The degree of saturation of each fatty acid in a fat or other lipid polymer . food fats derived from plant sources are liquid at room temperature and are called oils. Fatty Acids Soaps and Detergents Fats and Oils Waxes Phospholipids Eicosonoids Terpenes Steroids Lipid Soluble Vitamins Biosynthetic Pathways. Lipids are a class of organic compounds that are insoluble in water. Simply put, lipids are Plant oils are mostly found in the seed. The parent plant stores The monomers of the neutral fats are glycerol and fatty acid. Glycerol is a 3-carbon.
Like the other large biological molecules, they play essential roles in the biology of humans and other organisms. Also, many recent dietary studies see sugar as causing a lot more health problems than fat! Fats are just one type of lipid, a category of molecules united by their inability to mix well with water. Lipids tend to be hydrophobic, nonpolar, and made up mostly of hydrocarbon chains, though there are some variations on this, which we'll explore below.
The different varieties of lipids have different structures, and correspondingly diverse roles in organisms. For instance, lipids store energy, provide insulation, make up cell membranes, form water-repellent layers on leaves, and provide building blocks for hormones like testosterone.
Fats and oils A fat molecule consists of two kinds of parts: Glycerol is a small organic molecule with three hydroxyl OH groups, while a fatty acid consists of a long hydrocarbon chain attached to a carboxyl group. A typical fatty acid contains 12—18 carbons, though some may have as few as 4 or as many as To make a fat molecule, the hydroxyl groups on the glycerol backbone react with the carboxyl groups of fatty acids in a dehydration synthesis reaction. Triglycerides may contain three identical fatty acid tails, or three different fatty acid tails with different lengths or patterns of double bonds.
Synthesis of a tryacylglycerol molecule from a glycerol backbone and three fatty acid chains, with the release of three molecules of water. Image modified from OpenStax Biology. Fat molecules are also called triacylglycerols, or, in bloodwork done by your doctor, triglycerides. While many fatty acids are found in fat molecules, some are also free in the body, and they are considered a type of lipid in their own right.
Saturated and unsaturated fatty acids As shown in the example above, the three fatty acid tails of a triglyceride need not be identical to each other. Fatty acid chains may differ in length, as well as in their degree of unsaturation.
If there are only single bonds between neighboring carbons in the hydrocarbon chain, a fatty acid is said to be saturated. The thing that fatty acids are saturated with is hydrogen; in a saturated fat, as many hydrogen atoms as possible are attached to the carbon skeleton.
When the hydrocarbon chain has a double bond, the fatty acid is said to be unsaturated, as it now has fewer hydrogens. The double bonds in unsaturated fatty acids, like other types of double bonds, can exist in either a cis or a trans configuration. In the cis configuration, the two hydrogens associated with the bond are on the same side, while in a trans configuration, they are on opposite sides see below.
A cis double bond generates a kink or bend in the fatty acid, a feature that has important consequences for the behavior of fats. Saturated fatty acid example: Unsaturated fatty acid examples: Saturated fatty acids tails are straight, so fat molecules with fully saturated tails can pack tightly against one another. This tight packing results in fats that are solid at room temperature have a relatively high melting point. In contrast, cis-unsaturated fatty acid tails are bent due to the cis double bond.
This makes it hard for fat molecules with one or more cis-unsaturated fatty acid tails to pack tightly.
So, fats with unsaturated tails tend to be liquid at room temperature have a relatively low melting point — they are what we commonly call oils. For instance, olive oil is mostly made up of unsaturated fats 2 2. Trans fats are rare in nature, but are readily produced in an industrial procedure called partial hydrogenation.
In this process, hydrogen gas is passed through oils made mostly of cis-unsaturated fatsconverting some — but not all — of the double bonds to single bonds. Trans-unsaturated fatty acids can pack more tightly and are more likely to be solid at room temperature.
Partial hydrogenation and trans fats might seem like a good way to get a butter-like substance at oil-like prices. Unfortunately, trans fats have turned out to have very negative effects on human health.
