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4. Native tuber starches….

89

Chapter 4

Characterization of tuber starches and their application in tablets as

excipient

Starches are of commercial importance because of their inertness, abundance and cheapness.

Commercial starches are obtained from cereals (corn, waxy corn, high amylose corn, wheat

and various rice varieties) and from tubers and roots. Starches have become a valuable

ingredient in the food industry where they are used as thickeners, gelling, bulking and water

retention agents, and the pharmaceutical industry where they are used in tablet formulations

Starch is one of the most important excipients used in the pharmaceutical industry. The

International Joint Conference on Excipients rated starch among the top ten pharmaceutical

ingredients (Shangraw, 1992). Starch is used mainly as binders, dinsintegrants, fillers,

glidants, or lubricants in the pharmaceutical oral solid dosage forms.

Hence the present study was undertaken to examine some of the physicochemical, rheological,

mechanical, and micromeritic properties of selected tuber starches viz, cassava, arrowroot,

Xanthosoma, Dioscorea, and Amorphophallus, relevant to application as excipient in tablet

formulations.

4.1.1 Morphological properties of tuber starches

Morphological characteristics of starches from different tuber starches are presented in Table

4.1. The granule size is variable and ranges from 5 to 40 μm for cassava starch granules. The

average size of individual arrowroot starch granules ranges from 9 to 40 μm. The Xanthosoma

starch granules range from 10 to 50 μm in size. The highest granule size was observed for D.

alata and smallest for cassava and arrowroot starches. Morphological characteristics of

starches from different plant sources vary with the genotype and cultural practices. The

variation in the size and shape of starch granules is attributed to the biological origin

(Svegmark and Hermansson, 1993). The morphology of starch granules depends on the

biochemistry of the chloroplast or amyloplast, as well as physiology of the plant


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(Badenhuizen, 1969). Granule size plays an important role in the application for starch in the

food and other pharmaceutical industries.

Table 4.1 Granular properties of different tuber starches

Starch Granule shape Granule Size (µm)

Cassava Round, spherical 5 -40

Arrowroot Round, polygonal 9 -40

Xanthosoma Round 10-50

Dioscorea alata Oval, shell shaped, Elliptical 6-100

Amorphophallus Round-polygonal 5-35

4.1.2 Physicochemical properties

The physicochemical properties and functional characteristics of tuber starches depend on

various factors like the granule size, amylose to amylopectin ratio and biological origin.

4.1.2.1 Swelling volume and solubility

The swelling power and solubility of starches from different tuber starches ranged from 19 to

37 mL/g and 10 to 34% respectively (Table 4.2). Highest swelling power was obtained for

arrowroot starch whereas the lowest for Xanthosoma starch. The solubility was maximum for

Dioscorea starch and minimum for Xanthosoma starch. The swelling power of starch has been

reported to depend on water holding capacity of starch molecules by hydrogen bonding (Jane

et al., 1999). Hydrogen bonds stabilizing the structure of the double helices in crystallites are

broken during gelatinization and are replaced with water, and swelling is regulated by the

crystallinity of the starch (Tester and Karakalas, 1996). The strong swelling power of starch

granules makes it easy for them to reach their maximum viscosity and they are likely to

breakdown easily because of their weak intermolecular forces, thus becoming more sensitive

to shear force as the temperature increases. Therefore the starch granules are easily broken

down by shear forces, which are increased by the swelling power (Lee et al., 1997).


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Table 4.2: Physicochemical properties of tuber starches

4.1.2.2 Amylose content.

The total amylose content of tuber starches are listed in Table 4.3. The highest amylose

content was observed for arrowroot starch and lowest for the Xanthosoma starch. The

variation in amylose contents among the starches from different and similar plant sources in

various studies may also be attributed to some extent to the different starch isolation

procedures and analytical methods used to determine amylose content (Kim et al., 1995).

Generally the amylose contents of the starches are determined by colorimetric methods

without prior defatting and/or by not taking into account the iodine complexing ability of the

long external chains of tuber starches (Banks and Greenwood, 1975; Morrison and Karkalas,

1990) thus leading either to an underestimation (failure to remove amylose complexed lipids)

or to an overestimation (failure to determine amylose content from a standard curve containing

mixtures of amylose and amylopectin in various ratios) (Hoover, 2001). It is believed that

higher amylose content may be more useful in imparting glossiness while higher amylopectin

improves cohesiveness of starch.

