Lipids: Classification and Types

Lipids, Lipins, Lipoids

• Esters comprised of long-chain fatty acids and alcohols, or closely related derivatives (RCOOR).
• Refers to fat and fat-like substances found in plants and animals (RPS).
• Substances that are heterogenous in chemical composition.
• A collective term for fixed oils, fats, and waxes.

Classification of Lipids (Tyler)

• Fixed oils
• Fats
• Waxes
• Fatty acids
• Prostaglandins

Types of Lipids

• Simple lipids are esters of fatty acids and alcohol.
  • Fats and fixed oils are esters of fatty acids and glycerol.
  • Waxes are esters of fatty acids and high molecular weight (HMW) alcohols.
• Compound lipids have a fatty acid, an alcohol, and another compound.
  • Glycolipids and phospholipids are examples.
• Derived lipids are products of simple and compound lipids after hydrolysis

Classification of Lipids (RPS)

• Fixed oils and fats are esters of glycerol and fatty acids.
  • Olive oil is a fixed oil, and wool fat is a fat.
• Waxes are esters of high molecular weight monohydric alcohols and high molecular weight fatty acids.
  • Spermaceti is an example.
• Sterols are alcohols containing the cyclopentanoperhydrophenanthrene nucleus.
  • Cholesterol and ergosterol are examples.
• Phospholipids/phosphatides are esters containing glycerol combined with fatty acids, phosphoric acid, and certain nitrogenous compounds.
  • Lecithin is an example.
• Glycolipids/cerebrosides are substances isolated from the brain and other sources.
  • Upon hydrolysis, they yield fatty acids, galactose, and a nitrogenous compound.
    • Sphingosine is an example.

Fixed Oils and Fats

• Glyceryl esters (glycerides) of long-chain fatty acids.
• General reaction: C3H5(OH)3 + 3RCOOH → C3H5(OCOR)3 + 3H2O

Types of Glycerides

• Simple glycerides have the same fatty acid radical for all three positions.
  • Tristearin is an example.
• Mixed glycerides have different fatty acid radicals.

Differences Between Fixed Oils and Fats

• Fixed oils are liquid at room temperature, while fats are solid.
• Fixed oils have a high proportion of liquid glycerides, whereas fats have a high proportion of solid glycerides.

Solid Glycerides

• Glyceryl esters of saturated fatty acids that are solid at room temperature.

Saturated Fatty Acids

• Butyric acid (4 carbons) is found in butter.
• Caproic acid (6 carbons) is found in butter.
• Caprylic acid (8 carbons) is found in coconut oil.
• Capric acid (10 carbons) is found in palm oil.
• Lauric acid (12 carbons) is found in laurel.
• Myristic acid (14 carbons) is found in nutmeg.
• Palmitic acid (16 carbons) is found in palm.
• Stearic acid (18 carbons) is found in tallow.
• Arachidic acid (20 carbons) is found in peanut.
• Behenic acid (22 carbons) is found in bene oil.
• Lignoseric acid (24 carbons) is found in peanut.
• Cerotic acid (26 carbons) is found in waxes.
• Mellisic acid (30 carbons) is found in waxes.

Unsaturated Fatty Acids

• Oleic acid (18 carbons, 1 double bond) is found in olive oil.
• Linoleic acid (18 carbons, 2 double bonds) is found in corn.
• Linolenic acid (18 carbons, 3 double bonds) is found in linseed.
• Arachidonic acid (20 carbons, 4 double bonds) is found in lecithin.
• Clupanodonic acid (22 carbons, 5 double bonds) is found in fish oils.

Liquid Glycerides

• Glyceryl esters of polyunsaturated fatty acids that are liquid at room temperature.
• Examples include oleic, linolenic, linoleic, and ricinoleic acids.

Fixed Oils

• Have a high proportion of liquid glycerides.
• Most are liquid at room temperature, except cocoa butter, which is a solid vegetable oil.
  • Examples include olive oil, peanut oil, and castor oil.

