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Vegetable oils have been used as a feedstock for fatty acid methyl ester (FAME) production. The high cost of neat vegetable oil and its impact on food security have necessitated its replacement as a feedstock for FAME by used vegetable oil, also known as waste cooking oil (WCO). This study compares the properties and fatty acid (FA) compositions of samples of neat vegetable oil with those of samples of WCO, collected from restaurants and takeaway outlets at the point of disposal. The samples were subjected to property determination and pyrolysis gas chromatography mass spectrometer (PYGCMS) analysis. Analysis showed that degree of usage and the type of food items originally fried in the oil substantially affected its properties and FA composition. Density of neat vegetable oil varied between 904.3 and 919.7 kg/m3 and of WCO between 904.3 and 923.2 kg/m3. The pH of neat vegetable oil varied between 7.38 and 8.63 and of WCO between 5.13 and 6.61. The PYGCMS analysis showed that neat palm oil contains 87.7% unsaturated FA and 12.3% saturated FA, whereas neat sunfoil contains 74.37% saturated FA and 25% polyunsaturated FA. Generally, neat vegetable oils consisted mainly of saturated FAs and polyunsaturated FAs, whereas the WCO contained mainly of saturated FAs and monounsaturated FAs. This research confirms the suitability of WCO as feedstock for FAME.
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Omojola Awogbemi, http://orcid.org/0000-0001-6830-6434
International Journal of Low-Carbon Technologies 2019, 14, 417–425
© The Author(s) 2019. Published by Oxford University Press.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which
permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
doi:10.1093/ijlct/ctz038 Advance Access publication 10 July 2019 417
Comparative study of properties and fatty
acid composition of some neat vegetable oils
and waste cooking oils
..............................................................................................................................................................
Omojola Awogbemi*,†, Emmanuel Idoko Onuh and Freddie L. Inambao
GreenEnergySolutionsResearchGroup,DisciplineofMechanicalEngineering,Howard
College, University of KwaZulu-Natal, Durban 4041, South Africa
............................................................................................................................................
Abstract
Vegetableoilshavebeenusedasafeedstockforfattyacidmethylester(FAME)production.Thehighcost
of neat vegetable oil and its impact on food security have necessitated its replacement as a feedstock for
FAMEbyusedvegetableoil,alsoknownaswastecookingoil(WCO).Thisstudycomparestheproperties
and fatty acid (FA) compositions of samples of neat vegetable oil with those of samples of WCO, collected
from restaurants and takeaway outlets at the point of disposal. The samples were subjected to property
determination and pyrolysis gas chromatography mass spectrometer (PYGCMS) analysis. Analysis showed
that degree of usage and the type of food items originally fried in the oil substantially aected its properties
and FA composition. Density of neat vegetable oil varied between 904.3 and 919.7 kg/m3and of WCO
between 904.3 and 923.2 kg/m3. The pH of neat vegetable oil varied between 7.38 and 8.63 and of WCO
between 5.13 and 6.61. The PYGCMS analysis showed that neat palm oil contains 87.7% unsaturated FA
and 12.3% saturated FA, whereas neat sunfoil contains 74.37% saturated FA and 25% polyunsaturated FA.
Generally, neat vegetable oils consisted mainly of saturated FAs and polyunsaturated FAs, whereas the WCO
contained mainly of saturated FAs and monounsaturated FAs. This research conrms the suitability of WCO
as feedstock for FAME.
Keywords: chromatograms; FAME; fatty acid composition; neat vegetable oil; waste cooking oil
Corresponding author:
217080448@stuukzn.ac.za Received 22 March 2019; revised 17 May 2019; editorial decision 27 May 2019; accepted 27 May 2019
................................................................................................................................................................................