Starch source

Swelling

volume (mL/g)

Solubility

Total amylose

WBC In vitro

enzyme

digestibility

%

Cassava 24.8±0.36 24.7±0.45 24.73±0.4 72.3±0.29 32.7± 0.54

Arrowroot 37.0±0.8 34±0.20 31.76±0.11 81.2±0.17 38.1± 0.54

Xanthosoma 18.75±0.11 10.15±0.574 26.3±0.81 58.36±0.20 29.3 ± 0.56

Amorphophallus 21.87±0.88 15.23±0.03 25.1±0.14 45.4±0.19 20.2± 0.56

Dioscorea 27.3±0.32 29.37±0.37 25.7±0.11 92.8±0.84 24.5± 1.09


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4.1.2.3 Water binding capacity (WBC)

The water binding capacity values of tuber starches are shown in Table 4.3. The highest value

was obtained for Dioscorea starch (92.8 %) and lowest for Amorphophallus starch

(45.4%).The difference in WBC of starches separated from different tuber starches may be

attributed to the variation in granular structure and also loose association of amylose and

amylopectin molecules in the native starch granules (Soni et al., 1987).

4.1.2.4 In vitro enzyme digestibility.

The enzyme digestibility of tuber starches is presented in the Table 4.3. The digestibility was

higher for the arrowroot starch whereas Amorphophallus starch showed lower values. Factors

such as starch granule morphology, amylose to amylopectin ratio, molecular structure, degree

of branching, the physical stages of starch etc influences the digestibility of starches. The

enzyme digestibility of starch is one of the main criteria for its application in food and non-

food industries.

4.1.3 Retrogradation studies

4.1.3.1 Percentage light transmittance

Percent transmission at 650nm of starch paste is a measure of paste clarity (Table 4.3). The

light transmittance values of starch suspensions from all tuber starches decreased during

storage. This can be explained by greater swelling of the starch which allows more light to

pass through the granules instead of being reflected, because starch granule dissociates and

ability of the granules to reflect light diminishes (Craig et al., 1989). Turbidity development in

starch pastes during storage have been reported to be affected by factors such as granule

swelling, granule remnants, leached amylose and amylopectin, amylose and amylopectin chain

length (Jacobson et al.,1997). Paste clarity is related to the state of dispersion and the

retrogradation tendency of starch and hence will influence other technologically important

qualities of starch.


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Table 4.3: % transmittance values of different tuber starches.

Starch source Transmittance (%)

Number of days

Cassava 35.9 31.35 28.9 25.2 20.1

Arrowroot 25.2 21.2 18.6 13.2 10.1

Xanthosoma 8.2 7.3 5.6 3.7 2.03

Amorphophallus 22.0 19.0 18.2 7.03 4.36

Dioscorea 5.5 2.13 1.9 1.7 1.54

4.1.3.2 Least concentration of gellification (LCG)

The data of the least concentration of gellification of different tuber starches is presented in

Fig.4.1. Least concentration is one of the important factors describing the gelation capacity of

the starch. From fig 4.1, it is evident that the LCG value was higher for arrowroot (9%) starch

followed by cassava and Dioscorea starch (8%), where as it was low for Xanthosoma starch

(7%). The variation in the LCG values of various tuber starches may be due to the differences

in the granule size which are reflected in water absorption leading to gelatinization.

Fig 4.1: Least concentration of gellification of various tuber starches.

0 2 4 6 8 10

Cassava

Arrowroot

Xanthosoma

Amorphophallus

Dioscorea

LCG %


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4.1.4 Thermal properties

The thermal properties of different tuber starches are illustrated in the Table 4.4. The

difference in the range of gelatinization suggests that the degree of heterogeneity of

crystallites within granules of the studied starches is different. The endothermic peaks for

starches from different tuber starches appeared between 63.13 and 89.89oC. The results

indicated that heating caused the leaching out of cloudy solids. The highest onset (83.28° C),

peak (85.79° C) and endset (89.89° C) values were observed for Amorphophallus starch and

lowest values for cassava starch (63.13, 73.92, and 79.51 ° C respectively). The

gelatinization enthalpy values ranged between 13-16 J/g for the starches. ∆H value represents

the amount of thermal energy involved in the gelatinization process. At the molecular level,

this may be expected to involve the cleavage of existing hydrogen bonds between starch

molecules and the formation of the new bonds involving water to give a less ordered structure

with increased entropy (Paton 1987, Stevens and Elton 1971).

