifica Venezolana, 51(3), 143-149.
PMid:11265448. studied the
acetylation process in banana starches. Acetylation modified the starch
granule, decreasing the retrogradation tendency and increasing the
solubility and swelling capacity of banana starch considerably compared to
native starch. Acetylated banana starch also increased the paste
viscosity.
Other methods of chemical modification
The oldest chemical modification technique is acid modification. Products of
acid modification have several applications and uses in the food, paper,
textile and pharmaceutical industries (Hoover, 2000Hoover, R. (2000). Acid-treated starches. Food Reviews
International, 16(3), 369-392.
http://dx.doi.org/10.1081/FRI-100100292.
http://dx.doi.org/10.1081/FRI-100100292...
). Acid modification methods involve the application
of acidic solutions (commonly HCl and H2SO4) to form a
concentrated paste (35–40% of solids) at a temperature below Tg
for a specific duration depending on the desired viscosity or conversion
degree (Amaya-Llano et al., 2008Amaya-Llano, S. L., Martínez-Alegría, A. L., Zazueta-Morales, J. J.,
& Martínez-Bustos, F. (2008). Acid thinned jicama and maize starches as fat
substitute in stirred yogurt. LWT - Food Science and Technology (Campinas.),
41(7), 1274-1281.;
Thirathumthavorn & Charoenrein,
2005Thirathumthavorn, D., & Charoenrein, S. (2005). Thermal and
pasting properties of acid-treated rice starches. Starch/Staerke, 57(5),
217-222. http://dx.doi.org/10.1002/star.200400332.
http://dx.doi.org/10.1002/star.200400332...
). The mechanism of acid modification is also known as acid
hydrolysis (Amaya-Llano et al.,
2008Amaya-Llano, S. L., Martínez-Alegría, A. L., Zazueta-Morales, J. J.,
& Martínez-Bustos, F. (2008). Acid thinned jicama and maize starches as fat
substitute in stirred yogurt. LWT - Food Science and Technology (Campinas.),
41(7), 1274-1281.). Hydrolysis is produced randomly, breaking the α-1,4 and α-1,6
links and shortening the polymeric chains. Acid hydrolysis of starch
develops in two stages: an early stage in which hydrolysis preferentially
attacks the amorphous regions of granules at a high reaction rate and a
subsequent stage in which hydrolysis occurs in the crystalline region at a
slower rate (Wang & Wang, 2001Wang, L., & Wang, Y. J. (2001). Structures and physicochemical
properties of acid-thinned corn, potato and rice starches. Starch/Staerke,
53(11), 570-576.
http://dx.doi.org/10.1002/1521-379X(200111)53:11<570::AID-STAR570>3.0.CO;2-S.
http://dx.doi.org/10.1002/1521-379X(2001...
).
The hydrolysis rate and starch modification are in proportion to the
amylose:amylopectin ratio, as well as to the size and conformation of
granules (Hoover, 2000Hoover, R. (2000). Acid-treated starches. Food Reviews
International, 16(3), 369-392.
http://dx.doi.org/10.1081/FRI-100100292.
http://dx.doi.org/10.1081/FRI-100100292...
). After acid
hydrolysis, the molecular mass of the starch granules decreases, and its
crystallinity increases (Zuo et al.,
2014Zuo, Y., Gu, J., Tan, H., Qiao, Z., Xie, Y., & Zhang, Y. (2014).
The characterization of granule structural changes in acid-thinning starches by
new methods and its effect on other properties. Journal of Adhesion Science and
Technology, 28(5), 479-489.
http://dx.doi.org/10.1080/01694243.2013.843283.
http://dx.doi.org/10.1080/01694243.2013....
). Singh & Ali
(2000)Singh, V., & Ali, S. Z. (2000). Acid degradation of starch. The
effect of acid and starch type. Carbohydrate Polymers, 41(2), 191-195.
http://dx.doi.org/10.1016/S0144-8617(99)00086-7.
http://dx.doi.org/10.1016/S0144-8617(99)...
studied the influence of various acids used in starch
modification (HCl, HNO3, H2SO4,
H3PO4); the starch sources were wheat, corn, peas,
tapioca and potato. These authors concluded that H3PO4
produced a lower hydrolysis rate, whereas HCl and HNO3 resulted
in a higher reduction in molecular mass and consequently a higher hydrolysis
rate. Acid hydrolysis reduces the amylose content in starch granules, and
this reflects an increase in paste temperature and gelatinization enthalpies
(Lawal, 2004Lawal, O. S. (2004). Composition, physicochemical properties and
retrogradation characteristics of native, oxidised, acetylated and acid-thinned
new cocoyam (Xanthosoma sagittifolium) starch. Food Chemistry,
87(2), 205-218.
http://dx.doi.org/10.1016/j.foodchem.2003.11.013.
http://dx.doi.org/10.1016/j.foodchem.200...
). The use of dilute
acid solutions for starch modification improves gel consistency and reduces
paste viscosity due to depolymerization of the starch granule (Pérez & Bertoft, 2010Pérez, S., & Bertoft, E. (2010). The molecular structures of
starch components and their contribution to the architecture of starch granules:
a comprehensive review. Starch/Staerke, 62(8), 389-420.
http://dx.doi.org/10.1002/star.201000013.
http://dx.doi.org/10.1002/star.201000013...
; Ulbrich et al., 2015Ulbrich, M., Wiesner, I., & Flöter, E. (2015). Molecular
characterization of acid-thinned wheat, potato and pea starches and correlation
to gel properties. Starch/Staerke. 66, 1-14.).
Another important process for starch modification is oxidation, a process in
which functional groups such as carboxyl and carbonyl groups are introduced
in the starch molecule and depolymerize the molecule (Kuakpetoon & Wang, 2001Kuakpetoon, D., & Wang, Y. J. (2001). Characterization of
different starches oxidized by hypochlorite. Starch/Staerke, 53(5), 211-218.
http://dx.doi.org/10.1002/1521-379X(200105)53:5<211::AID-STAR211>3.0.CO;2-M.
http://dx.doi.org/10.1002/1521-379X(2001...
). During oxidation, it is
important to maintain the appropriate parameters, such as temperature and
pH. The reactive oxidants used include hydrogen peroxide, per-acetic acid,
potassium permanganate, sodium hypochlorite, chromic acid and nitrogen
dioxide (Sánchez-Rivera et al.,
2005Sánchez-Rivera, M. M., García-Suárez, F. J. L., Velázquez del Valle,
M., Gutierrez-Meraz, F., & Bello-Pérez, L. A. (2005). Partial
characterization of banana starches oxidized by different levels of sodium
hypochlorite. Carbohydrate Polymers, 62(1), 50-56.
http://dx.doi.org/10.1016/j.carbpol.2005.07.005.
http://dx.doi.org/10.1016/j.carbpol.2005...
; Sandhu et al., 2008Sandhu, K. S., Kaur, M., Singh, N., & Lim, S. T. (2008). A
comparison of native and oxidized normal and waxy corn starches:
Physicochemical, thermal, morphological and pasting properties. . LWT
-Food Science and Technology (Campinas.), 41(6),
1000-1010.;
Wang & Wang, 2003Wang, Y. J., & Wang, L. (2003). Physicochemical properties of
common and waxy corn starches oxidized by different levels of sodium
hypochlorite. Carbohydrate Polymers, 52(3), 207-217.
http://dx.doi.org/10.1016/S0144-8617(02)003041.
http://dx.doi.org/10.1016/S0144-8617(02)...
). In
recent years, starch modified by oxidation has had great use in the food
industry to form adherent surfaces and coatings (Lawal et al., 2005Lawal, O. S., Adebowale, K. O., Ogunsanwo, B. M., Barba, L. L.,
& Ilo, N. S. (2005). Oxidized and acid thinned starch derivatives of hybrid
maize: functional characteristics, wide-angle X-ray diffractometry and thermal
properties. International Journal of Biological Macromolecules, 35(1-2), 71-79.
http://dx.doi.org/10.1016/j.ijbiomac.2004.12.004.
PMid:15769518.
http://dx.doi.org/10.1016/j.ijbiomac.200...
).
Dual modifications
Dual modifications include chemical modifications and different types of
modifications combined. Dual modifications have been used in industry to
optimize modified starch functionality (Ashogbon & Akintayo, 2014Ashogbon, A. O., & Akintayo, E. T. (2014). Recent trend in the
physical and chemical modification of starches from different botanical sources:
a review. Starch/Staerke, 66(1-2), 41-57.
http://dx.doi.org/10.1002/star.201300106.
http://dx.doi.org/10.1002/star.201300106...
). This new approach involves the
combination of chemical and physical agents (e.g., acetylation assisted by
microwave, phosphorylation assisted by high pressures). Specifically, dual
chemical modifications involve two processes of chemical modification (e.g.,
acetylation/oxidation, crosslinking/acetylation,
crosslinking/hydroxypropylation) (Adebowale
& Lawal, 2002Adebowale, K. O., & Lawal, O. S. (2002). Effect of annealing and
heat moisture conditioning on the physicochemical characteristics of Bambarra
groundnut (Voandzeia subterranea) starch. Die Nahrung, 46(5), 311-316.
http://dx.doi.org/10.1002/1521-3803(20020901)46:5<311::AID-FOOD311>3.0.CO;2-Z.
PMid:12428444.
http://dx.doi.org/10.1002/1521-3803(2002...
; Carmona-Garcia et al., 2009Carmona-Garcia, R., Sanchez-Rivera, M. M., Méndez-Montealvo, G.,
Garza-Montoya, B., & Bello-Pérez, L. A. (2009). Effect of the cross-linked
reagent type on some morphological, physicochemical and functional
characteristics of banana starch (Musa paradisiaca). Carbohydrate Polymers,
76(1), 117-122.
http://dx.doi.org/10.1016/j.carbpol.2008.09.029.
http://dx.doi.org/10.1016/j.carbpol.2008...
; Huang et al., 2010Huang, Q., Fu, X., He, X., Luo, F., Yu, S., & Li, L. (2010). The
effect of enzymatic pretreatments on subsequent octenyl succinic anhydride
modifications of cornstarch. Food Hydrocolloids, 24(1), 60-65.
http://dx.doi.org/10.1016/j.foodhyd.2009.08.005.
http://dx.doi.org/10.1016/j.foodhyd.2009...
). Starches modified by two chemical methods,
such as emulsifiers, agglutinants and thickeners, are commonly used in the
food industry and are included as adsorbents of heavy metals in the non-food
industry (Ashogbon & Akintayo,
2014Ashogbon, A. O., & Akintayo, E. T. (2014). Recent trend in the
physical and chemical modification of starches from different botanical sources:
a review. Starch/Staerke, 66(1-2), 41-57.
http://dx.doi.org/10.1002/star.201300106.
http://dx.doi.org/10.1002/star.201300106...
).
4 Resistant starch (RS)
Starch is quantitatively the major source of energy in the human diet. Starch
digestibility is attributed to the interaction of several factors, including the
vegetal source, granule size, amylose/amylopectin ratio, degree of molecular
association between components, degree of crystallinity, amylose chain length and
presence of amylose-lipid complexes on starch granules (Cummings & Englyst, 1995Cummings, J. H., & Englyst, H. N. (1995). Gastrointestinal
effects of food carbohydrate. The American Journal of Clinical Nutrition,
61(Suppl. 4), 938S-945S. PMid:7900692.). Lipids are fatty acids
specifically interacting with amylose to form complexes and reduce starch
digestibility because their presence decreases enzymatic hydrolysis by amylase
(Taylor et al., 2015Taylor, J. R. N., Emmambux, M. N., & Kruger, J. (2015).
Developments in modulating glycaemic response in starchy cereal foods.
Starch/Staerke, 67(1-2), 79-89.
http://dx.doi.org/10.1002/star.201400192.
http://dx.doi.org/10.1002/star.201400192...
).
