The Effect of Variety and Drying On the Engineering
Properties of Fermented Ground Cassava
Chukwuneke J.L1*, Achebe C.H1, Okolie P.C1 and Okafor E.A2
1
Department of Mechanical Engineering, Nnamdi Azikiwe University, P.M.B 5025 Awka, Nigeria
2
School of Engineering, Energy Centre, Robert Gordon University, Aberdeen. AB10 1FR
*Corresponding Author E-mail: jl.chukwuneke@unizik.edu.ng
Abstract: - Many food processing industries use cassava as their basic raw material. The existence of
improved varieties of cassava demands that the effect of variety on the engineering properties of
fermented ground cassava is studied in order to generate data for design and optimum performance of
various driers used in cassava processing. This paper attempts to provide data on the engineering
properties such as moisture content, specific heat capacity, thermal conductivity, thermal diffusivity, bulk
density and mass transfer coefficient of some cultivars as well as determine the effect of variety on the
drying and engineering properties of fermented ground cassava using two high yield improved cultivars
(Tms 30572 and NR 8082) and one native cultivar (Akpu Bonny). General models were also obtained,
which could be used to predict the specific heat and thermal conductivity at different moisture content of
the cultivars. The specific heat capacity obtained ranged from 1.53kJ/kgK to 3.49kJ/kgK while the
thermal conductivity ranged from 0.24W/moC to 0.51W/moC for dried fermented ground cassava of these
cultivars. The highest moisture content of 48.66% was obtained after fermentation with the NR 8082
variety. At same moisture content, the specific heat capacity and thermal conductivity were found to be
different for cultivars with different proximate compositions but similar for cultivars with close proximate
compositions. The drying rate, thermal diffusivity and mass transfer coefficient of each cultivar varied
with proximate composition, hygroscopy, product surface area and change in density after drying.
Therefore, the same drying conditions cannot be used for drying the different cultivars except if they have
close engineering properties.
Keywords: Fermented ground cassava, Specific heat capacity, Thermal conductivity, Thermal diffusivity,
Bulk density, Effect of variety, Cultivars, Drying rate, Moisture Content, proximate compositions
.
1. INTRODUCTION
1.1. Background of the Study
The design, simulation, optimization, operation and control of food processing operations require basic
engineering properties of foods. Food technologists require data on engineering properties for various
purposes such as process design, quality assessment and evaluation.
Cassava is widely grown in Africa and some other parts of the world. It plays a central role in the diets of
most Nigerians. This is why [1] attributed garri (a staple food from drying of fermented cassava flour) as
the commonest food amongst the teeming poor West African people. Fermented cassava flour is,
therefore, one of the most important cassava products and the methods of processing depend on local
customs. However, the industrial utilization of cassava roots into various food and non-food uses is
expanding by the day.
Consequently, food industries need to understand the various engineering or physical properties of ground
cassava in other to use it as a raw material. These properties include;
1. Specific heat capacity which is the amount of heat (kJ) needed to raise the temperature of a unit mass
(kg) by a unit change in temperature (k).
2. The thermal conductivity which is the amount of energy, in form of heat, "conducted through a body
of unit area and unit thickness in unit time when the difference in temperature between the faces
causing heat flow is unit temperature difference [2].
3. The thermal diffusivity determines how fast heat propagates or diffuses through a material.
Knowledge of these engineering properties is necessary not only because they are important on their own
but they are the commonest indicators of other properties and qualities [3].
These engineering properties are known to be affected by density, moisture content and temperature, and
will help the engineer to generate data for the design and operation of driers for cassava processing.
Drying is an inevitable unit operation in the food processing industries since dehydrated foods normally
last longer due to the absence of microbial activities.
1.2. Aims and Objectives
A review of pertinent literature revealed that such data on engineering properties of foods were lacking
[3]; Hence the objectives of this study are to determine; at various stages of drying fermented ground
cassava into garri:
1. The moisture content. 2. The specific heat capacity. 3. The thermal conductivity. 4. The thermal
diffusivity. 5. The bulk density. 6. The mass transfer coefficient. 7. To determine the effect of variety on
the drying and engineering properties of fermented ground cassava.