Table 4.4: Thermal properties of different tuber starches

Starch

Gelatinization Temperatures (°C)

H (J/g) To Tp Te

Cassava 63.13±0.04 73.92±0.11 79.51±0.12 13.69

Arrowroot 72.51±0.04 75.63±0.12 80.34±0.10 15.78

Xanthosoma 78.04±0.01 80.75±0.01 85.75±0.11 14.05

Dioscorea 77.51±0.50 80.06±0.05 83.7±0.073 17.98

Amorphophallus83.28±0.01 85.79±0.21 89.89±0.20 16.11

4.1.5 Pasting properties

The Rapid Visco-Analyser (RVA) has been extensively used for measuring starch paste

viscosity. The pasting profile of various tuber starches is presented in Fig 4.2.


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Fig.4.2: RVA pasting profile of various tuber starches.

Pasting properties of starch are affected by amylose and lipid contents and by branch chain

length distribution of amylopectin.

The highest peak viscosity was observed for cassava starch (Table 4.5), whereas the lowest

value for the arrowroot starch. The final viscosity value was higher for Amorphophallus starch

and lower for the arrowroot starch. The setback of the final viscosity and holding strength

indicated that the value obtained from the formation of rearrangement of excreted amylose

molecules from starch granules after swelling, and the values ranged from 293 to 1059 cP. The

pasting temperature of Dioscorea starch showed higher value (90°C) compared to other

starches. The increase in viscosity observed during heating of starch in water was mainly

attributed to the swollen granules and also to the amount of solubilized carbohydrates with

reference to amylose, further continuous heating and shearing at a high temperature (95oC)

promotes the weakening and susceptibility of the starch granules to shear damage. The

difference in branch chain length distribution of amylopectin, crystallinity, granular size

distribution and presence of other components play an important role in the observed

differences in pasting properties among starches.

0

500

1000

1500

2000

2500

3000

1 16 31 46 61 76 91 106

121

136

151

166

181

visc

osit

y (c

P)

Temperature (0)

cassava

Arrowroot

xantho

Dioscorea

amorpho


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Table 4.5: Pasting properties of tuber starches

4.1.6 Rheological properties.

Rheology concerns the flow and deformation of substances and in particular to their behavior

in the transient area between solids and fluids. One of the most important features of starch in

food systems is its ability to give structure by the formation of a gel. Dynamic viscoelastic

methods can provide an excellent tool for studying rheological changes without breaking the

structure. From dynamic rheological tests in the linear viscoelastic ranges, the storage

modulus, G’, and the loss modulus G”, and tanδ= (G”/G’), the loss factor can be obtained. G’

values are a measure of the deformation energy stored in the sample during the shear process,

representing the elastic behavior of a sample. In contrary G” value is a measure of the

deformation energy used up in the sample during the shear and lost to the sample afterwards

representing the viscous behavior of a sample.

Three types of dynamic tests can be conducted to obtain useful properties of gels, gelation and

melting.

1. Frequency sweep studies in which G” and G’ are determined as a function of frequency (ω)

at fixed temperatures.

2. Temperature sweep in which G’ and G” are determined as function of temperature at fixed

ω.

Starch Viscosity parameters (cP) Pasting

Temperature

(°C) PV BD FV SB

Cassava 2489.3 ±0.11 1487.0 ±0.4 1409.3 ±0.5 406.0±0.35 69.3±0.50

Arrowroot 1604.5±0.21 1072±0.13 825±0.23 293±0.65 79.9±0.11

Xanthosoma 1624±0.13 203±0.1 2552±0.10 644±0.21 87.9±0.01

Dioscorea 1744±0.03 247±0.08 2461±0.70 1059±0.07 90±0.28

Amorphophallus 2077±0.21 169±0.21 2852±0.26 644±0.20 87.±0.09


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3. Time sweep in which G’and G” are determined as a function of time at fixed ω and

temperatures (Rao 1999.)

4.1.6.1 Frequency sweep analysis.

The viscoelastic properties of various starches at varying frequency are depicted in Fig 4.2

Fig 4.3: Frequency dependency of tuber starch gel on storage modulus

From the figure 4.3, it is clear that as the frequency increased, the dynamic moduli also

showed significant variation. The storage modulus value was higher for the Dioscorea starch,

whereas it is lowest for cassava starch at frequency of 10 Hz (Table 4.7). In case of the phase

angle, cassava starch showed the highest value while Dioscorea starch the lowest.

Table 4.6: Dynamic moduli of tuber starches at a frequency of 10Hz

Starch type

Frequency 10 (Hz)

Storage Modulus

(Pa)

Loss Modulus

(Pa) Complex viscosity

(Pa.S)

Phase angle

(°)

Cassava 0.00525 105 1.67 90

Arrowroot 188 168 4.02 41.8

Xanthosoma 1330 498 22.6 20.5

Amorphophallus 670 448 12.8 33.7

Dioscorea 3240 856 53.4 14.8

0500

100015002000250030003500

stor

age

mod

ulus

frequency (Hz)

cas

aro

xantho

dio

amor


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The loss modulus values also showed same pattern, with the highest values for Dioscorea

starch (Fig 4.4). The highest G’ and G” and the lowest tanδ, values of Dioscorea starch

confirm the formation of the most rigid gel structure compared to the other starches. For the

other starches the magnitudes of G’ and G” increased with increase in frequency with the high

frequency dependency, suggesting a solid elastic-like behavior. Whatever the concentration

and pasting temperature, a solid-like behavior was exhibited with G’>G” and G’ almost

independent of frequency. It can also be noted that the loss modulus steadily increased as the

frequency increased. These overall tendencies indicate that the system is structured by the

packing of the swollen starch granules which is the determining factor governing the visco-

elastic behavior of microgel suspensions (Evans 1986; Tecante and Doublier, 1999).

Fig 4.4 : Frequency dependency of tuber starch gel on loss modulus

4.1.6.2 Temperature sweep analysis

Dynamic rheological properties of tuber starches showed significant variation during the

heating process. Table 4.8 summerizes the storage modulus and loss modulus values of

starches at four different temperatures. As the temperature increased, G’ and G” increased,

reached a maximum and then dropped during the heating cycle. The initial increase of G’

could be attributed to the degree of granular swelling to fill the entire available volume of the

system (Eliasson, 1986). Among the different starches, Xanthosoma starch had the maximum

G’ and G’’ values. The differences in G’, G” and tan δ during the heating cycle may be

0100200300400500600700800900

0.1

0.14

70.

215

0.31

6

0.46

4

0.68

1 1

1.47

2.15

3.16

4.64

6.81 10

Loss

mod

ulus

(G")

frequency (Hz)

cas

aro

xanth

dio

amor


99

attributed to the difference in the starch granular structure which in turn depends on their

biological origin (Svegmark and Hermansson 1993). The extent of breakdown in G’ is

measured as the degree of disintegration of starch granules (Singh and Singh. 2001).

Table 4.7 Dynamic moduli of tuber starches at different temperature

Starch Temperature (°C)

30 50 70 90

Storage modulus (Pa)

Cassava 199 116 347 129

Arrowroot 1000 111.0 52.1 27.0

Xanthosoma 14100 2510 794 550

Amorphophallus 1280 337 189 55

Dioscorea 3436 396 191 79

Loss modulus (Pa)

Cassava 225 188 308 203

Arrowroot 326 150 146 116

Xanthosoma 2190 675 344 207

Amorphophallus 401 164 134 109

Dioscorea 401 164 134 29

Phase angle (°)

Cassava 48.6 58.3 41.5 57.6

Arrowroot 18 53.5 70.3 20.9

Xanthosoma 8.84 15.1 24.2 14.8

Amorphophallus 17.5 28.9 35.3 22.8

Dioscorea 12.1 27.1 44.4 6.29

The phase angle value (tanδ) ( ratio of storage modulus to loss modulus ) was highest (57.6⁰)

for cassava starch at 900C and lower for Xanthosoma starch (14.8⁰) The tanδ has been reported

to decrease corresponding to a sol to gel transition i.e. a three dimensional gel network is

constructed from the amylose reinforced by strong interaction among the swollen starch


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particles (Vasanthan and Bhatty 1996).The greater breakdown may be attributed to the more

large sized starch granules which are fragile in nature while small sized granules of starch may

be responsible for the low G’ breakdown values.

4.2 Tabletting properties of tuber starches

4.2.1 Density, flow and compression studies of tuber starches

The variation of drying loss of various starches is given in Table 4.8.a. Among the starches,

Xanthosoma starch had the lowest value of 10.08% and arrowroot had about 11.87%. Cassava,

Amorphophallus and Xanthosoma starches had similar values. There is not much variation as

true density values among the different starches with the values ranging from 1.43 to 1.48

g/cm3.

Table 4.8 a : Powder properties of tuber starches

Starch type Loss on

drying (%)

Bulk density

(g/cm3)

Tapped

density

(g/cm3)

True

density

(g/cm3)

Cassava 10.32 0.623 0.873 1.4765

Arrowroot 11.87 0.695 0.873 1.4391

Xanthosoma 10.08 0.665 0.922 1.4746

Amorphophallus 10.27 0.653 0.780 1.4311

Dioscorea 11.75 0.742 0.952 1.4470

The bulk density of a powder partially describes its packing behavior (Esezobo 1986 and Isimi

2000). Higher bulk density is advantageous in tabletting because of a reduction in the fill

volume of the die. The bulk density values of Amorphophallus starch (0.653 g/cm3) and

Xanthosoma starch (0.665 g/cm3) were almost same. Cassava starch showed the lowest value

for bulk density (0.623 g/cm3) and Dioscorea starch exhibited the highest bulk density (0.742

g/cm3). However the tapped density values varied significantly from 0.780 to 0.952 g/cm3).

The lowest value was observed for Amorphophallus starch (0.780 g/cm3) and the highest value


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for Dioscorea (0.952 g/cm3). These differences may be due to difference in particle shape, size

and percentage of fines, which significantly affect the packing arrangement of particles.

Table 4.8 b: Powder properties of tuber starches

Starch Angle of

repose (°)

Hausner

ratio

Carr’s

Compressibity

(%)

Cassava 38.61 1.402 28.65

Arrowroot 38.61 1.257 20.45

Xanthosoma 35.03 1.387 27.89

Amorphophallus 45.46 1.193 16.20

Dioscorea 45.46 1.283 22.08

Lower value of angle of Repose (less than 25°) indicates good flow property for the powders.

The angle of Repose of a particle is affected by the particle size distribution and it usually

increases with decrease in particle sizes. From table 4.9.b, it was observed that the angle of

repose values for different starches ranged from 35° to 45.46°. The higher values for all the

starches indicated the poor flowing nature for the different starch samples.

The Hausner ratios provide an indication of the degree of densification which could result

from the vibration of the feed hopper during tabletting with higher values predicting

significant densification of the powders. The ranking for the Hausner ratio of the starches was

generally cassava (1.40) > Xanthosoma (1.39) > Dioscorea (1.28) > arrow root (1.26)

Amorphophallus (1.19). From the value of Hausner ratio (value around 1.2), it was found that

Amorphophallus , arrow root and Dioscorea starches were found to have slightly better flow

property when compared with the other starch samples. The percentage compressibility of a

powder is a direct measure of the potential powder arch or bridge strength. The Carr’s

compressibility index calculated from the density data showed for cassava (28.65),

Xanthosoma (27.89) Dioscorea (22.08) and arrowroot (20.45) . In spite of the poor


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flowability of all the starches as suggested by the high angles of Repose values, the Carr’s

compressibility index indicates a better flow potential for starches obtained from arrowroot,

Dioscorea and Amorphophallus starches. This incongruity between the angle of Repose and

the Carr’s index values may be due to the fact Carr’s index is a one point determination and

does not reflect the ease or speed with which cohesion takes place. Typical Heckel plots were

constructed from the compression data of the starches. The values of slope K (the reciprocal

of yield value), and the intercept A (related to the movement of the particles during the initial

stages of compression) obtained from the Heckel plots are shown in Table 4.9. The value for

yield pressure (Py), relative apparent density (Do), the total densification due to the filling of

the die and particle rearrangement (DA), and the density contribution from individual particle

movement and rearrangement (DB) values are also included in the table.

Table 4.9: Parameters obtained from the Heckle plots of different tuber starches

Starch source Slope Intercept Do DA DB Py

Cassava 0.0152 0.6675 0.4219 0.4870 0.065 65.79

Arrow root 0.0061 0.7299 0.4829 0.5180 0.035 163.93

Xanthosoma 0.0088 0.6939 0.4512 0.5004 0.049 113.63

Dioscorea 0.0066 0.7735 0.5130 0.5386 0.0256 151.51

Amorphophallus 0.0111 0.6003 0.4569 0.4513 0.0056 90.09

The yield pressure values for Amorphophallus and cassava starch were lower than the other

native starches. Cassava starch was found to have the lowest yield pressure and hence the

softest material, more plastic and easily compressible even at low compression forces. The DA

values for the starches were greater than the DB values, indicating that more densification is

occurring by deformation, rather than by particle re-arrangement and movement. The high DA

value for Dioscorea may be due to its large particle size compared to other starches.

4.2.2 Tablet properties of the starch compact

The tablet prepared using different tuber starches are showed in Fig.4.5, (Plate-1). The

hardness values of tablets prepared using different tuber starches at four different


103

concentrations (2.5, 5, 7.5 and 10%) are presented in Table 4.10. Among various starches

used as binder, the highest value was obtained for arrowroot starch at the four different

concentrations and the lowest values for Dioscorea starch. The mechanical properties of the

tablet formulations were assessed by the crushing strength and friability of the tablets. While

crushing strength indicates the strength of the tablet, friability values provide a measure of

tablet weakness.

The hardness values of tablets prepared using the two concentrations (2.5 and 5%) were

generally lower than 5 kg indicating that the tablets were weak. The reduction in the crushing

force and subsequently tensile strength leads to reduction in interparticle bonding inside the

tablets. The decrease in tensile strength caused by a reduction of inter particle bonding, is

related to a larger relaxation of the tablets. These also reveal that the adhesive forces between

the granules starches are higher than its cohesive force. Generally, the tensile strength

increased with increase in the applied pressure for all the starches. Tablets compressed at

higher compaction pressure exhibited higher tensile strength. This is due to the fact that the

mean contact area between the particles increases in proportion to the compaction pressure

(Mohammed et al., 2005).


104

Fig 4.5 Tables prepared using different tuber starch mucilage as binder

Arrowroot Cassava

Dioscorea Amorphophallus


105

Table 4.10: Hardness values of paracetamol tablet prepared using starch mucilage as binder.

Source of starch Mean Force of fracture (kg)

Starch concentration in the paste , %

2.5 5 7.5 10

cassava 1.33 2.5 2.5 3.5

arrowroot 1.5 2.67 3.33 6.17

Xanthosoma 1 2.17 1.67 5.83

Dioscorea 0.83 1 2 3.33

Amorphophallus 0.83 3.5 3.17 5.33

Blank ( paracetamol with no binders) 0.5

The friability data of the tablets prepared are presented in Table 4.12. The friability of the

starches at 2.5 and 5% binder concentration increases resulting in capping. . This shows that

the compacts were fragile. The friability was reduced with increasing concentration of the

binders. There was increase in crushing strength with corresponding decrease in friability

values with binder concentration for all formulations. It has been established that the presence

of high concentration of plasto-elastic binding agent leads to an increase in plastic deformation

of the formulation and consequently to the formation of more solid bonds with increase in

tablet strength and resistance to fracture and abrasion (Iwuagwu et al, 1986).


106

Table 4.11: Friability of paracetamol tablets prepared using native tuber starches as

binder

Source of starch Weight loss, %


2.5 5 7.5 10

Cassava Failed the test.

(capping) 0.643 0.915 Failed Failed the

test. (capping)

Arrowroot “ 1.74 1.55 “

Xanthosoma “ 0.675 0.791 “

Dioscorea “ 1.57 3.35 “

Amorphophallus “ 2.254 1.113 “

Blank ( paracetamol with no binders) Failed the test. Tablets

exhibited capping tendency

Also, the disintegration time of tablets decreased with increasing the concentration of the

starch binders (Table 4.12). This observation was collaborated by the gelatinization (Table

4.5) and swelling power (Table 4.3) of starch chains and restricted swelling of the starch

granules. An increase was observed in disintegration time with increase in binder

concentration for all formulations, there were significant differences in disintegration time

between the formulations (Bangudu, 1993). All tablets failed the British Pharmacopoeia

specifications for disintegration of uncoated tablets within 15 minutes.


107

Table 4.12: Comparison of disintegration time of paracetamol tablets using tuber starches.