Until recently, starch was considered completely digested after cooking. This concept has been challenged by observations that some of starch crosses the colon, where it is subject to bacterial fermentations. Today, this indigestible starch is recognized as part of the dietary fiber fraction of food (Conde-Petit et al., 2001Conde-Petit, B., Nuessli, J., Arrigoni, E., Escher, F., & Amadò, R. (2001). Perspectives of starch in food science. Chimia, 55(3), 201-205.). Most polysaccharides of interest for nutrition (e.g., starch, dextrin, glycogen and cellulose) are unions of glucose units, differing only in the type of linkage. As a group, polysaccharides may contain monosaccharides in addition to glucose, either alone or combined.
Starch digestion begins in the mouth, with α-amylase enzymes present in saliva.
Enzyme activity is partially preserved until reaching the stomach. However, most
starch is digested in the small intestine by enzymes from the pancreas. Degradation
products of amylose are maltose and maltotriose, whereas amylopectin degradation
produces dextrins and oligomers formed by α-1,6 linkages. Until the end of the
intestine is reached, all of these polymers are degraded to glucose by enzymes such
as α-glycosidase and oligo-α-1,6-glucosidase. Glucose absorption is followed by an
immediate increase in glucoses levels in blood (Perera et al., 2010Perera, A., Meda, V., & Tyler, R. T. (2010). Resistant starch: a
review of analytical protocols for determining resistant starch and of factors
affecting the resistant starch content of foods. Food Research International,
43(8), 1959-1974.
http://dx.doi.org/10.1016/j.foodres.2010.06.003.
http://dx.doi.org/10.1016/j.foodres.2010...
).
Factors that affect starch digestibility include the structural characteristics of
the starch (i.e., the amylose:amylopectin ratio, degree of gelatinization,
retrogradation and formation of amylose complexes), the structural characteristics
of the food and the presence of other components such as soluble dietary fiber
(Conde-Petit et al., 2001Conde-Petit, B., Nuessli, J., Arrigoni, E., Escher, F., & Amadò,
R. (2001). Perspectives of starch in food science. Chimia, 55(3),
201-205.). RS is
defined as the sum of starch or the sum of starch degradation products that are not
absorbed by the small intestine in healthy individuals (Champ et al., 2003Champ, M., Langkilde, A. M., Brouns, F., Kettlitz, B., &
Bail-Collet, Y. L. (2003). Advances in dietary fibre characterisation. 2.
Consumption, chemistry, physiology and measurement of resistant starch;
implications for health and food labelling. Nutrition Research Reviews, 16(2),
143-161. http://dx.doi.org/10.1079/NRR200364. PMid:19087387.
http://dx.doi.org/10.1079/NRR200364...
).
RS is divided into five types that have been substantially affected by the
transformation process (Homayouni et al.,
2014Homayouni, A., Amini, A., Keshtiban, A. K., Mortazavian, A. M.,
Esazadeh, K., & Pourmoradian, S. (2014). Resistant starch in food industry:
a changing outlook for consumer and producer. Starch/Staerke, 66(1-2), 102-114.
http://dx.doi.org/10.1002/star.201300110.
http://dx.doi.org/10.1002/star.201300110...
). The first group (RS I) is the product of treatments in which
starch is physically inaccessible and the breakdown of the granular structure does
not occur (Hasjim & Jane, 2009Hasjim, J., & Jane, J. L. (2009). Production of resistant starch
by extrusion cooking of acid-modified normal-maize starch. Journal of Food
Science, 74(7), C556-C562. http://dx.doi.org/10.1111/j.1750-3841.2009.01285.x.
PMid:19895460.
http://dx.doi.org/10.1111/j.1750-3841.20...
). The
second group, RS II, consists of gelatinized starch (i.e., the starch has lost its
crystalline conformation and is composed primarily of amylose); this type is very
common in most starchy foods (Fuentes-Zaragoza et
al., 2011Fuentes-Zaragoza, E., Sánchez-Zapata, E., Sendra, E., Sayas, E.,
Navarro, C., Fernández-López, J., & Pérez-Alvarez, J. A. (2011). Resistant
starch as prebiotic: a review. Starch/Staerke, 63(7), 406-415.
http://dx.doi.org/10.1002/star.201000099.
http://dx.doi.org/10.1002/star.201000099...
). On the other hand, RS III is formed during starch
retrogradation, which occurs after manufacturing in the presence of water, cooling
and storage (Sanz et al., 2009Sanz, T., Salvador, A., Baixauli, R., & Fiszman, S. M. (2009).
Evaluation of four types of resistant starch in muffins. II. Effects in texture,
colour and consumer response. European Food Research and Technology, 229(2),
197-204. http://dx.doi.org/10.1007/s00217-009-1040-1.
http://dx.doi.org/10.1007/s00217-009-104...
; Yao et al., 2009Yao, N., Paez, A. V., & White, P. J. (2009). Structure and
function of starch and resistant starch from corn with different doses of mutant
amylose-extender and floury-1 alleles. Journal of Agricultural and Food
Chemistry, 57(5), 2040-2048. http://dx.doi.org/10.1021/jf8033682.
PMid:19256560.
http://dx.doi.org/10.1021/jf8033682...
). Chemical modifications to
produce gelling and emulsification agents result in RS IV. Starch containing
amylose-lipid complexes and requiring high temperatures of gelatinization are
recognized as RS V, which is water insoluble (Cummings & Englyst, 1995Cummings, J. H., & Englyst, H. N. (1995). Gastrointestinal
effects of food carbohydrate. The American Journal of Clinical Nutrition,
61(Suppl. 4), 938S-945S. PMid:7900692.; Jiang et
al., 2010Jiang, H., Jane, J. L., Acevedo, D., Green, A., Shinn, G.,
Schrenker, D., Srichuwong, S., Campbell, M., & Wu, Y. (2010). Variations in
starch physicochemical properties from a generation-means analysis study using
amylomaize V and VII parents. Journal of Agricultural and Food Chemistry, 58(9),
5633-5639. http://dx.doi.org/10.1021/jf904531d. PMid:20394425.
http://dx.doi.org/10.1021/jf904531d...
).
