Alex Nder Kwaghtongo
Mbakuha Science and Technical College, Lessel
This article presents a comparative study of the quality of palm oil and groundnut oil sold in markets within Vandeikya Local Government Area of Benue State. Samples of groundnut oil and palm oil were collected from Ihugh and Agbo Markets. The aim was to assess and compare the qualities of the oils and to know the safety of such oils for human consumption. The saponification values, iodine values and acid values of the palm oils and the groundnut oils from the two markets were analysed. Manganese, iron, copper, lead and zinc were also analysed using Atomic Absorption Spectrometry (AAS). The chemical parameters and the elements analysed were compared with the standards given by Standards Organisation of Nigeria (SON), Nigerian Industrial Standards (NIS) and CODEX standards. The result from the analysis fall within the standards of these regulatory bodies except lead (Pb) and iron (Fe) with maximum values of 2.65mg/kg and 142.24mg/kg respectively. Since the concentration of Pb and Fe exceed the acceptable limits of 0.1mg/kg and 25.0kg/mg respectively, these oils are not safe for human consumption.
Palm oil is derived from the mesocarp of the fruit of the oil palm. It has a light yellow to orange-red colour. Red palm oil gets its name from its characteristic dark red colour, which comes from carotenes, such as alpha-carotene, beta-carotene and lycopene which are responsible for the high vitamin A content. (Ugwu et al, 2002) It is semi-solid at room temperatures and contains several saturated and unsaturated fats in the forms of glyceryl laurate (0.1%, saturated), myristate (1%, saturated), palmitate (44%, saturated), stearate (5%, saturated), oleate (39%, monounsaturated), linoleate (10%, polyunsaturated), and alpha-linolenate (0.3%, polyunsaturated). (Baily, 1951).
Groundnut oil is a mild tasting oil derived from groundnut plant (Arachis hypogaea), a species in the legumes family (Fabaceas). Some common synonyms for groudnut are peanut, earthnut, goober, pinder, and ground pea. It is called “abun” by the Tiv people of Benue State. In 1753, Linneaus described the domesticated 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 roasted and is used in cookery, confectionery and pressed for edible oil. Both palm oil and groundnut oil are vegetable oils. Vegetable oils generally are water insoluble, edible liquids derived from plants, which consist predominantly of long-chain fatty acid esters derived from the simple alcohol, glycerol. Oil plays a crucial role in our everyday life. There are different types of oils which include edible oils, non edible oils, essential oils 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 palm oil and groundnut oil could be affected by improper post harvest handling, processing and storage. Again there is wide-spread speculation that palm oil is being adulterated for the sole purpose of profit maximization. The adulteration ranges from the use of dyes, water and other illegal food additives which could affect the quality of these oils, in terms of nutritive value, wholesomeness, utilization, safety and shelf-life. The quality of these oils is generally determined by the percentage of free fatty acid, moisture and dirt content. The produce is traditionally bought on a 5% free fatty acid basis with penalties for exceeding this figure (Hartley, 1988). Hence the need to assess the quality of the palm oils and groundnut oils sold in major markets in Vandeikya Local Government Area of Benue State, Nigeria.
Heavy Metals in Vegetable Oil
Heavy metals are metals with relatively high densities of 4.0g/cm3 and above (Baily, 1951). Heavy metals in trace amounts are of significant benefit to man. Inadequate trace elements in diet may constitute health problem that may be devastating. Heavy metals in large amounts are in general, characterized as being toxic or poisonous. Since trace elements provide nutritional value, they are sometimes referred to as micronutrients (Baily, 1951).
Palm oils and groundnut oils are essential daily condiments because of their various uses in our everyday living. These oils are therefore highly priced. Unfortunately, it has been reported that some brands of palm oils and groundnut oils are being adulterated with diesel, automobile hydrocarbon oil which is miscible with vegetable oils. This adulteration is alleged to change the quality of vegetable oils and consequently have negative effects on the consumers (Asemave, 2012).
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 stage of maturity, pollution, mode of processing, storage, and contaminations. These metals may enter the food material from the soil through uptake of mineral by crops, food processing, environmental contamination (as in application of fertilizer). Metals play important negative and positive roles in human life.
Hence, there is need to determine the concentration of both heavy metals, trace elements and some physicochemical parameters in these staple vegetable oils in Vandeikya Town, so that consumers will know the qualities of these vegetable oils.
Udensi et al (2004) worked on the physicochemical parameters of palm oil obtained at different locations in Abia state and reported that the saponification value (SV) ranged between 129.04 and 198.03mgKOH/g of oil. The free fatty acid (FFA) of the palm oil samples ranged between 2.73 and 2.89mgKOH/g of oil, and the iodine value (IV) between 52.61 and 53.48 gI2/g.
Musa and Suleiman (2012) did a study of the phyisco-chemical properties of some commercial groundnut oil brands sold in Sokoto. They also extracted groundnut oil from the laboratory using solvent extraction. The analysis of their result showed that the saponification value for oil samples gotten from Sokoto main market, old market, Kara market, Mabera market and their laboratory were 187, 185.13, 201.4, 215.05 and 175mgKOH/kg respectively. Bosku (2002) analysed the saponification values for turkey vegetable oil, groundnut oil and palm oil and obtained the values of 186.0, 165.0 and 140.0mgKOH/g respectively. Agbaire (2012) carried out a quality assessment of palm oil sold in some major markets in Delta State and found out that the saponification of the oil ranged
between 45.76– 198.75mgKOH/g.
Furthermore, the saponification values reported by Anyasor et al (2009) carried out for groundnut oil from seeds of six varieties: boro red, boro light, mokwa, ela, campala and guta as well as oils from three geographical zones in Northern, Eastern and Western Nigeria. He reported that the saponification values for local vegetable oil was found to be significantly higher than the refined vegetable oil The eastern oil has the highest saponification value. (140.25mgKOH/g).
Asemave (2012) carried out an analysis of some physico-chemical parameters in groundnut oil and soya bean oil in Nigeria
Musa and Suleiman (2012) also analysed the acid value of oil samples gotten from Sokoto main market, old market, Kara market, Mabera market and their laboratory to be 6.86, 3.01, 2.44, 3.2 and 1.88 mgKOH/g respectively. Asemave (2012) carried out an analysis of some physico-chemical parameters in palm oil, groundnut oil and soya bean oil in Nigeria. The acid values were found to be 5.5, 4.90 and 4.20mgOH/g respectively. The quality assessment of palm oil sold in some major markets in Delta State was analyzed and the acid values was found to range between 2.73–2.93mgKOH/g (Agbaire, 2012). The acid values as given by the Standard Organization of Nigeria (SON) (2000) and Nigerian Industrial Standard (NIS) (1992) is 3.5mgKOH/g.
Asemave (2012) also carried out comparative analysis of some metals in groundnut oil and soya bean oil in Nigeria. In groundnut oil, the concentrations (mg/kg) of Fe, Cu, Cr, Pb, Al and Cd were obtained as 8.5109, 0.0633, 2.7067, 0.1631, 1.7742 and 0.0207 respectively. For soyabean oil sample, the concentration levels (mg/kg) were 8.7519, 0.0633, 2.7067, 0.1631, 0.3837 and 0.0200 for Fe, Cu, Cr, Pb, Al and Cd respectively.
Collection of Samples
Two varieties of edible oils namely: groundnut oil and palm oil were bought from two major markets (Agbo and Ihugh Markets) in Vandeikya Local Government of Benue State Nigeria for a period of two months (September and October, 2012). Four palm oil samples of 100cm3 each were collected from two sellers on two Ihugh Market days. Also, four groundnut oil samples of 100cm3 each were collected from two sellers on two Ihugh Market days. The same method was applied in collecting palm oil and groundnut oil samples from Agbo Market, giving a total of sixteen (16) samples.
The collected oil samples were packed in polyethylene bottles and stored below 200C until analyses were carried out.
Determination of heavy metals by Atomic Absorption Spectrometry (AAS)
Using an electronic weighing balance, 2g of each of the samples was weighed in a beaker. Concentrated nitric and sulphuric acids (5cm3) were added followed by hydrogen peroxide (2cm3) and 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 plastic bottle for metal analysis by AAS method.
Determination of Copper (Cu)
Preparation of Copper Standard Solution
A mass of 1.00g of Cu was dissolved in 15cm3 of conc. HNO3 acid and 1cm3 of H2SO4. It was boiled until the dense white fumes of SO3 ceased. The solution was transferred into a clean 1000cm3 volumetric flask and diluted to the mark with deionized water to give 1000ppm Cu. Copper standards of 2,4,6,8 and 10ppm were prepared by several dilutions. The sample and standard solutions were aspirated at 345nm with a clean flame of burner height 24mm using air/acetylene burner. A calibration curve was prepared from the reading of the standards. The sample reading was extrapolated from the standard curve.
Cadmium, Iron, Lead, and Manganese were similarly determined.
Chemical Characterization of Palm Oil and Groundnut Oil
Determination of Acid Value.
The method used was the Dutch method (1992). Solvent mix: 2 part toluene to 1 part ethanol (volume/volume) was prepared and neutralized with 2 drops of 0.1355M KOH. Each of the oil samples (3.0g) was weighed into a flask and 40cm3 of the solvent mix prepared was added.
The resultant mixture was warmed in a water bath to dissolve, then cooled and titrated with the 0.1355M KOH, using 3 drops of 1% phenolphthalein as indicator and a pink endpoint was obtained. A blank was prepared and the same treatment was given to the blank. The acid value was calculated using.
Determination of Saponification Value (SV)
To a weighed 4.0g sample of oil in a round bottom flask, 50cm3 of 0.532M KOH was added. Phenolphthalein (1cm3) was added from a micro pipette. A blank was also prepared: Both were separately connected to a reflux condenser under heat for 40 minutes. The resultant solution was titrated rapidly with 0.5M HCl along with the blank.
Determination of Iodine Value
Preparation of Hannus Reagent.
Hannus reagent was prepared by weighing 6.5g of iodine and 25cm3 of bromine into 500 cm3 of volumetric flask and dissolving with glacial acetic acid. The solution was made up to the mark with distilled water and stored in an amber coloured bottle. KI solution (10%) was prepared by dissolving 10g of KI in distilled water and making up to the mark in a 100cm3 flask.
A 0.1M Na2S2O3.5H2O solution was prepared by dissolving 24.80g of the thiosulphate with distilled water in a one liter volumetric flask and making up to the mark and then stored in an amber coloured bottle. 2%(W/V) starch solution was prepared by dissolving 2g of starch in a 100cm3 volumetric flask and making up to the mark.
To 4.0g of oil in a stoppered glass flask, 10cm3 of chloroform was added with shaking to dissolve the oil. Hanus reagent (25cm3) was added from the burette. Blank was concurrently prepared. Both were allowed to stand in the dark for 1 hour to complete the reaction between the double bond of the oil and the liberated iodine. Excess of the liberated iodine after adding 15cm3 of 10% KI solution and 50cm3 of distilled water was titrated with the 0.1M Na2S2O3.5H2O solution prepared to a pale yellow colour. A few drops of 2% starch indicator solution was added while the thiosulphate was added drop wise until the blue colour that developed on addition of indicator disappeared. The same treatment was given to the blank.
Palm oil and groundnuts oil obtained at Agbo and Ihugh Markets in Vandeikya L.G.A of Benue State were analyzed for chemical parameters. The results for the analyses are presented in Tables 4.1and 4.2.
Table 4.1. Chemical parameters of palm oil samples obtained from Ihugh and Agbo Markets in Vandeikya L.G.A
|Mean values In Ihugh Market.||Mean values In Agbo Market.||SON/NIS standards (2000)
|Saponification Value (KOH/g)||181.6 + 5.5||176.2 + 3.3||195-205|
|Acid Value (mgKOH/g)||5.4 + 0.4||7.6 + 0.3||3.5-4.0|
|Iodine Value (gI2/100g)||56.6 + 2.9||56.0 + 1.5||45.0-53.0|
Table 4.2. Chemical parameters of groundnut oil samples obtained from Ihugh and Agbo Markets in Vandeikya L.G.A
In Ihugh Market.
|Mean values In Agbo Market.||SON/NIS standards (2000)
|Saponification Value (KOH/g)||169.9 + 3.5||178.1 + 2.6||195-205|
|Acid value (mgOH/g)||5.3 + 0.3||3.4 + 0.5||3.5-4.0|
|Iodine Value (gI2/100g)||75.1 + 2.3||76.7 + 2.4||45.0-53.0|
The concentration of some metals in palm oil and groundnut oil obtained in Vandeikya L.G.A were analyzed and the results are presented in Tables 4.3 and 4.4
Table 4.3. Average values of the elemental analysis of palm oil obtained from Agbo and Ihugh Markets in Vandeikya L.G.A
|Palm oil from Agbo Market.||Palm oil from Ihugh Market.||CODEX Standards (2011)|
|Mn||7.1786 + 1.70||3.9580 + 0.91||2.7|
|Fe||135.69 + 7.04||107.13 + 15.85||25.0|
|Cu||0.2670 + 0.04||0.0687 + 0.02||0.4|
|Pb||2.6527 + 0.61||0.8717 + 0.28||0.1|
|Zn||0.6733 + 0.12||2.0209 + 0.18||2.0|
Table 4.4. Average values of the elemental analysis of groundnut oil obtained from Agbo and Ihugh Markets in Vandeikya L.G.A
|Groundnut oil from Agbo Market.||Groundnut oil from Ihugh Market.||CODEX Standards (2011)|
|Mn||6.7143 + 3.50||6.7138 + 2.23||2.7|
|Fe||127.93 + 14.47||142.24 + 12.30||25.0|
|Cu||0.1051 + 0.04||0.2962 + 0.14||0.4|
|Pb||1.8584 + 0.56||1.2668 + 0.29||0.1|
|Zn||0.6538 + 0.37||2.0889 + 0.58||2.0|
Saponification Value (SV) is an indication of molecular weight of triglycerides of oils. High saponification value indicates high proportion of short chain fatty acids. Since SV is inversely proportional to the average chain length of fatty acid (Muhammad et al, 2006), the shorter the average chain length (C4-C12) the higher the saponification value. From the result in Tables 4.1 and 4.2, saponification value of palm oils in Agbo and Ihugh Markets were 176.2 and 181. 6mg KOH/g respectively while the saponification values for groundnut oil in Agbo and Ihugh Markets were reported in Table 4.1 and 4.2 as 178.1 and 169.9mgKOH/g respectively. All the saponification values are lower than the Standard Organization of Nigeria (SON) 2000 and Nigerian Industrial Standard (NIS) 1992 range of 195 – 205 mgKOH/g. The values are higher than that reported by Anyasor et al (2009) 140.25mgKOH/g but conform to the range given by Agbaire (2012) of 145.76 – 198.75mgKOH/g and that of Musa and Sulieman (2012) range of 175 – 215.05mgKOH/g.
The acid value is a measure of the free fatty acids in oils. Fatty acids are usually in the triglyceride form but during processing, they may get hydrolyzed to free fatty acids. Free fatty acids may also arise from oxidation. The higher the Acid Value (AV) the higher the Free Fatty Acids (FFA) which also means a decrease in oil quality. As shown in Table 4.1 and 4.2, the Acid Value obtained for palm oil from Agbo and Ihugh Markets was 7.6 and 5.4mgKOH/g respectively. The Acid Values for groundnut oil obtained from Agbo and Ihugh Markets as shown in Tables 4.1 and 4.2 were 3.4 and 5.3mgKOH/g respectively. It is only the acid value of the groundnut oil obtained from Agbo Market that conforms with the SON/NIS standards range of 3.5-4.0mgKOH/g while others are higher than the standards. This implies that the oil with high AV is of low quality.
The acid values for palm oil and groundnut oil obtained in Ihugh Market are comparable to 5.54 and 6.86mgKOH/g values reported by Asemave (2012) and Musa and Suleiman (2012) respectively. Acid values in this work are higher than the range of values reported by Agbaire (2012) of 2.73 – 2.93mgKOH/g.
Iodine value is the measure of the level of unsaturation in oils. The iodine values obtained for palm oil from Abgo and Ihugh Markets as represented in Tables 4.1 and 4.2 were 56.0 and 56.6gI2/g respectively. The iodine values (IV) for groundnut oil obtained from Agbo and Ihugh Markets as shown in Table 4.1 and 4.2 were 76.7 and 75.1 gI2/g respectively. Iodine values in this work are higher than the standards range stipulated by SON/NIS (2000/1992) of 45 – 53 gI2/g. Iodine values in this work are within the range of 43.72 – 95.87gI2/g reported by Musa and Suleiman (2012) and 60.90 – 81.30gI2/g reported by Buldini (2006). This means the oils are highly unsaturated.
Considering the elemental analysis result in Tables 4.3 and 4.4, the manganese (Mn) concentration was 7.1786 and 3.9580mg/kg for palm oil in Agbo and Ihugh Markets respectively while the concentration in groundnut oil from Agbo and Ihugh Markets was 6.7143 and 6.7138mg/kg respectively. High concentrations of Mn can lead to hypertension. The procedure involved in extracting the oil which is unable to remove some impurities could have contributed to the high level of Mn and other trace metals.
