Physicochemical
Analyses of Coconut (Cocos nucifera L.)
Oil Obtained by Solvent (Aqueous and n-Hexane) Extraction Methods
Adebayo T.
Bale*, Abdulfatai T. Ajiboye, Isiaka A.
Idiaro
Department of Chemistry and Industrial Chemistry, Faculty of
Pure and Applied Sciences, Kwara State University, P.M.B 1530, Malete, Ilorin,
Nigeria.
*Correspondence: adebayo.bale@kwasu.edu.ng; Tel.: (+2348060445810)
INTRODUCTION
Coconut
(cocos nucifera L.) is known in many
languages by its local names for example it has been known as “Agbon” in
Yoruba, as “Kwakwa” in Hausa and as “Aku oyinbo” in Igbo. Coconut oil, or copra
oil is an edible oil extracted from the kernel or meat of mature coconut
harvested from the coconut palm (cocos
nucifera). Because of its high saturated fat content, it is slow to oxidize
and thus, resistant to rancidification, lasting up to six month 24 oC
(75 oF) without spoiling (Coconut oil, 2015) [1]. Historically coconut oil has been a life saver
for many people, the health and nutritional benefits derived from coconut oil
is unique and compelling. Dayrit et al.,
2001 [2] had stated that medium chain triglyceride, a fraction of coconut oil
has been identified as an important, medically efficacious food. Indeed, diet
for critically ill children, premature infants and hospitalized patients use
medium chain triglycerides as principle source of food which proves to be
anticholosterogenic. Coconut oil has been called the healthiest dietary oil on
earth. It is being used for thousands of years by pacific islanders and in
Asia. It is marvelous oil gifted by nature from perennial palm tree. It is
known for its nutrition, health and medicines to cure various diseases and keeps
the body shiny without wrinkling and fit to work (Jarimopas, 2007) [3]. So many
research have been conducted on the extraction processes and physicochemical
analyses of coconut (cocos nucifera L.) oil. Okene et al., 2014 [4] study the physicochemical properties of coconut
oil. The solvents used were isopropanol and petroleum ether. The physicochemical
parameters of the extracted oil were determined by standard methods of
analysis.
Probir et al., 2014 [5] also evaluate the
extraction and physicochemical properties of coconut oil. The Coconut copra was
subjected to aqueous and solvent extractions (using n-hexane). Additionally,
the oil was extracted from the copra in soxhlet assembly using petroleum ether.
Physicochemical and phytochemical analyses were conducted for the extracts and
the oil, with commercial coconut oil as the experimental control. Fatty acid
composition analyses showed mainly medium chain fatty acids in the copra oil
with lauric acid as the predominant fatty acid (51.88 % and 44.84 % in soxhlet
extracted and commercial oils respectively).
Sani et al., 2014 [6] reported on evaluation
of physicochemical properties, phytochemicals and mineral composition of cocos
nucifera (coconut) kernel oil. The oil was extracted using soxhlet apparatus and the physicochemical characterization, together
with the phytochemical
screening and determination
of the mineral composition
were carried out
using standard methods. The
oil was observed
to have clear
white appearance, liquid at room temperature
and has a
nutty smell when
fresh and unpleasant
when rancid. Cocos nucifera L.
seed kernel was found to have low oil content of 26.61 %.
Che Man
et al., 2012 [7] reported the physicochemical properties of virgin coconut oil
extracted from different processing methods. The Virgin Coconut Oil (VCO) was
prepared from fresh-dry (grated coconut route), chilling and thawing, enzymatic
and fermentation method. All of the VCO produced conformed physicochemically to
the standards established by the Asian and Pacific Coconut Community (APCC) and
Codex Alimentarius Commission. The highest FA (fatty acid) was lauric acid in
all of the VCO and ranged from 46.36 – 48.42 %. The aim of this research is to extract coconut oil by solvent
(aqueous and n-hexane) extraction methods, evaluate and compare the
physicochemical properties of the oil extracts.
MATERIALS AND METHODS
Materials
The essential materials used during the
research work are mature coconut fruit obtained from akodudu in Ilorin, Kwara
State, Nigeria, Analytical grade n-hexane, oven, soxhlet apparatus, rotary
evaporator, titration apparatus and cloth.
Methods
Extraction of the oil
The oil was obtained via two different
solvent extraction methods;
i.
