A Comprehensive Review on Assessment of Adulteration Detection Techniques In Edible Oils

In order to reduce the cost of edible oils, mixing is often carried out by traders or suppliers with certain specific adulterants, this is called adulteration. For example, vanaspati is mixed with ghee, in this case the vanaspati is called adulterant fat and ghee is called adulterated fat. Stated differently, adulteration occurs when two oils or fats are combined and one of the oils or fats is less expensive than the other. The less expensive oil is referred to as adulterant, and additional oil that has undergone mixing is referred to as adulterated oil or fat. Thus, groundnut, sunflower, safflower, and soybean oils, among others, are combined with mineral oil. The other oil is referred to as adulterated oil, and the mineral oil is known as adulterant.  Adulteration simply nothing but the mixing of similar looking inferior material into superior material for the purpose of increase in profit margin Adulteration has long been a problem in the oil trade. Sometimes it's intentional, sometimes it's accidental.(1)  In actuality, at today's bulk material handling plants, it is challenging to prevent unintentional contamination. Here, pipes and common valves must be used to pump oil of varied grades. However, costly oil is typically expensive, thus chemical tests have long been developed to characterize them, with an emphasis on cheap forgeries to test for purity. Some tests are so helpful that nontechnical colleagues who buy, sell, and trade oil still frequently use them today and speak the same language. Although there are more advanced analytical techniques available, the cost of the required equipment prevents average industrial workers from using them.(2) Different physiochemical parameters of edible oils were studied to monitor the compositional quality of edible oils.(3) These parameter includes density measurement, viscosity, boiling point, iodine value, saponification value, acid value, peroxide value etc. Different alalytical methods are also used for quantitative evaluation of edible oils are gas chromatography (GC), High Performance Liquid Chromatography (HPLC), Ultra Visible Spectrometry (UV) and Fourier Transform Infrared (FT-IR) Spectroscopic techniques.  FT-IR has several advantages over other traditional physical and chemical methods due to its ease of sample processing, speed and low requirement for sufficient quantities of hazardous solvents, improving the signal-to-noise ratio, reducing scanning time and high energy requirements throughout the process, in this method all wavelengths are recorded simultaneously.(4) The Halphen’s test (5), can detect upto 0.1% of crude cottonseed oil or stearine in oil mixtures. Oils containing as little as 1% sesame oil will give a crimson red colour in the Boudouin (6) or modified Villavechia (7) test. The modified Renard tests (8) claims to be able to detect as little as 5-10% groundnut oil in oil mixture, and are used as a criterion of purity for groundnut oil itself. Ramachandraiah et al.(9) have reported a test for detection of neem oil (0.5%) in other oils by observing the change in colour of a thin copper strip on heating at 200?. Number of instrumental techniques such as thin layer chromatography (TLC), near infrared spectroscopy (NIR), differential scanning colorimetry (10) etc. are available for the detection of adulteration of olive oil and butter.  chakraborty et al.(11) reported thin layer chromatography of glycerides as a tool for the detection of adulteration in fats and oils. Raut et al. (12) also reported that thin layer chromatography method has been evolved to detect the presence of water-melon seed oil in groundnut and sesame oils. The method is suitable for detection of water-melon seed oil upto 5% in groundnut and sesame oils.

Current issues in edible oil adulterations:

Admixing cold press oil with refined one: Refined oils are used in the adulterations of cold press oil. During refining processes, trans fatty acids and steradienes are formed which are generally absent in cold press oil. Trans fatty acids are not essential and they do not promote good health. The consumption of trans fatty acids increases risk of coronary heart disease.

High price oil adulterations with low price oil:

The substitution of more expensive oil by cheaper one is so profitable for producers and there are inspires to do it oil. Some oils are more prone to be adulterated due to their higher price and limited accessibility.

Mustard oil adulterated with argemone oil

In number of cases, adulteration of Argemone mexicana (Family: Papaveraceae) seed oil in edible oils has been reported as cause of epidemic dropsy.

