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

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, saponi ﬁ cation value and refractive index were below the FAO/WHO recommended level, and the acid value was higher than the normal range.


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 ------------------------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][7][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.

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.

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 (C 2 H 2 ) 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.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].

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.

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 (5cm 3 ) were added, followed by hydrogen peroxide (2cm 3 ), 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 50cm 3 using de-ionized water and then transferred into a plas tic bottle for metal analysis by the AAS method [13].

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.
Where V 2 = titre value for blank, V 1 = 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 s tarch as an indicator.A blank was prepared alongside the oil samples.Peroxide was obtained by Equation 3. (Eq.3) Where V 2 = titre value for blank, V 1 = 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 H 2 SO 4 , for blank (mL), B= Volume of H 2 SO 4 (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 cm 3 of the oil samples was placed in a 100 cm 3 tes t tube vigorously mixed with 5cm 3 of 0.1% phloroglucinol solution in diethyl ether and 5 cm 3 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.

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 95 0 C with 3.4 mL of 0.5M KOH in dry methanol (CH 3 OH).
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 900 o C 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 100 0 C 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)

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 cm 3 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 20 o C 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).

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 our daily diet consumption, and its market growth is now considered for its acceptability and economy, not minding the composition and nature.

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).

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]

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][32][33][34][35][36][37].

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 proinflammatory reactions, blood clots, and allergic reactions.
Comparative analysis of groundnut oil by AAS and GC-FID Ijah Silas Ioryue et al   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

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.

Conclusion
The work compared locally produced groundnut oils produced and sold within and around northcentral 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.

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.

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.

, 5 and 6 .Fig. 1 .
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

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

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

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

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

2.2.2.Gas chromatography analysis
-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.

Table 2 :
The physical parameters of the groundnut oil purchased in the North Central Nigeria markets Comparative analysis of groundnut oil by AAS and GC-FID Ijah Silas Ioryue et al

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

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

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

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

Table 7 .
Percentage composition of phospholipids found in locally produced Groundnut oil in north central Nigeria (mg per 100 gram)