Vol.4, No.5B, 96-99 (2013) Agricultural Sciences
doi:10.4236/as.2013.45B018
Thermal properties of some selected nigerian soups
Raji Akeem Olayemi1, Akinoso Rahman2
1Department of Food Agric and Biological Engineering, College of Engineering and Technology, Kwara State University, Malete,
Ilorin, Nigeria;
2Department of Food Technology, University of Ibadan, Oyo State, Nigeria; [e-mail]
Received 2013
ABSTRACT
A preliminary investigation was carried out on the
thermal properties of “Ewedu” (Corchorusolito-
rus), “Ila” (Hibiscus esculentus), “Ogbono” (Irvin-
gi a gabon ensis) and ” Kuka” (Adanso nia digitata)
soups, because information on the thermal prop-
erties of these soups has not been established.
The specific heat capacity, thermal conductivity
and thermal diffusivity parameters were deter-
mined as a function of their proximate composi-
tions by applying additivity principles. The proxi-
mate composition obtained for the soups were:
ewedu (moisture content; 88.60 ± 0.14% , protein;
6.00 ± 0.01%, fat; 1.05 ± 0.05% , ash; 1.81 ± 0.01% ,
crude fiber; 1.47 ± 0.02%, carbohydrate; 1.05 ±
0.04% and energy 34.27 ± 1.89 k/cal/10 g), Ila
(moisture content; 77.25 ± 0.35%, protein; 15.94
± 0.08%, fat; 2.13 ± 0.04%, ash; 1.90 ± 0.14%,
crude fiber; 1.15 ± 0.07%, carbohydrate; 1.48 ±
0.11% and energy 87.61 ± 3.31 k/cal/10 g), Og-
bono (moisture content; 68.87 ± 0.14%, protein;
18.70 ± 0.42% , fat; 6.12 ± 0.11%, ash; 4.55 ± 021% ,
crude fiber; 1.04 ± 0.60%, carbohydrate; 1.90 ±
0.01% and energy; 133.08 ± 0.60 k/cal/10 g) and
Kuka (moisture content; 78.54 ± 0.06%, protein;
8.80 ± 0.41%, fat; 2.29 ± 0.01% , ash; 2.09 ± 0.01% ,
crude fiber; 0.88 ± 0.02%, carbohydrate; 7.42 ±
0.08% and energy 85.64 ± 0.17 k/cal/10 g). The
specific heat capacity, thermal conductivity and
thermal diffusivity for the soups were; ewedu
(3.851 kJ/ kg/K, 0.530 W/m/K and 1.358 x 10-7
m2/s), Ila (3.554 ± 0.01 kJ/kg/K, 0.483 W/m/K and
1.281 x 10-7 m2/s), ogbono (3.332 kJ/kg/K, 0.447
W/m/K and 1.220 x 10-7 m2/s) and kuka (3.586
kJ/kg/K, 0.494 W/m/K and 1.296 x 10-7 m2/s)re-
spectively. The values obtained for the thermal
properties showed that the soups can mildly
retain or dissipate heat during canning and
freezing.
Keywords: Soups; Proximate Composition;
Thermal Properties; Processing
1. INTRODUCTION
Vegetables are important constituents of any type of
diet in many Nigerian homes. Despite that, they add va-
rieties to the menu. As valuable sources of nutrients es-
pecially in rural areas where they con tribute substantially
to protein, mineral, vitamins, fiber and other nutrients
which are usually in short supply in most daily diets [1].
Besides, they add flavour, variety, taste, colour and aes-
thetic appeal to what would otherwise be a monotonous
diet [2,3]. They are mostly in abun dance shortly after the
rainy season but become scarce during the dry season
when cultivated types are used. Some eventually find
their way to urban markets [1].Vegetables have gained a
widespread acceptance as a dietary cons tituent in Nigeria,
generally forming a substantial portion of the diet in the
preparation o f sou ps and stews[3].
Nigeria is a multi-cultural society with different tradi-
tional soups which are indigenous to differen t ethnic groups
and tribes. The soups are consumed along with traditional
dietary staples, obtained from cassava, yam, cocoyam,
sweet potatoes, plantain and maize [4]. Though, there is
no universally accepted short list of such plants men-
tioned above, different tribes in Nigeria have evolved
their preferences and feedi ng habits.
During processing and storage, many foods are either
heated or cooled. Cooling, cooking, pasteurization, de-
hydration, commercial sterilization and freezing involve
heat transfer [5] and the design of such processes re-
quires a detailed knowledge of the thermal properties of
the materials involved.
Although the recipe and nutritional contents of stews
and soups commonly consumed in Nigeria had been es-
tablihed in order to serve as a reference for interested
individuals, corporate organizations, researchers, medical
practitioners, nutritionists and dieticians, public health
workers and food technology programmes [6], informa-
tion on the thermal p r op erties of these so up s has not been
established. The parameters stated above will serve as a
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R. A. Olayemi, A. Rahman / Agricultural Sciences 4 (2013) 96-99 97
Copyright © 2013 SciRes. Openly accessible at http://www.scirp.org/journal/as/
basis for future research in canning of Nigerian soups
and also establish the possibilities of extending the shelf
life of the local soups under frozen storage. Soups to be
considered are chosen because they are popularly
consumed along with staple foods from the three major
tribes in Nigeria and these are prepared from “Ewedu”
(Corchorusolitorus), “Ila” (Hibiscusesculentus), “Og-
bono” (Irvingiagabonensis) and ” Kuka” (Adansoniadig
itata).
2. MATERIALS AND METHODS
2.1. Materials
The ingredients used for the preparation of the above
soups were purchased from Local markets at Ipata and
Ago in Ilorin, Kwara State Nigeria.
2.1.1. Preparation of Soups
Selected Nigerian soups mentioned above were pre-
pared using facilities of the department of Food Agric
and Biological Engineering, Kwara State University Ni-
geria. The preparation methods used for the selected
soups were those earlier established by recipe book of
the Federal Institute of Industrial Research, Oshodi [6].
Each dish was prepared in triplicates and analyses were
carried out on wet basis.
2.1.2. Sample Collection and Preparation
Each soup was cooled to room temperature and equal
portions of the dishes were homogenized with a warring
blender.
2.2. Proximate Composition Analysis
Each sample was analysed for moisture, ash, crude fat,
and crude fiber using the methods of the Association of
Official Analytical Chemists[7]. Nitrogen was deter-
mined by Kjeldahl method and percentage nitrogen was
converted to crude protein by multiplying the value with
6.25[8]. Carbohydrate was determined by the difference
of the sum of all the proximate compositions from 100%.
The energy value was calculated using the Atwater fac-
tors 0f 4, 9, and 4 for protein, fat, and carbohydrate re-
spectively [9].
2.3. Determination of Thermal Properties
The specific heat capacity, thermal conductivity and
thermal diffusivity of the soups were determined as a
function of their proximate compositions by applying
additivity principles.
2.4. Specific Heat Capacity (Cp) and
Thermal Conductivity (K)
The above parameters were determined based on weight
fraction of water, fat, ash, protein and carbohydrate com-
ponent of food using the equations stated below[10].
1.424 1.5491.6750.8374.187
pcpf a
CXXXX w X


0.580.1550.25 0.160.135
wpcf
kXXX Xa X


2.5. Thermal Diffusivity
This was determined based on weigh t fraction of water,
fat, protein and carbohydrate component of food using
the equation stated below [11].
66
66
0.146 100.10 10
0.075 100.08210
wf
p
c
DXX
X
X


 

X was the fraction of food component, and the sub-
scripts; w, f, p, c and a represented water, fat, protein,
carbohydrate and ash respectively.
St atistical Analysis
Data were reported as mean ± standard deviation. Sta-
tistical analyses were carried out using SPSS for Win-
dows, version14.0 (SPSS Inc. Chicago, IL.USA).
3. RESULTS
Table 1. Proximate composition of some selected nigerian soups.
Soups MC% CHON% Fat% Ash% CF% CHO% E(k/cal/10 g)
Ogbono 68.70 ± 0.14 18.70 ± 0.42 6.12 ± 0.11 4.55 ± 0.21 1.04 ± 0.60 1.90 ± 0.01 133.08 ± 0.60
Ewedu 88.60 ± 0.14 6.00 ± 0.01 1.05 ± 0.05 1.81 ± 0.01 1.47 ± 0.02 1.05 ± 0.04 34.27 ± 1.89
Ila 77.25 ± 0.35 15.94 ± 0.08 2.125 ± 0.04 1.90 ± 0.14 1.15 ± 0.07 1.475 ± 0.11 87.61 ± 3.31
Kuka 78.54 ± 0.06 8.80 ± 0.14 2.29 ± 0.01 2.09 ± 0.01 0.875 ± 0.02 7.415 ± 0.08 85.64 ± 0.17
MC = Moisture Content(% wb); CF = Crude Fibre(% wb); CHON = Protei n Content(% wb); E = Ener gy,k/cal/10 g.

R. A. Olayemi, A. Rahman / Agricultural Sciences 4 (2013) 96-99
98
Table 2. Thermal properties of some selected nigerian soups.
Soups CP( kJ/kg/K) K(W/m/K) D(m2/s)
Ogbono 3.3315 ± 0.00 0.4470 ± 0.00 1.22E-07
Ewedu 3.8505 ± 0.00 0.5295 ± 0.00 1.36E-07
Ila 3.5535 ± 0.01 0.4825 ± 0.00 1.28E-07
Kuka 3.5860 ± 0.00 0.4935 ± 0.00 1.30E-07
Cp = Specific Heat Capacity, KJ/ Kg/K; K= Thermal Conductivity ,W/m/K;
D=Thermal Diffusivity,m/s2
4. DISCUSSION
The results of the proximate compositions and thermal
properties of some selected nigerian soups were pre-
sented in Tables 1 and 2. The moisture content of the
soups determine their suitability to microbial attack and
hence spoilage [12]. The moisture content of “Ogbono”
(68.70 ± 0.14%) is lower than those of “Ila”,
“Ewedu”and “Kuka. This indicated that Ogbono with
lower moisture content, might have storage advantage
over others. Ash content is an index of mineral contents
in biota[13]. The observed ash content from the present
study ranged between 1.81 ± 0.01 to 4.55 ± 0.21%, with
Ogbono having the highest ash content. This could mean
that the minerals in Ogbono are higher th an that of others.
Proteins are important in the body due to their numerous
roles[14,15]. The protein content of the soups ranged
from 6.00 ± 0.01 to 18 .70 ± 0.42%, and Ogbono had th e
highest. Ewedu and Kuka with lower protein content
(6.00 ± 0.01% and 8.80 ± 0.14%) might not be able to
contribute significantly to the daily protein requirements
of 22 - 56 g [16]. Fats are saturated lipids at room tem-
perature[17,15] which are known to play protective roles
in the body system[12]. Some important fatty acids such
as omega-3-fatty acid, etc, are derived from fats. These
fatty acids are noted for their roles in the body system
[18].The crude fat content of the soups were in the range
of 1.05 ± 0.05 to 6.12 ± 0.11%. Variation in the fat con-
tents might be as a result of different quantities of exter-
nal red oil added to the soups as stated in the recipe book.
Adequate intake of dietary fiber can lower the level of
serum cholesterol and reduce the risk of developing hy-
pertension, constipation, diabetes, colon, cancer and
coronary heart disease [19]. The fiber content of the
soups ranged between 0.875 ± 0.02 to 1.47 ± 0.02%,
with having the highest fiber content. The recommended
dietary allowance (RDA) values of carbohydrate for
adults, pregnant and lactating mothers are 130 g, 175 g,
and 210 g respectively [15]. The carbohydrate content
and the estimated calorific value of the soups were very
low, but this is not a concern since they are been con-
sumed along with starch based dietary staples[4].
The thermal properties express the reaction of a sub-
stance when a change in temperature occurs. Specific heat
capacity determines the amount of heat a substance can
absorb [10]. The specific heat capacity obtained ranged
from 3.3315 ± 0.00 to 3 .8505 ± 0.00 kJ/kg/K. These val-
ues are slightly below the specific h eat capacity of water.
It has been proved that there is direct correlation between
the specific heat capacity and moisture content of food
product [20]. This implies that as the moisture content
increases, the specific heat capacity increases. This was
noticed in the soup samples, with Ewedu having the
highest moisture content and specific heat capacity. The
thermal conductivity of a material is a measure of its
ability to transmit heat[21,10].The thermal conductivity
estimated ranged between 0.4470 ± 0.00 and 0.5295 ±
0.00 W/m/K. Highest value was reported for Ewedu.
This connotes that ewedu will have a greater advantage
of absorbing and dissipating heat during processing and
storage than others. It was observed that thermal conduc-
tivity of food depended on the structure and chemical
composition of the sample and it increased with increas-
ing water content for all food products at temperature
above freezing [19]. Similar results were obtained in this
study for the thermal conductivity of soups. The thermal
diffusivity quantifies a material`s ability to conduct heat
relative to its ability to store heat [11].The results ob-
tained indicated that thermal diffusivity increased with
increase in moisture content, as it was observed in ther-
mal conductivity and specific heat capacity of the soup
samples.
5. CONCLUSIONS
The present study shows that the chemical composi-
tions and water fractions greatly influence the thermal
properties of sou ps.
The values of the thermal properties obtained shows
that the soups can considerably retain or dissipate heat
during canning and freezing.
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