Morphology and functional properties of corn, potato
and tapioca starches
Sangeetha Mishra, T. Rai*
Dairy Chemistry Division, National Dairy Research Institute, Karnal 132001, India
Abstract
In this study, morphology and functional properties of commercial native corn, potato and tapioca starches were evaluated. Morphological
study with light and scanning electron microscopy revealed that these starches had unique granule characteristics. The starches were
observed to be almost insoluble in water at 20 8C but upon heating to 70 8C, they were solubilized in water to an extent of 3.89, 13.49 and
14.36% for corn, potato and tapioca starches, respectively. Among these, corn starch held less water as compared to potato and tapioca
starches. The viscosity of starches was almost same at low concentration (0.1%, w/v) but increased curvilinearly with the increase in
concentration to 0.5% in ascending order for tapioca, corn and potato starches and at high concentration (5%, w/v) they showed shear
thinning behaviour. Corn starch exhibited high viscosity stability to shear. The pasting curves of starches during cooking, using rapid visco-
amylograph indicated that corn showed higher degree of crystallinity since it gelatinized apparently at higher temperature. Other pasting
properties of starches like peak viscosity, final viscosity and breakdown were higher for potato compared to corn followed by tapioca but the
setback tendency gave an opposite trend. Potato starch gelled at lower concentration followed by corn and then tapioca starches. Texture
profile analysis results showed that potato starch gel was harder, sticky, gummy and chewy than that of corn and tapioca starch gels. The
moisture sorption isotherm described with the help of GAB equation revealed that potato starch had higher heat sorption and monolayer
moisture content compared to corn and tapioca starches.
q
2005 Elsevier Ltd. All rights reserved.
Keywords: Starch; Gelatinization temperature; Functional properties; Morphology; Pasting characteristics; Sorption isotherm
1. Introduction
Polysaccharides are often used in certain food products
mainly for their thickening and gelling properties. The
presence of small amounts of these materials can bind large
quantities of water, bringing about a desirable change in the
texture of a food product. Starches from cereals, tubers and
roots are widely used in the food industry as stabilizers or
texture modifiers. Particularly starches are attractive food
ingredients for textural modification because they are both
natural and safe.
Increasing knowledge of the granular structure and
functional properties of starches has enabled chemists to
process them in novel way or to modify starches to meet
special demands of the food and other industries. In past,
both light and scanning electron microscopy have been
extensively used to relate granule morphology to starch
genotype and pasting properties (
). It is claimed that identifi-
cation of native starch sources is required for desirable
functionality and unique properties (
Moreover, various reports suggested that pasting character-
istics (
Lai, 2001; Wiesenborn, Orr, Casper, & Tacke, 1994
rheological properties of paste and gels (
Orr, & Grant, 1995; Wiesenborn et al., 1994
) and other
functional properties (
Wotton & Bamunuarachchi, 1978;
) of starches vary with species and variants.
However, despite the availability of a large number of
reports on the characteristics of different starches, the
literature regarding the functional properties of commercial
native starches is scarce. Because of the amount and
quantity needed to make starch industrially feasible, the
present study is restricted to the corn, potato and tapioca
starches only. Further, the present study is expected to give
Food Hydrocolloids 20 (2006) 557–566
www.elsevier.com/locate/foodhyd
0268-005X/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.foodhyd.2005.01.001
* Corresponding author. Tel.: C91 184 2259162; fax: C91 184 2250042.
E-mail addresses: trai@ndri.hry.nic.in (T. Rai), rai_tk@rediffmail.com
(T. Rai).
a deeper insight into the functional properties of native
starches with respect to their morphology and compositional
profile under different processing conditions.
2. Materials and methods
2.1. Collection of starches
Three commercial native starches [corn (CDH), potato
(CDH) and tapioca (National Starch & Chemical Co.)] were
characterized with respect to their morphology, physico-
chemical and functional properties.
2.2. Light microscopy
Light microscopy was employed for characterizing
native starches with respect to appearance, shape and size
of the granules (
2.3. Scanning electron microscopy
Starch samples were dehydrated through a graded
acetone series (70, 90 and 100% for 15 min each). The
samples were allowed to air dry at room temperature,
grounded and filtered through a sieve of fine pore size. The
dry starch was sprinkled onto circular aluminium stubs with
double sticky tape. The excess powder was properly brushed
to get a uniform layer of sparsely scattered powder particles.
