What are Oils and Fats?
Fats are molecules made up of a fatty acid chain with a glycerol head. There are several different kinds of fats determined by the number of carbon atoms in the fatty acid chain and a number of double bonds in the chain. It is a subgroup of lipids. The principal difference between fats and oils is that fats are composed of high amounts of saturated fatty acids which take a solid form at room temperature whereas oils are composed of mainly unsaturated fatty acids which take a liquid form at room temperature. In this article, we will discuss the various tests of oils and fats.
Analysis of Fats and Oils
Fats and oils can be tested by using the following methods:
1. Acrolein Test
In the acrolein test, we take the given food sample, prepare the extract of the given food sample. Then add potassium bisulphite to the above extract. A Pungent irritating odour evolves to form the solution confirms the presence of Fats in the food.
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2. Baudouin Test
This test is used to identify the adulterant (vanaspati ghee) in the desi ghee. The food sample is treated with the mixture, containing 5 ml hydrochloric acid, 2% fufral solution in the alcohol. A rose-red colour appears after some time (around 5-10 minutes) in the solution confirms the presence of vanaspati in the desi ghee.
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3. Translucent Spot Test
Take the food sample and place it between the folds of filter paper and rub it lightly. Presence of translucent spots on the filter paper confirms the presence of fats in foodstuff.
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4. Solubility Test
Take the given food sample, prepare the extract of the given food sample. Then add the above extract to the chloroform solution or alcohol solution. If the extract gets dissolved into the solution, it confirms the presence of Fats in the food.
By using the above methods, the analysis of fats and oils can be done.
Did You Know?
Our nervous system is covered with a sheet of fat.
Vitamin A, D, E, K are fat containing vitamins.
Fats play an important role in the brain development of children.
Unsaturated fats are healthier than saturated fats.
FAQs on Tests of Oils and Fats
1. What are the common laboratory tests used to identify the presence of oils and fats?
Several tests are used to identify oils and fats, which are chemically known as triglycerides. The primary tests include:
- Translucent Spot Test: A simple physical test where the substance leaves a greasy, translucent spot on paper.
- Solubility Test: Fats and oils are insoluble in water but soluble in organic solvents like alcohol, ether, and chloroform.
- Acrolein Test: This test confirms the presence of glycerol or fat. When fat is heated with a dehydrating agent like potassium bisulphate (KHSO₄), it produces a pungent smelling compound called acrolein.
- Baudouin Test: Specifically used to detect the presence of vanaspati ghee (hydrogenated oil) in pure desi ghee.
- Hubl’s Test: Used to determine the degree of unsaturation in an oil or fat.
2. How does the simple translucent spot test work to detect fats in a food sample?
The translucent spot test is a basic physical test for fats. To perform it, a small amount of the food sample is crushed and rubbed onto a piece of paper. The paper is then allowed to dry. If the spot where the sample was rubbed becomes oily and translucent (allowing light to pass through but not being fully transparent), it indicates the presence of fats. This happens because the oil from the fat seeps into the paper's pores, changing its refractive index and making it appear translucent.
3. What is the chemical principle behind the Acrolein test for fats?
The Acrolein test is a specific test for the presence of glycerol, which is the backbone of a fat molecule. When an oil or fat is strongly heated with a dehydrating agent like potassium bisulphate (KHSO₄), the glycerol component dehydrates to form an unsaturated aldehyde called acrolein (prop-2-enal). This compound has a very sharp, pungent, and irritating odour, which is a positive confirmation for the presence of fat or oil.
4. What is the significance of the Baudouin test in food quality analysis?
The Baudouin test is crucial for detecting food adulteration, specifically the mixing of vanaspati ghee (hydrogenated vegetable oil) with pure desi ghee. Vanaspati contains sesamol, which gives a characteristic colour reaction. In the test, concentrated hydrochloric acid and a 2% furfural solution are added to the sample. The appearance of a rose-red colour in the acidic layer confirms the presence of vanaspati ghee, ensuring the purity and quality of the ghee product.
5. How can you chemically differentiate between a saturated fat (like butter) and an unsaturated oil (like vegetable oil)?
The key chemical difference is the presence of double bonds in the fatty acid chains of unsaturated oils. This can be tested using Hubl's test or by using bromine water. When a few drops of bromine water (which is brownish-orange) are added to an unsaturated oil, the bromine adds across the double bonds, causing the colour to disappear. In contrast, saturated fats have no double bonds, so they do not react with the bromine water, and its brownish-orange colour persists. This reaction is a fundamental method for determining the degree of unsaturation.
6. Why is the Saponification Value important for characterising oils and fats?
The Saponification Value is a measure of the average molecular weight of the fatty acids in a fat or oil sample. It is defined as the number of milligrams of potassium hydroxide (KOH) required to saponify (turn into soap) one gram of the fat. A higher saponification value indicates that the fat contains a higher proportion of short-chain fatty acids. This value is extremely important in the soap and cosmetic industries to determine the type and amount of alkali needed to produce soap with desired properties from a particular batch of oil or fat.
7. Can chemical tests also detect if an oil or fat has gone bad (rancid)?
Yes, chemical tests can detect rancidity, which is the chemical decomposition of fats. Rancidity can be of two types: hydrolytic and oxidative. The extent of rancidity is often measured by determining the Acid Value. The Acid Value is the mass of potassium hydroxide (KOH) in milligrams that is required to neutralise the free fatty acids in one gram of the chemical substance. A higher acid value indicates a greater degree of hydrolysis, meaning the fat has broken down and is likely rancid, often resulting in an unpleasant odour and taste.