The RS is undigested starch that reaches the end of the digestive system, where it is
the substrate of fecal microflora. Fermentation products from the RS are short chain
fatty acids with different physiological and probiotic effects (Conde-Petit et al., 2001Conde-Petit, B., Nuessli, J., Arrigoni, E., Escher, F., & Amadò,
R. (2001). Perspectives of starch in food science. Chimia, 55(3),
201-205.). The scientific
interest in RS has increased significantly in recent decades because of its capacity
to produce high levels of butyrate throughout the colon (Fuentes-Zaragoza et al., 2011Fuentes-Zaragoza, E., Sánchez-Zapata, E., Sendra, E., Sayas, E.,
Navarro, C., Fernández-López, J., & Pérez-Alvarez, J. A. (2011). Resistant
starch as prebiotic: a review. Starch/Staerke, 63(7), 406-415.
http://dx.doi.org/10.1002/star.201000099.
http://dx.doi.org/10.1002/star.201000099...
). Butyrate is the most important
energy source for colonocytes and has demonstrated beneficial effects on metabolism
and cell growth; it also inhibits a variety of factors that propagate the
initiation, progression and growth of colon tumors (Champ et al., 2003Champ, M., Langkilde, A. M., Brouns, F., Kettlitz, B., &
Bail-Collet, Y. L. (2003). Advances in dietary fibre characterisation. 2.
Consumption, chemistry, physiology and measurement of resistant starch;
implications for health and food labelling. Nutrition Research Reviews, 16(2),
143-161. http://dx.doi.org/10.1079/NRR200364. PMid:19087387.
http://dx.doi.org/10.1079/NRR200364...
). The RS associated with small chains of
fructooligosaccharides act synergistically in the digestive system to cause a
prebiotic effect that benefits human health (Fuentes-Zaragoza et al., 2011Fuentes-Zaragoza, E., Sánchez-Zapata, E., Sendra, E., Sayas, E.,
Navarro, C., Fernández-López, J., & Pérez-Alvarez, J. A. (2011). Resistant
starch as prebiotic: a review. Starch/Staerke, 63(7), 406-415.
http://dx.doi.org/10.1002/star.201000099.
http://dx.doi.org/10.1002/star.201000099...
).
5 Unconventional starches
The overall starch market is continually expanding, and the current demand is covered by four conventional sources: wheat, corn, potato and cassava. There are significant differences in the starch properties of these conventional groups in addition to the differences in their amylose-amylopectin ratios and the characteristics of these molecules. Non-amylosic components such proteins, lipids and phosphate groups are also important differences in the characteristics of conventional and unconventional starches.
Emmambux & Taylor (2013)Emmambux, M. N., & Taylor, J. R. N. (2013). Morphology,
physical, chemical, and functional properties of starches from cereals, legumes,
and tubers cultivated in Africa: a review. Starch/Staerke, 65(9-10), 715-729.
http://dx.doi.org/10.1002/star.201200263.
http://dx.doi.org/10.1002/star.201200263...
studied the
starch properties of cereals, legumes and tubers grown in Africa. The starch
granules of certain cereals and beans possessed the common characteristics of small
size, slightly porous surfaces and special paste properties, making them an
interesting alternative for industry. These properties suggest treatments involving
shearing operations or mimetic agents of fats because of their organoleptic
characteristics and texture (D’Silva et al.,
2011D’Silva, T. V., Taylor, J. R. N., & Emmambux, M. N. (2011).
Enhancement of the pasting properties of teff and maize starches through
wet-heat processing with added stearic acid. Journal of Cereal Science, 53(2),
192-197. http://dx.doi.org/10.1016/j.jcs.2010.12.002.
http://dx.doi.org/10.1016/j.jcs.2010.12....
; Wokadala et al., 2012Wokadala, O. C., Ray, S. S., & Emmambux, M. N. (2012).
Occurrence of amylose-lipid complexes in teff and maize starch biphasic pastes.
Carbohydrate Polymers, 90(1), 616-622.
http://dx.doi.org/10.1016/j.carbpol.2012.05.086. PMid:24751084.
http://dx.doi.org/10.1016/j.carbpol.2012...
).
Starch from beans (Vigna unguiculata) had a very high degree of
retrogradation, which makes it suitable for incorporation into gluten-free pastes
because this feature helps to maintain the texture of the product.
Zhang et al. (2005)Zhang, P., Whistler, R. L., BeMiller, J. N., & Hamaker, B. R.
(2005). Banana starch: production, physicochemical properties, and digestibility
— a review. Carbohydrate Polymers, 59(4), 443-458.
http://dx.doi.org/10.1016/j.carbpol.2004.10.014.
http://dx.doi.org/10.1016/j.carbpol.2004...
studied the production,
physicochemical properties and digestibility of banana starch. Pulp in immature
bananas contains between 70-80% starch (dry basis); this amount is comparable to
starch in the endosperm of corn grains and potato pulp. Banana starch is resistant
to digestive enzymes (Faisant et al., 1995Faisant, N., Buléon, A., Colonna, P., Molis, C., Lartigue, S.,
Galmiche, J. P., & Champ, M. (1995). Digestion of raw banana starch in the
small intestine of healthy humans: structural features of resistant starch.
British Journal of Nutrition, 73(1), 111-123.
http://dx.doi.org/10.1079/BJN19950013. PMid:7857906.
http://dx.doi.org/10.1079/BJN19950013...
),
which makes its use viable and competitive in a market of low-carb food consumption
and products with reduced calories.
Almeida et al. (2013)Almeida, E. L., Marangoni, A. L., & Steel, C. J. (2013).
Starches from non - conventional sources to improve the technological
characteristics of pound cake. Ciência Rural, 43(11), 2101-2108.
http://dx.doi.org/10.1590/S0103-84782013001100028.
http://dx.doi.org/10.1590/S0103-84782013...
studied the use of
unconventional starches and commercial starches in the manufacturing of English cake
and compared their behavior in this product. Unconventional starches incorporated
into this formulation increased the sensory quality of the product. Starch from
beans, followed by Peruvian carrots, yielded better results compared to commercial
starch in terms of the technological quality of the paste during beating. Starch
present in chickpeas and beans showed similar characteristics to that of commercial
starch in terms of sensory properties, texture and moisture.
Today, chemical modifications of starch remain necessary. The industry requires these
chemical processes to meet the demand of consumers favoring natural products. A
simple way to impact starch properties is by mixing different types of native and/or
physically modified starch (Sandhu et al.,
2010Sandhu, K. S., Kaur, M., & Mukesh. (2010). Studies on noodle
quality of potato and rice starches and their blends in relation to their
physicochemical, pasting and gel textural properties. LWT - Food Science and
Technology (Campinas.), 43(8), 1289-1293.; Waterschoot et al., 2015bWaterschoot, J., Gomand, S. V., Fierens, E., & Delcour, J. A.
(2015b). Starch blends and their physicochemical properties. Starch/Staerke,
67(1-2), 1-13. http://dx.doi.org/10.1002/star.201300214.
http://dx.doi.org/10.1002/star.201300214...
).
The use of these mixtures, as well as enabling improvements in the starch properties
and pastes, also provides economic advantages when the replacement starch source is
cheaper than the conventional source. However, there are limited studies on the
physicochemical properties and functionality of starch mixtures (Waterschoot et al., 2015bWaterschoot, J., Gomand, S. V., Fierens, E., & Delcour, J. A.
(2015b). Starch blends and their physicochemical properties. Starch/Staerke,
67(1-2), 1-13. http://dx.doi.org/10.1002/star.201300214.
http://dx.doi.org/10.1002/star.201300214...
) and the use of
unconventional starches.
Currently, unconventional starches are often ignored or wasted during the isolation
or separation of bioactive compounds from raw materials such as seeds and legumes
(Braga et al., 2006Braga, M. E. M., Moreschi, S. R. M., & Meireles, M. A. A.
(2006). Effects of supercritical fluid extraction on Curcuma longa
L. and Zingiber officinale R. starches.
Carbohydrate Polymers, 63(3), 340-346.
http://dx.doi.org/10.1016/j.carbpol.2005.08.055.
http://dx.doi.org/10.1016/j.carbpol.2005...
; Yuan et al., 2007Yuan, Y., Zhang, L., Dai, Y., & Yu, J. (2007). Physicochemical
properties of starch obtained from . Dioscorea nipponica Makino
comparison with other tuber starchesJournal of Food Engineering, 82(4), 436-442.
http://dx.doi.org/10.1016/j.jfoodeng.2007.02.055.
http://dx.doi.org/10.1016/j.jfoodeng.200...
). These starches are
subjected to unit operations that often involve thermal or hydrothermal treatments,
causing alterations in the structural characteristics of the starch and physical
modifications and improving the physicochemical properties and characteristics of
the paste conformation. Additionally, raw materials from the extraction processes
remain in the extraction residues including the starch fraction and a small fraction
of bioactive compounds, which increase the technological and nutritive value (Braga et al., 2006Braga, M. E. M., Moreschi, S. R. M., & Meireles, M. A. A.
(2006). Effects of supercritical fluid extraction on Curcuma longa
L. and Zingiber officinale R. starches.
Carbohydrate Polymers, 63(3), 340-346.
http://dx.doi.org/10.1016/j.carbpol.2005.08.055.
http://dx.doi.org/10.1016/j.carbpol.2005...
; Santana & Meireles, 2014Santana, A. L., & Meireles, M. A. A. (2014). New starches are
the trend for industry applications: a review. Food and Public Health, 4(5),
229-241.). Starches present in legumes,
rhizomes, herbs and seeds are considered unconventional and may be used as
ingredients in the same manner as starches from cereals and tuber due to their
similar physicochemical and functional properties. These properties are improved by
modification treatments and may be used to develop new processes and consequently
new products (Santana & Meireles,
2014Santana, A. L., & Meireles, M. A. A. (2014). New starches are
the trend for industry applications: a review. Food and Public Health, 4(5),
229-241.).
6 Starch applications in the food industry
The biological function of starch in plants is as a reserve of carbon and energy. As
food, starch is the most abundant and important digestible polysaccharide. The
starches in food are commonly derived from grains or seeds (wheat, corn, rice, and
barley), tubers (potato) and roots (cassava) (Buléon et al., 1998Buléon, A., Colonna, P., Planchot, V., & Ball, S. (1998). Starch
granules: structure and biosynthesis. International Journal of Biological
Macromolecules, 23(2), 85-112. http://dx.doi.org/10.1016/S0141-8130(98)00040-3.
PMid:9730163.
http://dx.doi.org/10.1016/S0141-8130(98)...
; Waterschoot et
al., 2015aWaterschoot, J., Gomand, S. V., Fierens, E., & Delcour, J. A.
(2015a). Production, structure, physicochemical and functional properties of
maize, cassava, wheat, potato and rice starches. Starch/Staerke, 67(1-2), 14-29.
http://dx.doi.org/10.1002/star.201300238.
http://dx.doi.org/10.1002/star.201300238...
). Starch provides 70 - 80% of the calories consumed by humans
worldwide.
As food, starch functions as a structural agent because of the modifications
introduced during manufacturing. Starch is used in the food industry mainly as a
modifier of texture, viscosity, adhesion, moisture retention, gel formation and
films (Waterschoot et al., 2015aWaterschoot, J., Gomand, S. V., Fierens, E., & Delcour, J. A.
(2015a). Production, structure, physicochemical and functional properties of
maize, cassava, wheat, potato and rice starches. Starch/Staerke, 67(1-2), 14-29.
http://dx.doi.org/10.1002/star.201300238.
http://dx.doi.org/10.1002/star.201300238...
).
An important utilization of starch in the food industry is in baking flour. Among the bakery products, cakes and breads are the most important due to their high consumption. In the formulations of the baking industry, starch is one of the components responsible for the structure and properties of the final products. Other industrial processes include starch in small quantities as a food additive or a thickening and gelling agent.
Starch is often used in granular form and is thus is included in the confectionery industry as a molding powder for the various forms of sweets, which can be reused many times. Starch is also used in the preparation of diverse types of pasta in the preparation of noodles and those intended for extrusion and in the formulation of instant foods and fried foods.
In the food industry, edible films are barriers that prevent moisture transfer, gas
exchange, oxidation and the movement of solutes, while maintaining their
organoleptic properties (Dhall, 2013Dhall, R. K. (2013). Advances in edible coatings for fresh fruits
and vegetables: a review. Critical Reviews in Food Science and Nutrition, 53(5),
435-450. http://dx.doi.org/10.1080/10408398.2010.541568.
PMid:23391012.
http://dx.doi.org/10.1080/10408398.2010....
).
During manufacturing, films are incorporated as plasticizers, flavors, colors,
sweeteners, antioxidants and antimicrobials. Edible films have received much
attention due to their advantages over synthetic films. Edible films are produced
from renewable materials; they can be consumed together with coated food and
otherwise do not contribute to pollution because their degradation is faster than
synthetic films. Their main disadvantage lies in their mechanical and permeable
properties (Bourtoom, 2008Bourtoom, T. (2008). Edible films and coatings: characteristics and
properties. International Food Research Journal, 15(3),
237-248.). The basic
materials used to produce edible films are cellulose, starch, gums and chitosan; the
linear configuration of polymers can produce films with flexible, transparent and
oil resistant properties. For these reasons, amylose is the most important fraction
in starch granules. Typically, the starch granule is composed of 25% amylose and 75%
amylopectin. Edible films require starches with a high amylose content (≥ 70%). The
amylopectin molecule cannot adequately form films; the branched structure imparts
poor mechanical properties to the film, reducing its tensile strength and elongation
(Bourtoom, 2008Bourtoom, T. (2008). Edible films and coatings: characteristics and
properties. International Food Research Journal, 15(3),
237-248.; Dhall, 2013Dhall, R. K. (2013). Advances in edible coatings for fresh fruits
and vegetables: a review. Critical Reviews in Food Science and Nutrition, 53(5),
435-450. http://dx.doi.org/10.1080/10408398.2010.541568.
PMid:23391012.
http://dx.doi.org/10.1080/10408398.2010....
).
Polysaccharides are typically hygroscopic and therefore are poor barriers to moisture
and gas exchange. The use of plasticizers in the film composition improves the
barrier against moisture exchange and restricts microbial activity. The starch used
in edible film preparation is incorporated to partially or completely replace the
plastic polymers. Native starch does not produce films with adequate mechanical
properties and requires pretreatment, the use of a plasticizer, mixture with other
materials, genetic or chemical modification, or a combination of these treatments.
Among the plasticizers, for hydrophilic polymers, such as starch, are glycerol and
other low-molecular weight polyhydroxy-compounds, polyether, and urea. Processes
such as extrusion adjust the parameters of temperature and mechanical energy over
the starch paste, making it a thermoplastic material that is also suitable for the
production of edible films (Dhall,
2013Dhall, R. K. (2013). Advances in edible coatings for fresh fruits
and vegetables: a review. Critical Reviews in Food Science and Nutrition, 53(5),
435-450. http://dx.doi.org/10.1080/10408398.2010.541568.
PMid:23391012.
http://dx.doi.org/10.1080/10408398.2010....
).
7 Starch destined for non-food applications
New processing techniques and the current demands of biodegradable and renewable
resources have highlighted the versatility of starch and introduced it to new
markets. Furthermore, starch is a chemical feedstock for conversion into numerous
products with considerable value (Ellis et al.,
1998Ellis, R. P., Cochrane, M. P., Dale, M. F. B., Duffus, C. M., Lynn,
A., Morrison, I. M., Prentice, R. D. M., Swanston, J. S., & Tiller, S. A.
(1998). Starch production and industrial use. Journal of the Science of Food and
Agriculture, 77(3), 289-311.
http://dx.doi.org/10.1002/(SICI)1097-0010(199807)77:3<289::AID-JSFA38>3.0.CO;2-D.
http://dx.doi.org/10.1002/(SICI)1097-001...
).
In the pharmaceutical industry, starch is used as an excipient, a type of bonding agent to active drugs. Because of its content of amylose, starch is capable of forming an inclusion complex with many food ingredients, such as essential oils, fatty acids and flavoring ingredients. It therefore acts as an encapsulant and increases the shelf life of products.
Plastics obtained from oil are being replaced by natural polymers; starch is known
for its ability to form films in food packaging applications (Jiménez et al., 2012Jiménez, A., Fabra, M. J., Talens, P., & Chiralt, A. (2012).
Edible and biodegradable starch films: a review. Food and Bioprocess Technology,
5(6), 2058-2076. http://dx.doi.org/10.1007/s11947-012-0835-4.
http://dx.doi.org/10.1007/s11947-012-083...
). Edible and biodegradable starch films
can be obtained from native starch or its components amylose or amylopectin by two
main techniques: a wet method that includes a starch suspension and posterior drying
or a dry method that involves a thermoplastic process (Paes et al., 2008Paes, S. S., Yakimets, I., & Mitchell, J. R. (2008). Influence
of gelatinization process on functional properties of cassava starch films. Food
Hydrocolloids, 22(5), 788-797.
http://dx.doi.org/10.1016/j.foodhyd.2007.03.008.
http://dx.doi.org/10.1016/j.foodhyd.2007...
). Modified starches can also be used in film
production (Bourtoom, 2008Bourtoom, T. (2008). Edible films and coatings: characteristics and
properties. International Food Research Journal, 15(3),
237-248.; Campos et al., 2011Campos, C. A., Gerschenson, L. N., & Flores, S. K. (2011).
Development of edible films and coatings with antimicrobial activity. Food and
Bioprocess Technology, 4(6), 849-875.
http://dx.doi.org/10.1007/s11947-010-0434-1.
http://dx.doi.org/10.1007/s11947-010-043...
; Dhall, 2013Dhall, R. K. (2013). Advances in edible coatings for fresh fruits
and vegetables: a review. Critical Reviews in Food Science and Nutrition, 53(5),
435-450. http://dx.doi.org/10.1080/10408398.2010.541568.
PMid:23391012.
http://dx.doi.org/10.1080/10408398.2010....
; López et al.,
2010López, O. V., Zaritzky, N. E., & García, M. A. (2010).
Physicochemical characterization of chemically modified corn starches related to
rheological behavior, retrogradation and film forming capacity. Journal of Food
Engineering, 100(1), 160-168.
http://dx.doi.org/10.1016/j.jfoodeng.2010.03.041.
http://dx.doi.org/10.1016/j.jfoodeng.201...
)
For new industrial applications of starch, especially in plastic polymer production,
the hygroscopicity of starch is a disadvantage because the main feature of plastics
films is their hydrophobic property. Starch granule size, its form and associated
molecules influence film production. Wheat starch is typically associated with a
significant amount of protein, which may result in a Maillard reaction and cause
bleaching; therefore, this type of starch is not used in to manufacture
biodegradable plastics films (Ellis et al.,
1998Ellis, R. P., Cochrane, M. P., Dale, M. F. B., Duffus, C. M., Lynn,
A., Morrison, I. M., Prentice, R. D. M., Swanston, J. S., & Tiller, S. A.
(1998). Starch production and industrial use. Journal of the Science of Food and
Agriculture, 77(3), 289-311.
http://dx.doi.org/10.1002/(SICI)1097-0010(199807)77:3<289::AID-JSFA38>3.0.CO;2-D.
http://dx.doi.org/10.1002/(SICI)1097-001...
).
In the textile industry, starch films are also used during textile production as
fiber coatings. Native starch forms rigid and brittle films due to its cyclic
structure. Brittle films are not advantageous because they reduce protection,
increase friction and thus damage the thread. The polarity of native starch
minimizes the adhesion of synthetic fibers, affecting the tensile strength and
abrasion. Starch is commonly modified to improve the physical properties,
emulsifying ability and film formation (Zhang et
al., 2014Zhang, C., Xu, D., & Zhu, Z. (2014). Octenylsuccinylation of
cornstarch to improve its sizing properties for polyester/cotton blend spun
yarns. Fibers and Polymers, 15(11), 2319-2328.
http://dx.doi.org/10.1007/s12221-014-2319-9.
http://dx.doi.org/10.1007/s12221-014-231...
).
Many industrial processes use starch after partial or complete destruction of its
structure. When this occurs, the properties of its components and the relationships
between them increase their importance. Differences between the amount and type of
lipids originally present in the native starch may cause two starches with the same
amylose-amylopectin ratio to have different physical properties, such as viscosity
(Ellis et al., 1998Ellis, R. P., Cochrane, M. P., Dale, M. F. B., Duffus, C. M., Lynn,
A., Morrison, I. M., Prentice, R. D. M., Swanston, J. S., & Tiller, S. A.
(1998). Starch production and industrial use. Journal of the Science of Food and
Agriculture, 77(3), 289-311.
http://dx.doi.org/10.1002/(SICI)1097-0010(199807)77:3<289::AID-JSFA38>3.0.CO;2-D.
http://dx.doi.org/10.1002/(SICI)1097-001...
).
Starch solutions are viscous, and the ability of starch to change the viscosity of
other solutions and pastes is well known and exploited in the food industry. This
property is also used in the oil drilling industry, where starch is used to adjust
the viscosity of the mud used during drilling operations. Highly viscous starch
solutions are desirable for industrial processes involving starch pastes for
mechanical manipulation, such as the paper, corrugated and textile industries (Ellis et al., 1998Ellis, R. P., Cochrane, M. P., Dale, M. F. B., Duffus, C. M., Lynn,
A., Morrison, I. M., Prentice, R. D. M., Swanston, J. S., & Tiller, S. A.
(1998). Starch production and industrial use. Journal of the Science of Food and
Agriculture, 77(3), 289-311.
http://dx.doi.org/10.1002/(SICI)1097-0010(199807)77:3<289::AID-JSFA38>3.0.CO;2-D.
http://dx.doi.org/10.1002/(SICI)1097-001...
).
Several studies have concluded that is possible to produce a new generation of detergents in which the surfactants and bleaching components are derived entirely from starch. An estimated 50 to 60% of chemical products in formulations for powder detergents and 65 to 75% of liquid detergent formulations could be substituted with products derived from starch.
High viscosity is important in the adhesive field. Most native starches do not
maintain a stable viscosity when transformed to pastes and or subjected to high
shear velocity or longer heating periods. However, chemically modified starch
behaves properly under these conditions (Ellis et
al., 1998Ellis, R. P., Cochrane, M. P., Dale, M. F. B., Duffus, C. M., Lynn,
A., Morrison, I. M., Prentice, R. D. M., Swanston, J. S., & Tiller, S. A.
(1998). Starch production and industrial use. Journal of the Science of Food and
Agriculture, 77(3), 289-311.
http://dx.doi.org/10.1002/(SICI)1097-0010(199807)77:3<289::AID-JSFA38>3.0.CO;2-D.
http://dx.doi.org/10.1002/(SICI)1097-001...
).
The production of biodegradable plastics is still young when compared to the
petrochemical plastic industry. Starch will play an important role in its growth in
container production and in the form of biodegradable materials that conform to
suitable matrices because it is a relatively inexpensive material compared to other
polymers (Bourtoom, 2008Bourtoom, T. (2008). Edible films and coatings: characteristics and
properties. International Food Research Journal, 15(3),
237-248.; Dhall, 2013Dhall, R. K. (2013). Advances in edible coatings for fresh fruits
and vegetables: a review. Critical Reviews in Food Science and Nutrition, 53(5),
435-450. http://dx.doi.org/10.1080/10408398.2010.541568.
PMid:23391012.
http://dx.doi.org/10.1080/10408398.2010....
).