Because of a strong link between trans fats and coronary heart disease, the U. The characteristic colors, odors, and flavors that we associate with some of them are imparted by foreign substances that are lipid soluble and have been absorbed by these lipids. For example, the yellow color of butter is due to the presence of the pigment carotene; the taste of butter comes from two compounds—diacetyl and 3-hydroxybutanone—produced by bacteria in the ripening cream from which the butter is made.
Fats and oils are lighter than water, having densities of about 0. They are poor conductors of heat and electricity and therefore serve as excellent insulators for the body, slowing the loss of heat through the skin.
Chemical Reactions of Fats and Oils Fats and oils can participate in a variety of chemical reactions—for example, because triglycerides are esters, they can be hydrolyzed in the presence of an acid, a base, or specific enzymes known as lipases. The hydrolysis of fats and oils in the presence of a base is used to make soap and is called saponification.
Sodium carbonate or sodium hydroxide is then used to convert the fatty acids to their sodium salts soap molecules: Soaps Ordinary soap is a mixture of the sodium salts of various fatty acids, produced in one of the oldest organic syntheses practiced by humans second only to the fermentation of sugars to produce ethyl alcohol. Even so, the widespread production of soap did not begin until the s.
Soap was traditionally made by treating molten lard or tallow with a slight excess of alkali in large open vats. The mixture was heated, and steam was bubbled through it. After saponification was completed, the soap was precipitated from the mixture by the addition of sodium chloride NaClremoved by filtration, and washed several times with water.
It was then dissolved in water and reprecipitated by the addition of more NaCl. The glycerol produced in the reaction was also recovered from the aqueous wash solutions. Pumice or sand is added to produce scouring soap, while ingredients such as perfumes or dyes are added to produce fragrant, colored soaps.
Blowing air through molten soap produces a floating soap. Soft soaps, made with potassium salts, are more expensive but produce a finer lather and are more soluble. They are used in liquid soaps, shampoos, and shaving creams.
17.2: Fats and Oils
Dirt and grime usually adhere to skin, clothing, and other surfaces by combining with body oils, cooking fats, lubricating greases, and similar substances that act like glues. Because these substances are not miscible in water, washing with water alone does little to remove them. Soap removes them, however, because soap molecules have a dual nature. One end, called the head, carries an ionic charge a carboxylate anion and therefore dissolves in water; the other end, the tail, has a hydrocarbon structure and dissolves in oils.
The hydrocarbon tails dissolve in the soil; the ionic heads remain in the aqueous phase, and the soap breaks the oil into tiny soap-enclosed droplets called micelles, which disperse throughout the solution. The droplets repel each other because of their charged surfaces and do not coalesce.
The double bonds in fats and oils can undergo hydrogenation and also oxidation. The hydrogenation of vegetable oils to produce semisolid fats is an important process in the food industry. Chemically, it is essentially identical to the catalytic hydrogenation reaction described for alkenes. In commercial processes, the number of double bonds that are hydrogenated is carefully controlled to produce fats with the desired consistency soft and pliable.
Inexpensive and abundant vegetable oils canola, corn, soybean are thus transformed into margarine and cooking fats.
Fats and Oils - Chemistry LibreTexts
In the preparation of margarine, for example, partially hydrogenated oils are mixed with water, salt, and nonfat dry milk, along with flavoring agents, coloring agents, and vitamins A and D, which are added to approximate the look, taste, and nutrition of butter.
Preservatives and antioxidants are also added. In most commercial peanut butter, the peanut oil has been partially hydrogenated to prevent it from separating out. Consumers could decrease the amount of saturated fat in their diet by using the original unprocessed oils on their foods, but most people would rather spread margarine on their toast than pour oil on it. Many people have switched from butter to margarine or vegetable shortening because of concerns that saturated animal fats can raise blood cholesterol levels and result in clogged arteries.
However, during the hydrogenation of vegetable oils, an isomerization reaction occurs that produces the trans fatty acids mentioned in the opening essay.