Anal. Methods Environ. Chem. J. 6 (3) (2023) 103-120

Research Article, Issue 3

Analytical Methods in Environmental Chemiﬆry Journal

Journal home page: www.amecj.com/ir

AMECJ

Comparative analysis of groundnut oil quality in the north-

central zone of Nigeria: Determination and evaluation of

heavy metals, fatty acids, phospholipids, and iodine values in

groundnut oil

Ijah Silas Ioryue a *, and Terngu Timothy Uzah b

a Department of Biochemis try, Federal University of Technology, Ikot Abasi, Nigeria,

b Department of Chemis try Federal University of Petroleum Resources, Efrum, Nigeria

ABSTRACT

The research presents a comparative analysis of the quality of locally

produced groundnut oil (Arachis hypogaea) sold in the north-central

zone of Nigeria markets (Benue, Nasarawa, Kogi, Kwara, Niger and

Plateau S tates). The aim was to assess and compare the qualities of the

oils and to know the safety of human consumption. The groundnut oil

produced biodiesel, shampoo lubricants, and soap-making indus tries.

The concentrations of the heavy metals were analyzed with atomic

absorption spectrometry (AAS). It showed that the lead, zinc, and

copper (Pb, Zn, Cu) were within the FAO/WHO recommended limit,

while Cd (0.201-0.331 mg kg-1) was above the limit (0.07 mg kg-1). Also,

the gas chromatography (GC-FID) results indicated that twelve fatty

acids (linoleic > oleic > palmitic > s tearic > lignoceric > arachidic

acid > behenic > erucic > arachidonic > margaric > linolenic >

palmitoleic) were obtained in the groundnut oils in all markets

and fatty acids include caprylic acid, capric acid, lauric acid, and

myris tic acid were absent in oils. In addition, the magnitude of six

phospholipids (phosphatidylcholine > phosphatidylethanolamine

> phosphatidylinositol > phosphatidylserine > phosphatidic acid

> lysophosphatidylcholine) were also achieved, respectively. The

results showed that iodine, peroxide, saponiﬁcation value and

refractive index were below the FAO/WHO recommended level, and

the acid value was higher than the normal range.

Keywords:

Analysis,

Groundnut oil,

Atomic absorption spectrometer,

Fatty acid,

Phospholipids,

Gas chromatography

ARTICLE INFO:

Received 11 May 2023

Revised form 21 Jul 2023

Accepted 17 Aug 2023

Available online 29 Sep 2023

*Corresponding Author: Ijah Silas Ioryue

Email: silasoo4real@gmail.com

https://doi.org/10.24200/amecj.v6.i03.239

1. Introduction

Groundnut oil is a tas ting oil derived from the

groundnut plant (Arachishypogaea), a species in

the legumes family (Fabaceae). Some common

synonyms for groundnut are peanut, earthnut,

goober, pinder, and ground pea. It is called “abum”

by the Tiv people, “emansak” by the Ibibios,

“epa” by the Yorubas, ”Gyada’’ by the Hausas and

Asiboko by the Ibos. In 1753, Linnaeus described

the domes ticated groundnut species as Arachis

(derived from the Greek ‘‘arachis,’’ meaning

a weed), hypogaea (meaning an underground

chamber) or a weed with fruit produced below the

soil. Groundnut is eaten fresh or roas ted and is used

in cooking, confectionery and pressed for edible oil.

Palm oil and groundnut oil are both vegetable oils.

Vegetable oils are water-insoluble, edible liquids

derived from plants, which consis t predominantly

of long-chain fatty acid es ters derived from the

------------------------

104

simple alcohol glycerol. Oil plays a crucial role in

our everyday life. There are diﬀerent types of oils,

including edible, non-edible, essential oils [1], etc.

Edible oils include palm oil, coconut oil, groundnut

oil, etc. Rubber seed oil is an example of non-edible

oil. Essential oils include Jasmine oil, sandalwood

oils, etc. The quality of groundnut oil could be

aﬀected by improper pos t-harves t handling,

processing and s torage. Again, there is widespread

speculation that groundnut oil is being adulterated

for proﬁt maximization. The adulteration ranges

from using dyes, water and other illegal food

additives, which could aﬀect the quality of these

oils regarding nutritional value, wholesomeness,

utilization, safety and shelf-life. The percentage of

free fatty acid, mois ture and dirt content generally

determines the quality of this oil. The produce is

traditionally bought on a 5% free fatty acid basis

with penalties for exceeding this ﬁgure [2]. Hence,

there is a need to assess the quality of groundnut

oils sold in major markets in the north-central

zone of Nigeria. Heavy metals have relatively high

densities of 4.0g cm-1 and above [3]. Heavy metals

in trace amounts are of signiﬁcant beneﬁt to man.

Inadequate trace elements in diet may cons titute a

health problem that may be devas tating. In large

doses, heavy metals are generally characterized as

toxic or poisonous. Since trace elements provide

nutritional value, they are sometimes called

micronutrients [3]. Groundnut oils are essential

daily condiments because of their various uses

in our everyday lives. Unfortunately, it has been

reported that some brands of groundnut and

palm oils are adulterated with diesel automobile

hydrocarbon oil, which is miscible with vegetable

oils. This impurity is alleged to change the quality

of vegetable oils and consequently negatively

aﬀect consumers [4]. Vegetable oils and fats

contain trace levels of various metals depending

on many factors such as species, soil used for

cultivation, irrigational water, variety and s tage of

maturity, pollution, mode of processing, s torage,

and contaminations. These metals may enter the

food material from the soil through mineral uptake

by crops, food processing, and environmental

contamination (as in fertilizer application). Metals

play essential negative and positive roles in human

life [5]. Hence, there is a need to determine the

concentration of heavy metals, trace elements

and some physicochemical parameters in these

groundnut oils in the north-central zone so that

consumers will know the qualities of these

groundnut oils. Atomic absorption spectroscopy

(AAS) is a widely used analytical technique for

determining heavy metals concentration in water,

fats and oils [6-8]. It is a sensitive and reliable

method for measuring trace amounts of heavy

metals in water and oil samples. AAS has been

used in several s tudies to assess drinking water

quality and food samples from various sources,

including oils. Gas chromatography (GC) Flame

ionization detector (FID) is a well-es tablished

technique which is used to identify and quantify

the incorporation of fatty acids into lipid pools.

Chromatographic separation of lipids is typically

extracted from the sample using the solubility

of lipids in solvent mixtures of chloroform and

methanol. Sodium chloride is added to facilitate the

separation of the mixture into aqueous and organic

lipid-containing phases [9]. Complex lipid classes

of interes t can be separated from the total lipid

extract by solid phase extraction (SPE).

The s tudy aimed to assess the quality and

Nutritional values of locally produced groundnut

oil in the northern central zone of Nigeria (Benue,

Nasarawa, Kogi, Kwara, Niger and Plateau s tates).

Therefore, the AAS and GC-FID determined the

physicochemical parameters, the concentration of

heavy metals, and the concentration of fatty acids

and phospholipids in groundnut oil.

2. Material and Methods

2.1. Reagents and Materials

The reagents used for the analysis were all analytical

grades purchased from Emole Nigeria (NO: 33 Old

Otukpo Road high level, Makurdi, Benue S tate,

Nigeria). Cadmium, lead, zinc, and copper s tandard

solutions (500 mL; 1000 mg L-1) purchased from

Merck, Germany. The reagents such as nitric

acid (CAS number : 7697-37-2), sulfuric acid

Anal. Methods Environ. Chem. J. 6 (3) (2023) 103-120

105

Comparative analysis of groundnut oil by AAS and GC-FID Ijah Silas Ioryue et al

(CAS number: 7664-93-9), hydrochloric acid

(CAS number: 7647-01-0), hydrogen peroxide

(CAS number: 7722-84-1), sodium hydroxide

(CAS number: 1310-73-2), sodium thiosulphate

(CAS number: 7772-98-7), glacial acetic acid

(CAS number: 64-19-7), potassium hydroxide

(CAS number: 1310-58-3), potassium iodide (CAS

number: 7681-11-0), ethanol (CAS number: 64-17-

5), tetrachloromethane (CAS number: 56-23-5),

chloroform (CAS number: 67-66-3), Wiji’s solution

(CAS number: 7790-99-0), phloroglucinol (CAS

number: 108-73-6), diethyl ether (CAS number: 60-29-

7), methanol (CAS number: 67-56-1), boron triﬂuoride

(CAS number: 7637-07-2), n-hexane (CAS number:

110-54-3) were purchased from Merck, Germany.

Also, the phenolphthalein indicator (Sigma), s tarch

indicator (Sigma), polyethylene bottles (plas tic

bottles), weighing balance, beakers, oven, ﬁlter

paper, deionized water (DW), bottles, bath water

and heating were used for analysis groundnut oil.

2.2. Ins trumental

The measurements were made from Ahmadu Bello

University Zaria Laboratory for the analysis of

heavy metal samples using a Phoenix 986 atomic

absorption spectrometer (Biotech Engineering

Management Co. Ltd, UK) and Shimadzu GC-

FID (model GC-2014; Sweden) for the analysis

of Fatty acids and phospholipids in the groundnut

oils. Cadmium, lead, zinc and copper hollow

cathode lamps were operated according to the AAS

manufacturer’s ins tructions.

2.2.1. Atomic Absorption Spectrophotometer

A Phoenix 986 model (Biotech Engineering

Management Co. Ltd, UK) atomic absorption

spectrometer with four hollow cathode lamp

positions was employed. The light sources of the

diﬀerent elements were hollow-cathode lamps

from Cathoden, UK. The light beam through

Air-Acetylene was controlled by an aperture for

measuring absorbance in diﬀerent slit widths

depending on the calculated element. The oxidant

rate was 4.5 L min-1, and the fuel rate (C2H2) was

1.5 L min-1. The mos t sensitive Cd, Cu, Pb and Zn

absorption lines were used [10]. S tandard solutions

were inspired into the ﬂames after the burner had

been allowed to operate for 5-10 min. This way,

thermal equilibrium was attained before any ﬁnal

adjus tment to the absorbance mode, measuring

time, burner height, gas ﬂows or ampliﬁer gain. In

this case, maximum sensitivity will be expected.

All absorbance values are the average of ten

readings recorded successively from the diﬀerent

absorbance modes. The background absorption is

measured and subtracted from the total absorption

to determine the actual atomic absorption signal.