1.3. Significance of Study
The significance of this work cannot be overlooked just as cassava itself. Knowledge of the engineering
properties is necessary because they are the commonest indicators of other food qualities. Engineering
properties are important data needed for quality assessment and evaluation, design, operation and control
of driers since drying is an inevitable stage in the production of both food and agricultural products.
Also, knowledge of these properties and how they are affected by drying will enhance better
understanding of the heat and mass transfer phenomena for drying of agricultural products.
Moreover, it provides an opportunity to apply the principles of chemical and Mechanical engineering
processes which will help as a guide to any interested industrialist for future applications taking into
account the engineering properties of ground cassava.
1.4. Scope / Limitations
The study attempts to determine the various engineering properties such as moisture content, specific
heat, thermal conductivity and thermal diffusivity of fermented ground cassava only. The study is also
restricted to three varieties of cassava; two improved ones (Tms 30572 and NR 8082) and a native
variety.
2. METHODOLOGY
2.1. Sample Preparation
This involved the preparation of cassava cultivars, one native cultivar (Akpu Bonny) and two high yield
improved cultivars (Tms 30572 and NR 8082) all obtained from Root-crops Development Centre,
Agricultural Research Institute, Igbariam, Anambra State, Nigeia. The cultivars were harvested in the
month of April, peeled, washed, grated and packed in three different sacks for pressing. They were then
allowed to ferment for 72 hours. The mashed cassava was sieved with a mesh of 2.4mm. A hot circulating
air oven was used to determine the drying rates.
2.2. Determination of Engineering Properties
I. Moisture Content
The moisture content was determined before and after fermentation. Three different crucibles were
washed and dried in an air oven for about 40mins; 5.0g of each sample were carefully weighed into each
of the identified crucibles, it is then dried in a hot circulating air oven at 105°C for 24hours. Further
drying was continued until the final weight of dry sample became stable. The initial moisture content of
the samples was calculated as the total moisture loss divided by total sample weight and presented in
W  W2
percent wet basis.
(1)
X  1
 100
w
W1
Where: Xw = moisture content on wet basis, W1 = Initial weight of sample, W2 = Final weight of sample
after drying.
The moisture content on dry basis was calculated using;
Xd 
W1  W2 100

W1
1
(2)
The moisture content on dry basis at any time‘t’ was also calculated using the equation;
Xt (dry basis) =
𝑊1 −𝑊2
𝑊2
× 100
(3)
Where; W2 is the weight of dried sample and W1 is the weight of sample at any time t.
II. Proximate Compositions
The Association of Analytical chemists method was used to determine the carbohydrate, moisture,
protein, fat, fibre and ash (dry ashing method in a furnace) content of the samples [4]. The proximate
composition was determined after drying in an air oven at 70oC for 24hours.
III. Ash Content Determination
A silica dish was heated at 600oC, cooled and weighed; 2.0g of the sample was carefully transferred into
the dish. The dish was then placed into a muffle furnace and ashed at 600 oC for 3hours. It was then
allowed to cool in desiccators before taking the final weight. This procedure was carried out for all the
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑎𝑠ℎ
samples and the ash content was calculated thus;
% Ash = 𝐹𝑟𝑒𝑠ℎ 𝑊𝑒𝑖𝑔ℎ𝑡 × 100
(4)
IV. Fat Content Determination
Soxhlet extractor was used. An extraction flask was thoroughly washed and dried in hot oven for 30mins.
It was placed in desiccators to cool. 2.0g· of sample was accurately weighed and transferred into a rolled
ashless filter paper and placed inside the extractor thimble. The thimble was placed into soxhlet extractor.
Some reasonable quantities of petroleum ether, about three-quarter of the volume of the flask were placed
inside the extraction flask. The heater was switched on and the set up was heated for about 3hours at low
temperature so that the temperature of the petroleum ether is not exceeded. Finally, the extracted oil was
dried at 1000C and weighed. The difference in the weight of empty flask and the flask with oil gives the
oil content of the sample.