Aqueous extraction method (heating method)
ii.
Soxhlet extraction method (n-hexane)
Aqueous extraction method
The husk
of matured coconut was removed. The coconut copra (dried coconut flesh) was
finely ground into a paste and sieved using cheese cloth. The filtrate was
allowed to settle, which later separates out into two layers. The upper layer
is called curd while the lower layer is water. The curd was separated from the
mixture and allowed to stand for some time before any further step is taken.
The oil was obtained by heating the curd at a particular temperature.
Soxhlet (n-hexane) extraction method
The
coconut copra (dried coconut flesh) was crushed then subjected to solvent
extraction using the soxhlet apparatus. n-hexane is the solvent used for the
extraction process. The extraction was carried out at the boiling point of
n-hexane (68
oC) for 6
h. The resulting solution was a mixture of the solvent and the oil. The
n-hexane was distilled off in a rotary evaporator at 65 oC.
Oil Recovery
Oil recovery gives a quantitative measurement on the
effectiveness of different method of extractions on the amount of oil produced.
Below is the formula used for the calculation of the oil yield:-
Percentage yield
= mass of the oil extracted Χ 100
Mass of the total seed used
Physicochemical analyses
The
Physicochemical parameters of the extracted oil were determined by standard
methods of analysis. Physicochemical analysis involve the measurement of
various physical and chemical properties of the oil. Properties like the
colour, density, viscosity, specific gravity, acid value, oil yield,
saponification value and FFA (free fatty acid) value of the seed oil were
determined.
Determination of specific gravity
The specific gravity was determined by
weighing an empty 25 cm3 S.G bottle, the bottle was filled to the
mark with distilled water and weighed. The measurement was recorded. The same
amount of oil was also weighed and recorded after drying the bottle. Below is
the formula used for the calculation of the specific gravity of the oil:-
Specific
gravity = W₁
W₂
Where
W₁= weight of the oil W₂ = weight of the distilled
water
Determination of saponification value
25 cm3
of 10 % ethanolic KOH was added to 2 g of the oil and refluxed for 30 min. The
unreacted KOH was back titrated with 0.5 M HCl using 3 drops of
phenolphthalein. Saponification value was calculated using the following
equation;
Saponification
value = Vb–Va× 56.1 ×M
W(g)
Where Va
= titre value of oil Vb = titre value of the blank
M =
molarity of the HCl W = weight of
oil
56.1 =
molecular weight of KOH
Determination of free fatty acid
1 g of
the oil was weighed and introduced into 250 cm3 conical flask, to
this 3 drops of phenolphthalein was added followed by 20 cm3
ethanol. The mixture was titrated with 0.1 M NaOH solution until pink colour
appears. Free fatty acid was calculated by the following equation;
Free
fatty acid = T × M× 56.1
W (g)
Where T
= titre value M =
molarity of the titrant
W=
weight of oil 56.1= acid constant
Determination of acid value
The same
experimental procedure given for (FFA) was also used for the determination of
acid value, the value was calculated by the following equation;
Acid
value = T ×0.0282 × W
Where T = titre value
W =
weight of oil 0.0282=
constant
Determination of peroxide value
1 g of
the oil was weighed into 250 cm3conical flask to which was added a
solvent mixture of glacial acetic acid 10 cm3 and 10 cm3
chloroform was added. 1 g of KI was added and the mixture was heated in a water
bath for 5 min. To this whole mixture was added 20 cm3 of 5 % KI and
titrated with 0.002 M solution of Na2S2O3
using starch solution as indicator. The peroxide value was calculated using the
following equation;
Peroxide
value = V₂-V₁×M× 1000
W (g)
Where V₂
= titre value of oil
V₁ = titre value of the blank
M =
molarity of Na2S2O3 W = weight of oil
Determination of pH Value
The pH
of the oil was determined using HANNA pH meter.
Determination of viscosity of the oil
The
viscosity of the oil was determined using NDJ-1B Rotational viscometer.
Determination of The Density of The Oil
The
density of the oil was determined with the aid of the Borosilicate density
bottle.
Density = Mass
of oil (g)
Volume of oil (cm3)
RESULTS AND DISCUSSION
Physicochemical Analyses
The
physicochemical analysis of the oil extracts were determined by standard
methods of analysis. The following table presents the physicochemical
properties of the coconut oil obtained by the two (aqueous and n-hexane) extraction
methods.