Source of starch Mean Disintegration time, s


2.5 5 7.5 10

cassava 15.17 19.67 71.17 229.17

arrowroot 18.17 23.83 37.83 83.17

Xanthosoma 25.17 55.17 86.67 190.33

Dioscorea 14.33 23.67 33.50 48.83

Amorphophallus 1538.5 97.83 125.67 11.83

Blank ( paracetamol with no binders) Blank ( paracetamol with no

binders)

Table-4.14 shows dissolution time, here observation was done to evaluate the availability of

paracetamol drug after 30 minutes in the solution. The values increased with binder

concentration for all tablets prepared using the starch mucilage at different concentrations.

Table 4.13: Dissolution properties of paracetamol tablets.

Source of starch Mean Disintegration time, s


2.5 5 7.5 10

cassava 473.17 469.13 444.34 416.32

arrowroot 496.39 487.51 472.31 449.34

Xanthosoma 475.33 464.28 438.25 420.99

Dioscorea 463.04 451.02 430.70 406.56

Amorphophallus 468.27 454.69 432.11 419.76

Blank ( paracetamol with no binders) 493.81


108

For the tablets to pass the dissolution test, 80% of the drug should be released within the time

interval. In our study all the tablets from the different batches released 80% or more amount of

the drug. When no binding agent was used the amount of drug released was 493.81mg. As the

strength of the starch paste as binding agent increased, the drug release rate was found to

decrease (Rubeinstein and Wells 1997, Iwuagwu et al., 1986). In the case of arrowroot starch,

drug released was 475.33 mg for 2.5% w/w starch paste and 420.90 mg for 10% w/w starch

paste (Table 4.14).

4.3 Use of native tuber starches in edible film preparation.

The potential of starch as a material for edible films and for biomaterials has been widely

recognized (Krochta and Mulder-Johnston, 1997). It is an appropriate matrix-forming material

and it provides a good barrier to oxygen and carbon dioxide transmission, but a poor barrier to

water vapor (Arvanitoyannis et al., 1998, Pagella et al., 2002). Film characteristics are

dependent on the cohesion of the polymeric matrix, which in turn is dependent on the structure

of the polymer chains, the film obtainment process and the presence of plasticizer agents. The

most used plasticizers for starch-based films are sorbitol and glycerol (Gontard and Guilbert,

1992, McHugh and Krochta, 1994). Edible films were prepared using starch from various

tuber starches and their physical, mechanical properties were evaluated

4.3.1 Moisture content and film solubility

In general, the increase of moisture uptake will decrease the tensile strength of the film

prepared and thereby the quality and other properties of the capsule prepared from the same

film. The moisture content of the films prepared using various tuber starches are presented in

the Table.4.1. There was no significant variation in the moisture content values for the films

from all the starches. A slightly less moisture content was observed for the films prepared

using the Xanthosoma starch (12.9%). The plasticizer, i.e., the glycerol added to the

filmogenic solution is more hydrophilic in nature, and same amount of glycerol is added with

all the different starches for the film production, after the drying process the values showed the

similar trends


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Table 4.14: Physicochemical properties o films prepared from various tuber starches

Starch type Moisture content

(%)

Thickness of films.

(mm)

Water solubility

(%)

Cassava 13.1±0.01 0.11±0.01 34.33±0.11

Arrowroot 13.7±0.04 0.10±0.02 26.2±0.08

Xanthosoma 12.9±0.03 0.13±0.03 31.2±0.21

Dioscorea 13.0±0.05 0.14±0.02 31.5±0.05

Amorphophallus 13.3±0.02 0.10±0.01 30.2±0.07

. The solubility values of films prepared using the native tuber starches also showed the same

pattern. Film solubility increased as the temperature become higher. The plasticizer addition

also increased the solubility due to the hydrophilicity character of glycerol. Solubility of

edible film indicates their integrity in an aqueous environment, and higher solubility would

indicate lower water resistance (Gnanasambandam et al., 1997, Handa et al., 1999). The

method of gelatinization process used for the production of the filmogenic solution had a

remarkable effect on water solubility of the films. Cassava starch showed maximum solubility

of 34.3% whereas the arrowroot starch showed the minimum values of 26.2%. The

Xanthosoma, Dioscorea and Amorphophallus starches showed almost similar values of 30.2,

31.5 and 30.2 respectively.