The percentage fat is thus calculated as;
% fat =
𝐶−𝐴
𝐵
× 100
(5)
Where; A = weight of empty flask, B = weight of sample, C = weight of flask + oil after drying.
V. Moisture Content Determination
The sample for proximate analysis was heated at 600C in a hot air circulating oven for 24hours. The
moisture content was determined using 2.0g of sample on dry weight basis.
VI. Fibre Content Determination
2.0g of the sample was collected (W1) 150ml of preheated H2S04 was added and heated to boiling for
30mins. It was then filtered and the residue washed three times with hot water. 150ml preheated KOH
was added and heated to boiling for another 30mins, filtered, washed three time with hot water and three
times with acetone before drying at 1300C for 1 hour. The sample was then weighed (W2), ashed at 500oC
and the ash also weighed (W3). The fibre content is thus calculated;
% Fibre  W2  W3  100 (6)
W1
Where; W1 = weight of sample, W2 = weight after pretreatment & drying, W3 = weight after ashing.
VII. Protein Content Determination
2.0g of the dried sample was weighed into 30ml kjeldahl flask and 15m1 cone H2S04 and 1.0g of the
catalyst mixture (kjeldahl catalyst mixture, a mixture of 20g potassium sulphate, 1.0gram copper sulphate
and a pinch of selenium powder) were added. The mixture was heated until a greenish clear solution
appeared (about 30mins), it was heated for more 30mins before allowing to cool. 10ml of distilled water
was added to avoid caking. The digested solution was then transferred to the kjeldahl distillation
apparatus. A 50ml receiver flask containing 5ml boric acid indicator solution was placed under the
condenser of the distillation apparatus so that the tip is about 2cm inside the solution. The digested
sample in the apparatus had10ml of 40% NaOH solution added through the funnel stop-cork.
The distillation commenced immediately the steam by-pass was closed and the inlet stop-cork on the
steam jet arm of the distillation apparatus opened. When distillation reached about 35ml mark on the
receiver flask, the process was stopped by closing the inlet stop-cork first, then opening steam by-pass.
The resulting solution was then titrated to the first pink colour with 0.1M HCl.
Calculation follows thus;
Vol.HCl  14.01  0.1  6.25  50  100
1000  weight of sample  100
(7)
Where; 14.01 = Nitrogen standard, 50 = dilution factor, 6.25 = crude protein factor, 0.1 = concentration of
HCI, 1000 - ppm, 100ml distilled.
VIII. Carbohydrate Content Determination
The carbohydrate content was determined by difference (i.e. by subtracting other constituents in each
sample from 100%).
IX. Determination of Specific Heat Capacity
Specific heat capacities were determined using the various proximate compositions of the samples. These
were obtained by applying [5].
Cp = 4.180xw + 1.711xp + 1.929xf + 1.547xc + 0.908xa
(8)
Where; Cp is the specific heat capacity in kJ/kgK and x are respective mass fractions of water, protein,
fat, carbohydrate and ash, present in each cultivar.
X. Determination of Thermal Conductivity
The thermal conductivities of the samples were obtained by substituting the various proximate
composition of the sample in the expression developed by [6].
K = 0.24Xc + 0.155Xp + 0.16Xf + 0.135Xa + 0.54Xw
(9)
0
Where; K is the thermal conductivity W/m C of sample.
XI. Determination of Thermal Diffusivity
Thermal diffusivity (𝛼) determines how fast heat propagates or diffuses through a material. This was
determined from the thermal conductivity K, density ρ, and specific heat Capacity Cp using the
dimensionally correct equation developed by [7].
𝛼 = k/ ρCp (m2/s)
(10)
XII. Determination of Bulk Density
The bulk density was determined using a centrifuge tube, at intervals of drying until the density becomes
constant. The weight of the centrifuge tube and its content (sample) was noted, it was later tapped until
there was no longer change in volume, and the centrifuge tube and its content were reweighed.
The weight was later obtained. The bulk density was calculated using the expression.