Fats

• Contain a high proportion of solid glycerides.
• Most are solid at room temperature, except cod liver oil, which is a liquid animal fat.
  • Examples include woolfat and hydrogenated vegetable oil.
• Can occur in various plant parts, but seeds generally contain larger quantities.

Preparation of Fixed Oils and Fats

• Expression involves using hydraulic presses.
  • "Virgin oil" or "cold-pressed oil" is carried out in the cold.
  • "Hot-pressed oil" is carried out with heat.
• Extraction uses organic solvents.
• Rendering involves using steam with or without pressure.

Clarification

Can be carried out by:

• Decantation
• Filtration
• Bleaching
• Chilling

USP Tests/Analytical Characteristics (RPS)

• Acid value/acid number is the number of mg of KOH required to neutralize free fatty acids in 1g of a substance, indicating free fatty acids in an oil.
• Saponification value is the number of mg of KOH required to neutralize free fatty acids and saponify the esters in 1g of a substance.
• Iodine value is the number of g of iodine absorbed under prescribed conditions by 100g of the substance, indicating the degree of unsaturation.

Other Physical Constants

Serve as purity, quality, and identity tests:

• Specific gravity
• Refractive index
• Congealing point
• Color
• Odor

Gas Chromatography

• Useful for identifying fats and fixed oils.

Properties of Fats and Oils

• Greasy to the touch.
• Leave a permanent oily stain (translucent spot).
• Lighter than water
• Insoluble in water but soluble in water-immiscible solvents.
• Nearly pure fats and oils are colorless with a bland odor and taste.
• They decompose into acrolein/propenal (acrid and flammable) when heated strongly.
• They undergo hydrolysis to form glycerol and fatty acids.
• They undergo saponification (alkali hydrolysis) to form soap and glycerol.

Reactions

• C3H5(OCOR)3 + 3KOH → 3 RCOOK + C3H5(OH)3 produces soft soap.
• C3H5(OCOR)3 + 3NaOH → 3 RCOONa +C3H5(OH)3 produces hard soap.

Uses of Fats & Fixed Oils

• As an emollient.
• As a vehicle for other medications.
• For special therapeutic effects.
  • Stimulant cathartic and laxative effects.
• In arts and industry.
  • Manufacturing soap and paints.
• As food with high caloric value
  • As in parenteral nutrients.

Lipids Characteristics

• Lipids are a diverse group of organic compounds containing carbon, hydrogen, oxygen, nitrogen, and phosphorus.
• They are non-polar and hydrophobic, making them insoluble in water but soluble in organic solvents like ether, alcohol, chloroform, and benzene.
• They store twice the amount of energy compared to carbohydrates and proteins because they have a high proportion of C-H bonds and low oxygen.
• Act as insulating layer
  • Waxes in exoskeletons of insects.

Classification Based on Oxygen Absorption

Based on the ability to absorb O2, where O2 saturates the double bond to form oxides that may polymerize to create a hard film.

• Drying oils undergo oxidation when exposed to air, forming a tough, hard film.
• Non-drying oils remain sticky to the touch after exposure to air for an indefinite period.
• Semi-drying oils.

Sulfated/Sulfonated Oils

• Reacting H2SO4 with the oil while keeping the temperature chilled.

Hydrogenated Oils

• Passing H2 through the oil in the presence of Nickel/palladium, heating to 160 to 200 degrees causes the oil to solidify (saturate).

Waxes

• Vegetable waxes.
  • Carnauba and bayberry.
• Insect waxes.
  • Beeswax and lac wax.

Wax Uses

• Stiffeners to harden ointments.
• Preparation of cerates.
• Protective coatings.

