Lipids PDF

/ (fixed oils, fats, and waxes) (Lipids (fixed oils, fats, and waxes) are esters of long-chain fatty acids and alcohols. The chief difference between these substances is the type of alcohol; in fixed oils and fats, glycerol alcohol (C3H8O3) combines with the fatty acids called(glycerides); in waxe...

/ (fixed oils, fats, and waxes) (Lipids (fixed oils, fats, and waxes) are esters of long-chain fatty acids and alcohols. The chief difference between these substances is the type of alcohol; in fixed oils and fats, glycerol alcohol (C3H8O3) combines with the fatty acids called(glycerides); in waxes, the alcohol has a higher molecular weight, e.g., cetyl alcohol (C16H34O). Fats and Waxes may be of plant (olive oil, peanut oil) or animals origin (lard). Their primary function is food (energy) storage. The fixed oils and fats are important products used pharmaceutically, industrially, and nutritionally. Classification of lipids: Simple lipids: are esters of fatty acids with alcohol e.g.(fixed oil and fats- waxes). Compound lipids: are esters of fatty acids with alcohol containing another group e.g. (phospholipid). Examples of Compound lipids : 1- Phospholipids: compounds of fatty acids with glycerol and phosphoric acid. 2- Glucolipids : compounds of fatty acids with glycerol and carbohydrates. 3- Sulpholipids: containing sulfur. 4- Aminolipids: containing nitrogen. Fixed oils and fats differ only as to melting point; those that are liquid at normal temperatures are known as fixed oils, whereas those that are semisolid or solid at ordinary temperatures are known as fats. Fixed oils and fats of vegetable origin are obtained by compression. If the compression is carried out in the cold, the oil is known as a "virgin oil" or a "cold-pressed oil“. In contrast, if the compression is carried out in heat, the oil is known as a "hot-pressed oil." Animal fats are separated from other tissues by rendering with steam, with or without pressure. The heat melts the fat, which rises to the top and may be separated by decantation. Chemically, the fixed oils and fats are glycerides of fatty acids. Usually, the glycerides of unsaturated fatty acids are liquid, whereas the glycerides of saturated fatty acids of sufficient chain length are solid. Physical properties: fixed oils and fats are lighter than and insoluble in water, greasy to feel, leave a permanent translucent stain on paper and do not volatilize on exposure to air. They are freely soluble in ether, chloroform, light petroleum, but they are usually insoluble in alcohol ( an important exception being castor oil which dissolves in 3.5 volumes of alcohol 90%). Vegetable oils and fats may occur in various parts of the plants but as a general rules seeds contain larger quantities of them than do other parts of the plants e.g. cotton seed oil, lin seed oil, sesame, castor beans seeds, almond and others. BIOSYNTHESIS OF LIPIDS Acetate first reacts with CoA, and the acetyl-CoA thus formed is converted by reaction with carbon dioxide to malonyl CoA. This, in turn, reacts with an additional molecule of acetyl-CoA to form a 5-carbon intermediate, which undergoes reduction and elimination of carbon dioxide to produce butyryl-CoA. Malonyl-CoA again reacts with this compound to form a 7-carbon intermediate, which is reduced to caproyl- CoA. Repetition of the reaction resuits in a fatty acid containing an even number of carbon atoms in its chain. Thus, the malonyl portion of malonyl-CoA, a 3- carbon compound, is actually the source of the 2- carbon biosynthetic units of the fatty acids. Hardening and polymerization of fixed oils and fats: The unsaturated fixed oils and their glycerides are capable to add H2 to the double bond in the presence of catalyst. This property is used in fat industry. This process is called fat hardening whereby the fats are less susceptible to rancidification. Fat polymerization consists of heating the oil in an inert atmosphere, the prolong heating brings more of the unsaturated components to react with each other to give a more saturated oil or cyclic structure. -CH=CH- -C-C- -CH=CH- -C-C- The polymerized oil do not develop a rancid taste or color during storage. Hydrogenation of carbon- carbon double bonds in cheap oils as cotton oil, corn oil and soy bean oil converts these liquids into solid having a consistency comparable to that of lard or butter. This hardening of oils is the basis of an important industry that produces cooking fats. Hydrogenation not only changes the physical properties of fats but also changes the chemical properties: a hydrogenated fat becomes rancid much less readily than does a non- hydrogenated oil. Drying properties: Fixed oils are sometimes classified into drying oils, semidrying oils, and nondrying oils. This classification is based on their ability to absorb oxygen from the air. Oxygen saturates the double bonds to form oxides that may polymerize to form hard films. nondrying oils: it contains large quantity of oleic acid glycerides such oils may be thicken on exposure to air but do not dry e.g. olive oil. semidrying oils: contain both oleic and linoleic glycerides e.g. cotton seed oil, sesame oil. drying oils: contain linoleic acid glycerides e.g. lin seed oil. Evaluation of fixed oils and fats The united states pharmacopeia and the national formulary include several tests for fixed oil by means of which their identity, quality and purity may be determined. These tests are based upon the chemical constitution of the oil or fat: Acid value or acid number: indicates the amount of free fatty acid present in the oil. (no. of mg of KOH required to neutralize the free acids in 1gm of the substance). The saponification value: indicates the no. of mgs of KOH needs to saponify completely 1 gm of fat or oil. (no. of mgs of KOH needed to neutralize the free acids and saponify the esters in 1 gm of substance.) Iodine number: indicate the degree of unsaturation ( number of grams of iodine absorbed under certain conditions by 100 gm of the substance.) Other physical constants such as melting point, specific gravity and refractive index also serve as identity and quality test. Rancidity of fixed oils: Is the transformation in oils and fats during storage, during which a new compound is formed which may cause change of the consistency of the oil (taste and odor). Rancidity is due to presence of volatile, bad smelling acids and aldehydes. These compounds result in part at least from attack by oxygen at reactive allylic positions in the fat molecules. Hydrogenation slows down the development of rancidity presumably by decreasing the number of double bonds and hence the number of allylic positions. Types of rancidity: 1- Hydrolytic rancidity. 2- Oxidative rancidity. Hydrolytic rancidity: It is due to the production of free fatty acids, generally caused by the enzyme lipase (fat splitting enzyme). To overcome this type of rancidity we must keep the moisture with a certain limit to inactivate the enzyme by heat. Oxidative rancidity Its differentiated into: Rancidity occurs in a highly unsaturated fatty acids followed by polymerization (formation of cyclic polymers which are more stable). Rancidity in less saturated oils, it leads to development of rancid fixed oil or fat. To overcome this rancidity, antioxidant agent may be added to the fixed oil or fat e.g. propyl gallate and citric acid. Uses of fixed oils and fats Fixed oils and fats are employed in pharmaceuticals for their emollient properties. As ointments or creams, emulsions. They may be also used as vehicles for other medications. Some oils like castor oil have special therapeutic properties. In the arts and industry they are used in the manufacture of soaps, as drying oils in the manufacture of paints, varnishes and as lubricants FIXED OILS Castor Oil Castor bean or castor oil seed is the ripe seed of Ricinus cominunis plant (Fam. Euphorbiacea). Castor seeds contain from 45 to 55% of fixed oil. Castor bean pomace contains an allergen that causes allergic reactions in hypersensitive individuals. USES AND DOSE. Castor oil is a stimulant cathartic; the usual dose is 15 to 60 ml. Commercially, castor oil is used in the manufacture of soaps. Linseed oil Linseed or flaxseed is the dried ripe seeds of Linum usitatissimum plant. F: Linaceae. Uses: Lin seed oil is a demulcent and laxative. Olive Oil Olive oil is the fixed oil obtained from the ripe fruit of Olea europaea plant.(F. Oleaceae). Olive oil is sometimes called sweet oil. USES: Olive oil is used in the preparation of soaps, and plasters. It is also a demulcent, an emollient, and a laxative. Olive oil is a nutrient and is widely used as a salad oil. Cottonseed Oil Cottonseed oil is the refined, fixed oil obtained from the seed of cultivated plants of various varieties of Gossypium hirsutum plant. (Fam. Malvaceae). USES. Cottonseed oil is employed pharmaceutically as a solvent for a number of injections. A large amount is also used in the manufacture of soap. Sesame Oil Sesamum seed or sesame seed is the seed of one or more cultivated varieties of Sesarnum indicurn plant. (Fam. Pedaliaceae). USES: Sesame oil is used as a solvent for intramuscular injections. It has nutritive, laxative, demulcent, and emollient properties. FATS AND RELATED COMPOUNDS Theobroma Oil, obtained from the roasted seeds of Theobroma cacao plant. (Fam. Sterculiaceae). Theobroma oil is more commonly known cacao butter. Cacoa butter is used pharmaceutically as a suppository base. Lard Is the purified internal fat of the abdomen. Uses: lard is an emollient and is used as base for ointment. Lanolin Lanolin is the purified, fat like substance from the wool of the sheep. USES. Lanolin is used as an ingredient in many skin creams and cosmetics. Waxes Waxes are usually defined as esters resulting from the condensation of high-molecular- weight, straight-chain acids and high- molecular-weight, primary, straight chain alcohols. In plants, waxes are found in connection with the outer cell walls of epidermal tissue, particularly in fruits and leaves. The function of wax appears to be protection against the penetration or loss of water. Insects also secrete waxes for various purposes. Waxes are employed in pharmaceuticals to 'harden" ointments and cosmetic creams. In industry and the arts, waxes are used for protective coatings. Beeswax Yellow wax or beeswax is the purified wax from the honeycomb of the bee, Apis mellifera insect. (Fam. Apidae) USES. Yellow wax is a stiffening agent and is an ingredient in yellow ointment. It is also used as a base for plasters. Commercially, it is contained in a number of polishes.