Weight of sample (kg/m3)
Volume of sample
(11)
XIII. Determination of Mass Transfer Coefficient
This is a function of drying rate. The drying rate per unit area is proportional to the bulk density
difference or concentration difference [8].
dm
  f   p 
Adt
(12)
dm
 Kc  f   p 
Adt
Kc 
1
dm

 f   p Adt
(13)
Where;  f and  p are the bulk density of feed and products respectively, dm = change in mass after each
interval of drying, dt = time difference, A = surface area of the particles given as
2
A  N pM p  Dp
(14)
Where; Np = Number of particles per unit mass, Mp = Mass of products, D p = Mean particle diameter =
Dpd, d = Mass fraction retained on the sieve. A small quantity of about 0.5g of the dried product was
counted as accurate as possible to obtain the number of particles per unit mass. The samples were then
sieved in sieves of 0.8mm, 1.6mm and 2.0mm respectively to obtain the mean particle size diameter.
3. PRESENTATION OF DATA
3.1. Moisture content at Harvest: Weight of sample used =5.0g in each case
Cultivar
NR8082
Tms30575
Native
Table 1: Weight of sample at harvest
Weight of crucible (g) Weight of crucible + wet sample (g)
29.04
34.04
29.17
34.17
28.54
33.54
Crucible + sample (dried)(g)
30.64
31.045
30.368
Table 2: Weight of sample at intervals of drying and Weight of dried sample after 48hours
2.1. Weight of sample at intervals of drying
Cultivar
Weight of Weight of Weight Weight
Weight Weight Weight Weight
empty
petridish + after 10 after 20 after 30 after 40 after 50 after 60
petridish(g) sample (g) mins (g) mins (g) mins (g) mins (g) mins (g) mins (g)
NR8082
12.137
26.137
25.367
24.347
23.949
23.782
23.711
23.704
Tms30575 17.577
22.577
22.464
Native
19.845
24.845
23.648
2.2. Weight of dried sample after 48hours
20.737
22.905
20.395
22.633
20.321
22.590
20.281
22.586
Cultiver
NR 8082
Tms 30572
Native
Weight (g)
1.5385
2.3578
2.9597
20.261
22.586
Weight
after 70
mins (g)
23.704
20.261
-
3.2. Proximate Analysis: Weight of sample used = 2.0g in each case
Table 3: Table for Fat, Protein, Ash and Moisture content calculations
3.1. Table for Fat content calculations
Cultivar
NR 8082
Weight of empty flask (g)
32.664
Empty flask + extracted oil (g)
32.664
Weight of oil
Nil
Tms 30572
Native
33.930
33.724
33.930
33.724
Nil
Nil
3.2. Table for Protein content calculations
Cultivar
Initial burette reading (cm3)
Final burette reading (cm3)
Volume of HCl used (cm3)
NR 8082
20.60
20.70
0.1
Tms 30572
20.40
20.60
0.20
Native
20.70
20.90
0.20
3.3. Table for Ash content calculations
Cultivar
Weight of empty Silica dish + sample after Weight of sample Sample + silica Weight
silica dish (g)
treatment (g)
after pretreatment (g) dish after ash(g) of ash (g)
NR8082
26.210
26.284
Tms30572 29.062
29.121
Native
28.380
28.483
3.4. Table for Moisture content calculations
Cultivar
Weight of crucible + sample (g)
0.074
0.059
0.103
26.22
29.07
28.39
0.01
0.008
0.01
NR 8082
22.492
Weight of crucible + sample after Weight of moisture (g)
drying (g)
22.456
0.036
Tms 30572
Native
16.749
22.098
16.699
22.059
NR 8082
0.043
0.039
Table 4: Table for calculation of bulk density during drying
Tms 30572
Native Cultivar
Time
(min)
Mass of Volume of Time
Sample
Centrifuge (min)
(g)
Tube (cm3)
Mass of Volume of Time
Sample
Centrifuge (min)
(g)
Tube (cm3)
Mass of Volume of
Sample
Centrifuge
(g)
Tube (cm3)
10
3.930
0.006
10
4.887
0.009
10
3.803
0.0060
20
3.210
0.006
20
3.160
0.007
20
3.060
0.0065
30
2.812
0.006
30
2.818
0.0075
30
2.788
0.009
40
2.645
0.007
40
2.744
0.012
40
2.745
0.0095
50
2.574
0.012
50
2.704
0.017
50
2.741
0.017
60
2.567
0.016
60
2.684
0.045
60
2.738
0.025
3.3
Tabulated Results and Simple Calculations: (Mass of sample used = 5.0g in each case)
Cultivars
Table 5: Moisture content of cultivars before fermentation
Mass of dried crucible Mass of crucible + sample Weight
of %
moisture
+ wet sample (g)
after drying for 24hours
moisture (g)
content (wet basis)
NR 8082
Tms 30572
34.040
34.170
30.640
31.045
3.40
3.125
68
62.5
Native
33.640
30.368
3.172
63.44
Table 6: Moisture content of cultivars after dewatering and fermentation for 72 hours (wet basis)
Cultivar
Mass of petridish Mass of petridish + sample after Weight of moisture %
moisture
+ wet sample (g) drying to stable weight (g)
(g) expelled
content (wet basis)
NR8082
26.137
23.704
2.433
48
Tms30572 22.577
20.261
2.316
46.32
Native
Cultivar
NR 8082
Tms 30572
Native
24.845
22.586
2.559
45.18
Table 7: Moisture content at intervals of drying (wet basis)
10mins
20mins
30mins
40mins
50mins
53.09
25.05
9.54
3.04
0.27
82.08
17.73
4.99
2.24
0.75
33.74
11.64
1.71
0.15
-
60mins
-
Table 8: Hygroscopic properties of cultivars
Cultivar
MC (g)
MD (g)
2.892
% water %
reabsorbed Ash
12.66
1.05
%
Fat
Nil
%
%
Protein Fibre
0.22
3.20
%
%
Moisture Carbohydrate
1.80
93.73
NR8082
2.567
Tms30572 2.684
3.039
13.23
1.50
Nil
0.44
2.55
2.15
93.36
Native
3.081
12.40
0.15
Nil
0.44
4.60
1.95
92.86
2.741
MC = Mass of cassava after drying to final moisture (g), MD = Mass of dried sample 48 hours later after
drying (g)
Table 9: Effect of Variety on the surface Area and Mass Transfer Coefficient of the Cultivars
Cultivar
Surface Area (m2) Density
before Density
after Mass
transfer
drying (kg/m3)
drying (kg/m3)
Coefficient
Kc
m/s(x10-6)
NR 8082
Tms 30572
0.897
0.415
655
543
160.44
59.64
1.632 x 10-6
3.25 x 10-6
Native
0.850
551.2
171.3
2.332 x 10-6
Table 10: Effect of variety on the drying rate of the cultivars
Total drying time Drying rate after Drying rate after Drying rate of stable
(mins)
20 mins (kg/hr)
40 mins (kg/hr)
weight (kg/hr)
NR 8082
50
5.37
3.53
2.61
Tms 30572
60
5.52
3.38
2.32
Native
50
5.82
3.38
3.07
% Moisture Content (dry basis)
Cultivar
90
80
70
60
50
40
30
20
10
0
NR 8082
Tms 30572
Native
0
10
20
30
40
50
60
Time (mins)
Specific Heat capacity (kJ/kgK)
Fig. 1: Drying curve for the cultivars
4
3.5
3
2.5
2
1.5
1
0.5
0
NR 8082
Tms 30572
Native
0
10
20
30
40
50
% Moisture Content (wet basis)
Fig. 2: Specific Heat of Cultivars at Various Moisture Contents
60
Thermal Conductivity (W/m0C)
0.6
NR 8082
Tms 30572
Native
0.5
0.4
0.3
0.2
0.1
0
0
10
20
30
40
% Moisture Content (wet basis)
50
60
Fig. 3: Thermal Conductivity of Cultivars at Various Moisture Contents
Bulk density (kg/m2)
700
NR 8082
Tms 30572
Native
600
500
400
300
200
100
0
0
20
40
60
% Moisture Content (dry basis)
80
100
Fig. 4: Bulk density variations with Moisture Contents
Thermal diffusivity 𝛼(m2/s)
1.00E-03
NR 8082
Tms 30572
Native
8.00E-04
6.00E-04
4.00E-04
2.00E-04
0.00E+00
0
20
40
60
% Moisture Content (dry basis)
80
Fig. 5: Thermal Diffusivity Variations with Moisture Contents
100
4. DISCUSSION
4.1. Moisture Content
The moisture contents obtained before and after fermentation by drying the cultivars with a circulating air
oven is shown in Tables 6 and 7 respectively. The initial moisture content of cassava at harvest was not
stable and may be dependent on season. The cultivars used here were harvested in the month of April. NR
8082 had the highest moisture content of 68% at harvest, but Native cassava had the highest moisture
expelled after drying. This suggests that the native cassava was more porous than the improved cassava in
agreement with the studies in [9].
4.2. Drying Rate
The moisture content (dry basis) decreases as drying time increases for all the cultivars during the drying
process as shown in fig.1. The total drying time differed at approximately the same moisture content for
all the cultivars, Tms 30572 with almost the same moisture content (wet basis) with the Native cassava
after fermentation, had the longest total drying time of 60mins while native cassava had the shortest total
drying time of 50mins. Fig.1 suggests that two cultivars with same initial moisture content did not have
same drying characteristics. Other properties like the differences in chemical composition of the cultivars
may have contributed to this.
The drying rate decreased as the drying time increased for all the cultivars as show in table 2.1. This
implies that the drying rate decreased with increase in moisture content (wet basis) as against that
reported by [9]. The drying rate of NR8082 and Tms 30572 at stable weight was low compared with
native cassava. The native cassava had the highest drying rate of 3.07kg/hr at stable weight with shortest
drying time which also confirms its highly porous property, as show in table 2.1.
4.3. Proximate Composition
Table 8 shows the proximate composition of the cultivars. The improved cultivars had a slightly higher
percentage of carbohydrate (93.36 - 93.73%) than the native cultivar (92.86%). All the cultivars do not
contain fat since there was no oil extract from them. The geographical location of these cultivars as well
as time of planting and harvest may have been responsible for this. Tms 30572 and the native cultivar
have the same protein content higher than that of NR8082. The native cultivar ranked highest in fibre
content but contains the least percentage of ash. These might have contributed to its shortest drying time.
The type of drier used might have equally affected the total drying time as well as the drying rate. Also
the differences in the drying rate can be attributed to the difference in their chemical compositions. The
same drying condition cannot therefore be used for drying different cultivars.
4.4. Specific Heat Capacity and Thermal Conductivity
In order to determine the effect of moisture content on specific heat capacity and thermal conductivity,
the data in table 2.2 and the model equations of (8) were used to calculate the specific heat capacity and
(9) was used to calculate the thermal conductivity at various range of moisture contents. The specific heat
capacity increased with moisture content (wet basis) for all the cultivars. The native cultivar (fig. 2) had a
different specific heat capacity than the other cultivars. The native cultivar seems to have a lower ash and
carbohydrate content from other cultivars (Table 8) which might have contributed to this difference. The
two improved cultivars exhibited close specific heat capacities probably due to the fact that they had
approximately the same carbohydrate content. Tms 30572 and NR 8082 had very close specific heat at
different moisture contents showing that cultivars with similar chemical composition (ash and
carbohydrate) might have the same specific heat capacity. The specific heat capacities of Tms 30572 and
NR 8082 were high compared with the native cultivars, probably because of their high carbohydrate and
ash contents. More heat energy will therefore be required in other to dry cultivars with high ash and
carbohydrate content. The specific heat obtained from this work ranged from 1.53kJ/kgK-3.49kJ/kgK
which compare favorably with that of [9]; who obtained up to 3.5kJ/kgk.
The thermal conductivity of each of the cultivars also increased with moisture content (wet basis). The
native cultivar from (fig. 3) still exhibited a different thermal conductivity relative to other cultivars. The
two improved cultivars had almost the same thermal conductivity at different moisture contents. Tms
30572 and NR 8082 still exhibited higher thermal conductivity than the native cultivar.
4.5. Bulk Density
The bulk density of each cultivar decreased as the moisture content (dry basis) decreased during drying as
shown in fig.4, but it was almost stable with moisture content below 13% dry basis. This goes to suggest
the hygroscopic property of cassava as shown by [8] during the drying of a native cassava cultivar. At
particular moisture content under the same drying conditions the bulk density differed for each cultivar
which meant that the mass transfer rate would also differ for all the cultivars, since mass transfer rate is a
function of the density of the sample dried.
4.6. Thermal Diffusivity
The thermal diffusivity increased as moisture decreased, but was almost constant below the hygroscopic
moisture of about 13%. The thermal diffusivity also differed slightly for each cultivar when determined at
the same moisture as shown in fig.5. Thermal diffusivity determines how fast heat propagates or diffuses
through a material. From the results, the native cultivar and NR8082 with higher density had low thermal
diffusivity while the diffusion of heat is fastest in Tms 30572. NR8082 was the least porous (least thermal
diffusivity from fig.5) and also has high carbohydrate and least protein content; this should have
contributed to the low thermal diffusivity.
4.7. Hygroscopic Property and Porosity
The dried ground cassava from each cultivar was reweighed after 48 hours of drying and the results show
that 12.4% - 13.23% moisture was reabsorbed after the drying by the various cultivars. All the cultivars
exhibited hygroscopic property. Tms 30572 reabsorbed the highest moisture, indicating that it is more
porous and hygroscopic than the other cultivars. Its highest thermal diffusivity also goes to confirm this.
This must have also led to the increase in the rate of mass transfer of moisture from Tms 30572. This is in
contradiction with the results of the native cultivar’s porosity, which expelled the highest moisture with
the shortest drying time. It can therefore be said that the diffusion of heat and mass through the pores of a
cultivar does not depend on porosity alone but can also be affected by the chemical compositions of the
cultivar, as reported by [9].
4.8. Surface Area and Mass Transfer Coefficient
The surface area was obtained when the fermented ground cassava cultivars were dried to stable weight.
Tms 30572, with the least surface area of 0.415m2 has the longest drying time. The Native Cultivar with
surface are of 0.85m2 dried faster than Tms 30572 suggesting that the drying time does not entirely
depend on the surface are. The proximate composition of the cultivars has a great effect on the drying rate
even when the cultivars surface area is small. Tms 30572 has the highest mass transfer coefficient which
was due to its low product surface area and relatively lower density difference.
5. CONCLUSION AND RECOMMENDATION
The proximate composition of the cultivars had a very great impact on their engineering properties. The
difference in the drying rate could therefore be attributed to the difference in their chemical composition.
It can be said that the moisture content, specific heat capacity, and porosity also affected the rate of
diffusion of heat and mass through the cultivars. The specific heat capacity and thermal conductivity of
each cultivar varied with the proximate composition, water content and density, indicating that cultivars
with similar chemical composition had same specific heat capacities as could be seen in the improved
cultivars. More heat energy would be required to dry cultivars with high carbohydrate and ash content.
There was no trace of fat in all the cultivars probably as a result of the geographical location of the
samples.
Thermal diffusivity of each cultivar varied with the proximate composition, porosity, density as well as
the moisture content. Fermented ground cassava of any of these cultivars should not be dried below their
equilibrium moisture content about 13%), else moisture will be reabsorbed from the atmosphere. From all
indications, the improved variety is more porous, has high hygroscopic property and exhibited high rate
of mass transfer of moisture.
The mass transfer coefficient differed for each cultivar and was highest for cultivars with high protein
content and high drying rate.
Therefore, the same drying condition cannot be used for drying the fermented ground cassava cultivars
except if they have close engineering properties.
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