Wax Examples

• Spermaceti
• Beeswax
• Carnauba wax

Prostaglandins

• C20 metabolites are formed in the body from essential, unsaturated fatty acids in the diet.
• Have diverse pharmacological effects that go beyond those of steroids.
• Termination of 2nd trimester pregnancies
  • PGE2, PGE2a, 15-methyl PGE2a
• Maintain temporarily in neonates with patent ductus arteriosus and certain congenital heart disease.
  • Uses received FDA approval.

Other Potential Uses

• Induce labor at term (PGE2).
• Prevent premature labor (PGE).
• Induce menstruation.
• Increase fertility in certain conditions (PGE).
• Manage some types of hypertension (PGE1 & PGE2).
• Control certain cardiac arrhythmias (PGF2a).
• Correct some defects in RBC (PGE).
• Exert antithrombogenic and thrombolytic activity (PGE1).
• Control asthmatic seizures (PGE1).
• Inhibit gastric secretions in the treatment of peptic ulcers (PGE).

Prostaglandin Examples

• Prostaglandin F2a, PGE2a or Dinoprost.
  • Terminates 2nd trimester pregnancy.
• 15-Methylprostaglandin F2a, 15-methyl PGF2a, Carboprost.
  • Same use
• Prostaglandin E2, PGE2, Dinoprostone.
  • Same use
• Prostaglandin E1, PGE1, Alprostadil.
  • Produces vasodilation (used as palliative therapy to temporarily maintain neonates with patent ductus arteriosus and congenital heart defects)
  • Inhibits platelet aggregation.
  • Stimulates intestinal and uterine smooth muscle.

Fatty Acids

• Obtained from the hydrolysis of fats or oils.
• Salts are used as pharmaceutic necessities.

Fatty Acid Examples

• Stearic acid salts of Ca, Mg, Na, Zn, Al esters used as glyceryl monostearate & propylene glycol monostearate.
• Oleic acid as ethyl oleate.
• Linoleic & Linolenic acids.
  • Also known as vitamin F.
  • Obtained from soybean oil and other suitable vegetable oils.
• Undecylenic acid.
  • Prepared by pyrolysis of ricinoleic acid.
  • Has antifungal properties.
  • Combines with Zn undecylenate in ointments and powders to treat athlete's foot.
  • Ca salt used in powders for diaper rash.
• Sodium morrhuate.
  • Na salts of the fatty acids of cod liver oil.
  • Sclerosing agents to obliterate varicose veins.

Grades of Olive Oil

• Virgin Oil
  • By pressing the peeled pulp free from the endocarp
    • 1st grade- less pressure
    • 2nd grade- same pulp but more pressure
• Technical oil
  • Same pulp in #1 + hot water & pressed
• "Sulfur olive oil"
  • Same pulp in # 1 instead of hot water carbon disulfide is used then expressed
• Tournant oil
  • Fallen, decomposed or fermented fruits which contain large amounts of free fatty acids are pressed

Saturated vs Monounsaturated FO

• Coconut Oil (Saturated)
• Palm oil (Saturated)
• Palm kernel oil (Saturated)
• Castor oil (Monounsaturated)
• Olive oil (Monounsaturated)
• Peanut oil (Monounsaturated)
• Rapeseed oil (Monounsaturated)

Polyunsaturated FO

• Soybean oil
• Cottonseed oil
• Sesame oil
• Almond oil
• Persic oil
• Corn oil
• Safflower oil
• Sunflower oil
• Linseed oil
• Codliver oil

Important Saturated Fatty Acids

• Caproic (C6)
• Caprylic (C8)
• Capric (C10)
• Lauric (C12)
• Myristic (C14)
• Palmitic (C16)
• Stearic (C18)
• Arachidic (C20)

Soybean Oil

• World's most important seed oil
• Contains lecithin

Test For Lipids

• The solubility test indicates the property of solubility of lipids in organic solvents and insolubility in water.
  • The oil will float on water because of lesser sp gr
  • Mix Oil & water
  • Add 3mL of solvents, and 5 drops of sample. Oil/Lipid is insoluble in water and ethanol, but is soluble in chloroform and ether
• A translucent spot test/grease test is run
• A reaction of fats test is run
  • A pH will ne neutral if fresh
  • It'll be acidic when exposed to air
• An acrolein test (test for the presence of glycerol) is run
  • Used to detect glycerol and fats.
  • Most lipids are found in the form of triglycerides, an ester formed from glycerol and fatty acid.
  • The principle is that when a fat is heated strongly in the presence of dehydrating agent such as KHSO4, the glycerol portion of the molecule is dehydrated to form the unsaturated aldehyde, acrolein CH2=CH-CHO, which can be distinguished by its irritating acrid smell and as burnt grease.
• Run a Sudan IV test
  • used to find other fat-soluble molecules
• Tests for unsaturation w iodine
  • This test is specific for double bonds in the lipid’s chain.
  • Add a prepared sample, add a few drops of orange or iodine, mix, and observe. No color change means saturated lipid and colorless means unsaturated lipid
• Run a saponification test
  • add 1 mL of oil to 5 mL of NAOH, heat content of the TT on a water bath. Move 5 mL water

Procedure for Sudan IV Test

• Place 1 mL of sample into a clean test tube.
• Set up positive (oil solution) and negative (distilled H2O) controls
• Add distilled H2O to each tube.
• Add Sudan IV to each tube.
• Check for red areas and how they separate in clumps or layers
• Color should be well dispersed for a negative result
• Sudan IV turns fats red by sticking to non-polar lipids that aren't soluble in H2O. The presence of lipids forms red areas.

Other Test

• Dichromate tests yield a blue color if positive and a brown on negative
• Chromic tests

Uses & Details Regarding Fixed Oils

• Castor oil (Ricinus communis)
  • Stimulant cathartic
  • UD is 15-60 mL
• Olive oil (Olea europaea)
  • Pharmaceutic aid
  • Setting retardant for dental cements
  • Demulcent and emollient
  • Laxative nutrient
  • Salad oil
• Used in soaps
• Plasters and liniments
• Peanut oil / Arachis oil (Arachis hypogaea)
  • Solvent for IM inj.
• Soybean oil (Glycine soja) is used medicinally as a food for diabetes, as an ingredient in parenteral nutrition, as a source of lecithin, and for manufacturing varnishes, insulators, etc.
• Cottonseed oil (Gossypium hirsutum) is a solvent for injection, hydrogenated as a substitute for lard, and used for manufacturing soap.
• Sesame oil (Sesamum indicum) is a pharmaceutic aid and solvent in IM injection, and has nutritive, laxative, demulcent, and emollient properties.
• Almond oil, also known as salad oil (Prunus amygdalus) is emollient and used as an ingredient in cosmetics.
• Persic oil, also known as Apricot Kernel oil and Peach Kernel oil (Prunus armeniaca) is a vehicle and pharmaceutic necessity.
• Coconut oil (Cocos nucifera)
  • ingredient in combination products for oral administration (as balanced dietary supplements)
  • contains MCT (Medium Chain Triglycerides)
• Corn oil (Zea mays)
  • solvent for inj
  • solvent for irradiated ergosterol
• Sunflower oil (helianthus annuus)
  • Alternative to corn and sunflower oil
• Ethiodized oil
  • iodine addn product of the ethyl ester of the fatty acids of poppy seed oil

Details Regarding fats and related compounds

• Theobroma oil (Theobroma Cacao)
  • Used for Suppository base
  • Called "food of the gods"
• Hydrogenated vegetable oils
  • tablet lubricant
• Lanolin/ Hydrous Wool fat (Ovies aries)
  • water-absorbable ointment base
• Anhydrous Lanolin/Wool fat (Ovies aries)
  • 0.25% water
• Lanolin Alcohols
  • emulsifying agent in ointment formulations

Wax Details

• Spermaceti (Physeter macrocephalus)
  • Emolient. Desirable ingredient in cold creams.
• Jojoba oil (