1INTRODUCTION
Energy demand has continued to increase due to increased popu-
lation and continued development of the industrial sector over the
past few decades. With mounting evidence of the negative envi-
ronmental eects of incessant combustion of fossil fuel, renewable
or green energy sources are gaining wide acceptance globally
[13].Amongthe green energy alternatives, biodiesel has received
substantial attention and research in recent years. Biodiesel fuel
is sustainable and environmentally friendly, can be produced by
households and is economically advantageous, especially consid-
ering the unpredictability of petroleum-based diesel fuel prices
and the absence of strong policies to minimize the use of fossil
fuels [4]. The increasing demand for sustainable and environmen-
tallyfriendlyalternativestofossilsourcedfuelhasmadethesearch
for a readily available, economical and environmentally accept-
able feedstock for sustainable biodiesel production inevitable
[5,6].
High cost and threat to food security have made the use of
edible oil as biodiesel feedstock unrealistic and impractical. The
huge amount of land required for cultivation, the high cost of
farming,the longwaitingperiod between plantingandharvesting,
aswellasthethreatofdeforestationandtowildlifehavemadethe
useofinediblecropsasfeedstockunattractive[7,8]. These chal-
lenges have shied attention to the adaptation of used vegetable
oil as feedstock. Used vegetable oil, also known as waste cooking
oil (WCO), is produced when vegetable oil sourced from palm,
soybean, sunower, cottonseed, olive, palm kernel and rapeseed
or animal fats like butter, sh oil and tallow are used to cook or
fry food [9]. With feedstock accounting for between 70% and 75%
of the production cost of biodiesel, the use of WCO has resulted
in a substantial reduction in production costs, thereby signi-
cantly reducing the cost of biodiesel fuel, which makes WCO
more viable as a substitute fuel for internal combustion engines
particularly the unmodied compression ignition engines [10].
The adaptation of WCO as feedstock for biodiesel production
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Figure 1. Consumption of vegetable oils worldwide by oil type (million metric tonnes) [13].
Table 1. Estimated waste cooking oil collected in a year [16,18,19]
Country m3/year
The Netherlands 67 000
Italy 60 000
Portugal 28 000
Spain 270 000
Germany 250 000
Hungary 5500
Norway 1000
alsohelpsinproperdisposalofWCO;oersadditionalincometo
households, restaurants and fast-food outlets; prevents blockage
of drains; minimizes water contamination; and preserves aquatic
habitat [11]. The use of WCO as biodiesel feedstock also promotes
employment generation and ensures social inclusion by engaging
youths in the collection of WCO, thereby promoting community
environmental education and campaigns [12].
Globally, consumption of vegetable oils has continued to
increase, particularly in the last 5 years as shown in Fig. 1,with
palm oil topping the list [13]. The largest percentage of these
vegetableoilsisusedinhouseholds,restaurantsandfast-food
outlets for cooking and frying. Table 1 shows the estimated WCO
collected by some countries. Canada is reported to generate
between 120 000 and 135 000 tonnes of WCO per year [14,15],
while the USA produced 0.6 million tons of yellow grease in
2011. The UK and the European Union countries generated
700 000–1 000 000 and 200 000 tonnes of WCO per year,
respectively [16]. While 60 000 tonnes of WCO is collected yearly
in South Africa, an estimated 200 000 tonnes of WCO is produced
from households, bakeries, takeaway outlets and restaurants
but uncollected annually [17,18]. Japan, China and Malaysia
generated 6000, 45 000 and 60 000 tonnes of WCO, respectively,
annually. Of WCO generated globally, >60% is estimated to be
disposed of inappropriately [18,19].
ItisevidentthatnotallWCOsareusedforbiodieselproduction
or other fuel production processes. There are justiable fears
that some unscrupulous elements are ltering and rebottling the
collected used vegetable oil for resale to unwary members of
the public. Repeated consumption of food prepared with repack-
aged WCO predisposes consumers to deleterious health conse-
quences including diabetes, hypertension, vascular inammation,
and other pathologies [2022]. Available statistics showed that
WCO contributed 17% and 9% of the feedstock for the production
of 11.92 million tons and 26.62 million tons of biodiesel by the
European Union and globally, respectively, in 2015 [23]. Most
people are not aware that WCO can be converted to fuel; hence,
they dispose indiscriminately. A well-coordinated program of
awareness for collection, transportation and conversion of WCO
is required to motivate participants in the WCO chain.
