INTRODUCTION:

Edible oils made significant contributions to people's diets in a large number of countries, including reparations of weary tissues and the creations of new cells as well as a useful source of energy¹, as a major source of protein, lipids and fatty acids for human nutrition.

Vegetable oils and fats are often used in frying, salad dressing, pasty shortens, margarine, cooking and manufacturing of ice cream. Worldwide, vegetable oils and fat represent approximately 80–85% of edible oils and public fats². Edible oils are the world's most important food. For three purposes, the human body uses oils and fats in its diet, for example as an energy source, as a structural element and for making strong biological regulators. In metabolic reactions in the human body oils and fats also play an important role.³

Cooking oil is typical practice in food preparation, particularly during deep-frying, to reduce costs⁴. Deep frying is one of the world's most common and oldest food processes. Heat and mass transport are included. In order to decrease costs, oils are used for frying again and again⁵. The composition of oil changes, which in turn modify the flavour and stability of the chemicals, changes during frying due to hydrolysis, oxidation and polymerization.⁶During deep-fried frying, several elements such as fresh oil recharging, frying conditions, initial frying pet quality and reduced oxidative stability depend on distinct reactions⁷. Atmospheric oxygen immediately responds with lipids and other organic oil components, which cause oils to lose food quality and damage human health⁸. Oil structural breakdown.

Changes in physical appearance of the oil, such as increased viscosity and colour darkening occur when heated repeatedly, which may change the fatty acid makeup of the oil. The oil is heated by a series of chemical events such as oxidation, hydrolysis and polymerization. Many oxidative chemicals are created during this process, such as hydroperoxide and aldehydes, that might be taken into the fried food⁹.

Increased heating temperature and time in vegetable oils may change the antioxidant activity. The physical and chemical properties of the oils are altered by heating. The oil is reheated to degrade the quality of the oil by forming more saturated molecules such hydroperoxides, monomers or dimers and trimers with a lower proportion of unsaturated fats. Initially, antioxidants may prevent lipid peroxidation¹⁰. The antioxidant content of the oil progressively reduces by repeated heating. As a consequence there will be no protective action against free radicals and oxidative damage from remaining diminished antioxidants in the oil¹¹.

The oxidation and thermal stability of fat or oil are dependent on their triacylglycerols, their degree and nature, their antioxidant content, the prooxidant presence, and the circumstances of storage. The oil becomes more oxidation- and thermal-degraded when highly unsaturated dual bonds increase. The oxidation process subsequently decreases both the nutrient value and the safety of fried foods through secondary product development due to peroxidation of polyunsaturated fatty acids (PUFAs). The degree of deterioration in oil is assessed by the peroxide index. During the oxidation process, the peroxide index assesses the amount of peroxides generated in the vegetable oil. The level of rancidity of oxidation depends on the number of episodes of frying. The greater the peroxide index is, the more frequently vegetable oil is warmed. Peroxide production affects the chemical stability of the frying oil. The increased peroxide value reflects the chemical resilience of the petroleum¹².

Oil repeated heating increases lipid oxidative degradation, creates dangerous species of reactive oxygen and deplets the cooking oil's inherent antioxidants.

Long-term intakes of warmed oil products can seriously damage the antioxidant safety net, resulting in pathological conditions such as hypertension, diabetes and vascular inflammation¹³.

Different physical and chemical parameters of edible oil were used to monitor the compositional quality of oils (Ceriani et al., 2008, Mousavi et al., 2012). These physicochemical parameters include iodine value (IV), saponification value (SV), Acid value (AV), viscosity, density and peroxide value (PV)^14-29.

METHODOLOGY:

1. Heating of edible oils:

Various edible oils are chosen such as sunflower oil, palm oil, ground nut oil, sesame oil. The oils are heated by their boiling points. The temperature was recorded via thermometer. If these oils reach their boiling point, remove some amount for qualitative testing. Continue to heat up to 3 hours and collect samples per hour. Record up to 3 hours each temperature. Conduct qualitative testing for these hot samples.