For this reason, a continuum source of deuterium

arc lamp in ultraviolet has been used to measure

only the background contribution to the absorption

signal, which has essentially zero atomic

absorption sensitivity at the regular resolution for

atomic absorption ins truments. In this case, the

background correction is automatically carried out

by a background correction sys tem [11]. The limit of

detection (LOD) and limit of quantiﬁcation (LOQ)

for heavy metal (Pb, Zn, Cu, Cd) determination

was achieved by AAS and is shown in Table 1. The

lowes t qualitative and quantitative concentrations

for the tes ted linearity range were calculated

for each metal according to the guidelines of

ICH,2000. LOD and LOQ were calculated using

the expression m × S/c, where m = 3.3 for the LOD

and 10 for the LOQ, S is the s tandard deviation of

the intercept, and c is the slope of the calibration

curve tes ted for linearity.

Table 1. The LOD and LOQ of AAS For heavy metal determination

Parameter Pb Zn Cu Cd Average

LOD( mg L-1) 0.088 0.052 0.077 0.028 0.06125

LOQ (mg L-1) 0.433 0.208 0.231 0.112 0.2455

106

2.2.2.Gas chromatography analysis

Shimadzu GC-FID model GC-2014 Sweden was

equipped with a ﬂame ionization detector and

capillary column (30 m, 0.53 mm) with a s tationary

phase fused silica. The chromatographic conditions

were detector temperature 280°C, injector

temperature 250°C, initial column temperature

120°C for 1 min, programmed to increase at a rate

of 10°C per minute up to 200°C and then at four

°C per minute up to the ﬁnal temperature of 220°C.

Nitrogen and hydrogen for chromatography R, as

the carrier and auxiliary gas, respectively, have a 1.3

mL min-1 ﬂow rate. As a determination, one μL of

the derived sample was injected, alternatively with

a sample volume/internal s tandard ratio of 80/20.

Fatty acids and phospholipids were identiﬁed by

comparing the s tandards’ retention times and

relative retention times with those of the samples.

The quantiﬁcation was by internal s tandardization

using the methyl es ters of lauric acid as the internal

s tandard. The value of fatty acids and phospholipids

were calculated according to AOCS methodology

(mg per 100 g-1) [12].

2.3. General Procedure

Firs t, the groundnut oil (Arachis hypogaea) samples

were prepared by diges tion procedure, and then

parameters such as iodine value, the concentration

of free fatty acid, Acid value, color, odour, peroxide

value, saponiﬁcation value and refractive index

were determined. Also, heavy metals (Cd, Pb Zn

and Cu), Fatty acids and phospholipids in groundnut

oil were determined.

2.3.1. Diges tion of groundnut oil (Arachis

hypogaea)

Firs t, 2.0 g of each sample was weighed in a beaker.

Concentrated nitric and sulphuric acids (5cm3) were

added, followed by hydrogen peroxide (2cm3), then

heated on a heating mantle until a clear solution was

obtained. The content of the beaker was allowed to

cool and then ﬁltered. The resulting solutions were

made up to 50cm3 using de-ionized water and then

transferred into a plas tic bottle for metal analysis

by the AAS method [13].

2.3.2. Procedure for determination of

parameters in groundnut oil

Acid value was determined by the titrimetric

method of Kupwade and Desai [14]. 5g of the

oil sample was weighed, and 75 mL of hot,

neutral alcohol was added with a few drops

of phenolphthalein. The mixture was shaken

vigorously and titrated with 0.1M NaOH

solution with cons tant shaking until the pink

coloration remained permanent. The acid value

was calculated using Equation 1(V= titration

endpoint value).

Acid value=(V×5.6) / (Weight of sample)

(Eq.1)

The iodine value was determined according to

the titrimetric method of Pearson [15]. 2.0 g of

oil sample was weighed into a dry glass s topper

bottle of 250 mL Capacity, and 10 mL of carbon

tetrachloride was added to the oil. About 20 mL

of Wij’s solutions were then added and allowed

to s tand in the dark for 30 min. 15 mL of (10%)

potassium iodide and 100 mL of water were added

and then titrated with 0.1M sodium thiosulphate

solution using s tarch as indicator jus t before the

endpoint. A blank was also prepared alongside

the oil samples. The iodine value was calculated

by Equation 2.

Iodine value= (V2-V1)×1.269 / Weight (g)

(Eq.2)

Where V2= titre value for blank, V1= titre value

for sample(s)

The peroxide value was evaluated according

to AOAC [16]. A 2.0 g oil sample was weighed

into a tube, and 1g of powdered potassium

iodide with 20 mL of solvent mixture (glacial

acetic acid and Chloroform) was added. This

was then placed in boiling water for 30s. The

content was poured into a flask containing 20

mL of 5% iodide solution. The tube was washed

with 25ml of dis tilled water and titrated with

0.002N sodium thiosulphate solution using

Anal. Methods Environ. Chem. J. 6 (3) (2023) 103-120

107

s tarch as an indicator. A blank was prepared

alongside the oil samples. Peroxide was

obtained by Equation 3.

(Eq.3)

Where V2= titre value for blank, V1= titre value for

sample(s)

The Saponiﬁcation value was determined according

to the titrimetric method of Pearson [15].

2.0 g of oil sample was weighed into a conical ﬂask,

and 25 mL of alcoholic potassium hydroxide was

added. The solution was heated in boiling water for

one hour. 1 mL of 1% phenolphthalein was added

and titrated with 0.5N HCl. A blank was prepared

alongside the oil samples. The formula calculated

the value by Equation 4.

(Eq.4)

Where N= Concentration of HCl acid used,

A= Volume of H2SO4, for blank (mL),

B= Volume of H2SO4 (mL),

56.1= Equivalent weight of potassium hydroxide,

W= weight of oil

The colour of the oil samples was determined

by visual comparison, while the odour of the oil

samples were determined using a glass s toppered

bottle rinsed with 4 M HCl internally and

externally and rinsed with dis tilled water. The

bottle was halfway ﬁlled with the oil sample and

shaken vigorously for about 2 minutes. The s topper

was then removed, and the odour was observed

by putting nos trils near the mouth of the bottle.

The rancidity of the oil samples was determined

qualitatively using the Kries Tes t, as described by

Pearson [15]. 5.0 cm3 of the oil samples was placed

in a 100 cm3 tes t tube vigorously mixed with 5cm3

of 0.1% phloroglucinol solution in diethyl ether

and 5 cm3 of concentrated HCI for about 20s.

The presence of pink colour indicates incipient

rancidity. The refractive index (RI) was determined

using a mathematical expression [17] and shown in

Equation 5.

RI=1.45765 + 0.0001164/V (Eq.5)

RI: the Refractive Index

V : Iodine Value

2.3.3. Procedure for analysis of fatty acid,

phospholipid, and heavy metals

50 mg of the extracted fat content of the sample was

saponiﬁed (es teriﬁed) for ﬁve) minutes at 950C with

3.4 mL of 0.5M KOH in dry methanol (CH3OH).

The mixture was neutralized by using 0.7M HCl.

3 mL of the 14% boron triﬂuoride in methanol was

added. The mixture was heated for ﬁve minutes at

the temperature of 900oC to achieve a complete

methylation process. The fatty acid methyl

es ter was thrice extracted from the mixture with

redis tilled n-hexane. The content was concentrated

to 1.0 mL for Gas Chromatography analysis (GC-

FID), and 1μm was injected into the injection pot

of GC-FID. The modiﬁed method of Liu et al.

[18] was employed to determine the extracted oil

phospholipid content. 0.01g of the extracted fat was

added to the tes t tubes to ensure complete dryness

of the oil for phospholipid analysis. The solvent

was completely removed by passing the s tream of

nitrogen gas on the oil. 0.4 mL of chloroform was

added to the tes t tube’s content, followed by the

addition of 0.10 mL of the chromogenic solution.

The range of the tube was heated at the temperature

of 1000C in a water bath for about 1min and 20s.

The content was allowed to cool to the laboratory

temperature, and 5 mL of the hexane was added, and

the tube with its content shook gently several times.

The solvent and the aqueous layer were allowed to

be separated, and the hexane layer was recovered

and allowed to be concentrated to 1.0 mL for gas

chromatography analysis (GC) using a pulse ﬂame

photometric detector (FPD). Also, the heavy metals

determined by F-AAS after sample preparation (Acid

diges tion; microwave) of groundnut oil (Fig.1)

Comparative analysis of groundnut oil by AAS and GC-FID Ijah Silas Ioryue et al

108

2.4. Scope of the ﬆudy, collection of oil samples,

and s tudy area

The s tudy was res tricted to parameters such as iodine

value, fatty acid/phospholipid concentration, acid

value, colour, odour, peroxide value, saponiﬁcation

value, refractive index, heavy metals, Fatty acid

and phospholipid in groundnut oil in North central

Nigeria. The concentration of heavy metals (Cd,

Pb Zn and Cu), fatty acid and phospholipid in

groundnut oil were determined by F-AAS and GC

-FID, respectively. The s tudy covered an analysis of

groundnut oil in 2022. Groundnut oil was bought

from six s tates in north-central Nigeria markets for

two months (September and October 2022). Three

groundnut oil samples of 100 cm3 each were collected

from three sellers in each market, giving eighteen

samples. The collected oil samples were packed in

polyethylene bottles and s tored below 20oC until

analyses were used. The s tudy was conducted in

north-central Nigeria, one of Nigeria’s geopolitical

zones. It comprises six s tates, including the federal

capital territory, Abuja. The s tates include Benue,

Nasarawa, Plateau, Kogi, Niger and Kwara (Fig. 2).

3. Results and Discussion

The results obtained from the physical and chemical

analysis of locally produced groundnut oil (Arachis

hypogea oil) sold in six markets in North Central

Nigeria are presented in Table 2, 3 and Figure 3. The

physical parameters of the ground nut oil are shown

in Table 2. Also, the oil’s heavy metal contents, the

percentage composition of fatty acids, saturated

and unsaturated fatty acids, and phospholipids were

presented in Tables 4, 5, 6 and 7 and Figures 3, 4, 5

and 6. Oil cons titutes a signiﬁcant composition of

Anal. Methods Environ. Chem. J. 6 (3) (2023) 103-120

Fig.1. Procedure for sample extraction/separation of fatty acid, phospholipid and heavy metals

from groundnut oil before determination by GC-FID and F-AAS

109

our daily diet consumption, and its market growth is

now considered for its acceptability and economy,

not minding the composition and nature.

3.1. Physical parameters

The sampled groundnut oil in Makurdi, Laﬁa and

Lokoja was amber-yellow, while Jos, Minna and

Ilorin were golden yellow. No abnormal odour

of the sampled oil was noticed; hence, it was

agreeable or acceptable. The s tate of all the oil was

liquid (Table 2).

Table 2: The physical parameters of the groundnut oil purchased in the North Central Nigeria markets

Market Colour Odour S tate (25oC)

Makurdi Amber Yellow Agreeable Liquid

Laﬁa Amber Yellow Agreeable Liquid

Jos Golden Yellow Agreeable Liquid

Minna Golden Yellow Agreeable Liquid

Lokoja Amber Yellow Agreeable Liquid

Ilorin Golden Yellow Agreeable Liquid

Comparative analysis of groundnut oil by AAS and GC-FID Ijah Silas Ioryue et al

Fig. 2. Map of north central Nigeria showing the sampling s tates.

110

3.2. Chemical properties of the oil

The s tudy indicated that oil in the Makurdi market

was relatively high in fat content (135%), while the

Lokoja market has the lowes t value (70%), as shown

in Table 3 and Figure 3. The order of fats content

was Makurdi<Jos< Ilorin<Minna<Laﬁa<Lokoja.

The iodine value is a measure of the total

unsaturation of oils, as well as an indicator of their

susceptibility to oxidation. The iodine values of all

oil samples from the Northcentral markets were

below the WHO speciﬁcation (86-166 g I2/100g

of oil) range. The higher the iodine number, the

more C=C bonds in the fat [19]. This shows that

the groundnut oil samples from the Lokoja market

contain higher unsaturated fatty acids than any

other market sampled. The chemical analysis of

iodine value indicated that the Lokoja market has

the highes t value, followed by the Laﬁa market.

The increasing order was Lokoja >Laﬁa> Minna

>Makurdi> Jos >Ilorin. A high iodine value denotes

a high degree of unsaturation caused by the extent

of oxidation and degree of heat treatment during

oil processing. The peroxide value is the weight

of active oxygen contained in one gram of oil or

fat [20]. Peroxide value measures peroxides and

hydroperoxides formed in the initial phases of lipid

oxidation. It, therefore, determines the degree of oil

oxidation and indicates the level of deterioration

of oils and fats. Freshly reﬁned oil should have

no peroxide value. In this s tudy, it was observed

that the groundnut oil from all the markets showed

peroxide values (Table 3 and Figure 3) lower than

the FAO/WHO (14) recommendation range(≤10

mili equivalent oxygen per kg), thus indicating

less susceptibility to oxidation with Lokoja

market having the highes t (1.13 meq per kg) and

Minna market having the lowes t (0.42 meq per

kg). According to Hassan [21], a low peroxide

value indicates the oil’s oxidative s tability and a

high peroxide value indicates poor oil resis tance

to peroxidation during s torage [22]. Therefore, it

is likely that s torage for a long time may lead to

rancidity of the oil. A rancid tas te often becomes

noticeable when the peroxidative value exceeds

20 meq per kg [23]. Peroxide value is critical for

examining the quality and s tability of fats and oils,

s tages of oxidation and spoilage extent [24]. Thus,

the ground nut oil obtained from these locations

will not harm human health due to its nonprone

oxidation. The acid value is used to measure the

quality of the oil since the acid value indicates the

extent of hydrolysis and deterioration. The higher

the fatty acid value, the higher the level of free fatty

acids, which translates into decreased oil quality.

The acid values from Laﬁa and Minna markets

were approximately similar in value. In this

s tudy, the acid value in all the markets was higher

compared to FAO/WHO [10] speciﬁcation (≤ 0.6

mg KOH per gram of oil), and it followed Lokoja

>Laﬁa >Minna>Jos> Ilorin >Makurdi order. The

high acid values indicate free fatty acids present in

the groundnut oil, which may be due to exposure

to atmospheric oxygen or due to the method used

for the extraction. According to Demian [25], acid

values measure the extent to which glyceride in the

oil has been decomposed by lipase and other actions

such as light and heat. The determination is often

used as a general indication of the condition and

edibility of oil. According to Badmos et al. [26],

a low acid value indicates the s tability of oils over

a long period and protection agains t rancidity and

peroxidation. No rancidity was detected in any of

the sampled groundnut oil in north-central Nigeria

(Table 3 and Figure 3).

The saponiﬁcation value measures the fatty acids’

average molecular weight (or chain length). It is a

measure of oxidation during s torage and indicates

the oil deterioration. An increase in saponiﬁcation

value in oil increases the volatility of the oils. It

enhances the quality of the oil because it shows the

presence of lower molecular weight components

in 1.0 g of the oil, which will yield more energy

on combus tion [27]. The saponiﬁcation values

from the Northcentral markets were below the

FAO/WHO [10] speciﬁcation (187-196 mg KOH

per gram of oil) range. This property makes it less

useful in soap making. The lower saponiﬁcation

value observed in this s tudy sugges ts that the mean

molecular weight of fatty acids is high, as low

saponiﬁcation indicates the presence of long-chain

Anal. Methods Environ. Chem. J. 6 (3) (2023) 103-120

111

fatty acids, and higher saponiﬁcation value indicates

lower chain fatty acids since saponiﬁcation value

is inversely proportional to the average molecular

or chain length of the fatty acid. The s tudy shows

that the Jos market has the highes t saponiﬁcation

(142.25 mg KOH per gram) while the Minna

market has the lowes t value (37.23 mg KOH per

gr). The increasing order of saponiﬁcation was

Minna >Lokoja>Ilorin>Laﬁa >Makurdi >Jos. All

the groundnut oil sampled has the same refractive

index (1.46) in North Central Nigeria.

Comparative analysis of groundnut oil by AAS and GC-FID Ijah Silas Ioryue et al

Fig.3.Chemical properties of the groundnut oil sold in north-central Nigeria

Table 3. Chemical Analysis of the groundnut oil sold in north-central Nigeria

Market Fat content

(%)

Iodine Value

(wij’s)

Peroxide value

(meq kg-1)

Acid Value

(%) Rancidity Saponiﬁcation

value(mgKOH g-1)

Refractive

Index

Makurdi 135 1.35 0.70 4.43 Nil 127.02 1.46

Laﬁa 78 1.73 0.60 2.12 Nil 113.10 1.46

Jos 128 0.67 0.80 2.52 Nil 142.25 1.46

Minna 89 1.67 0.42 2.22 Nil 37.23 1.46

Lokoja 70 2.62 1.13 1.62 Nil 46.44 1.46

Ilorin 97 0.12 0.84 3.01 Nil 52.46 1.46

112

3.3. Heavy metals analysis

Lead serves no useful purpose in the human

body, but its presence in the body can lead to

toxic eﬀects, regardless of the exposure pathway.

In this s tudy, the minimum (0.052 mg kg-1) and

maximum (0.114 mg kg-1) levels of lead in the

groundnut oil recorded were approximately equal

to the threshold limit of lead es tablished by WHO

[28]. The highes t and lowes t values were noticed

from Laﬁa and Ilorin markets, respectively.

Lead in the oil may result from anthropogenic

activities such as using leaded petrol during

extraction. The order of lead in the oil was

Ilorin>Makurdi>Jos>Lokoja>Minna>Laﬁa

(Table 4 and Figure 4). Cadmium mean

concentration (Saponiﬁcation of groundnut oil)

in the groundnut oil samples in North central

Nigeria was above the recommended limit of

daily tolerable intake level of 70 μg for Cd for the

average 70kg man and 60 μg of Cd per day for

average 60 kg woman [4]. The highes t and lowes t

values were found in Laﬁa and Jos, respectively

(Table 4 and Figure 4). The increased order of

cadmium was Jos<Makurdi<Minna<Ilorin<

Lokoja< Laﬁa. The element is toxic even at low

levels, resulting in nausea, vomiting, abdominal

cramps, headache, diarrhea, and shock. The

increase in the mean levels of Cd observed in the

groundnut oil was attributed to environmental

pollution from emissions from municipal was te

incinerates, indus trial eﬄuents, and plants’

absorption. Zinc content of the samples ranged

from 0.119 -0.061 mg kg-1. However, the

concentration of zinc in the oil samples from

the four markets (Makurdi, Jos, Lokoja and

Ilorin) analyzed were within the threshold limit

(0.1mg kg-1) speciﬁed by WHO [28], while

Laﬁa and Minna market values were above the

threshold limit es tablished by the world health

organization (WHO). Therefore, groundnut

oils from these four markets were within the

acceptable nutritional margins regarding zinc

(Table 4 and Figure 4). Copper is essential for the

human body, but high intake can cause adverse

health problems like headaches, s tomachaches,

dizziness, vomiting and diarrhea [29]. In Figure 4,

the copper content of samples of groundnut oil

from all the markets was below the threshold

limit; this may probably be a result of low

indus trial activity in the area, low contamination

of the soil in which the groundnut seed used in

the production of the oil were cultivated [30]. The

highes t and lowes t values from the research were

0.110 and 0.011 mg kg-1, respectively. The order

was Jos>Makurdi>Minna>Ilorin>Lokoja>Laﬁa.

The maximum level of Cu tolerable for a healthy

man and woman is 0.9 mg kg-1 daily. The results

obtained were within acceptable limits of Cu

speciﬁed by the WHO. Also, heavy metal and

VOCs can be extracted /separated from diﬀerent

matrix by nanotechnology before determination

by F-AAS, ET-AAS and GC-FID [31-37].

Anal. Methods Environ. Chem. J. 6 (3) (2023) 103-120

Table 4. Mean Concentration of heavy metals (mg kg-1) in groundnut oil Purchased in North Central Nigeria

Market Pb

Mean

Makurdi 0.061 0.202 0.061 0.105

Laﬁa 0.110 0.333 0.119 0.011

Jos 0.062 0.201 0.063 0.110

Minna 0.113 0.212 0.115 0.103

Lokoja 0.072 0.331 0.071 0.101

Ilorin 0.052 0.322 0.082 0.102

FAO/WHO,1999 0.114 0.07 0.1 0.9

S.D: S tandard Deviation

113

3.4. Analysis of fatty acids composition

Table 5 and Figure 5 show the percentage

composition of fatty acids in locally produced

groundnut oil in six markets in north-central

Nigeria. The results indicated twelve fatty acids

in the oils. Comparatively, fatty acid detected in

both markets in North central Nigeria includes

palmitic acid, palmitoleic acid, margaric acid,

s tearic acid, oleic acid, linoleic acid, linolenic acid,

arachidic acid, arachidonic acid, behenic acid,

erucic acid and lignoceric acid. Fatty acids absent

in the oils include caprylic, capric, lauric, and

myris tic acid. The order of fatty acid composition

in all the samples in all the markets is linoleic >

oleic > palmitic > s tearic > lignoceric > arachidic

acid > behenic > erucic >arachidonic > margaric

>linolenic>palmitoleic acids. Phospholipids results

showed six phospholipids: phosphatidylcholine,

phosphatidylethanolamine, phosphatidylinositol,

phosphatidylserine, phosphatidic acid and

Lysophosphatidylcholine. The order of magnitude was

phosphatidylcholine > phosphatidylethanolamine

> phosphatidylinositol > phosphatidylserine >

phosphatidic acid > Lysophosphatidylcholine [23].

The s tudy es tablishes that all the fatty acid types

present were found in the sampled locally produced

groundnut oil in all the markets in north-central

Nigeria. This result obtained was like that of

Kupwade and Desai [14], except that they detected

caprylic acid, capric, lauric, and myris tic acids and

detected oleic acid to be the mos t predominant,

with a percentage of 58.68%. Linoleic acid, the

predominant acid in all the sampled markets, is an

omega-six fatty acid and plays a vital role in pro-

inﬂammatory reactions, blood clots, and allergic

reactions.

Comparative analysis of groundnut oil by AAS and GC-FID Ijah Silas Ioryue et al

Fig. 4. Concentration of heavy metals (mg kg-1) in groundnut oil

114 Anal. Methods Environ. Chem. J. 6 (3) (2023) 103-120

Table 5. Percentage composition of fatty acid in locally produced groundnut oils

Fatty acid Makurdi

Market

Laﬁa

Market

Jos

Market Minna Market Lokoja Market Ilorin Market

Caprylic acid (C8:0) 0.00 0.00 0.00 0.00 0.00 0.00

Capric acid (C10:0) 0.00 0.00 0.00 0.00 0.00 0.00

Lauric acid (C12:0) 0.00 0.00 0.00 0.00 0.00 0.00

Myris tic acid (C14:0) 0.00 0.00 0.00 0.00 0.00 0.00

Palmitic acid (C16:0) 13.58 12.51 11.59 12.65 13.68 12.55

Palmitoleic acid (C16:1) 0.02 0.70 0.03 0.87 0.71 0.02

Margaric acid (C17:0) 0.08 0.05 0.06 0.09 0.09 0.06

S tearic acid (C18:0 4.27 4.59 4.37 4.69 5.00 4.91

Oleic acid (C18:2) 38.25 40.75 39.46 38.43 40.87 40.46

Linoleic acid (C18:2) 42.39 36.38 43.49 42.49 36.48 42.29

Linolenic acid (C18:3) 0.06 0.56 0.06 0.57 0.06 0.55

Arachidic acid (C20:0) 0.38 0.71 0.39 0.63 0.78 0.33

Arachidonic acid C20:4) 0.09 0.42 0.42 0.09 0.09 0.42

Behenic acid (C22:0) 0.16 2.89 2.99 0.17 0.16 2.87

Erucic acid (C22:1) 0.12 0.23 0.13 0.24 0.22 0.23

Lignoceric acid (C24:0) 0.39 0.22 0.83 0.22 0.37 0.21

Fig. 5. Percentage of saturated and unsaturated fatty acids found in locally produced groundnut oil

in north-central Nigeria

115

The result of the percentage composition of saturated,

unsaturated, and monounsaturated fatty acids are

presented in Table 6 and Figure 6, which showed that

the percentage composition of total unsaturated fatty

acid is more than saturated and monounsaturated

fatty acid in all the locally produced groundnut

oil marketed in North central Nigeria (Makurdi,

Laﬁa, Jos, Lokoja, Minna and Ilorin) with Makurdi

(81.85%) and Jos (78.03%) having the highes t and

lowes t values respectively. The highes t composition

of TSFA, MUFA and PUFA was found in Laﬁa

(20.97%), Ilorin (41.88%) and Jos (42.80%), while the

lowes t composition was found in Lokoja (18.85%),

Makurdi (38.39%) and Minna (37.22%) respectively.

The higher the composition of unsaturated fatty acid,

the higher its potential as an indus trial feeds tock and

vice versa. In the polymer indus try, unsaturated fatty

acids are converted to epoxides poly oils, precursors

in making plas tics. The order of fatty acids was

TUFA>PUFA>MUFA>TSFA.

Comparative analysis of groundnut oil by AAS and GC-FID Ijah Silas Ioryue et al

Fig. 6. Percentage of saturated, unsaturated, and monounsaturated fatty acids composition in north-central Nigeria

* TSFA = Total saturated fatty acid * TUFA = Total unsaturated fatty acid;

* MUFA = Monounsaturated fatty acid * PUFA = Polyunsaturated fatty acid;

Table 6. Percentage of saturated, unsaturated, and monounsaturated fatty acids composition

Fatty acid Makurdi market Laﬁa market Jos market Minna market Lokoja market Ilorin market

TSFA% 18.86 20.97 18.96 20.79 18.85 20.79

TUFA% 81.85 79.03 78.03 81.49 79.21 81.83

MUFA% 38.39 41.68 38.39 41.77 38.48 41.88

PUFA% 42.56 37.35 42.80 37.22 42.11 37.76

* % = Percentage; * TSFA = Total saturated fatty acid

* TUFA = Total unsaturated fatty acid.

* MUFA = Monounsaturated fatty acid.

* PUFA = Polyunsaturated fatty acid.

116

3.5. Analysis of phospholipids composition

The phospholipids analyzed in locally produced

groundnut oil sold in north central Nigeria are

presented in Table 7 and Figure 7. Six phospholipids

were identiﬁed, with phosphatidylcholine having

the mos t signiﬁcant percentage of phospholipid

composition in all the markets and sampled

groundnut oil. In contras t, lysophosphatidylcholine

had the leas t in all the markets. The order of magnitude

was phosphatidylcholine > phosphatidylethanolamine

> phosphatidylinositol > phosphatidylserine >

phosphatidicacid > lysophosphatidylcholine.

The highes t concentration of phosphatidylcholine

was found in Ilorin market (349.22) and the

leas t in Makurdi market (259.86). This research

analysis agrees with Adeyeye et al. [38] who

reported phosphatidylcholine as the mos t

abundant phospholipid in animals and plants as

the main building blocks of membrane bilayers.

Phosphatidylcholine, known to reduce body fat

and required in the body for cell functioning

Williams, Dowhan [39], was detected in large oil

concentrations.

Anal. Methods Environ. Chem. J. 6 (3) (2023) 103-120

Fig. 7. Percentage composition of phospholipids found in groundnut oil in north-central Nigeria

Table 7. Percentage composition of phospholipids found in locally produced Groundnut oil

in north central Nigeria (mg per 100 gram)

Phospholipid Makurdi

Market

Laﬁa

Market

Jos

Market

Minna

Market

Lokoja

Market

Ilorin

Market

Phosphatidylethanolamine 84.87 64.35 85.78 65.53 83.86 63.34

Phosphatidylcholine 259.86 347.04 295.86 346.11 260.84 349.22

Phosphatidylserine 3.39 9.93 3.45 9.68 3.29 9.90

Lysophosphatidylcholine 1.18 2.52 1.19 2.51 1.17 2.50

Phosphatidylinositol 79.53 67.89 78.60 68.98 79.43 69.89

Phosphatidic acid 2.93 10.81 2.99 10.76 2.79 10.18

117

4. Conclusion

The work compared locally produced groundnut

oils produced and sold within and around north-

central Nigeria markets. The assessment of the

physicochemical parameters of the groundnut oil

samples revealed that iodine, saponiﬁcation, and

peroxide values were lower than the threshold

limit values (TLVs) except for acids greater than

the reference value (FDA/WHO). Heavy metals

(Zn, Pb, Cu, and Cd) contents of the groundnut oil

from the six markets were detected by F-AAS and

GC-FID. The results showed cadmium and zinc

appeared to be the predominant metal contaminants

and were the only elements that exceeded the

recommended safe dietary exposure level. The oils

had twelve fatty acids, which include palmitic acid

(C16:0), palmitoleic acid (C16:1), margaric acid

(C17:0), s tearic acid (C18:0), oleic acid (C18:1),

linoleic acid (C18:2), linolenic acid (C18:3),

arachidic acid (C20:0), arachidonic acid (C20:4),

behenic acid (C22:0), erucic acid(C22:1) and

lignoceric acid (C24:0). It es tablishes that capric

acid, caprylic acid, lauric acid and myris tic acids

are absent in the oil while linoleic acid was the

highes t in composition in all the sampled oil in all

the markets in north central Nigeria followed by

oleic acid which GC-FID analyzed. The oils show

potential for indus trial application as biodiesel,

lubricants, plas tics, and soap due to the presence

of unsaturated and some saturated fatty acids.

However, the oils will also help make shampoo. The

assessment of phospholipid levels of the groundnut

oils was also carried out with GC-FID, producing

six phospholipids, namely phosphatidylcholine,

phosphatidylethanolamine, phosphatidylinositol,

phosphatidylserine, phosphatidic acid and Lys

phosphatidylcholine. Phosphatidylcholine can

help treat liver diseases and serves as a precursor

of choline, a compound in the synthesis of

acetylcholine, which can improve memory and

muscle function.

5. Recommendation

It is recommended that further research into the

use of these oils for some indus trial processes

be embarked upon, and medical value should be

checked. Also, groundnut oil contains high levels

of phosphatidylcholine, among other legumes.

Hence, it is advised that people should consume

locally produced groundnut oil more often than

other vegetable oils.

6. Signiﬁcance of the S tudy

Groundnut oil is the chief source of edible oil. For

the production of soap, margarine, and cosmetics

and with the growing awareness in environmental

pollution, groundnut oil is to be analyzed to

ascertain its pollution level and nutritional value.

This s tudy is signiﬁcant for the following reasons;

(i) To provide a physicochemical database for

groundnut oil that could be used as a basis for

future s tudies.

(ii) To create awareness of its contamination/

pollution level.

7. Acknowledgement

The authors would like to express unique words of

thanks and their acknowledgement to the Faculty of

Sciences, Ahmadu Bello University Zaria, Nigeria,

for their support and to the chief Technologis t for

his encouragement in carrying out this s tudy.

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