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Isolation and Characterization of Starch
obtained from Cocoyam cultivated at Akungba
Akoko, Ondo State, Nigeria
Jacob Olalekan Arawande*1,2 and Adeleke Omodunbi Ashogbon2
1Chemistry Department, University of Medical Sciences, Nigeria
2Department of Chemical Sciences, Adekunle Ajasin University, Nigeria
Submission: October 25, 2018; Published: January 10, 2019
*Corresponding author: Dr. Jacob Olalekan Arawande, Chemistry Department, University of Medical Sciences, PMB. 536, Ondo-City, Ondo-State, Nigeria
How to cite this article: AJacob O A, Adeleke O A. Isolation and Characterization of Starch obtained from Cocoyam cultivated at Akungba Akoko, Ondo State, Nigeria. Nutri Food Sci Int J. 2019. 8(2): 555732. DOI:10.19080/NFSIJ.2018.08.555732.
This research was carried out to determine the yield, chemical composition, functional, pasting and gelatinization properties of starch isolated from cocoyam cultivated at Akungba Akoko. Cocoyam starch was isolated from matured corms of cocoyam and was analyzed for percentage yield, chemical composition, functional and pasting properties. The percentage yield of starch in the cocoyam was 11.47±0.11%. The starch contained moisture content, crude protein, lipid, ash, amy lose, amylopectin and phosphorus of 15.05±0.19%, 0.05±0.00%, 0.07±0.00%, 0.21±0.02%, 23.50±0.02%, 76.50±0.01% and 0.76±0.18mg/100g respectively. The pH, bulk density, dispersibility, water binding capacity and water absorption index of 7.19±0.02, 0.88±0.09 g/ml, 86.50±0.18%, 72.13±0.26% and 162.51±0.42% accordingly. The swelling power of the starch ranged between 0.79±0.02 and 7.96±0.10 while its solubility ranged between 6.12±0.09g/100g and 14.03±0.14 g/100g. The peak, trough, breakdown, setback and final viscosities of the starch were 480.63±0.02, 245.75±0.09, 234.88±0.18, 123.75±0.26 and 368.38±0.42 RUV respectively while its peak time and pasting temperature were 5.01±0.00 minutes and 84.23±0.01℃. The onset, peak and conclusion temperatures of the starch were found to be 81.30±0.11℃, 85.20±0.19℃ and 93.00±0.21℃ accordingly and its enthalpy of gelatinization was 12.10±0.13J/g. Cocoyam starch possessed excellent qualities that can make it useful for food and non- food applications.
Akungba Akoko is a town located in Akoko land, Ondo-State, Nigeria where cocoyam is one of the commonest cultivated plants. The cocoyam cultivated in this part of the country is given much attention because it is a common food usually consumed especially during the period of “food scarcity” when the normal yam is out of stock around January to March before the availability of early year maize in April/May. Due to much availability of cocoyam at this period of the year, it is being underutilized thereby leading to wastage because most people in the town usually cultivate the plant since farming is the major preoccupation in the town. Though a State University is located in the ancient town, most workers of the University don’t reside in the town as a result of lack of regular supply of electricity hence workers prefer to live in nearby towns and city.
Starch is a renewable, biodegradable, edible polymer as a major storage polysaccharide in plants with natural abundance next to cellulose and chitin. Starch plays an important role in food products, either as a major component or as a food additive . It is an important naturally occurring polymer of glucose, with diverse applications in food and polymer science, found in roots, rhizomes, seeds, stems, tubers and corms of plants, as microscopic granules having characteristic shapes and sizes . Annual worldwide starch production is 66.5 million tons and the growing demand for starches has created interest in identifying new sources and modifications or derivatives of this polysaccharide . The different botanical sources of starches are cereal, legume, root and tuber . Starch is the basic source of energy for majority of the world’s population. In human nutrition, starch plays a major part in supplying the metabolic energy that enable the body to perform its different functions . It is found accompany with other reserved such as protein, fats, lipids and some phosphates. Starch consists of major and minor components. The major components of starch are amylose (normally 20-30%) and amylopectin (normally 70-80%)  while the minor components are lipids, protein, phosphorus and mineral . Although, these components are at very low level in the starch granules but they play an important role in the physicochemical properties of starch . Utilization of starch in both food and non-food industries depends on its physical, chemical and functional properties . These properties are unique for different crops
and varieties. Therefore, understanding the physiochemical and
functional properties of starch from different sources can help in
utilization of starch for the different applications .