The stubs were coated with gold to approximately 200!
thickness in Hitachi 1B-3 ion coater. The ion current was
maintained at 6 mA with a fine vacuum of 0.07 Torr for
4 min. The observations were made using Hitachi S-405
Electron Microscope at 1000! magnification at an accel-
erating potential of 25 kV. The images of selected area were
recorded on a black and white high speed (200 ASA)
photographic film with the help of attached camera
assembly.
2.4. Physico-chemical properties
The pH of starch samples was determined by a
microprocessor controlled pH meter (Thermo Orion,
Model 420). The intensity of whiteness of starches was
measured in terms of percent reflectance value by using
reflectance meter (Model CL-28, Elico Pvt. Ltd, India).
The moisture content of starches was determined by the
method of
. The lipid and protein contents
were estimated by
and micro-Kjeldahl
method (
), respectively. The total starch content
was estimated by phenol–sulphuric method (
) and ash content by
method. The total
phosphorus content was determined by a method of
and reducing sugar by the method
described by
. The amylose
equivalent was determined by the method of
2.5. Functional properties
2.5.1. Solubility
The solubility of starch samples was determined at 20
and 70 8C by the method of
with a
slight modification. About 0.5 g of the sample was taken
accurately in a 100 ml beaker and 50 ml distilled water was
added to it The dispersion was stirred intermittently for 1 h
and was allowed to stand overnight for proper hydration at
20 8C. For cold water solubility, the sample was centrifuged
(Kubota, Japan) at 10,000 rpm for 30 min at 20 8C. While
for hot water solubility, the dispersion was heated to 70 8C
for 1 h with intermittent stirring and then centrifuged. The
percent solubility was calculated from the starch content in
the supernatant and in the dispersion before centrifugation.
2.5.2. Water holding capacity (WHC)
WHC was determined by the method of
with a slight modification. A suspension of 1% starch
(on dry matter basis) in 10 ml distilled water was agitated
intermittently for 1 h and centrifuged (Hitachi, Japan) at
30,000 rpm for 15 min at 25 8C. The free water was
decanted and the wet starch was weighed. WHC was
calculated using the following equation:
WHC ðg H
2
O g
1
starchÞ
Z
Mass of wet starch K Mass of dry starch
Mass of dry starch
:
2.5.3. Viscosity
The viscosity of starch samples was measured by the
method of
. The flow time was determined in an
Ostwald viscometer which was immersed in a thermo-
statically controlled water bath maintained at G1 8C of the
required temperature. The starch samples were quantitat-
ively dissolved in 1 N KOH solution. The necessary time for
the flow of starch solution (0.1–0.5%, w/v) at different
temperatures (20–60 8C) was noted with the help of a
stopwatch. Flow time was reproducible to G0.1 s. The
density of starch solutions was measured using pycnometer
Viscosity ðcPÞ Z
d
s
t
s
d
a
t
a
!
h
a
;
where d
s
, density of starch solution at specific temperature;
d
a
, density of 0.1 N KOH at the same temperature; t
s
, flow
time of certain volume of starch solution at specific
temperature; t
a
, flow time of same volume of 0.1 N KOH
at the same temperature; and h
a
, viscosity of 0.1 N KOH,
which was determined using the following equation
h
a
Z
d
a
t
a
d
w
t
w
!
h
w
;
S. Mishra, T. Rai / Food Hydrocolloids 20 (2006) 557–566
558
where d
w
, density of water at specific temperature; t
w
, flow
time of certain volume of water at the same temperature;
and h
w
, viscosity of water.
2.5.4. Flow properties
The flow properties, viz. consistency coefficient (K) and
flow behaviour index (n) were worked out from the flow
curve of shear rate (r) versus shear stress (t) using the power
law equation
t Z K
n
g
;
where t, shear stress (Pa); g, shear rate (s
K
1
); K,
consistency coefficient (Pa s
n
); and n, flow behaviour index.
The shear stress was calculated by multiplying apparent
viscosity with respective shear rate. The starch solution
(5%, w/v) was heated at 85 8C for 15 min followed by
cooling to 20 8C and after adjusting pH to 7.0G0.1, the
apparent viscosity was measured using a programmable
coaxial cylinder viscometer with digital display (Contraves
Rheomat 108 E/R) fitted with the measuring system 33 at
shear rate ranging from 100 to 500 s
K
1
.