MATERIAL AND METHODS

For edible oil samples there are number of methods is used to detect adulteration like physicochemical test, Laboratory test (chemical test), and analytical test. In physicochemical test density measurement, Boiling point determination, Moisture content, Peroxide value, Acid value, Saponification value, Iodine value. In laboratory test Modified nitric acid test, Nitric acid test, Azo dye test, Sodium azide test, Molybdate test, Halphen’s test, Modified Boudouin test, Hexabromide test, Solvent partition method.

Physicochemical test:

The following physicochemical tests are performed for detection of physicochemical characteristics that determine the quality and help to describe the present condition of oils.

Density Measurement:

Densities of all oil samples were measured by a Relative Density (R.D) bottle or density bottle with a capacity of 10 ml, according to the following formula:

Density (?) = Mass of the oil sample (M) /Volume of the R.D bottle (V) g/ml

Moisture content:

Ten grams of the oil sample were added to each of three crucibles after they had been weighed. The samples were weighed after being cooled in desiccators and dried to consistent weights at 105°C in an oven. For every sample, the process was carried out three times, and the average value was ascertained.(13)

Boiling point determination:

The boiling point of all oil samples were determined by a thermometer ±1°C using Thiele tube. The boiling point depends upon the degree of unsaturation of fatty acids.(14)

Saponification number:

The saponification value is determined by taking 1.0 g of the oil sample into a conical flask, Adding 25 ml of 0.5 N alc. KOH and heating it in a special condenser for 30-40 minutes to ensure that sample was completely dissolved. After cooling the sample, titrated with 0.2 N HCL using Phenolphthalein as an indicator until a pink endpoint was obtained. An empty sample is determined with the same time conditions.(15)

Saponification value = (B-T) × N × 56.1/WB= ml of HCL required by blank

T= ml of HCL required by oil sample

N=Normality of HCL

W=Weight of oil in gram

Peroxide value:

Peroxide value is determined by taking 5gm of oil into 500 ml conical flask and dissolved in 30 ml acetic acid: chloroform (3:2) mixture and added 0.5 ml saturated KI solution mix well And stand for 1min then added 30 ml of water and titrated against 0.01 N Sodium thiosulphate using starch solution as an indicator with vigorous shaking until blue colour disappear.(16)

Peroxide value = (S-B) ×W×N

S = Volume of sodium thiosulphate consumed by the sample oil

B = Volume of sodium thiosulphate used for blank

W = Weight of oil sample

N = the Normality of sodium thiosulphate

Acid value:

Approximately 5g of oil was introduced into a 250 ml conical flask. Then, 25 ml of neutral ethyl alcohol is added to it and then brought to a boil in a water bath. Phenolphthalein indicator solution (1-2 drops) was added and then the mixture, while still warm, was titrated with a stirred potassium hydroxide standard solution. Endpoints were recorded until the first pink persisted for 30 seconds.(17)

Acid value = V×N×56.1/W

V = Volume of standard KOH solution in ml

N = Normality of standard KOH solution.

W = Weight of oil sample in grams.

Iodine value:

The iodine value of oils was determined according to AOAC method. About 0.25 g oil sample was taken in a conical flask and dissolved in 10 ml CCl4. 30 ml Hanus solution was added and the mixture was allowed to stand for 45 min in dark with occasional shaking. 10ml 10% KI solution and 100 ml distilled water were added and washed down any free iodine on the stopper. The iodine was titrated with previously standardized Na2S2O3 solution which added starch indicator was added and titration was continued until blue color entirely disappeared. Bottle was shaken violently so that any iodine remaining in solution in the CCl4 might be taken up by the KI solution. The volume of Na2S2O3 solution required for the experiment was noted. A blank experiment was conducted along with the sample.(18)  Percent weight of iodine absorbed by the oil sample was calculated by the following formula:

1 ml 1N Na2S2O3 = 0.127 g I2

Iodine value = (B-A) × N × 0.127 × 100/W

B = ml of 0.1N Na2S2O3required by blank

A = ml of 0.1N Na2S2O3 required by oil sample

N = Normality of Na2S2O3

W = Weight of oil in gm.