Though much research works have been reported on starch
and cocoyam. Aboubakar studied physiochemical, thermal
properties and microstructure of taro (Colocasia esculenta) flours
and starches. Adebayo & Itiola  reported the evaluation
of breadfruit and cocoyam starches as exodis-integrants in a
paracetamol tablet formulation. The proximate composition and
selected functional properties of African breadfruit and sweet
potato flour blends was studied by Akubo . Oladebeye et al.
 researched on functional, thermal and molecular behaviours
of ozoned-oxidized cocoyam and yam starches. Physicochemical
properties of starches of sweet potato (Ipomea batata) and red
cocoyam (Colocasia esculenta) cormels was reported Oladebeye, et
al. . Ashogbon  worked on physicochemical properties of
bambarra groundnut starch and cassava starch blends. However,
there is no or little information on the yield and properties of
starch isolated from cocoyam cultivated in Akungba Akoko, Ondo-
State, Nigeria. Therefore, the focus of this work is to isolate and
determine the chemical composition, functional, pasting and
gelatinization properties of starch obtained from cocoyam species
prevalent at Akungba Akoko, Ondo-State, Nigeria with the view of
enhancing the utilization of cocoyam that is yearly wasted in this
part of the country.
Twenty big tubers of cocoyam were bought at Ibaka Market,
Akungba Akoko, Ondo- State and all chemicals used were of good
analytical grade purchased from a reliable vendor in Akure, Ondo-
The method described by Akanbi, et al.  & Agboola, et
al.  was used for starch isolation and percentage yield. The
cocoyam tubers were weighed and peeled. The peeled cocoyam
tubers were washed, sliced and crushed with Home Flower
blender (Model NO: HFB-3489). The blended pulp was suspended
in 5 litres of distilled water at room temperature for two hours and
the suspended pulp was sieved using muslin clothe which retained
the fibre. The fibre was rewashed to remove adhering starch. The
extracted starch was allowed to sediment for two hours and the
supernatant was decanted off. The extracted starch was washed
with 5 litres of distilled water thrice until white and odourless
starch was obtained. This was finally suspended in distilled water
and left for another 24 hours and the supernatant was finally
decanted off. The sediment was re-suspended in distilled water
and centrifuged at 300 revolutions per minute for 15 minutes. The
resulting wet starch was dried in an oven at 40℃ for 2 days. The
dried starch was weighed, ground to powder, packaged in glass
jar and stored for analysis. The percentage yield was calculated.
The moisture content, ash content, crude protein, lipid
and phosphorous of cocoyam starch was determined by AOAC
international standard method  while the amylose and
amylopectin contents were determined by method described by
Takahashi & Seib .
The functional properties of cocoyam starch determined were
pH, bulk density, dispersibility, water binding capacity, water
absorption index, swelling power and water solubility index.
Determination of pH: 5g of cocoyam starch was weighed in
triplicate into a beaker and 20ml of distilled water was added and
mixed together. The resulting suspension was stirred for 5 minutes
and left to settle for 10 minutes. The pH of the supernatant was
measured using a calibrated pH meter .
Determination of bulk density: This was determined by
the method of Wang & Kinsella  as modified by Ashogbon &
Akintayo . 10ml capacity graduated measuring cylinder was
weighed (W1) and the cylinder was filled with the starch sample
by gently tapping the bottom of the cylinder on the laboratory
bench several times until there was no other contraction of the
powdery starch level after filling to the 10ml mark. The weight of
the measuring cylinder with its content was obtained (W2).
Determination of starch dispersibility: This was
determined by the method described by Kulkarrni et al.  as
modified by Akanbi et al. . 10g of starch sample was accurately
weighed into measuring cylinder and 100ml of distilled water was
added to it and it was left to stand for 3 or 4 hours during which
pure and sediment layers were formed. The lower layer meniscus
from upper layer meniscus gave the dispersibility.