Iron (Fe) has the highest concentration in all the oil samples. The concentrations of Fe was 135.6969 and 107.1383mg/kg in palm oil from Agbo and Ihugh Markets respectively. For groundnut oil from Agbo and Ihugh, the amount of Fe was 127.3294 and 142.2388mg/kg respectively. These concentrations are higher than the 11.370mg/kg for palm oil and 8.5109mg/kg for groundnut oil as reported by Asemave (2012). The concentration of Fe is much higher than the standard from African Food Fortification Regulation (2002) of 40.7mg/kg. Even though Fe is an essential nutrient of blood, large amounts can lead to its accumulation in the body, leading to tissue damage and hyperhaemogloburia as reported by Asemave et al., (2012).
The concentration of copper (Cu) was found to be 0.2670 and 0.0687mg/kg for palm oil obtained from Agbo and Ihugh Markets respectively. The amount of Cu in groundnut oil from Agbo and Ihugh Markets was 0.1051 and 0.2962mg/kg respectively. These values when compared to the 0.078mg/kg for palm oil and 0.0633mg/kg for groundnut oil as reported by Asemave (2012) are higher. Excess of Cu is found to cause gastro-intestinal disorder. The results obtained are within the acceptable limits.
The concentrations of lead (Pb) in palm oil obtained from Agbo and Ihugh Markets was 2.6527 and 0.8717mg/kg respectively, while the values for groundnut oil obtained from Agbo and Ihugh Markets were 1.8584 and 1.2668mg/kg respectively. Lead level of 10µg/kg or above is a cause for concern. Lead has harmful health effects even at lower levels and there is no known safe exposure level. This means that even the low concentration of lead present in vegetable oil is harmful, if the oil samples are consumed for a very long period of time, since lead accumulates. In addition, exposure to amounts of Pb above 0.01 mg/kg is detrimental to health as it may result in possible neurological damage to fetus, abortion and other complications in children, under three years of age (Ali et al., 2005). Lead also causes cancer, interfers with Vitamin D metabolism, affects mental development in infants and is toxic to the central and peripheral nervous systems.
The concentration of zinc (Zn) was 0.6733 and 2.0209mg/kg in palm oil from Agbo and Ihugh Markets respectively, while for groundnut oil from Agbo and Ihugh, the amount of Zn was 0.6538 and 2.0889mg/kg respectively. The values obtained in this work for Zn are within the tolerable limits.
The result in this work shows that the saponification values and acid values of palm oil in both markets are higher than the values for groundnut oil. The iodine values for groundnut oil in the two markets are higher than the values for palm oil.
This implies that the groundnut oils sold in these two markets will have a longer shelf life than the palm oils. The densities, refractive indexes and colours for the two oils from the two markets showed no difference. Since the concentration of Pb and Fe differ much with the tolerable standards provided by SON and NIS, the oils are not safe for consumption and industrial use.
Considering the elemental analysis, Lead (Pb) in palm oil obtained from Agbo Market is higher (2.1413mg/kg) than the palm oil from Ihugh Market (0.8717mg/kg). Also the groundnut oil from Ihugh Market has a higher concentration of Pb (1.8002mg/kg) than that obtained from Agbo Market (1.5917mg/kg). The concentration of Manganese (Mn) found in groundnut oil from the two markets is higher than the NIS and SON standards.
Iron (Fe) concentration is quite high in all the samples from the two markets. Even though Fe is good for human health, excess accumulation may be harmful. All other elements analysed were found to be within the tolerable limit set by various regulatory bodies. If measures are taken to reduce the concentration of Pb, Mn, and Fe to the acceptable limits, then the oils obtained in this locality can be recommended for use without any fear of harm on the consumers.
The human body uses oil and fats in the diet as energy source, as structural component, and to make powerful biological regulators. These metals present in edible oils could be from the soil, pollution or even from the manufacturing process. Some elements such as Zn, Cu, Fe can act as nutrients and are important for growth and development, while others such as Pb may be harmful, especially when consumed in the wrong proportion. The dangers of these metals can be prevented. There should be an appropriate regulatory measures and establishment of facilities for sound collection and disposal of hazardous waste, containing heavy metals with high concentration. Production in both industries and at local levels should be done using stainless steel equipment. The dumping of refuse around production plants should be avoided since refuse dump areas are a common source of heavy metals.
Lastly, based on the results of this research, it can be suggested that the relevant Vandeikya Local Government regulatory departments to create awareness on the need to reduce the consumption rate of these oils until further researches prove that the concentration of Pb and Mn is within tolerable limits.
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