The importance of utilizing WCO for biodiesel production
has been well documented, but some knowledge gaps still exist
with regard to the following: how local use of specic oil source
alters their suitability for use as feedstock; how acid values and
levels of saturation are altered by their primary applications; and
what challenges these pose to the transesterication process at
any given location [24,25] The degree of usage of vegetable oil
is believed to aect some of the properties, including the acid
value and iodine value, which dictates the ease of conversion of
the resulting WCO [26,27]. Given the importance of WCO in
the renewable fuel value chain, proper characterization of the
feedstock is necessary to inform a research-based policy on how
to unlock the actual economic value as well as combat the current
recycling of WCO for human consumption, bearing in mind the
attendant risks to public health.
Fatty acids (FAs) can be either saturated FAs (SFAs) or unsatu-
rated FAs (USFAs) depending on the nature of carbon-to-carbon
bonds. SFAs are carboxylic acids with between 12 and 24 single
carbon-to-carbon bond and are chemically less reactive. They
contain the maximum number of hydrogen atoms that a single
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Comparative study of properties and fatty acid composition of some neat vegetable oils and waste cooking oils
bond carbon atom can accommodate between the successive
carbon atoms. The melting point of SFA has been found to
increase with chain length, and those SFAs with 10 carbon atoms
or more (capric, lauric, myristic, palmitic, margaric, stearic,
arachidic and behenic acids) are solids at room temperature.
Conversely,USFAs,unlikeSFAs,haveoneormorecarbon-to-
carbon double bonds. USFAs can either be monounsaturated FAs
(MUFAs) or polyunsaturated FAs (PUFAs) having one double
bond or more than one double bond, respectively. Chemical
reactivity increases with an increase in the number of double
bonds. Oleic acid is the most naturally occurring MUFA.
Other examples of MUFAs include caproleic, lauroleic, elaidic,
myristoleic and palmitoleic acids. USFAs exist either in a cis-
conguration or trans-conguration. Most cis-congurations
are available in most of the naturally occurring USFAs, while
the trans-conguration is precipitated due to hydrogenation
and other technical processes. Notable examples of PUFAs with
thenumberofdoublebondsincludelinoleicacids;twodouble
bonds, linolenic acids; three double bonds, arachidic acids;
four double bonds, eicosapentaenoic acids; ve double bonds,
docosahexaenoic acids; and six double bonds [2830].
In one research, Vingering et al.[31] determined the FA
composition of some commercial vegetable oil in the French
market and reported that sunower oil, for example, contains
SFA, MUFA, and PUFA of 11.3%, 31.7% and 56.3%, respectively.
Hellier et al.[32] experimentally carried out the FA compositions
of seven vegetable oils, including palm oil and sunower oil, and
reported that while palm oil contains 40–47% palmitic acid and
36–44% oleic acid, sunower oil is made up of 49–57% linoleic
and 14–40% oleic acids. They also reported the density (at 20C)
and dynamic viscosity (at 59.7C) of 910 kg/m3and 19.4 mPa·s
for palm oil and 916.9 kg/m3and 17.2 mPa·s for sunower oil,
respectively. The FA composition of edible vegetable oil was
determined aer repeated cooking at elevated temperature by
Banani et al.[33] using gas chromatography coupled to mass
spectrometry (GCMS). It was reported that the oleic, linoleic,
palmitic, stearic and linolenic acids contents were found to be
29.83%, 28.85%, 15.86%, 4.87% and 2.49%, respectively. The
density at 15Candviscosityat40
C were found to be 910 kg/m3
and23.12 mm2/s, respectively. Kumar and Negi [34]comparedthe
FA composition of vegetable oil before and aer repeated use and
concluded that repeated use of vegetable oil alters the composition
and induces various polymerized derivatives, hydrocarbons,
and glyceride molecules, which make the oil unsafe for human
consumption and disposal to the environment.
According to Panadare and Rathod [35], fresh vegetable oil
undergoes lots of physio-chemical transformations during frying,
which alters its properties, FA proles and other ngerprints
depending on factors like cooking duration, frying temperature
and types of food items the oil was used for. In a research,
Knothe and Steidley [36]analyzedtheusedandunusedvegetable
oil samples collected from 16 restaurants using FA prole,
viscosity and acid value as a basis for comparison. They observed
that WCO undergoes hydrogenation and oxidative degradation
processes during high-temperature frying capable of altering its
ngerprints. Owing to changes in FA prole of the oils during
frying, the properties of the oil were altered by increasing in
SFA and MUFA relative to PUFA. They attributed the changes
in properties and FA composition to the eects of structural
morphology of the fuel. Also, the palm oil used to fry the food
items was reported to show an increased degree of saturation,
higher viscosity, elevated cetane numbers, oxidative stability
and other ngerprints of fatty acid methyl ester (FAME). The
alteration in the ngerprint of the fuel as a result of the change
of FA prole during frying was attributed to the known eects
of compound structure on biodiesel properties. Due to the
eect of high-temperature degradation during cooking, biodiesel
derivedfromsuchfeedstockisexpectedtoexhibitahigherdegree
of saturation and greater oxidative stability. Also, the biodiesel is
expected to possess elevated kinematic viscosity, higher cloud
point and cetane number than does the biodiesel form of neat
vegetable oil.
The objective of this research is to compare the properties and
the FA composition of neat vegetable oil with WCO from such
oils. The aim is to determine how the duration of usage and
thetypeoffoodfriedintheoilaectsomepropertiesandthe
FA composition of WCO compared with their neat vegetable oil
source. The questions being investigated are as follows: How do
duration of usage and the composition of food items fried by the
neat vegetable oil inuence the properties and FA composition of
the WCO? How do the properties and FA composition of neat
vegetable oil vary from those of WCO from the same source?
What is the eect of consumption of these WCOs on human
and the eect of their disposal on aquatic and terrestrial habitats?
This current eort is limited to analysis of four samples of neat
vegetable oil and six samples of WCO obtained from restaurants,
bakeries, and takeaway outlets collected at the point of disposal.
Thedegreeofusagewasnotcontrolled,butthehistoryofthe
samples was collected from the users.
2MATERIALS AND METHOD
2.1 Material collection
Samples of neat vegetable oil and as-produced WCO were col-
lected from restaurants, takeaway outlets and bakeries randomly
fromDurban,KwaZulu-NatalProvince,SouthAfrica.Thedegree
andrateofusageoftheoilswerenotmonitored.TheWCOswere
collected as-produced and while awaiting disposal by the various
outlets. The samples were collected for property determination
and pyrolysis gas chromatography mass spectrometry (PYGCMS)
analysis. Popular restaurants and fast-food outlets turned down
requests for used oil samples and referred our requests to their
regional oces. The samples used in the research were collected
from small and owner-operated restaurants and takeaway outlets.
2.2 Treatment of WCO
The samples were poured into a beaker and heated at 110Cinan
electric heater for 15 min to remove moisture. The WCO sample
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Table 2. Some properties and methods/instruments of determination
[37,38]
Property Unit Method/instrument
Density at 20Ckg/m
3ASTM D 1298
Kinematic viscosity at 40Cmm
2/s ASTM D445
Acid value AOCS Ca 4a-40
Iodine value cg/g AOCS Cd 1B-87
Molecular weight g/mol Calculated
pH pH meter
Congealing temperature C Digital thermometer
was allowed to cool to room temperature and subjected to vacuum
ltration process to remove any food residue and other suspended
solid matter in the sample. The clean WCO samples were stored
in an airtight glass container.
2.3 Property determination of neat vegetable oil and
WCO samples
The iodine value, pH, density, congealing temperature, acid value,
viscosity, cetane index and an acid number of neat vegetable oil
and clean WCO samples were determined using the appropriate
methods [37]andequipmentasshowninTable 2.
i. pH: The pH of the WCO was determined with the aid of a
pH meter.
ii. Congealing temperature: The congealing temperature of
the samples was determined by putting 20 ml of the sample
of neat vegetable oil and WCO in a 100-ml beaker, inserting
the probe of a digital thermocouple into the sample and
putting it into deep freeze. The temperature of the neat and
WCO samples was monitored through a thermometer. The
congealing temperature is the mean of the temperatures at
the commencement and completion of gelation of the oil
samples.
iii. Density and kinematic viscosity: The density and kine-
matic viscosity of the neat vegetable oil and WCO samples
were determined by a viscometer at 20CusingaDMA
TM
4100 M density meter.
iv. Iodine value: The iodine value of the WCO samples
was determined in accordance with the AOCS Cd 1b-87
method.
v. Acid number: The acid value of the WCO samples was
determined in accordance with the AOCS Ca 5a-40
method.
vi. Molecular weight: Calculated from the molecular weight
of the individual FAs in the neat vegetable oil and WCO
samples.
2.4 Determination of FA composition of neat vegetable
oil and WCO samples
The FA composition of the neat vegetable oil and WCO samples
was determined by PYGCMS on Shimadzu gas chromatograph
mass spectrometer using an ultra-alloy-5 capillary column and
GCMS-QP2010 Plus soware. The choice of PYGCMS rather
than the normal GCMS was due to the low volatility nature of
the samples, which might clog the column of the GCMS machine.
The selected carrier gas was helium, while 2 μl of sample was
injected at column oven temperature and injection temperature of
40C and 240C,respectively.Thetotalow,columnow,linear
velocity and purge ow were set and maintained at 58.2 ml/min,
1.78ml/min, 48.1 cm/s and3.0ml/min, respectively,ata total time
of 92.33 min. Split injection mode was adopted.
3RESULT AND DISCUSSION
3.1 Eects of usage on properties and FA composition
Properties of samples of neat vegetable oil are shown in Table 3.
ThepHofthefourneatvegetableoilsamplesvariesbetween
6.34 and 8.63, while the congealing temperature varies between
10.25C and 0.3C. Though their density is almost the same,
depot margarine presented the highest viscosity value when com-
pared with other neat vegetable oil samples. Table 4 shows the
sources, points of collection, usage, duration and properties of the
WCO samples. Though the numbers of days of usage were known,
the numbers of cycles of usage and frying temperature were not
known.
The pH of WCO samples varies between 5.13 and 6.61, indi-
catingaweakacid,whichconrmsitssuitabilityasabiodiesel
feedstock. It was observed that sausage triggered higher pH values
thandidsh.Thismightbearesultoffatsfromshbeingmore
acidic than those of beef [39]. WCO samples from bakeries were
the most acidic samples. The reduction in the acidity of waste
palm oil aer repeated frying can be attributed to the eects
of thermal degradation and contamination from the food items.
Almost all the neat vegetable oil samples witnessed a reduction in
pH as a result of usage. Samples D and F have the highest con-
gealing temperature followed by sample B from depot margarine,
while sample C has the least congealing temperature of 6.3C
(see Table 4). The change in the congealing temperature can be
traced to the eects of contamination of the food items.
The results in Table 4 show that the subjection of vegetable
oil to high temperature over a period of time has degraded and
reduced its quality. Though the densities of neat vegetable oil are
not remarkably dierent from each other, the densities of WCO
vary with usage, generally. The density of the six WCO samples
varied between 904 and 923 kg/m3.SampleE,whichwasused
for7days,hasahigherdensitythanhassampleCfromthesame
source, used for the same purpose but for a longer duration. It can
be deduced, therefore, that the density of WCO samples reduced
withincreaseddurationofusage.Thisthermaldissociationcanbe
attributable to decomposition of the double chain in the carbon
chain caused by pyrolysis. The viscosity of the WCO samples
ranges between 33.46 mm2/sforsampleA(usedtofryshand
potatoes) and 48.32 mm2/s for sample B (taken from a bakery).
Table 5 shows that only nine FAs are present in the samples and
in low percentages, with the highest being 45% linoleic acid in
palm oil. Linoleic acid, capric acid and stearic acid are common in
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Comparative study of properties and fatty acid composition of some neat vegetable oils and waste cooking oils
Table 3. Properties of neat vegetable oil samples
Samples pH Congealing temperature (C) Density at 20C(kg/m
3)Viscosityat40
C(mm
2/s) Molecular weight (g/mol)
Sunower 7.38 8.65 919.21 28.744 670.82
Sunfoil 8.63 9.8 919.6 28.224 119.71
Palm oil 6.34 10.25 919.48 27.962 535.08
Depot margarine 6.39 0.3 919.72 29.334 563.87
Table 4. Specications and properties of the WCO samples
Sample Source oil Outlet Usage Usage
(days) pH Congealing
temperature
(C)
Density at
20C
(kg/m3)
Viscosity
at 40C
(mm2/s)
Iodine
value
(cg/g)
Acid
value Molecular
weight
(g/mol)
A Sunower oil Restaurant Fish and chips 14 5.34 5.15 920.4 31.381 111.1 2.29 51.94
B Depot margarine Bakery Doughnuts 14 5.13 4.9 917.18 40.927 54.9 2.87 534.01
C Sunfoil Takeaway Chips 14 6.14 6.3 919.8 43.521 116.7 0.72 55.18
D Palm oil Takeaway Fish and chips 14 5.73 12.3 904.3 44.254 81.7 0.66 135.66
E Sunfoil Restaurant Chips 7 6.61 3.4 923.2 35.236 110.3 1.44 395.28
F Palm oil Takeaway Chips and
sausages 14 6.19 14.7 913.4 38.407 54.2 1.13 586.05
Table 5. Fattyacidcompositionofneatvegetableoilsamples
Fatty acid Neat vegetable oil samples
Common name Formula Acronym Sunower oil Sunfoil Palm oil Depot margarine
Palmitic acid CH3(CH2)14COOH C16:0 32.21 8.07
Linoleic acid CH3(CH2)4CH=CHCH2CH=CH (CH2)7COOH C18:2 21.98 3.26 45.50 24.57
Erucid acid CH3(CH2)7CH=CH (CH2)11COOH C22:1 — 6.83
Caprylic acid CH3(CH2)6COOH C8:0 0.22 1.68 0.56 1.06
Enanthic acid CH3(CH2)5COOH C7:0 0.51 0.82 —
Capric acid CH3(CH2)8COOH C10:0 0.51 3.79 2.43 2.84
Stearic acid CH3(CH2)16 COOH C18:0 9.27 2.87 2.67 4.22
Arachidic acid CH3(CH2)18 COOH C20:0 12.36
Lauric acid CH3(CH2)10COOH C12:0 1.12 0.86 0.83
Saturated fatty acid, SFA (%) 71.48 74.37 12.3 40.92
Monounsaturated fatty acid, MUFA (%) 11.45
Polyunsaturated fatty acid, PUFA (%) 28.52 25.63 76.25 59.08
all the samples, while arachidic acid only appeared in one sample.
Sunower oil and sunfoil contain mainly SFAs, while palm oil and
depot margarine contain mainly PUFAs. However, only palm oil
contains MUFAs as shown in Fig. 2.
As shown in Table 6, the WCO samples have a fewer number
of FAs and in smaller quantities. This further conrms the sam-
ples’ suitability as FAME feedstock [40]. Oleic acid is the most
frequently occurring acid, appearing in all the samples. As shown
in Table 6,samplesB,C,DandFhavemoreSFAs,whilesamplesA
and E have more MUFAs and PUFAs, respectively. For example,
sample D (used to fry beef) is composed of SFA and MUFA, as
conrmed by Abbas et al.[41].
The mainly SFAs in neat sunower oil were converted to mostly
MUFAs in WCO sample A, while the SFAs in neat sunfoil oil were
also converted to PUFAs in WCO sample E.
Conversely, the neat palm oil and depot margarine, which were
mostly made up of PUFAs, were converted into SFAs in samples B,
D and E aer repeated high-temperature cooking. These may be
attributed to the eect of prolonged exposure to high temperature.
The variation in the FA compositions of samples C and E, despite
beingfromthesamesunfoilandusedtofrypotatochips,shows
that the SFA in sunfoil is converted into the PFAs in sample E and
SFAsinsampleC.Thismaybeattributedtothegreaterdurationof
usage of sample C compared with sample E. Food items, especially
sh and beef, greatly aect the FA composition of WCO from
those sources [39]. As shown in Table 6,theobserveddierence
in the level of saturation between sample D and F was due to the
fact that sh contains more unsaturated oil than does sausage. So
even though both samples are from the same primary oil source,
what they were used for altered the FA composition.
Generally, due to repeated and high cooking temperature, the
PYGCMS showed the presence of hydrocarbons and polymerized
derivative of glyceride. The transformation and the mechanism
for generation of cyclic and noncyclic hydrocarbon in vegetable
oil during high-temperature repeated cooking can be dicult to
predict as a result of the myriads of reactions that produce many
unstable intermediate hydrocarbons, including the weak C–H
bond. Also, a persistent increase of peroxide value during multiple
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O. Awogbemi et al.
Figure 2. SFA, MUFA and PUFA compositions of neat vegetable oil samples.
Table 6. Fatty acid composition of WCO samples
Fatty acid Waste cooking oil samples
Common name Formula Acronym A B C D E F
Oleic acid CH3(CH2)7CH=CH (CH2)11 COOH C18:1 0.8 18.02 0.59 0.72 2.74 14.39
Palmitic acid CH3(CH2)14COOH C16:0 0.36 43.2 — 5.98 40.21
Linoleic acid CH3(CH2)4CH=CHCH2CH=CH (CH2)7COOH C18:2 0.10 — 33.89 —
Erucid acid CH3(CH2)7CH=CH (CH2)11 COOH C22:1 0.26 — — — —
Caprylic acid CH3(CH2)6COOH C8:0 0.20 0.15
Undecylic acid CH3(CH2)9COOH C11:0 1.85 0.43 0.52 —
Stearic acid CH3(CH2)16COOH C18:0 ——1.14——
Myristic acid CH3(CH2)12COOH C14:0 — — — — — 17.04
Nonadecylic acid CH3(CH2)17 COOH C19:0 — — — 9.76
Saturatedfattyacid,SFA(%) 3271 739315 80
Monounsaturated fatty acid, MUFA (%) 62 29 27 7 6 20
Polyunsaturated fatty acid, PUFA (%) 6 — — 79 —
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Comparative study of properties and fatty acid composition of some neat vegetable oils and waste cooking oils
Table 7. Some harmful chemicals in WCO and their eects
Chemical Eects Reference
2,3-Dihydroxypropyl elaidate C21H40O4• Harmful if ingested [47]
• Causes severe eye irritation
1-Hexanol C6H14O •Harmfulifconsumedortouchestheskin [48]
• Causes severe eye irritation
Palmitic acid C16H32 O2•Causesacuteskin,eyeandrespiratoryirritations [49]
• Harmful to aquatic life with long-lasting eects
Linoleic acid C18H32 O2• Triggers skin, eye and respiratory irritations [50]
• The possibility of causing long-lasting damaging eects on aquatic life
i-Propyl 14-methyl-pentadecanoate C16H32O2• Toxic to aquatic animals and wildlife habitat [51]
•Causeseyeandskinirritationsandlunginjury
• Long-term destructive health eects
• Acute mammalian inhalation toxicity
1-Heptene C7H14 • Highly combustible liquid and vapor [52]
•Maybedangerousifswallowedandentersairways
• Poisonous to aquatic life with long grave consequence
cis-9-Hexadecenal C16H30O • Causes skin, acute eye and respiratory irritations [52]
• Harmful if inhaled
• Extremely poisonous to aquatic life
high temperatures energized water to act as a weak nucleophile
foresterlinkage,whileheatmasstransferandinducedoxygen
aggravated thermal oxidation [34,42].
3.2 Eects of usage of vegetable oil on health and
aquatic habitat
Human consumption of used vegetable oil has undesirable eects
on human health. Available facts reveal that consumption of SFA
such as palmitic acid is injurious to cardiovascular health [43]. As
shown in Table 6, most WCO samples consist mainly of SFAs and
MUFAsand less of PUFAs.Accordingto the Food andAgriculture
Organization report of an expert consultation on fats and FAs in
human nutrition, the SFAs and MUFAs in the WCO samples are
higher than those recommended for human consumption. Intake
of major SFAs including lauric, myristic and palmitic acids not
only increases low-density lipoprotein (LDL) cholesterol but also
increases the risk of diabetes. Replacing SFA with PUFA decreases
the risk of coronary heart disease (CHD). Recommended human
consumption of SFAs is less than 10%. Also, consumption of
MUFAs is capable of increasing high-density lipoprotein (HDL)
cholesterol concentrations, while consumption of oleic acid may
aggravate insulin resistance, unlike the PUFAs. The eects of
consumption of PUFAs on human health have been traced to
the prevention of cardiovascular disease (DVD), coronary heart
disease (CDH), cancer, diabetes, renal diseases, inammatory,
thrombotic and autoimmune disease, hypertension as well as
renal diseases and rheumatoid arthritis [4446]. The PUFAs in
the neat vegetable oil samples have been converted to SFAs and
MUFAs as a result of the thermal degradation occasioned by
repeated subjection of the oil to high temperature during cooking
and frying. This has made the WCO injurious for human con-
sumption.
Contamination of aquatic habitat by WCO as a result of
improper disposal has negative eects on aquatic animals. Apart
from the FA composition in WCO, the PYGCMS also revealed
other components of the oil. Tabl e 7 shows other components of
WCO and their eects on human, wildlife and aquatic habitats.
Inappropriate disposal and consumption of WCO should be
discouraged by enforcing relevant regulations. Apart from the
use of WCO as feedstock for FAME, WCO has been found to
have household, personal and industrial applications. Hexanol
is useful as a fuel, a fuel additive and a avoring agent. 2,3-
Dihydroxypropyl elaidate and 1-hexanol, which are present in
some of the WCO samples, can be used in plastic and rubber
products, lubricants and lubricant additives, greases, paint and
coating additives, pigment solvents, cleaning and furniture care
products, food packaging and personal care products, among
other industrial and household applications [47,48].
4CONCLUSION
The application of WCO, in contrast to neat edible oil and inedible
oil, as feedstock for FAME has been found to be economically
benecial. The use of WCO reduces the high production cost of
biodiesel; solves problems associated with the disposal of WCO;
eliminates problems associated with contamination of aquatic
and terrestrial habitats, and blocking of drains and pipelines as
a result of inappropriate disposal methodologies; and generates
additional income for households and small-scale businesses.
This research has shown that the properties and FA composition
of neat vegetable oil can be modied by the degree of usage and
food items. The exposure to high temperature during cooking,
duration of usage, and what oil was used to fry have been found
to substantially aect the properties and FA compositions of the
oils. More importantly, this research has proved that the duration
ofusageandthevarietyoffoodhaveconsiderableinuenceon
the properties and FA composition of used vegetable oil. To a
very large extent, neat vegetable oil is made up mostly of SFA
International Journal of Low-Carbon Technologies 2019, 14, 417–425 423
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O. Awogbemi et al.
and PUFA; WCO, on the other hand, consists mainly of SFA and
MUFA. Human consumption and inappropriate disposal of WCO
result in serious health challenges and negatively aect terrestrial
and aquatic animals.
During the course of collecting these samples, it was discovered
that all the outlets were not willing to give out their used oil
because they had signed agreements with some companies that
buy the used oils from them. Unconrmed reports indicate that
a large percentage of these oils are ltered and sold to unsuspect-
ing consumers, with attendant health implications. Appropriate
policies should be introduced not only to discourage human
consumption of WCO but to also ensure all WCOs are channeled
towards industrial and energy applications, most especially fuel.
In order for the country to meet its share of renewable fuel quota,
especially for transport vehicles, tax holidays and other incentives
should be granted to small-scale fuel reners to convert WCO to
biodiesel, hydrogenated green diesel and other forms of fuel for
internal combustion engines. Strict penalties against inappropri-
ate disposal and consumption of WCOs should be enforced by
relevant government agencies.
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