Determination of water binding capacity: This was carried
out using the Medcaf and Gillies  method. 37.5ml of distilled
water was added into 2.5 ml of the cocoyam starch and was
centrifuged for 10minutes at 3000rpm. Then the weight of the
centrifuge tube and content was determined after decanting the
water and allowed to drain for another 10 minutes, the bound
water was determined by the change in weight. It was calculated
by the formula,
Determination of water absorption index: This was determined
by modified method of Ruales et al. . 2.5g of starch
was suspended in 30ml of distilled water at 30℃ in a centrifuge
tube, stirred for 30 minutes intermittently and then centrifuged at 3000rpm for 10 minutes. The supernatant was decanted, and
the weight of the gel formed was recorded. The water absorption
index (WAI) was the calculated as gel weight per gram dry sample.
Determination of swelling power and water solubility
index: Swelling power (SP) and water solubility index (WSI)
determination were carried out in the temperature range of 60-
90℃ at 10℃ interval using the method of Takashi and Seib .
1g of starch sample was accurately weighed and 50ml of distilled
water was added and gently mixed together. The slurry was heated
in a water bath at 55℃, 65℃, 75℃, 85℃ and 95℃ for 15minutes.
During heating, the slurry was gently stirred to prevent clumping
of the starch. After 15 minutes, the tubes containing the paste were
centrifuged at 3000rpm for 10minutes using SPETRA U.K (Merlin
503) centrifuge. The supernatant was immediately decanted after
centrifuging. The weight of the sediment was taken and recorded.
The moisture content of the gel was thereafter determined to get
the dry matter content of the gel.
Determination of pasting properties of cocoyam starch:
The pasting properties of cocoyam starch was analysed using
a Rapid Visco Analyzer (Newport Scientific, RVA Super 3, and
Switzerland). Starch suspension containing 9% w/w dry starch
basis; 28g total weight) was equilibrated at 30℃ for 1 minute,
heated at 95℃ for 5.5 minutes at a rate of 6℃/minutes, held at
95℃ for 5.5 minutes, cooled to 50℃ at a rate of 6℃/minute and
finally held at 50℃ for 2 minutes. Parameters recorded were
pasting temperature (PT), peak viscosity (PV), trough viscosity
(TV), final viscosity (FV) and peak time (Pt). Breakdown viscosity
(BV) was calculated as the difference between PV minus TV, while
total setback viscosity (SV) was determined as FV minus TV. All
determinations were performed in triplicate and expressed in
rapid viscosity unit (RVU) .
Determination of gelatinization properties of cocoyam
starch (Thermal analysis): The gelatinization properties of
cocoyam starch were studied using a Differential Scanning
Calorimeter (DSC-Q100, TA Instruments, New Castle, DE, USA).
Cocoyam starch slurries were prepared at 1:3 dry starch/water
ratios, hermetically sealed using a DuPont encapsulation press
(DuPont Co., Delaware, USA) and reweighed. The sample was
heated at a rate of 5℃/min from 20 to 100℃. Onset Temperature
(To), peak temperature (Tp), conclusion temperature (Tc) and
enthalpy of gelatinization (ΔH) and all determinations were
performed in triplicate .
The percentage yield and chemical composition of cocoyam
starch is presented in Table 1. The percentage yield of cocoyam
starch was 11.47±0.11% and this value is lower than 14.26%
starch yield obtained from breadfruits . The moderately
low starch value is of significant importance in domestic and
industrial food utilization. The moisture content of the cocoyam
starch was 15.05±0.19%, which is higher than 9.36±0.02%
reported by Oladebeye et al. . The high moisture content of
the starch suggests its instability against microbial activity. Hence
the starch needs to be further dried in order to be within the 10%
stipulated standard of the revised regulation of the Standards
Organisation of Nigeria  so as to prolong its shelf life over
a long storage period. Akubo  reported that the lower the
initial moisture content of a product to be stored, the better the
storage stability of the product. The crude protein, lipid and ash of
cocoyam starch were 0.05±0.00%, 0.07±0.00% and 0.21±0.02%
respectively. The ash and fat contents as reported by Oladebeye et
al.  were 1.88 ±0.02% and 0.52±0.01%, respectively. The lipid
and protein contents are minor component of starch and they are
very important because of their anti-swelling effect and influence
on the pasting parameters . The low value of lipid content of
cocoyam starch may suggest that the starch and other products
made from it are not susceptible to rancidity. The amylose and
amylopectin contents of cocoyam starch were 23.05±0.02% and
76.50±0.01% accordingly. The amylose content was lower than
81.07±0.04% reported for red cocoyam tubers by Oladebeye et al.