Chemical test (Laboratory test):

IS: 548 (Part-II)-1976 addresses the common qualitative techniques for adulterant detection. The majority of these techniques rely on the precipitate's or turbidity's characteristic colour or appearance developing.(19)

Detection of Synthetically Made Artificial Mustard Oil:(20)

To synthesize synthetic mustard oil, some inexpensive vegetable oils are coloured with oil soluble yellow dye, and then the necessary amount of synthetic allyl isothiocyanate is added. The mixed oil has the same appearance and scent as real mustard oil, but its production costs are significantly lower, making it advantageous for dishonest producers and distributors.

Sodium Azide Test:

Take 100 ml of the mustard oil sample suspected of being artificial mustard oil, mix in 100 ml of Sodium Azide solution (2 gram per 100 ml), and heat the oil mixture upto 3 hours on a hot plate or by direct heating. Allow the aqueous and oil layers to separate by cooling the flask and transferring the contents to a 250 ml separating funnel. Discard the oily layer and collect the lower aqueous layer in a beaker. To eliminate any remaining oily substance, wash the aqueous layer twice with 50 ml of Diethyl ether each time. Filter this aqueous solution and boil it to reduce it to around half its original volume. In a test tube, put 1 ml of bismuth nitrate solution and 1 ml of the above-mentioned concentrated solution. If a bright yellow precipitate forms, the oil sample contains synthetic mustard oil. When natural mustard oil is tested in the same way, it gives a negative result.

V = Volume of standard KOH solution in ml

N = Normality of standard KOH solution.

W = Weight of oil sample in grams

Detection of Argemone Oil:

It is occasionally discovered that edible oils, particularly mustard oil, contain argemone oil (Argemone mexicana Linn). But horrible diseases like dropsy, necrosis, high tension glaucoma, diarrhea, vomiting, and anemia are brought on by argemone oil. There are reports of the oil causing toxic symptoms, and the presence of alkaloid sanguinarine and dihydro- sanguinarine is thought to be the cause of toxicity.(21)

Modified nitric acid test:(22)

5 ml of oil sample in a dry test tube and mix it successively with 0.5 ml of 2% salicylic acid in methanol, Add 2 ml of conc. Nitric acid, followed by 2 - 4 drops of conc. sulphuric acid, and shake. A crimson-red or deep orange-red colour develops within 20-30 seconds if Argemone oil adulteration is present in edible oil. The crimson red or orange-red colour formation is due to the formation of nitrosalicylate salt of hydrolysed sanguinarine.

Detection of Rice Bran Oil:(23)

Rice bran oil is used as edible oil in Japan, China, India and other rice producing countries. Physically refined rice bran oil is similar to mustard oil in colour and density. Rice bran oil is price wise cheaper to mustard oil so it is frequently used as an adulterant in mustard oil. The literature describes a quick and easy colorimetric technique for identifying rice bran oil in vegetable oil.(24) Oryzanol is one of the significant minor components in rice bran oil that Tsuchiya discovered.

Azo Dye Test:

In this procedure, 1 ml of rice bran oil containing oil sample is mixed with 2-4 ml of 10% (w/v) sodium hydroxide solution in a dry test tube and shake for 5-10 minutes to formed an emulsified solution (a). In a separate dry test tube, dissolve 1- 2 drops of aniline in dilute hydrochloric acid. After cooling to 0-5°C, add 2-3 ml of 5% (w/v) sodium nitrite solution and shake, resulting in the formation of benzene diazonium chloride solution (b), combine solution (a) and solution (b). Within 10-20 seconds, if orange-red colour develops, indicating the presence of rice bran oil as an adulterant in edible oil sample. In this method, aniline is first undergo diazotization to produce benzene diazonium chloride in the presence of dil. hydrochloric acid and sodium nitrite solution at temperatures between 0 to 5 degrees Celsius. Following that, the coupling reaction of compound and compound in a basic solution medium that leads to the formation of a reddish orange colored dye, phenylazo-?-oryzanol or phenylazoferulic acid.

