Difference Between Monounsaturated and Polyunsaturated Fats
In nutrition, biology, and chemistry, fat refers to any ester of fatty acids, or a mixture of such compounds, most commonly found in living beings or food.
Triglycerides (triple esters of glycerol) are the primary constituents of vegetable oils and animal fatty tissue; or, to put it another way, triglycerides that are solid or semisolid at room temperature, excluding oils. The word can also be used as a synonym for lipid, which refers to any biologically important material made up of carbon, hydrogen, or oxygen that is insoluble in water but soluble in non-polar solvents.
Apart from triglycerides, the word may also include mono- and diglycerides, phospholipids (such as lecithin), sterols (such as cholesterol), waxes (such as beeswax), and free fatty acids, which are generally found in smaller quantities in the human diet.
Saturated Fat
What is Saturated Fat?
Saturated fat is a form of fat in which all or most of the fatty acid chains are single bonds. Glycerol and fatty acids are the two types of smaller molecules that make up fat. Long chains of carbon (C) atoms make up fats. Single bonds (-C-C-) attach certain carbon atoms, while double bonds (-C=C-) connect others. Single bonds may be formed when double bonds react with hydrogen. Since the second bond is broken and each half of the bond is bound to (saturated with) a hydrogen atom, they are called saturated.
Since saturated fats have higher melting points than unsaturated fats, it's common knowledge that saturated fats are solids at room temperature, while unsaturated fats are liquids of varying degrees of viscosity.
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Unsaturated Fats
Unsaturated fats have one or more double bonds between hydrogen and carbon. The term unsaturated refers to a molecule with less than the maximum number of hydrogen atoms bound to each carbon. The generic name indicates the number of double bonds—monounsaturated for molecules with one double bond and polyunsaturated for molecules with two or more double bonds.
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Monounsaturated Fat
Monounsaturated fatty acids (MUFAs) have a single double bond, whereas polyunsaturated fatty acids (PUFAs) have two or more double bonds. Even on the same molecule, natural fats typically contain several different saturated and unsaturated acids. Many vegetable oils, for example, have saturated palmitic and stearic acid residues attached to positions 1 and 3 (sn1 and sn3) of the glycerol hub, whereas the middle position (sn2) is normally held by an unsaturated one, such as oleic.
Polyunsaturated Fat
Polyunsaturated fatty acids (fatty acids with more than one carbon-carbon double bond) are present in small quantities. Multiple double bonds are almost always separated by a CH2 group, a regular spacing motif resulting from the biosynthetic mechanism that introduces the double bonds into the hydrocarbon chain.
Cis -Trans Polyunsaturated Fat
The cis-trans isomerism, or the spatial arrangement of the C–C single bonds adjacent to the double bonds, is another important classification of unsaturated fatty acids. In nature, most unsaturated fatty acids have certain bonds in the cis ("same side") of configuration.
Trans Polyunsaturated
While trans polyunsaturated fatty acids are not generated biosynthetically by mammals, they are produced synthetically by partial hydrogenation of fats and oils in the manufacture of margarine by microorganisms in the guts of ruminant animals such as cows and goats (the so-called trans fats). Ingestion of trans fats has been shown to have negative metabolic effects.
Let’s see now the difference between saturated and unsaturated fats.
Saturated VS Unsaturated Fat
Saturated Fat Good or Bad
Since it transfers cholesterol to your liver to be expelled from your body, HDL is known as "healthy cholesterol." HDL aids in the removal of extra cholesterol from the body, making it less possible for it to clog the arteries.
LDL is known as "poor cholesterol" because it transports cholesterol to the arteries, where it can build up in the walls of the arteries. Atherosclerosis is an accumulation of plaque in the arteries caused by too much cholesterol. Blood clots in the arteries are more likely as a result of this. A stroke or heart attack may occur when a blood clot breaks free and blocks an artery in your heart or brain.
Did You Know?
Fats are important for keeping skin and hair healthy, as well as insulating body organs from shock, maintaining body temperature, and promoting healthy cell function. Fat also acts as a protective barrier against a variety of diseases. When a chemical or biotic material reaches dangerously high levels in the bloodstream, the body can effectively dilute—or at least preserve the equilibrium of—the offending substance by storing it in fresh fat tissue.
Adipose tissue, also known as fatty tissue, is the body's way of storing metabolic energy for long periods of time in animals. Adipocytes (fat cells) are fat storage cells that store fat from the diet and liver metabolism. These cells can degrade their stored fat to supply fatty acids and glycerol to the circulation when they are under energy stress. Several hormones regulate these metabolic activities (e.g., insulin, glucagon, and epinephrine). The hormone leptin is also produced by adipose tissue.
FAQs on What Are Unsaturated Fats in Chemistry?
1. What is an unsaturated fat in chemistry?
An unsaturated fat is a type of fat or fatty acid in which there is at least one carbon-carbon double bond (C=C) within the fatty acid chain. This double bond means the molecule contains fewer hydrogen atoms than the maximum it could hold, making it 'unsaturated' with hydrogen. These fats are typically liquid at room temperature and are commonly found in plant-based sources. For more details, you can explore the fundamentals of Unsaturated Fat.
2. What is the main difference between saturated and unsaturated fats?
The primary difference lies in their chemical structure and physical properties.
- Saturated Fats: Contain only single bonds between carbon atoms in their fatty acid chains. This allows the molecules to pack tightly together, making them solid at room temperature (e.g., butter, lard).
- Unsaturated Fats: Contain one or more double bonds between carbon atoms. These double bonds create 'kinks' or bends in the molecule, preventing them from packing closely. As a result, they are typically liquid at room temperature (e.g., olive oil).
3. What are the different types of unsaturated fats?
Unsaturated fats are mainly classified into two types based on the number of double bonds in their structure:
- Monounsaturated Fats: These fats have only one carbon-carbon double bond in their fatty acid chain. Examples include olive oil, canola oil, and avocados.
- Polyunsaturated Fats: These fats have two or more carbon-carbon double bonds. This category includes omega-3 and omega-6 fatty acids, found in sources like walnuts, flaxseeds, and fatty fish like salmon.
4. Which common foods are good sources of unsaturated fats?
Unsaturated fats are essential for a healthy diet and are found in a variety of foods. Good sources include:
- Nuts and Seeds: Almonds, walnuts, peanuts, chia seeds, and flaxseeds.
- Vegetable Oils: Olive oil, sunflower oil, canola oil, and peanut oil.
- Avocados: A rich source of monounsaturated fats.
- Fatty Fish: Salmon, mackerel, and sardines are high in omega-3 polyunsaturated fats.
5. Why are most unsaturated fats liquid at room temperature?
The liquid state of most unsaturated fats is a direct result of their molecular geometry. The presence of cis-double bonds creates distinct kinks or bends in the fatty acid chains. These kinks prevent the molecules from packing closely and neatly together. Due to weaker intermolecular forces (van der Waals forces) between the spaced-out molecules, less energy is required to overcome them, resulting in a lower melting point and a liquid state at room temperature. Saturated fats, lacking these kinks, pack tightly and are solid. The tests of oils and fats often rely on these structural differences.
6. How does the structure of unsaturated fats affect their chemical properties?
The carbon-carbon double bonds in unsaturated fats are key to their chemical reactivity. These double bonds are electron-rich sites, making them more susceptible to chemical reactions compared to the single bonds in saturated fats. A significant property is their vulnerability to oxidation. When exposed to oxygen, heat, or light, the double bonds can break, leading to the formation of smaller, volatile compounds that cause the fat to become rancid. This process is known as oxidative Rancidity.
7. What is the difference between cis- and trans-unsaturated fats, and why are trans fats considered unhealthy?
Both cis and trans fats are types of unsaturated fats, but they differ in the spatial arrangement of hydrogen atoms around the double bond.
- Cis-fats: The hydrogen atoms are on the same side of the double bond, creating a bent shape. This is the natural form found in most unsaturated fats.
- Trans-fats: The hydrogen atoms are on opposite sides of the double bond. This creates a more linear, straight structure, similar to a saturated fat.
8. Is ghee a saturated or unsaturated fat?
Ghee, or clarified butter, is predominantly a saturated fat. Although it is liquid when heated, it solidifies at cooler room temperatures, which is a characteristic property of saturated fats. While it does contain a small percentage of monounsaturated and polyunsaturated fats, its composition is over 60% saturated fat. This is a key distinction covered in topics like Carbon and Its Compounds in the NCERT Solutions for Class 10 Science Chapter 4.
9. How can you chemically test for the presence of unsaturation in a fat or oil sample?
The presence of double bonds (unsaturation) in a fat or oil can be detected through simple chemical tests that rely on the reactivity of the C=C bond. Two common methods are:
- Bromine Water Test: When a few drops of reddish-brown bromine water are added to an unsaturated fat, the double bonds react with the bromine in an addition reaction. This causes the bromine water to lose its colour and become colourless. Saturated fats will not react, and the solution will remain reddish-brown.
- Baeyer's Test: Adding a cold, dilute, alkaline solution of potassium permanganate (KMnO₄), which is purple, to an unsaturated fat will decolourise the solution as the KMnO₄ is reduced and the fat is oxidised at the double bond.