. However, the amylose content was within 18-24% reported
by Jane and 16.65±0.15% -30.85±0.63% reported by Aboubukar
et al. . The difference in value might be as a result of difference
in species and agricultural environment where the plants were
cultivated. The amylose and amylopectin contents of starches are
significant as they affect pasting, gelatinization, retrogradation,
swelling power and enzymatic vulnerability of starches .
Phosphorus was 0.76±0.18mg/100g and this value falls within
0.76mg/100g and 1.36mg/100g reported by Aboubukar et al.,
. Phosphorus has been reported to be covalently linked to
starch and affects its properties .
Table 2 depicts the functional properties of cocoyam starch.
The pH value of the cocoyam starch was 7.19±0.02 which is
slightly higher than 6.513±0.0058 reported by Akanbi et al. 
for breadfruit starch. Though the pH value was within the range
7.38±0.04 and 7.03±0.02 reported for bambarra groundnut starch and cassava starch blends by Ashogbon . The pH is an important
property in starch industrial applications, being generally used to
measure the degree of acidity or alkalinity of liquid media. The
cocoyam starch has bulk density of 0.88±0.09g/ml. The bulk
density is a measure of the degree of coarseness of starch sample.
The bulk density of cocoyam starch was the same with the 70%
bambarra groundnut starch and 30% cassava starch blend (that
is 0.88±0.01g/ml) reported by Ashogbon . However, the
bulk density value was higher than 0.72±0.01 and 0.75±0.01g/
ml reported for white cocoyam corms and cormels respectively
by Oladebeye et al. . The high value of cocoyam starch bulk
density connotes that less packaging space is required for it. Bulk
density, as a function of suitability of starch as disintegrants and
binder in tablet formulation, suggests that cocoyam starch as
alternative binder and disintergrants in pharmaceuticals.
Values represent means of triplicate determination ± standard deviation.
The value of dispersibility of cocoyam starch obtained is
86.50±0.18% and this value is much higher than 40.667±0.5774%
obtained for breadfruit starch as reported by Akanbi et al. .
But the value is within 83.00±0.03 and 87.00±0.06% reported
for bambarra groundnut starch and cassava starch blends by
Ashogbon . Dispersibility is a measure of reconstitution of flour
or flour blends in water, the higher the dispersibility the better
the flour reconstitutes in water . Cocoyam starch has water
binding capacity and water absorption index of 72.13±0.26%
and 162.51±0.42% respectively. The water binding capacity and
water absorption index of cocoyam starch is higher than that of
breadfruit starch (water binding capacity of 8.267±0.2309% and
water absorption index 104.933±0.2309%) as reported by Akanbi
et al. . Oladebeye et al.  reported that water binding
capacity for sweet potato and red cocoyam starch as 84.91±0.02%
and 82.74±0.03% accordingly and these values are higher than
that obtained for cocoyam starch.
Table 3 presents the swelling power and solubility index at
different temperatures of cocoyam starch. The swelling power
and solubility index of cocoyam starch increases with increase in
temperature of the starch, but there was a sudden increase from
75℃ to 95℃. Swelling power of cocoyam starch ranged between
0.79±0.02 and 7.96±0.10 over a temperature range of 55℃ to
95℃. Cocoyam starch solubility ranged between 6.21±0.09 and
14.03±0.14g/100g over a temperature range of 55℃ to 95℃.
The swelling power has been related to the associative binding
within starch granules and apparently, the strength and character
of the micellar network is related to the amylose content of the
starch, low amylose content, produces high welling power .
Swelling power and solubility are measures of the magnitude of
the interaction between starch chains within the amorphous and
crystalline domain . The swelling power of starches is of great
significance in tablet and capsule formulations as it is believed
that disintegrants works through a swelling and wicking action
. As a result, starches with higher swelling power would be
expected to release the active pharmaceutical ingredient from
its compacts at a faster rate, where starch acts as a disintegrant.
Solubility represents the amount of solubilized starch molecules
present at a certain temperature.
Values represent means of triplicate determination±standard deviation.
The pasting properties of cocoyam starch are presented in
Table 4. The peak viscosity and trough viscosity of cocoyam starch
are 480.63±0.02 RUV and 245.75±0.09 RUV respectively while its
breakdown viscosity and setback viscosity are 234.88±0.18 RUV
and 123.75±0.26 RUV accordingly. The peak viscosity of cocoyam
starch is higher than the values obtained for bambarra groundnut
starch and cassava starch blends but lower than 553.75±0.10
RUV for pure cassava starch as reported by Ashogbon . Both
values of breakdown viscosity and setback viscosity for cocoyam
starch were higher that values (7.92 and 40.08 accordingly)
obtained for breadfruit starch by Akanbi et al. . The trough
viscosity of cocoyam starch is lower than 247.04±0.20 RUV for
bambarra groundnut starch but higher than 162.58±0.10 RUV for
cassava starch . Breakdown viscosity is a measure of granule
disruption or lesser affinity of starch to resist shear force during
heating while the setback viscosity is a measure of the degree
of retrogradation of starch, mainly amylose , implying that
a high setback viscosity value means a high tendency of starch
to retrogradation. The final viscosity, peak time and pasting
temperature of cocoyam starch are 368.38±0.42 RUV, 5.01±0.00
minutes and 84.23±0.01℃ respectively and the values for peak
time and pasting temperature are higher than values obtained
for bambarra groundnut starch and cassava starch as reported
by Ashogbon . Oladebeye et al.  reported lower values
for pasting temperature and peak time for sweet potato and red
cocoyam starches. The final viscosity value of cocoyam starch was
lower than that of bambarra groundnut starch but higher than
that of cassava starch . The final viscosity indicates the ability
of starch samples to form past . The peak time is a measure of the rate at which equilibrium is attained between swelling and
polymer leaching, and rupture and polymer alignment .
Values represent means of triplicate determination ± standard deviation.
RUV = Rapid Visco Unit (Unit of Viscosity); BV = PV – TV; SV = FV
– TV; PV = Peak Viscosity; TV = Trough Viscosity; BS = Breakdown
Viscosity; SB = Setback Viscosity; FV = Final Viscosity; Pt = Peak Time;
PT = Pasting Temperature.
Table 5 depicts the gelatinization properties of cocoyam
starch. The onset temperature, peak temperature and conclusion
temperature of cocoyam starch are 81.80℃ 0.110C, 85.20℃
0.190C and 93.00℃ 0.210C respectively while its enthalpy of
gelatinization is 12.10±0.13 J/g. Oladebeye et al.  gave the onset
temperature, peak temperature and conclusion temperature of
cocoyam starch are 77.24±0.11℃, 79.52±0.01℃ and 86.14±0.58℃
respectively and all these values are lower than the obtained
values. However, the enthalpy of gelatinization for cocoyam
starch reported by Oladebeye et al.  is higher (15.19±3.12 J/g)
than obtained value. The differences in these values may be as a
result of differences in the agricultural environments in which
the cocoyam were planted. The gelatinization temperature and
enthalpy of starches depend on the microstructure and degree of
crystallinity within the granules, and also on the granule size and
amylose-to-amylopectin ratio .
Values represent means of triplicate determination ± standard
To = Onset Temperature; Tp = Peak Temperature; Tc = Conclusion
Temperature; ΔH = Enthalpy of Gelatinization.
The results of the research work on cocoyam starch obtained at
Akungba - Akoko, Nigeria revealed that it has an array of chemical,
functional, pasting and gelatinization properties that makes it
suitable in many areas for food and non-food applications. With
the values of functional properties obtained for cocoyam starch,
it is very useful as binder in pharmaceutical, cosmetic and paper
industries. The cocoyam starch needed to be further dried so as
to stay unspoiled due to its high moisture content when stored
over a long period. Further research work can be conducted if the
cocoyam starch is blended with other starches from other sources
in different proportion and observed the effect of blending on
chemical, functional, pasting and gelatinization properties of