In recent years, starch has been studied for the production of nanoelements as
nanocrystals that result from the breakdown of the amorphous region in
semicrystalline starch granules by acid hydrolysis or for the production of
nanoparticles from gelatinized starch (Le Corre et
al., 2010Le Corre, D., Bras, J., & Dufresne, A. (2010). Starch
nanoparticles: a review. Biomacromolecules, 11(5), 1139-1153.
http://dx.doi.org/10.1021/bm901428y. PMid:20405913.
http://dx.doi.org/10.1021/bm901428y...
). These nano compounds have unique properties due to their nano
size compared to conventional size materials. Nanoparticles can be used as fill
material in filtration and form effective barriers in flexible packaging (Bondeson et al., 2006Bondeson, D., Mathew, A., & Oksman, K. (2006). Optimization of
the isolation of nanocrystals from microcrystalline cellulose by acid
hydrolysis. Cellulose (London, England), 13(2), 171-180.
http://dx.doi.org/10.1007/s10570-006-9061-4.
http://dx.doi.org/10.1007/s10570-006-906...
).
8 Conclusions, perspectives and future trends
Starch has a major role in the food industry not only in for its nutritional value, but also for its broad technological functionality. The amylose and amylopectin polymers, lipids, proteins and phosphorus present in granules have significant effects on the physicochemical properties and functionality of starch.
Starch is rarely consumed in its native form; this form is also not commonly used in industry because native starches have restricted solubility in water, which limits industrial applications. Several methods have been developed for the production of modified starch, with a variety of features and applications.
Modification processes can greatly improve the characteristics of native starch by altering its physicochemical properties and structural attributes and increasing its technological value. Starch characteristics depend on the modification used and are necessary for its use in industry; they include cold water solubility, viscosity and swelling capacity after cooking, retrogradation tendency, loss of structural order after gelatinization and consequent syneresis of systems conformed by starch. The industry of starch modification is constantly evolving. Starch is a highly flexible polymer, and there are several ways to modify its structure and obtain a functional product with adequate properties for specific industrial applications, increasing its added value.
Physical modification of starch can enhance its water solubility and reduce the size of the starch granules. Physical methods for the treatment of native granules include combinations of temperature and moisture, pressure, shear and irradiation. Physical modification is simple, inexpensive and safe. These modification techniques are preferred because they do not require chemical or biological agents that may be harmful to health.
Physical modifications of starch consist of three categories. i) PGS is produced by cooking until complete gelatinization with subsequent drying, which destroys the granular structure and increases the swelling capacity, solubility, viscosity and dispersion capacity in cold water. ii) Hydrothermal modifications do not destroy the granular structure and occur at temperatures above Tg and below Tgel of the granule (these parameters are different for each botanical source) in the presence of water. Two processes for the latter modification were considered: ANN, which requires water in intermediate quantities or excess (40-76%, w/w), and HTM, which uses a restricted water content in a dispersion medium (≤ 35%, w/w). Hydrothermal modifications reduce starch solubility, swelling capacity and amylose leaching and increase the crystallinity and Tgel of the starch granules. In starch pastes, modifications reduce the viscosity and increase the stability. iii) Physical non-thermal modifications are preserve the quality of nutrients that may be contained in the starch paste and are susceptible to heat. The use of high pressure reduces the swelling capacity and viscosity of starch; vacuum pressures have the opposite effect, increasing the swelling capacity and reducing the degree of polymerization. Microwaves modify the dielectric properties of starch and its morphology and crystallinity, and ultrasound modifies the swelling capacity of granules and pastes. Industrial processes such as grinding and extrusion also physically modify starch granules.
Chemical modification of starch involves the introduction of functional groups to the starch molecule without affecting the morphology or granule size distribution. Cationization modifies the dielectric properties of granules depending on their substitution degree, reducing the paste temperature and increasing its viscosity. Crosslinking of polymeric chains increases the degree of polymerization in starch granules, modifying its solubility in organic solvents and reducing its swelling capacity. Acetylation results in the esterification of starch, increasing its swelling capacity and solubility. Other chemical modifications, such as acid hydrolysis and oxidation, reduce the degree of polymerization of starch and the paste viscosity.
Not all starch is digestible, and the indigestible portion is part of the fraction of dietetic fiber or RS. Chemical modifications such as crosslinking are used to increase the amount of RS, and these starches are included in paper and textile processes.
The starch industry is in constant expansion, and modification processes increase its versatility. When starch is physically or chemically modified, it can be adapted for different purposes in food and/or non-food industries. Applications of starch modifications (physical or chemical) can increase the use of unconventional starches and vegetal residues containing starch in industry. Depending on cost and accessibility, the use of conventional starch can be replaced in whole or in part by unconventional starches in industrial processes when appropriate. Determining the required characteristics of starch for each process is necessary to select the best modification method according to the application requirements, market trends, availability, structural characteristics and cost.
Acknowledgements
Sylvia C. Alcázar-Alay thanks the Brazilian agency CAPES/PECPG for doctoral fellowships (Process 5532116). M. A. A. Meireles thanks CNPq (301301/2010-7) for the productivity grant. The authors acknowledge CNPq (560914/2010-5) and FAPESP (2012/10685-8) for financial suppot.
-
Practical Application: Use of unconventional starches and vegetal residues containing starch in industry.
-
Acronyms: Glass transition temperature (Tg), Resistant Starch (RS), Rapid Visco Analyzer (RVA), Onset temperature (To), Peak temperature (Tp), Conclusion temperature (Tc), Differential Scanning Calorimeter (DSC), Gelatinization temperature (Tgel), Supercritical fluid extraction (SFE), Pre-gelatinized starch (PGS), Melting temperature (Tm), Annealing (ANN), 2,3-epoxypropil trimethyl ammonium chloride (EDMAC), Sodium tripolyphosphate (STPP), Sodium phosphate (STMP), Octenyl succinic anhydride (OSA), 2,3-epoxypropyl trimethyl ammonium chloride (ETMAC), 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CTA), Dimethyl sulfoxide (DMSO), Sodium trimetaphosphate (STMP), Sodium tripolyphosphate (STPP), Epichlorohydrin (ECH), Phosphoryl chloride (POCl3).
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Publication Dates
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Publication in this collection
June 2015
History
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Received
22 May 2015 -
Accepted
25 May 2015