2.5.5. Viscosity stability to heat, acid and shear
The viscosity stability of starch samples to heat, acid and
shear was determined at 20 8C by the method of
using Rheomat. In each case, the
starch samples (5%, w/v) were heated at 85 8C for 15 min
and were cooled before the measurement.
Heat stability. This was evaluated by measuring the
viscosity change of starch samples (5%, w/v; pH 7.0) after
autoclaving at 121 8C for 15 min. The ratio of the viscosity
at shear rate 500 s
K
1
after processing and to the viscosity
before processing was taken as heat stability index (HSI).
Higher the HSI, better the stability.
Acid stability. This was determined by viscosity
measurement before and after acid treatment. The viscosity
of 5% starch samples was determined at pH 7.0 and 3.0. The
acid stability index (ASI) was calculated from the ratio of
starch viscosity at pH 3.0 to viscosity at pH 7.0 at same
shear rate (500 s
K
1
). Higher the ASI, better the acid
stability.
Shear stability. This was measured by the submission of
5% starch samples to shear rate of 1000 s
K
1
. The ratio of
viscosity at shear rate of 1000 s
K
1
to viscosity at shear rate
of 100 s
K
1
was taken as shear stability index (SSI). Higher
the SSI, better the shear stability.
2.5.6. Pasting properties
Pasting properties of corn, potato and tapioca starches
were determined using a Rapid Viscoamylograph (RVA)
Model 3-D (Newport Scientific Pty. Ltd, Australia) by
Standard Method No. 162 (1995)
. Starch suspension was
prepared by placing 3.0, 3.0 and 2.0 g of corn, tapioca and
potato starches, respectively, in an aluminium canister
which contained 25.0 g of distilled water. A programmed
heating and cooling cycle was used at constant shear rate
(160 rpm), where the sample was equilibrated at 50 8C for
1 min and then heated to 95 8C at a rate of 12.16 8C/min and
held for 2.5 min. It was again cooled to 50 8C at the same
rate and hold for 2 min. A plot of paste viscosity in
centipoise (cP) versus time was used to determine peak
viscosity (PV), pasting temperature, final viscosity (FV),
breakdown viscosity (BKDZPVKtrough) and setback
viscosity (SBZFVKtrough).
2.5.7. Gelling properties
Least concentration gelation. The least concentration for
gelation of starches was determined by the method of
Benhura and Katayi-Chidewe (2000)
. Five milliliters of
starch solutions (2–12%, w/v) in test tubes (10!100 mm
2
)
covered with marbles, were heated at 85 8C in a water bath
for 15 min, cooled immediately in ice chilled water bath and
kept overnight at 4 8C. The gelation was confirmed by
inverting the test tubes. The gels were further heated to
90 8C for 10 min to check the thermo-reversibility.
Texture profile analysis (TPA). Various texture profile
parameters of starch gels, viz. hardness, adhesiveness,
cohesiveness, springiness, gumminess and chewiness were
measured from force–time curves. The gels were prepared
by suspending starch in water to obtain 20% (w/w)
concentration and were heated in a water bath at 85G1 8C
for 15 min and cooled immediately to about 4 8C in ice
chilled water bath. The tests were performed using the
Texture Expert Exceed (Stable Micro Systems, UK) fitted
with 25 kg load cell. The texture analyzer was programmed
to compress a free standing cylindrical gel (1 cm dia., 1 cm
length) to 80% of its original height. The deformation curve
obtained from a two-bite deformation cycle employing a
75 mm compression platen was used to determine the
above-mentioned textural characteristics of starch gels at
25 8C. The texture analyzer settings used were: pretest, test
and post-test speed—5.0, 2.5 and 10.0 mm s
K
1
, respect-
ively; trigger type—auto 5.0 mm, threshold—5 g, time—
17.5 s; data acquisition rate—250 pps. Each measurement
was carried out in triplicate.
2.5.8. Moisture sorption behaviour
The moisture sorption behaviour of starch samples was
determined by the method of
. For this saturated
solution of different reagent grade salts like lithium
chloride, potassium acetate, potassium carbonate, potassium
iodide and potassium nitrate were prepared in order to
obtain a
w
in the range of 0.113–0.946 as described by
. After equilibration at 20G1 8C, the
moisture content in the samples was determined by
gravimetric method and expressed as g H
2
O/100 g dry
solids. The equilibrium moisture contents were plotted
against water activities (a
w
) to establish moisture sorption
isotherms. The moisture sorption behaviour was studied
with the help of Guggenheim–Anderson–deBoer (GAB)
model.
S. Mishra, T. Rai / Food Hydrocolloids 20 (2006) 557–566
559
The GAB equation is expressed as
M Z
CkM
o
a
w
ð1 K ka
w
Þð1 K ka
w
C
Cka
w
Þ
;
where M is the moisture content of the material (g
H
2
O/100 g dry solids); M
o
is the monolayer moisture
content (g H
2
O/100 g dry solids); K is the constant related to
multi-layer molecule properties; C is Guggenheim constant
related to the heat of sorption for the first layer; and a
w
is the
water activity at 20 8C.
3. Results and discussion
3.1. Microscopic study of starches
3.1.1. Light microscopy
The diversity in the shape and size of starch granules
utilizing light microscopy could be a useful tool in the
identification of different starch species. In the present study,
starch granules were observed to be polyhedral, flattened
ellipsoid or spherical particles (
). The size of granules
ranged between 3.6 and 53.6 mm (
). Corn starch
exhibited the polyhedral granules with size ranging from 3.6
to 14.3 mm (mean 12.2 mm). The majority of potato starch
granules on the other hand, were flattened ellipsoids with few
spherical that varied from 14.3 to 53.6 mm in size. The
granules of tapioca starch were slightly larger than corn and
ranged between 7.1 and 25.0 mm. However, they differed in
appearance from the latter in that they are round in shape
with a few possessing irregular truncated structure.
Apart from the shape and size of the granules, other
characteristic feature considered in the identification of the
starch species was the position of hilum which is often
described as the nucleus around which the granule has
grown. The series of concentric striations around the hilum
were also observed. The hilum was seen at the centre of
granules in the form of either dot or short line in corn and
tapioca but as a dot situated eccentrically at the small end of
the granule in case of potato starch. Further, the presence of
numerous concentric striations in the potato starch granules
resulted in the resemblance with oyster shells. Similar
observations were made in earlier studies while character-
izing the starches from different sources (
) although the range of granule diameters reported in
the literature is wide.
3.1.2. Scanning electron microscopy (SEM)
SEM study revealed that the starches differed in granule
shape and size ranging from large (potato) to small
Fig. 1. Light microscopy of: corn (A), potato (B), and tapioca (C) starches
(!100).
Table 1
Morphology of native corn, potato and tapioca starch granules
Characteristic
Source of starch
Corn
Potato
Tapioca
Granule size
(mm)
12.2 (3.6–14.3)
30.5 (14.3–53.6)
15.0 (7.1–25.0)
Microscopic
appearance
Polyhedral
Oval/flattened
ellipsoid
Spherical/
truncated
Position of
hilum
Centric
Eccentric
Centric
Striations
Absent
Present
Absent
S. Mishra, T. Rai / Food Hydrocolloids 20 (2006) 557–566
560
(corn and tapioca) and oval (potato) to polyhedral (corn) or
spherical with some truncated (tapioca) granules. Moreover,
the smooth surface of granules was viewed at 1000!
magnification (
). Small grooves were also observed in
some granules of tapioca starch. SEM has been used to
relate granule morphology to starch genotype (
). The variation in size and shape of starch granules
may be due to the biological origin (
claimed that
the morphology of starch granules depends on the
biochemistry of the chloroplast or amyloplast and physi-
ology of the plant.
3.2. Physico-chemical properties
The pH was observed to be lower for tapioca (4.80) than
for corn and potato starches that showed values of 6.24 and
7.15, respectively (
). The lower pH of tapioca starch
might be due to the presence of comparatively more
impurities that has got incorporated into the starch during
processing.
Reflectance value, which is a measure of the degree of
whiteness, is of importance in relation to the physical
appearance of the food. Being a basic raw material,
the whiteness of starches was evaluated, owing to the fact
that the latter can impart its colour to the food product. Since
the quantification of the degree of whiteness is difficult with
unaided eyes, a reflectance meter was used to determine the
whiteness of commercial starches from different sources.
showed that tapioca starch had lesser degree of
whiteness (87.0%) compared to potato starch which showed
95.5% of reflectance value, although corn starch had very
high degree of whiteness (99.0%).