2. Physicochemical estimation:

Different physicochemical properties such as Acid value, Saponification value, Iodine value, Peroxide value, Density, Viscosity tests are performed for every sample.

i. Acid Value:

a. Preparation of 0.1N KOH solution:

Dissolve 1.4g of potassium hydroxide in isopropyl alcohol and transfer into a 250ml volumetric flask and makeup the volume with isopropyl alcohol.

b. Preparation of Titrating Solvent:

To prepare 2Lt of titrating solvent, add 1000ml Toulene to 990ml Isopropyl alcohol and add 10ml distilled water.

Procedure:

Weighed and deposited 1g of sample in a conical bottle. Add the conical flask 125 ml titrating solvent and shake it thoroughly. Please add 2 or 3 drops to the indication of Phenolphtalein. The aforementioned solution has a headline of 0,1 N KOH up to 20-30 seconds of a pale pink colour. It records the volume consumed. A blank operation that does not contain samples is repeated with the above approach.

The Acid value can be calculated by using following formula:

Acid value = 56.1 x N x V

Where,

N = Normality of KOH; V = Volume of KOH consumed; W = Weight of sample taken

ii. Saponification value:

a. Preparation of 0.5 N HCl:

Pipette out 10.43 ml of HCL and transfer it into a 250ml volumetric flask containing distilled water and makeup the volume with distilled water.

b. Preparation of alcoholic KOH:

Weigh 2.08g of KOH and transfer into a Round bottom flask and add 250ml of alcohol to it. Reflux the solution for about 30min. Then dissolve 8.33g of KOH in this refluxed solution keeping temperature 15degrees Celsius. Allow to stand overnight. Filter the solution.

Procedure:

Sample 1 g pipette and transfer to a round bottom flask, then add 12.5 ml of alcoholic KOH solution. Refuse the solution until it becomes evident. Add the phenolphthalein indicator to the refluxed solution. Titrate 0.5 N HCL to the aforementioned combination until the colour is gone (i.e. pink to colorless). It records the volume consumed. A blank operation that does not contain samples is repeated with the above approach.

The value of saponification is based on the formula:

Saponification Value = 56.1 (b – a) N

Where, N = Normality of HCL, b = Volume of HCL consumed for blank, a = Volume of HCL consumed for test, W = Weight of sample taken.

iii. Iodine value:

a. Preparation of 1% of starch solution:

Draw a 100ml glass beaker in 50ml of distilled water. Install beaker and boil the water on a hot plate. Boil. 0.1g starch weight and put to the boiling water. Remue the starch solution to dissolve in water by use of a glass rod. Clear and translucent solution shows that the starch is totally dissolved. Filter now using filter paper for the hot starch solution. Pick up the filtrate after 30min. 1% starch solution is ready to be used as an indicator in titration.

b. Preparation of 0.1N sodium Thiosulfate:

The weight of sodium thiosulfate crystal is 2.5 g and transfer to an 80 ml pure water 100ml volumetric flask. Shake it in the water for the chemical to dissolve. Heat the bottle for a further 10 minutes to completely dissolve sodium. Turn off the heating after 10min and cool the bottle at room. Add water to the remaining 100ml volume after chilling. Prior to usage, standardise the solution.

c. Sample and Blank preparation:

Sample weight can vary depending on the Expected Iodine Value of the sample. Sample can be weighed by using the table1 given below:

Expected Iodine value	Range of sample weight (g)
5	5.0770-6.3460
10	2.5384-3.1730
50	0.5288-0.6612
100	0.2538-0.3173
150	0.1700-0.2125
200	0.1269-0.1586

Data in the table above are used to weigh the sample. Transfer the iodine flask from the sample. Drain tetrachloride 25 ml of carbon and add in the sample flask and shut the flask directly with its stopper. Pipette out a tetrachloride 25ml of carbon and pour into the blank flask and close the flask immediately with its stopper. Wij's solution's 25ml pipette and fill it with a sample and a blank flask. For the correct mixing, shake and spin both flasks together. On all round surface of the stopper add potassium iodide crystal. Keep the two flasks 30 minutes in dark.

Procedure:

Take a desktop solution with 0.1 N of sodium thiosulfate. Measure 100ml of water distilled and fill in the sample and wash the stopper into the flask again to shake the flask. Measure and ready to use 1ml starch solution. The titration of sodium thiosulfate start with 0.1N. When the colour of the solution is lighter, add 1% starch solution. Shake the bottle and restart the titration. Solution of milky white colour marks the titration's end point. Shake the bottle for about 30 seconds to ensure unaltered colour. Shake the flask vigorously and titrate again for a few sec if the blue colour returns. Replay Blank's similar process. Note the readings of the office ²⁸. Then use the following formula to compute the iodine value:

Iodine Value = 12.69(B – S) N

Were,

B = Volume in ml of sodium thiosulfate solution required for Blank, S = Volume in ml of sodium thiosulfate solution required for sample, N = Normality of sodium thiosulfate solution, W = Weight in g of sample.

iv. Peroxide value:

a. Preparation of 1% of starch solution:

Draw a 100ml glass beaker in 50ml of distilled water. Install beaker and boil the water on a hot plate. Boil. 0.1g starch weight and put to the boiling water. Remue the starch solution to dissolve in water by use of a glass rod. Clear and translucent solution shows that the starch is totally dissolved. Now use filter paper to filter the heated starch solution. Pick up the filtrate after 30min. 1% starch solution is ready to be used as an indicator in titration.

b. Preparation of 0.01 N Sodium Thiosulfate solution:

Dissolve 0.25g Sodium Thiosulfate and add 0.02 g Sodium carbonate in 80 ml Distilled water. Good mix. If required, heat the solution to completely dissolve the thiosulfate and chill it at room temperature. Add sufficient distilled water to get the final volume of 100ml.

Procedure:

Sample weighs 4.96 g and dissolves in 30ml of acetic acid. Transfer to a conical flask the above solution. Add 0.5 ml of potassium saturated jod and dilute by 30 ml of purified water. Add an indicator of 0.5 ml of starch. Spread 0.01 N Thiosulphate Solution with titrate. List the volume and see the change in colour. Without sample, repeat the same processes for blank. Then use the formula to compute the peroxide value:

Peroxide Value = [(Vs – Vb) x N x 100]

Where, Vs = Volume of sodium thiosulfate solution for Blank, Vb = Volume of sodium thiosulfate solution for test, N = Normality of sodium thiosulfate solution, W = Weight of sample taken.

v. Density:

Sample density is determined by means of the "Bottle of specific gravity." The specified bottle of gravity was washed and dried with distilled water. The weight of the vacuum gravity bottle was considered 'W1.' The particular bottle was filled with water and tissue paper was applied to the external surface of the bottle. The weighed bottle was taken as "W2." Remove the water distilled from the bottle and sample and tissue paper dry the exterior surface of the bottle. The bottle was taken as "W3." Weighed By utilising the following formula, the oil density sample may be computed:

Density of sample = weight of sample x Density of water

weight of water

vi. Viscosity:

In "Ostwald viscometer" or "Capillary viscometer," the viscosity is determined in the form of oil samples. The viscometer has been cleaned and dried with distilled water. The viscometer was now filled with water distilled and set on a suitable stand upright. Water had been filled to the mark on the viscometer. The time has been taken to determine if the water flows from A to B. For the samples, the same technique has been repeated. With the following formula, the viscosity of liquids can be determined:

η2 = η1 x ρ2 x t2

ρ1 x t1

Where, η1 = Absolute viscosity of water, t1 = Time of flow of water, η2 = Absolute viscosity of sample, t2 = Time of flow of sample, ρ1= Density of water, ρ2 = Density of sample.

RESULTS AND DISCUSSION:

Four different edible oils (sunflower oil, groundnut oil, palm oil and sesame oil) were heated at varied times such as 1 hour, 2 hours and 3 hours, respectively. At their regular boiling point. The physical and biological features of these four distinct food oils were evaluated Important differences in the oils have been noted. The physical and chemical qualities of all these four oils are considerably different. The physico-chemical and biological parameters have shown prolonged changes in temperature and heating dependence. There have been detected physical properties such as peroxide, iodine, saponification value, acid, and density.

Table 1: Estimation of physico-chemical parameters of different edible oils

S. No.	Sample	Time interval		A.V.	S.V.	I.V.	P.V.	Density (g/cc)
S. No.	Sample	Time	Temp.	A.V.	S.V.	I.V.	P.V.	Density (g/cc)
1.	Sun flower oil	Normal-BP	232 °C	0.561	187.935	101.52	10.48	0.895
		1hr	230 °C	1.683	157.08	84.672	11.088	0.8991
		2hr	250 °C	2.805	123.42	83.24	13.91	0.914
		3hr	280 °C	3.366	100.98	80.70	19.15	0.931
2.	Groundnut oil	Normal-BP	235 °C	0.561	185.13	82.23	2.21	0.898
		1hr	245 °C	1.122	173.91	80.05	3.42	0.883
		2hr	240 °C	1.683	154.275	78.67	5.54	0.920
		3hr	238 °C	2.24	129.03	77.29	7.05	0.909
3.	Palm oil	Normal-BP	235 °C	0.561	199.155	48.97	1.81	0.889
		1hr	220 °C	2.244	165.945	47.34	7.25	0.871
		2hr	210 °C	5.049	148.665	43.68	7.86	0.906
		3hr	230 °C	5.61	123.42	40.02	9.27	0.903
4.	Sesame oil	Normal-BP	210 °C	0.561	187.935	100.03	3.83	0.899
		1hr	205 °C	1.683	168.3	93.64	7.25	0.902
		2hr	215 °C	2.44	154.275	89.70	11.89	0.928
		3hr	220 °C	3.366	129.03	84.88	12.5	0.913

Table 2: Estimation of total cholesterol of different edible oils

S. No.	Time interval	Sample-1 (SN)	Sample-2 (GN)	Sample-3 (PM)	Sample-4 (SE)
1	Normal-B.P	148.7±2.539	141.2±62	150.33±32.1	138.11±52
2	1hr.	173.8±15.62	176.35±16.3	193.9±4.82	166.1±1.687
3	2hrs.	185±13.22	179.51±11.3	194.3±16.3	169.12±1.31
4	3hrs.	191.2±15.3	185.32±18.23	198.10±1.33	171.12±2.51

The above V values are expressed as Mean ± SEM, n=6.Used one way ANOVA to calculate statistical significance

of various groups at*P<0.05, * *P<0.01, ***P<0.001 by using D unnette multiple comparison test.

Fig 1: Charts showing the cholesterol content at different times

The glucose levels of sunflower oil is ranging from (118±1.80-138.1±3.21), Ground nut oil is ranging from (109.11±1.13-132.3±1.51), Palm oil is ranging from (120.1±3.13-133.1±1.51), and Sesame oil is ranging from (130±1.40).

Table 3: Estimation of tri-glycerides of different edible oils

S. No.	Time interval	Sample-1 (SN)	Sample-2 (GN)	Sample-3 (PM)	Sample-4 (SE)
1	Normal-B.P	148.7±2.539	141.2±62	150.33±32.1	138.11±52
2	1hr.	153.12±16	149±3.12	155.21±19	139.9±11.2
3	2hrs.	153.12±16	158±1.12	161.32±20.1	142.2±23.78
4	3hrs.	167.72±89.1	165±72.1	176.12±10.1	146±33.18

The above V values are expressed as Mean ± SEM, n=6.Used one way ANOVA to calculate statistical significance of various groups at*P<0.05,* *P<0.01,***P<0.001 by using D u nnette multiple comparision test.

Fig 1: Charts showing the triglyceride content at different times

CONCLUSION:

In this investigation, four various edible oils were heated and warmed up to 3 hours at their regular boiling point. The above hot samples were analysed qualitatively. After study of saponification results all different oils were heated in a continuous 3 hours compared to 2 hours, 1 hours and at normal boiling place. All different oils show low saponification values.

Lower the saponification value, more freely available fatty acids and triglycerides, which can contribute to cardiovascular disease. Results showed a rise in acid values as continuous heating. The high value of acid shows high acidity. Results showed that the value of iodine was reduced as continuous heating. Lower iodine implies that the fatty acids are highly saturated. Not beneficial for health were saturated fatty acids. Sinoxide values have been increased as continuous heating. Increased detection butxide suggests detection. Palm oil, in comparison to other oil, has a high saponification value, acid value, peroxide and iodine value. In case of biological studies, total cholesterol, tri-glycerides and glucose levels were high in 3hrs. heated oils than 2hrs., 1hr. and at normal boiling point. Levels in oils are as follows Palm oil > Sunflower oil > Ground nut oil > Sesame oil.

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Received on 11.09.2021 Modified on 24.11.2021

Asian J. Research Chem. 2022; 15(1):35-41.

DOI: 10.52711/0974-4150.2022.00005