Detection of Sesame Oil:

Modified baudouin test: (25)

Take a 25 ml measuring cylinder (or test tube) with glass stopper, put 5 ml sesame oil, Add 5ml Hydrochloric acid, and 0.4 ml furfural solution. Shake vigorously for two minutes after inserting the glass stopper. Allow the mixture to separate for a few minutes. The presence of sesame oil is indicated by the formation of a pink colour in the acid layer. Add 5 ml of water and shake again to confirm. Sesame oil is present if the colour in the acid layer persists. If the colour vanishes, the adulterant is no longer present. In above test the pink colour is formed due to the formation of addition compound by the reaction of sesamol with furfural in presence of hydrochloric acid. This test is sensitive to the extent of 0.2% of sesame oil in other oils. This test is sensitive to the extent of 0.2% of sesame oil in other oils.

Detection of Linseed Oil(26) (Hexabromide Test):

When highly unsaturated fatty acid such as linolenic acid containing oil, e.g. linseed oil, is treated with bromine in chloroform and then with alcohol and ether, the formation of a precipitate of hexabromide indicates the presence of linseed oil in other oil sample.

Detection of Cottonseed Oil:

Raw cottonseed oil contains two unordinary fatty acids, i.e. malvalic acid and sterculic acid. Both acids belong to the category of cyclopropenic acids which is responsible for the traditional Halphens reaction. High levels of cyclopropenic acids (specially sterculic acid) could show toxicity.

Halphen colour test:

In a dry test tube, place 5 ml of filtered and dried oil, then add an equal volume of Sulphur 1.0 % (w/v) solution in carbon disulfide, followed by an equal volume of amyl alcohol. Shake completely before heating in a water bath (70-80°C) for a few minutes, shaking occasionally, until carbon disulfide is cooked out and foaming stops. Place the tube in oil

bath or a saturated brine bath at 110-115°C and let it there for 1 to 2 hours. The presence of cottonseed oil is shown by a red color at the end of this period.(27)

Detection of Castor Oil (Molybdate Method):

Molybdate method is a rapid test for the detection of castor oil to an extent up-to 1.0% or more in other oils. In this test take 1ml of the oil in a dry test tube and dissolve it in 10 ml petroleum ether. Shake vigorously for 2 minutes and add 1-2 drops of molybdate reagent (Dissolve 1.25 g of ammonium molybdate in 100 ml of conc. sulphuric acid). Instantaneous development of white turbidity indicates presence of castor oil as an adulterant in test sample.

Determination of antioxidant activity (DPPH method)

The antioxidant properties of each oil sample were also investigated by determining the free radical scavenging activity of the DPPH radical. Briefly each oil sample was diluted upto 10?g/ml with ethanolic solution, to this 1ml of DPPH solution was added. 0.004% DPPH solution in ethanol was used as a free radical. The mixture was vigorously shaken and left to stand for 15min in the dark (until the absorbance stabilized). The reduction of the DPPH radical was determined by measuring the absorbance of the mixture at 517 nm. The radical scavenging activity (RSA) was calculated as the percentage of DPPH discoloration using the following equation.[27]

%RSA = (AbC) – (AbS) / (AbC) × 100

Whereas is the absorbance of the solution when the sample extract is added at a particular

level and ADPPH is the absorbance of the DPPH solution.

DISCUSSION:

The above physicochemical parameters are reported in Table no.1, here is the sample of edible oils such as Soyabean oil, Peanut oil, Mustard oil, Olive oil, Sunflower oil, Sesame oil, Ricebran oil which shows the quality and safety of edible oils, also give information about present condition about edible oils.(27) The above laboratory or chemical tests are reported in Table no.2, here is the sample of edible oils such as Soyabean oil, Peanut oil, Mustard oil, Olive oil, Sunflower oil, Sesame oil, Ricebran oil which shows which type of adulterant is present in edible oil samples.(27)

Table 1: Physicochemical characteristics of edible oil samples

Table 2: chemical test for adulteration detection of edible oil samples

CONCLUSION: