Lipids (fixed oils and fats )

Classification
By structure:
1. Simple: fats, oils, waxes, steroids.
2. Complex: phospholipids, spingolipids, glycolipids.
3. They derivatives: hormones, fat-solubility vitamins
On the basis of whether they undergo hydrolysis reactions in alkaline
solution:
1. Saponifiable lipids can be hydrolyzed under alkaline conditions to
yield salts of fatty acids.
2. Nonsaponifiable lipids do not undergo hydrolysis reactions in
alkaline solution.

LIPIDS
Lipids are a class of biological molecules defined by low solubility in water
and high solubility in nonpolar solvents.
As molecules that are largely hydrocarbon in nature, lipids represent highly
reduced forms of carbon and, upon oxidation in metabolism, yield large
amounts of energy. Lipids are thus the molecules of choice for metabolic
energy storage.

Lipids
•Lipids (fixed oils, fats, and waxes) are esters of long-chain fatty
acids and alcohols, or of closely related derivatives. The chief
difference between these substances is the type of alcohol; in
fixed oils and fats, glycerol combines with the fatty acids; in
waxes, the alcohol has a higher molecular weight, e.g., acetyl
alcohol[CH3(CH2)15OH].

• Fats and oils are made from two kinds of molecules: glycerol (a type
of alcohol with a hydroxyl group on each of its three carbons) and
three fatty acids joined by dehydration synthesis. Since there are
three fatty acids attached, these are known as triglycerides.

triglyceride
H2C
HC
H2C
O
O
O
C
C
C
R
R'
R''
O
O
O
• where R, R', and R" are long alkyl chains;
the three fatty acids RCOOH, R'COOH and
R"COOH can be all different, all the same,
or only two the same.

Structure of Fatty Acids
• The “tail” of a fatty acid is a long
hydrocarbon chain, making it
hydrophobic. The “head” of the molecule
is a carboxyl group which is hydrophilic.
Fatty acids are the main component of
soap, where their tails are soluble in oily
dirt and their heads are soluble in water
to emulsify and wash away the oily dirt.
However, when the head end is attached
to glycerol to form a fat, that whole
molecule is hydrophobic.
(CH2)6COOH
H3C
Linoleic acid

•The terms saturated, mono-unsaturated,
and poly-unsaturated refer to the number of
hydrogens attached to the hydrocarbon tails
of the fatty acids as compared to the number
of double bonds between carbon atoms in
the tail.
•Fats, which are mostly from animal
sources, have all single bonds between the
carbons in their fatty acid tails, thus all the
carbons are also bonded to the maximum
number of hydrogens possible.

• Since the fatty acids in these triglycerides contain the
maximum possible amount of hydrogens, these would be
called saturated fats.
• The hydrocarbon chains in these fatty acids are, thus, fairly
straight and can pack closely together, making these fats
solid at room temperature.

•Oils, mostly from plant sources, have some double bonds
between some of the carbons in the hydrocarbon tail,
causing bends or “kinks” in the shape of the molecules.
• Because some of the carbons share double bonds, they’re
not bonded to as many hydrogens as they could if they
weren’t double bonded to each other. Therefore these oils
are called unsaturated fats.

• Because of the kinks in the hydrocarbon tails, unsaturated
fats (or oils) can’t pack as closely together, making them
liquid at room temperature.

• In unsaturated fatty acids, there are two ways the pieces of
the hydrocarbon tail can be arranged around a C=C double
bond (cis and trans).
• In cis bonds, the two pieces of the carbon chain on either
side of the double bond are either both “up” or both
“down,” such that both are on the same side of the
molecule.
• In trans bonds, the two pieces of the molecule are on
opposite sides of the double bond, that is, one “up” and one
“down” across from each other.

•Naturally-occurring unsaturated
vegetable oils have almost all cis bonds,
but using oil for frying causes some of
the cis bonds to convert to trans bonds.

• If oil is used only once like when you fry an egg, only a few of the
bonds do this so it’s not too bad. However, if oil is constantly reused,
like in fast food French fry machines, more and more of the cis
bonds are changed to trans until significant numbers of fatty acids
with trans bonds build up. The reason for this concern, is that fatty
acids with trans bonds are carcinogenic, or cancer-causing.
• Although most vegetable oils are liquid at ordinary temperatures and
most animal fats are solid, there are notable exceptions, such as
cocoa butter, which is a solid vegetable oil, and cod liver oil,
which is a liquid animal fat.

Properties of Triglycerides
Hydrogenation
•Unsaturated compounds react with H2
•Ni or Pt catalyst
•C=C bonds C–C bonds
Hydrolysis
•Split by water and acid or enzyme catalyst
•Produce glycerol and 3 fatty acids
16

Hydrogenation
17
CH
CH2
CH2 O
O
O
C
O
(CH2)5CH CH(CH2)7CH3
C
O
C
O
+
H23
Ni

Product of Hydrogenation
Hydrogenation converts double bonds in oils to single bonds. The solid products are used to make
margarine and other hydrogenated items.
18
CH
CH2
CH2 O
O
O
C (CH2)14CH3
O
C (CH2)14CH3
O
C (CH2)14CH3
O

Hydrolysis
Triglycerides split into glycerol and three fatty
acids (H+ or enzyme catalyst)
19
CH
CH2
CH2 O
O
O
C (CH2)14CH3
O
C (CH2)14CH3
O
C (CH2)14CH3
O
H2O+3
3+ HO C (CH2)14CH3
O
CH
CH2 OH
OH
CH2 OH
H+

Saponification and Soap
•Hydrolysis with a strong base
•Triglycerides split into glycerol and the salts of
fatty acids
•The salts of fatty acids are “soaps”
•KOH gives softer soaps
20

Saponification
21
3+ Na+ -
O C (CH2)14CH3
O
CH
CH2 OH
OH
CH2 OH
CH
CH2
CH2 O
O
O
C (CH2)16CH3
O
C
O
(CH2)16CH3
(CH2)16CH3C
O
+ 3 NaOH
salts of fatty acids (soaps)

Production of fixed oils and fats
• Fixed oils and fats of vegetable origin are obtained by:
1. Extraction by expression
Fixed oils are obtained by expression in hydraulic presses.
If the expression is carried out in the cold, the oil is known
as a "virgin oil" or a "cold-pressed oil." In contrast, if the
expression is carried out in heat, the oil is known as a "hot-
pressed oil."
2. Extraction by solvents
Sometimes organic solvents are used for the extraction of
oils.

• 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.

Biosynthesis of lipids
• The biosynthesis of saturated and unsaturated fatty acids is from
combinations of acetate units (acetate pathway).

Applications of fixed oils and fats
1. Soap manufacture
2. Suppositories, tablet coating
3. Dietary supplements
4. Emulsifying agents
5. Manufacture of paints, varnishes and lubricants
6. Therapeutic uses (castor oil).

Examples
• Castor oil
• Olive oil
• Peanut oil
• Soybean oil
• Sesame oil
• Almond oil
• Cottonseed oil
• Corn oil
• Safflower oil
• Cocoa butter

Waxes
wax is а monoester formed from the reaction of а long-chain
monohydroxy alcohol with а fatty acid molecule.
Example
Biological role: They serve as protective coatings on leaves, stems, and
fruit of plants and the skin and fur of animals.

Waxes
• Like fats, waxes are esters of fatty acids. The alcohol, however, is not glycerol
but usually a long-chain, high-molecular weight alcohol.
• In plants, waxes are generally found covering the external parts, like the
epidermis of leaves and fruits, where their main function is to prevent the
loss of water.

• Wax is also produced by insects, e.g. the honeycombs of bees and
wasps.
USES OF WAX
1. Wax is used in pharmacy to make soft ointments harder and to
prepare lip salves.
2. The technical uses of waxes are substantial, e.g. in shoe polishes
and car waxes.

Waxes  fixed oils and fats
• Wax has a melting point above approximately 45 °C (113 °F) (which
differentiates waxes from fats and oils).
• Fats and oils my be saponified by means of either aqueous or
alcoholic alkali but waxes are only saponified by alcoholic alkali. (this
fact is used for the detection of fats when added as
adulterants to waxes).

Examples
• Jojoba wax (Simmondsia chinensis)
• