Physicochemical Properties and Fatty Acid Composition of Citrullus lanatus (Egusi Melon) Seed Oil
In this study, the physicochemical properties and fatty
acid composition of Citrullus lanatus (egusi melon) were
investigated. Oil from the seeds of Citrullus lanatus (egusi melon)
was extracted with petroleum ether as solvent. The ether extract was evaluated
for its specific gravity, refractive index, acid, iodine, peroxide and
saponification values. The fatty acid profile analysis of the oil was
also carried out by Gas Liquid Chromatography. The oil has a specific
gravity of 0.93 and refractive index of 1.45 indicating that the oil is
less thick compared to most drying oils with refractive indices between
1.48 and 1.49. Its acid, iodine, peroxide and saponification values were
3.5 ±0.3, 110 ±8.2, 8.3 ±4.6 and 192 ±43.7, respectively.
These values are within recommended range for edible oils. The oil has
four main fatty acids: palmitic, stearic, oleic and linoleic acids, linoleic
acid being the most abundant. The fatty acid content of the oil showed
that 71.9% is unsaturated. These results indicate that egusi melon oil
could be a good source of table oil. Its high content of linoleic acid
is of particular interest especially in the fight against atherosclerosis.
Egusi melon (Citrullus lanatus) belongs to the family of Cucurbitaceae
which has a tremendous genetic diversity, extending to vegetative and
reproductive characteristics (Ng, 1993). They thrive in tropical, subtropical,
arid deserts and temperate locations. Egusi melon is an annual, herbaceous,
monoecious plant with a non-climbing creeping habit. After planting, they
completely cover the soil surface within 3 weeks and flowering starts.
Pollination is by insects. Often the fruits are ready to harvest 90-120
days (3-4 months) after sowing (Ng, 1993). The fruits are indehiscent
smooth berries, very large and seedy and when sound can be removed, washed
In West Africa, a region where soups are integral to life, egusi melon
(Citrullus lanatus) seeds are a major soup ingredient and a common
component of daily meals. Coarsely ground up, they thicken stews and contribute
to widely enjoyed steam dumplings. Some are soaked, fermented, boiled
and wrapped in leaves to form a favourite food seasoning. Egusi melon-seed
meal is compacted into patties that served as a meat substitute. Despite
being a significant foodstuff even by global standard, egusi melon is
hardly known to nutritionists outside a few West African nations. Little
nutritional detail on egusi melon oil is readily available to an international
readership. Research studies have shown that these seeds contained about
50% oil (Olaofe et al., 1994), 42-57% oil (Fokou et al.,
2004), 44-53% oil (Achu et al., 2005) for seeds cultivated in different
bioclimatic regions of Cameroon. These studies showed that egusi melon
seeds contained good amounts of oil that can be exploited. The aim of
the present study therefore is to determine some physical and chemical
properties as well as the fatty acid composition (which could be used
in determining the quality of the oil) of egusi melon oil obtained locally
from a South Western region of Nigeria.
MATERIALS AND METHODS
Chemicals: All chemicals used were of analytical grade and were
products of BDH Chemicals Ltd., Poole, England unless otherwise stated.
Collection and preparation of seeds sample: This study was carried
out between October to November, 2007. Egusi melon seeds used for this
study were obtained from a local market in Iwaro-Oka Akoko, Ondo State,
Nigeria and were identified as Citrullus lanatus by a taxonomist
in the Department of Crop Science, Faculty of Agriculture, University
of Benin, Nigeria. The seeds were screened to remove bad ones, shelled
manually and further screened. The seeds were then dried to constant weight
in an oven at 70°C, ground using mechanical grinder, put in air-tight
containers and stored in desiccators for further analysis, some of the
seeds was subsequently deposited at the herbarium of the faculty.
Oil extraction: Oil from the seeds of egusi melon was extracted
by continuous extraction in Soxhlet apparatus (Cehmglass) for 8 h using
petroleum ether (60-80°C boiling range) as solvent according to the
method described (AOAC, 1980). At the end of the extraction the extraction
solvent was evaporated in a rotary evaporator (Cehmglass). The extracted
oil was used for feed formulation and the remaining stored in light proof,
airtight and moisture proof container at -4°C for further analysis.
Physicochemical properties analysis: The physicochemical indices
(acid, iodine, peroxide and saponification values and specific gravity
and refractive index) were carried out according to the methods described
Fatty acid composition analysis: The fatty acid profile of egusi
melon oil was determined by gas liquid chromatography (Hewlett Packard,
RESULTS AND DISCUSSION
Table 1 shows the yellowish colour oil had specific
gravity of 0.93 indicating that it is less dense than water. The result
of the refractive index, 1.45 is in close agreement with the value of
1.46 obtained for B. sapida (Akintayo et al., 2002) oil.
This shows that the oil is less thick compared with most drying oils whose
refractive indices were between 1.48 and 1.49 (Duel, 1951). The acid value
of 3.5±0.3 mg KOH g-1 is relatively low compared to
that reported for tropical almond (7.6 mg KOH g-1) and similar
to that of fluted pumpkin (3.5 mg KOH g-1) (Christian, 2006).
The low acid value of the oil indicates that it is good as edible oil.
The iodine value of egusi melon seed oil, 110.0±8.2 mg iodine g-1
is similar to those of unsaturated fatty acid-rich oils such as peanut
(86.0-107.0), cottonseed (100.0-123.0), sesame (104.0-120.0), sunflower
(118.0-141.0) but lower than that of soybean oil (124.0-139.0) (Aremu
et al., 2006). Egusi melon seed oil however has iodine value higher
than those of saturated fatty acid-rich oils such as Theobroma cacao,
cocoa butter (32.0-42.0) (Ige et al., 1984), coconut (6.0-10.0),
palm oil (50.0-55.0), palm kernel (14.0-1.0) (Aremu et al., 2006).
||Physicochemical properties of egusi melon seed oil
|*Values are mean±standard deviations of triplicate
Egusi melon oil has a peroxide value of 8.3±4.6 mg equiv. of O2
kg-1 of oil. This value is higher than the value recorded for
Bauchinia racemora (4.9) seed (Amoo and Moza, 1999). Peroxide value
depends on a number of factors such as the state of oxidation (quantity
of oxygen consumed), the method of extraction used and the type of fatty
acids present in the oil. The high peroxide value recorded for egusi melon
oil in this study may be due to too much exposure of the seeds to sun
during drying, causing lipid oxidation resulting from the absorption of
oxygen, which increases the formation of peroxides. Secondly, it may be
attributable to heating of the oil during its extraction process. Heat
favours oxidation of fatty acids increasing the formation of peroxides
(Cheftel and Cheftel, 1992). Thirdly, the oil contains mostly polyunsaturated
fatty acids which easily undergo oxidation, raising peroxide value of
the oil. The peroxide value obtained in this study is however lower than
15 mg equiv. O2 kg-1 of oil (the maximum level for
cold pressed and virgin oils) (Aremu et al., 2006), showing that
egusi melon oil is good for consumption.
The saponification value of egusi melon oil was 192.0±43.7 mg
KOH g-1 which agrees with values obtained for some vegetable
oils ranging from 188-196 mg KOH g-1 (Pearson, 1976). However,
there are some vegetable oils with higher saponification values such as
coconut oil (253.0 mg KOH g-1), palm kernel oil (247.0 mg KOH
g-1) and butter fat (225.0 mg KOH g-1) (Aremu et
al., 2006). As reported by Pearson (1976) oil with higher saponification
values contain high proportion of lower fatty acids. Therefore, the values
obtained for egusi melon oil in this study show that it contains high
amounts of higher fatty acids.
Table 2 shows the fatty acid profile of egusi melon
oil. Table 2 showed that palmitic (13.5%), stearic,
(13.7%), oleic (14.5%) and linoleic, (56.9%) are the main fatty acid present
in egusi melon. The linoleic acid level in egusi seed oil obtained in
this study is similar to that of egusi seeds from Niger (30.0-74.0%) (Lazos,
1986). These results show that egusi melon oil is better than animal fats
in their content of linoleic acid, while animal fats contain mostly oleic
acid (29.0-48.0%) (NRC, 1989).
||Fatty acid composition (% of methyl fatty acids) of
egusi seed oil
Present results are also similar to that of previous study on Cucurbita
pepo seed oil which was found to contain mostly palmitic, stearic,
oleic and linoleic acids, with linoleic acid as the most abundant
(Murkovic et al., 1996; Younis et al., 2000). Present
values are also similar to those of corn, cottonseed, sunflower, soybean
and sesame oils. They are different from those of peanut and palm olein
oils, (which have oleic acid as the most abundant) and palm and coconut
oils (contain mostly saturated fatty acids, palmitic and lauric acids
respectively) (Aremu et al., 2006).
From our results, egusi oil is observed to be poor in linolenic acid
(0.5). Linolenic acid though an omega-3 fatty acid with positive health
effects is easily susceptible to peroxidation, hence, it is undesirable
in edible oils because of the off-flavours and potentially harmful oxidation
products formed. As reported by Warner and Gupta (2003), a decrease from
2 to 0.8% linolenic acid content in oils improved flavour quality and
oxidative stability of fried foods. This therefore shows that the lower
the linolenic acid content of oil, the more suitable is the oil for frying.
Egusi oil contained 57.4% poly unsaturated fatty acid majorly composed
of linoleic acid which is an essential fatty acid. This indicates that
egusi seed oil is a good source of edible oil such as cooking and frying
oil, making it good for the fight against cardiovascular diseases.
The present study indicates that egusi seed oil has acid, iodine, peroxide
and saponification values within recommended limits. The iodine value
is close to those of unsaturated fatty acid-rich oils (corn, cottonseed,
sesame, sunflower and peanut oils) showing that the oil is rich in unsaturated
fatty acids. Egusi seed oil is very rich in essential fatty acids (linoleic)
but poor in linolenic acid. The fatty acid profile follows the same pattern
as that of corn, cottonseed, soybean and sesame oils but has a lower linoleic
acid level compared to soybean. The acceptable acid and peroxide values,
high linoleic acid and low linolenic acid content of egusi seed oil suggest
it could be a good source of edible oil (for cooking and frying) and a
potential antidote for the fight against cardiovascular disease.
Further research is being carried out on the proximate amino acid and
mineral composition of egusi seed as well as its potential atherogenicity
Achu, M.B., E. Fokou, C. Tchiégang, M. Fotso and F.M. Tchouanguep, 2005.
Nutritive value of some Cucurbitaceae
oilseeds from different regions in cameroun. Afr. J. Biotechnol., 4: 1329-1334.Direct Link |
Akintayo, E.T., E.A. Adebayo and L.A. Arogundade, 2002.
Chemical composition, physicochemical and functional properties of akee (Bilphia sapida
) pulp and seed flours. Food Chem., 77: 333-336.CrossRef | Direct Link |
Amoo, I.A. and L. Moza, 1999.
Extraction and physicochemical properties of oils from Bauchinia racemosa
seeds. Riv. Ital. Sostanze Grasse, 76: 399-400.Direct Link |
Official Methods of Analysis. 13th Edn., Association of Official Analytical Chemist, Washington, DC., USA., pp: 56-132Direct Link |
Aremu, M.O., A. Olonisakin, D.A. Bako and P.C. Madu, 2006.
Compositional studies and physicochemical characteristics of cashew nut (Anarcadium occidentale
) flour. Pak. J. Nutr., 5: 328-333.CrossRef | Direct Link |
Cheftel, J.C. and H. Cheftel, 1992.
Introduction a la biochimie et a la technologie des aliments. Technique et documentation. Paris Cedex, 1: 243-330.
Agatemor, C., 2006.
Studies of selected physicochemical properties of fluted pumpkin (Telfairia occidentalis
Hook F.) seed oil and tropical almond (Terminalia catappia
L.) seed oil. Pak. J. Nutr., 5: 306-307.CrossRef | Direct Link |
Duel Jr., H.J., 1951.
The Lipids: Their Chemistry and Biochemistry. Vol. 1. Inter Science Publishers, New York, pp: 53-57Direct Link |
Fokou, E., M.B. Achu and M.F. Tchouarguep, 2004.
Preliminary nutritional evaluation of five species of egusi seeds in cameroun. Afr. J. Food Agric. Nutr. Dev.,Direct Link |
Ige, M.M., A.O. Ogunsua and O.L. Okon, 1984.
Functional properties of the proteins of some Nigerian oilseeds: Conophor seeds and three varieties of melon seeds. J. Agric. Food Chem., 32: 822-825.CrossRef | Direct Link |
Murkovic, M., A. Hillebrand, J. Winkler, E. Leitner and W. Pfannhauser, 1996.
Variability of fatty acid content in pumpkin seeds (Cucurbita pepo
L.). Zeitschrift fur Lebensmittel-Untersuchung und-Forschung, 203: 216-219.CrossRef | Direct Link |
Ng, T.J., 1993.
New Opportunities in Cucurbitaceae. In: New Crops. Janick, J. and J.E. Simon (Eds.). Wiley, New York, pp: 538-546Direct Link |
National Rearch Council NRC, 1989.
Recommended Dietary Allowances. 10th Edn., National Academy Press, Washington, DC. USA., pp: 284Direct Link |
Olaofe, O., F.O. Adeyemi and G.O. Adediran, 1994.
Amino acid and mineral compositions and functional properties of some oil seeds. J. Agric. Food Chem., 42: 878-881.Direct Link |
Pearson, D., 1976.
The Chemical Analysis of Foods. 7th Edn., Churchill Livingstone, London, ISBN-13: 9780700014576, pp: 7-11.
Warner, K.A. and M. Gupta, 2003.
Frying quality and stability of low and ultra low. J. Am. Chem. Soc., 80: 275-280.CrossRef | Direct Link |
Younis, Y.M., S. Ghirmay and S.S. Al-Shibry, 2000.
African Cucurbita pepo
L. Phytochemistry, 54: 71-75.CrossRef | Direct Link |