Table 1: Physicochemical properties of the coconut oil extracts
|
S/N
|
Physicochemical properties
|
Aqueous (heating method) Extraction
|
Soxhlet (n-hexane) extraction
|
|
1
|
Colour
|
Brownish
|
Pale
yellow
|
|
2
|
% Oil yield
|
7.91
|
8.89
|
|
3
|
Density
|
0.89 g/cm3
|
0.89
g/cm3
|
|
4
|
Specific gravity
|
0.91
|
0.91
|
|
5
|
Viscosity
|
4.0 mpa.s
|
3.8 mpa.s
|
|
6
|
pH value
|
4.7
|
5.1
|
|
7
|
Saponification
value
|
196.35±13.3
mgKOH/g
|
266.4±0.95
mgKOH/g
|
|
8
|
FFA
|
0.56±0.1 mgKOH/g
|
0.95± 1.5 mgKOH/g
|
|
9
|
Acid
value
|
0.00028±0.01
mgKOH/g
|
0.0047±0.000282 mgKOH/g
|
|
10
|
Peroxide value
|
0.2±0.2 meq peroxide/g
|
2.0±0.5 meq peroxide/g
|
Table 1
shows the physicochemical properties of the coconut oil obtained by aqueous
(heating method) and soxhlet (n-hexane) extraction methods. Coconut oil extracts
obtained in this study by the aqueous (heating method) and soxhlet (n-hexane) extraction
methods were brownish and pale yellow in colour respectively. The oil yield was
lower (7.91 and 8.89 %) than 21.61 % reported by Sani et al., (2014).
The specific
gravity value obtained in this study was 0.91 for the oil obtained by the two
extraction methods, which indicate that the oil is less dense than water. The
specific gravity of coconut oil extracts is in the same range with that reported
by Okene et al., (2014), which was
0.92. The saponification value obtained for the coconut oil extracts in this
study was 196.35 mg KOH g-1 and 266.4 mg KOH g-1 for the
oil obtained by aqueous (heating method) and soxhlet (n-hexane) extraction
respectively. Because of high saponification value, the coconut oil is suitable
for soap making (Ikhuoria and Maliki, 2007) [8]. The acid value obtained for the
coconut oil extracts in this study was (0.00028 mg KOH g-1 and
0.0047 mg KOH g-1), which was lower than the value (0.156) reported
by Okene et al., 2014 and also lower
than the value (0.79 mg KOH g-1) obtained by Sani et al., (2014). The peroxide value (2.0
meq/g for the soxhlet extracted oil) was higher than the value (0.46 meq/g)
reported by Okene et al., (2014) and
lower than the value (10.00 meq/g) obtained by Sani et al., (2014).The free fatty acid value obtained in this study was
0.56 mg KOH/g and 0.95 mg KOH/g for the oil obtained by aqueous (heating
method) and soxhlet (n-hexane) extraction respectively, was higher than the value
(0.1 mg KOH/g) obtained by Okene et al.,
(2014) and lower than the value (20.49 mg KOH/g) obtained by Sani et al., (2014). The PH value
obtained was 4.7 and 5.1 for the oil obtained by aqueous (heating method) and
soxhlet (n-hexane) extraction respectively. The acidic nature of the oil
extracts might indicate a prolonged shelf-life.
CONCLUSION
The
soxhlet (n-hexane) extraction method adopted in this study has a comparative
edge over the aqueous (heating method) extraction. The higher oil yield,
saponification value (SV), Free fatty acid (FFA), acid value (AV) and peroxide
value (PV) of the solvent extracted oil is an indication that it is more
cost-effective, less prone to deterioration and more suitable for soap making.
The oil
obtained by the aqueous (heating method) extraction will be more preferable as
an edible oil due to the benign (environment-friendly) solvent (water) used for
the extraction.
Overall,
this research is an indication that great potential exists for the use of
coconut oil. The oil is suitable for both domestic and industrial use. It has
reduced the sole dependence on palm oil and peanut oil.
ACKNOWLEDGEMENTS
The authors appreciated
the support of all members of staff in the laboratory at the Department of Chemistry and Industrial
Chemistry, Kwara State University (KWASU), Malete, Kwara State, Nigeria.
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