4.3.2 Thickness and Color of films

The thickness of the film prepared using the native tuber starches is presented in Table 4.16

Thickness of the film changes depending on starch source and gelatinization method. The film

prepared has an average thickness of 0.11. Also, films with plasticizers were thinner than un

plasticized films. In the case of films prepared with normal Xanthosoma and Dioscorea starch,

the thickness values were 0.13 and 0.14 respectively, which was higher than those prepared

from cassava, arrowroot and Amorphophallus starch. The reason for the slight difference in


110

the film thickness may be due to the differences in the granule size of the starch (Sa´nchez-

Hernandez et al., 2002).

The colour L, a and b values of films prepared from various tuber starches are presented in

Table 4.3.2. The L values, which represent brightness of film samples, were 34.5 to 83.41.25,

‘a’ values were 0.11 to 0.76, and ‘b’ values were 1.73–4.22. Among different starch film

samples, Dioscorea film had the highest color difference (DE) value (15.3), and cassava and

Xanthosoma starch film had the lowest value (2.34 and 2.11 ), indicating that cassava and

Xanthosoma starch formed the most transparent films.

Table 4.15: Color values of tuber starch based films

Starch source L a b Total color

difference

Cassava 70.12 -0.11 2.33 2.34

Arrowroot 69.11 -0.21 1.73 6.11

Xanthosoma 83.41 -0.43 4.22 2.11

Dioscorea 34.5 -0.76 2.43 15.3

Amorphophallus 59.0 -0.32 1.11 3.21

The DE value of Dioscorea starch films was significantly high, due to the slight coloration of

starch formed due to the presence of mucilage contaminated during the extraction process of

the starch. The Amorphophallus and Arrowroot starches showed a DE value of 3.21 and 6.11

respectively.

4.3.3 Mechanical properties of films

The mechanical property studied is the maximum elongation obtained by the film stripes. The

tensile strength and elongation at break of starch films were affected by heating temperature


111

and heating time. The optimum heating temperature and heating time of film solutions

provided the films with higher tensile strength but lower both elongation at break and water

vapor permeability. The maximum elongation was obtained by the cassava starch followed by

Dioscorea starch (35.2 and 33.6 respectively). The minimum elongation was obtained for

arrowroot starch followed by Amorphophallus starch.

Fig. 4.6: Elongation capacity of tuber starch films

The tensile behavior of films with of glycerol could be associated to those of ductile polymers

since tensile strength decreased and elongation at break increased significantly compared with

unplasticized films. Similar results were obtained by Bonacucina et al., (2006). Plasticizers

interfere with polymeric chain association facilitating their slipping and thus enhancing film

flexibility. Glycerol decreases the rigidity of the network, producing a less ordered film

structure and increased the ability of polymer chains movement (Sothornvit and Krochta,

2005).

Conclusion

From the above preliminary evaluation tests, it was found that starch from all the tuber

starches showed significant variations in their physicochemical, thermal and rheological

properties. The rheological and pasting profile also reveals the low performance of these

starches with unstable viscosity profile. The flow and other micromeritic properties showed

that the flow properties are not good enough to meet the industrial applications. The above

0

10

20

30

40


112

said properties were more evident when tablets were prepared and evaluated. Mucilage

concentration of 7.5 and 10% w/w could be used as binding agents for preparing tablets and

cassava starch was found to have somewhat better binding properties when compared with the

other starches. Even though the native starch possesses average binding properties, the

disintegration properties are not favorable. As per the literature, all these shortcomings

necessitate the modification of the starches either by physical/chemical or enzymatic methods.

All these modification processes and the characterization, and evaluation of the excipient

functionality of these modified starches are presented in the following chapters.

Films were developed using starches from different tuber starches, and their physical

and mechanical properties evaluated. Native starch is a brittle polymer and is therefore

plasticized. Glycerol is compatible with amylose and interferes with the amylose packing. The

tuber starches showed relatively below average performance. Since the samples does not give

desirable thickness that will be suitable for the capsules. The moisture content was also very

high so that it will become easily hydrated. The films prepared using the Dioscorea starch

showed a slight coloration of the film prepared which is not suited for the film thereby for the

capsule production. The analysis of mechanical properties of the starch film revealed that the

films are brittle and easily be brockened. Attempts were made to overcome this shortcoming

with the use of modified starch and are summarized in the following chapters.

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