The study (
) revealed that commercial starches
like corn, potato and tapioca contained comparatively same
level of starch with different amylose levels. The amylose
content (in terms of amylose equivalent) was observed to be
significantly lower in tapioca (16.27%) than potato
(24.95%) and corn (25.60%) starches (P!0.05). These
values were slightly higher than those reported by
man (1969) and Rapaille and Vanhemelrijck (1992)
for
potato (22%) starch, but comparable to that for corn (26%)
and tapioca (17%) starches. In addition, the starches were
also found to contain 0.80–0.88% of reducing sugar that
could be present in starch or produced during processing
(
). The range of moisture
contents in these starches varied from 7.54 to 9.37%.
Tapioca starch showed slightly lower moisture content
(7.54%) than corn starch (7.74%). Potato starch had
significantly (P!0.05) higher moisture level (9.37%) than
other starches.
Among the minor constituents, the lipid content of
starches varied from 0.32 to 1.22%. It was observed that
potato and tapioca starches had significantly (P!0.05)
lower lipid level (0.32 and 0.51%, respectively) than that of
corn starch (1.22%). The higher lipid content is undesirable
since it could be responsible for off flavours, high turbidity,
higher pasting temperature and lower viscosity of starches
(
). Similarly, corn starch contained significantly
(P!0.05) higher protein (1.21%) while potato and tapioca
starches had significantly less protein content (0.61 and
0.51%, respectively). Protein may also have adverse effect
as these led to mealy flavour and have a tendency to foam
(
). Corn starch had significantly higher ash
Fig. 2. Scanning electron microscopy of corn (A), potato (B) and tapioca
(C) starches (Magnification !1000).
Table 2
Physico-chemical characteristics of corn, potato and tapioca starches
Constituent
Source of starch
CD (P!0.05)
Corn
Potato
Tapioca
pH at 20 8C
6.24
a
G
0.04
7.15
b
G
0.04
4.80
c
G
0.03
0.13
Reflectance value (%)
99.0
a
G
0.3
95.5
b
G
0.8
87.0
c
G
1.0
2.6
Moisture (%)
7.74
a
G
0.06
9.37
b
G
0.18
7.54
a
G
0.14
0.47
Lipid (%)
1.22
b
G
0.16
0.32
a
G
0.07
0.51
a
G
0.08
0.38
Protein (%)
1.21
b
G
0.15
0.61
a
G
0.06
0.51
a
G
0.07
0.35
Starch (%)
89.27G1.82
89.44G0.64
90.99G0.67
NS
Ash (%)
0.36
b
G
0.05
0.19
a
G
0.02
0.20
a
G
0.05
0.15
Total phosphorus (mg%)
23.16
b
G
0.83
41.31
c
G
0.61
7.54
a
G
0.40
2.21
Reducing sugar (%)
0.88G0.06
0.80G0.05
0.83G0.02
NS
Amylose equivalent (%)
25.60
b
G
1.17
24.95
b
G
0.68
16.27
a
G
0.32
2.78
Data represent meanGSE of three determinations. The mean values bearing different superscripts in each row differ significantly (P!0.05); NS, non-
significant.
S. Mishra, T. Rai / Food Hydrocolloids 20 (2006) 557–566
561
content as compared to potato and tapioca (P!0.05). The
total phosphorus content in potato starch (41.31 mg%) was
found to be significantly (P!0.05) higher than that of corn
(23.16 mg%) and tapioca (7.54 mg%).
also
reported more bound phosphate ester groups in potato
starches as compared to other starches. The higher
phosphate content was claimed to cause a lower pasting
temperature, higher viscosity and improved clarity (
have also reported that
the phosphate group effectively forced the starch chains
apart and allowed easier access of water during
gelatinization.
3.3. Functional properties of starches
3.3.1. Solubility
It was observed that corn, potato and tapioca starches
(
) exhibited very low solubility at 20 8C (1.01, 1.21
and 1.90%, respectively) and formed only a temporary
suspension when stirred in water. The low solubility of
starches could be attributed to the semi-crystalline structure
of the starch granule and the hydrogen bonds formed
between hydroxyl groups in the starch molecules (
). Further, the solubility of these
starches exhibited slightly higher values (3.89, 13.49 and
14.36%, respectively) at 70 8C. It is obvious from the results
that in both the cases, the cereal starch (corn) exhibited
lower solubility. This could be due to the fact that cereal
starches have a more compact structure and different
crystallinity than tuber starches (
). However,
the increase in solubility at high temperature (70 8C) was
more in case of potato and tapioca starches. This could be
because of the temperature used, which was well above the
gelatinization temperature of potato and tapioca starches,
but less than the required for corn starch. The observation is
supported by the fact that when the temperature of an
aqueous starch suspension is raised above the gelatinization
range, hydrogen bonds continue to disrupt followed by the
attachment of water molecules to liberated hydroxyl groups
and resulting in the continuous swelling of the granule.
3.3.2. Water holding capacity (WHC)
From the results (
) it was observed that potato
starch held slightly more water (10.44 g H
2
O g
K
1
) than that
of tapioca (10.06 g H
2
O g
K
1
) and corn (7.92 g H
2
O g
K
1
)
starches. The variation in WHC of these starches could be
due to the difference in the degree of the engagement of
hydroxyl groups to form hydrogen and covalent bonds
between starch chains (
). Further
differences in the degree of availability of water binding
sites among the starches may have role in the variation of
water binding capacity (
3.3.3. Viscosity
The results of viscosity of different starches (corn, potato
and tapioca) under alkaline conditions are presented in
It was revealed that at low concentration (0.1%, w/v) the
viscosity of starches was almost similar (0.97, 0.97 and
0.96 cP at 30 8C, respectively). However, the viscosity of all
these starches increased with increasing concentration to
0.5%. Similarly, the viscosity of starches decreased curvili-
nearly with increasing temperature, e.g. the viscosity of
corn, potato and tapioca starches decreased from 1.88, 1.94
and 1.80 cP at 20 8C to 0.77, 0.83 and 0.75 cP at 60 8C,
respectively.
3.3.4. Flow properties
The flow properties of corn, potato and tapioca
starch dispersions were studied in the shear rate range
100–500 s
K
1
and the results are presented in
. All the
tested starch systems behaved to a very good approximation
(r
2
Z0.991–1.000) as power law liquid over this range of
shear rates. The good fit of power law model confirmed the
linearity of the curves for these starches. The starch paste
showed pseudoplastic behaviour (shear thinning) and the
flow behaviour index (n) was observed to be least for potato
starch (0.35) followed by tapioca (0.36) and corn (0.38)
starches. Similarly, the consistency indices (K) of corn,
potato and tapioca starches were 14.17, 24.31 and
12.96 Pa s
n
, respectively.
postulated that secondary bonds between the hydrodynamic
units, either directly or through intermediate water mol-
ecules cause the non-Newtonian behaviour of cooked starch
pastes.
3.3.5. Viscosity stability to heat, acid and shear
The viscosity stability to heat, acid and shear of the
starches was studied with an aim to find out their process
tolerance since starch paste functionality may be reduced by
prolonged heating or exposure to high temperature by too
much stirring during or after cooking (high shear con-
ditions) or by exposure to low pH. As evident from
among the starches, corn exhibited higher heat stability
index (HSI) and acid stability index (ASI) indicating the
higher resistance for viscosity change when subjected to
Table 3
Some functional properties of corn, potato and tapioca starches
Functional properties
Source of starch
Corn
Potato
Tapioca
Solubility (%) at 20 8C
1.01
1.21
1.90
Solubility (%) at 70 8C
3.89
13.49
14.36
WHC (g H
2
O g
K
1
starch)
7.92
10.44
10.06
Flow properties
Flow behaviour index (n)
0.381
0.348
0.363
Consistency index (K, Pa s
n
)
14.17
24.31
12.96
Coefficient of determination (r
2
)
0.991
1.000
0.979
Heat stability index (HSI)
1.25
0.36
0.73
Acid stability index (ASI)
0.97
0.51
0.74
Shear stability index (SSI)
0.10
0.14
0.11
Least concentration gelation
(% starch, w/v)
6.00
4.00
8.00
Data represent mean of two independent determinations.
S. Mishra, T. Rai / Food Hydrocolloids 20 (2006) 557–566
562
either higher temperature or to acidic condition of the
starch. The shear stability index (SSI), however, was
observed to be higher for potato starch. The reduction of
the viscosity stability of starches might have occurred as a
result of the destruction of the intra-granular hydrogen
bonds, which maintain the integrity of the granule during
gelatinization (
3.3.6. Pasting characteristics
The pasting curves (
) obtained from rapid
viscoamylograph (RVA) was a measure of the viscosity of
starch suspension during the heating cycle which reflects the
molecular events occurring in starch granules and provided
a means of comparing the behaviour of corn, potato and
tapioca starches during cooking. It was observed that
starches like potato and tapioca formed pastes at lower
temperature unlike corn starch, which gelatinized appar-
ently at higher temperature because of its higher degree of
crystallinity. The results are supported by the fact that in
general root starches gelatinize more rapidly and at lower
temperature than cereal starches (
The peak viscosity was maximum for potato starch
(4927.0 cP) than the other starches in spite of the fact that
it also showed higher values for breakdown viscosity
(
). This behaviour could be attributed to the fact that
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
0.1
0.2
0.3
0.4
0.5
Concentration (%,w/v)
Viscosity (cP)
0
0.5
1
1.5
2
2.5
20
30
40
50
60
Temperature (˚C)
Viscosity (cP)
Corn
Potato
Tapi oc a
Fig. 3. Viscosity of corn, potato and tapioca starches as a function of concentration (at 30 8C) and temperature (at 0.5%, w/v).
Fig. 4. RVA curves of native corn, potato and tapioca starches.
S. Mishra, T. Rai / Food Hydrocolloids 20 (2006) 557–566
563
potato starch became swollen very rapidly above the
gelatinization temperature and the bonding forces within
the granules were of similar strength that breakdown over a
small temperature range (
). Further, the
maximum viscosity was attained when the granules were in
their most swollen state, yet still intact resulting in peak
viscosity. Continued heating of paste at this point, however,
caused the granule to rupture and accompanied by the fall in
viscosity (
). The secondary increase
in viscosity (setback) during the cooling phase which is
associated with the retrogradation phenomenon and related
to amylose content was observed to be minimum for potato
starch (412.0 cP) unlike corn and tapioca starches. This
retrogradation or setback was claimed to be influenced by
the various factors, viz. amylose content, length of amylose
molecules and the state of dispersion of the amylose chains
(
). Thus, although the amylose content was
higher in potato starch, the higher degree of polymerization
(DP) of its amylose molecules might be responsible for
lower setback. Further, the final viscosity was observed to
be higher for corn starch (2530.0 cP).
The differences among the pasting characteristics of the
starches arose obviously due to the variation in the starch
source. It is claimed that, the process of gel formation and
setback depends on polymer association especially of the
linear amylose fraction present in the starch molecule
(
3.3.7. Gelation
Least concentration gelation (LCG). When a cooked
paste of starch cools without agitation intermolecular bonds
are formed both within and between the swollen starch
granules and their fragments. The study of the minimum
concentration required to form gel (
) showed that
potato starch gelled at lower (4.0%, w/v) concentration and
was followed by corn (6.0%, w/v) and tapioca (8.0%, w/v)
starches. The observation can be explained in terms that it is
the linear fraction that readily set up into a solid gel and
since the amylose content was observed to be higher in corn
and potato starches, these form gel at lower concentration in
comparison to tapioca starch. Thus, differences in the
amylose–amylopectin ratio could be responsible for LCG as
it is the amylose that readily forms gel due to the fact that
straight chains can orient themselves in a parallel alignment
so that a large number of hydroxyl groups along the chain
are in close proximity to those on adjacent chains resulting
in gelation while the alignment is inhibited in case of
amylopectin due to its branched structure (
However, the observation was not in agreement with the
report of
according to whom tuber/
root starches gelled much less readily than cereal starches.
Texture Profile Analysis (TPA). TPA stimulates the
human chewing action by subjecting a sample to a
compressive deformation (first bite) followed by a relax-
ation and a second deformation (second bite). The
instrument recorded force over time and from the resulting
stress strain curve, several parameters were obtained.
revealed that in general potato starch yielded gel
that showed higher cohesiveness, gumminess and chewi-
ness. This could be due to the higher DP of amylose fraction
that caused relatively weak gel tendencies with texture
towards gummy and cohesive side (
However, unlike the earlier report (
) that
cereal starches gave stronger gels, in the present study,
potato starch formed firm gel comparable to that of corn
starch. But,
Whittenberger and Nutting (1948)
reported that
the gel strength is correlated with the extent of granule
swelling which might have implicated with the present
observation. The gel obtained from corn starch was brittle,
stronger and adhesive and showed higher springiness.
Tapioca starch gel, on the other hand, was softer, less
springy, gummy and chewy. The variation among the
texture of gels obtained from these starches could be due to
Table 4
Pasting properties of corn, potato and tapioca starches
Pasting properties
Starch source
Corn
Potato
Tapioca
Peak viscosity (PV, cP)
2609.00
4927.00
1769.00
Gelatinization temperature (8C)
78.25
67.15
66.20
Final viscosity (FV, cP)
2530.00
2227.00
2451.00
Breakdown (BKD, cP)
818.00
3112.00
177.00
Setback (SB, cP)
739.00
412.00
859.00
Values are mean of duplicate determinations.
Table 5
Texture profile analysis results of corn, potato and tapioca starches
Gel characteristics
Source of starch
CD (P!0.05)
Corn
Potato
Tapioca
Hardness (N)
12.04
b
G
1.69
13.53
b
G
0.58
7.20
a
G
0.36
0.64
Brittleness (N)
6.52
b
G
0.11
4.10
a
G
0.14
3.75
a
G
0.13
0.43
Adhesiveness (N mm)
K
0.55
a
G
0.06
K
0.92
b
G
0.04
K
0.49
a
G
0.04
0.17
Cohesiveness
0.15G0.01
0.19G0.01
0.19G0.02
NS
Springiness (mm)
1.69G0.12
1.68G0.23
1.55G0.18
NS
Gumminess (N)
1.78
a
G
0.22
2.57
b
G
0.20
1.37
a
G
0.16
0.67
Chewiness (N mm)
3.06
ac
G
0.62
4.26
bc
G
0.45
2.17
a
G
0.48
1.81
Data represent meanGSE of three independent determinations. The mean values bearing different superscripts in each row differ significantly (P!0.05);
NS, non-significant.
S. Mishra, T. Rai / Food Hydrocolloids 20 (2006) 557–566
564
the difference in the nature of the starch and the presence of
impurities including fats, proteins, etc. that resulted in gels
of widely different properties (
3.3.8. Moisture sorption behaviour
The moisture sorption isotherm curve (
) compared
the equilibrium moisture contents of different starches. The
adsorption curves described in terms of type II, sigmoidal
shaped isotherm showed that potato starch adsorbed higher
moisture content at all water activities (0.113–0.946)
followed by tapioca starch. Corn starch on the other hand
adsorbed lesser moisture content at corresponding water
activity (a
w
). Moisture sorption behaviour of starches was
studied with the help of Guggenheim–Anderson–deBoer
(GAB) model.
also reported that cereal
starches adsorbed less moisture than root starches. As
evident from
, GAB equation had very good fit with
experimental data (r
2
Z0.958–0.986). The monolayer
moisture content (M
o
) of starches calculated from the
GAB equation was higher in case of potato as compared to
corn and tapioca starches. The constant K which permits the
GAB model being applicable to higher a
w
(at multiple layer
moisture region) was found to be 0.65–0.73. Moreover, heat
of sorption (Q
s
) which gives information on interaction
forces between the water vapour molecules and the
adsorbent surface (binding energy) was found to be higher
for potato starch (2037 cal/mol H
2
O) followed by corn and
tapioca starches (1810 and 1624 cal/mol H
2
O, respectively).
4. Conclusion
It can be concluded that study on functional properties of
three major commercial native starches like corn, potato and
tapioca can become impetus to their selection and appli-
cation in food industry. The study revealed that tuber and
root starches contained less protein, lipid and ash contents as
compared to that of cereal starch. All these starches had
unique properties because of their characteristic distinct
granules when seen under microscope. The high viscosity of
potato starch can be utilized to have an advantage in instant
soups and sauces but the high viscosity stability to acid and
heat of corn starch suggested an array of potential application
in fermented milk products.
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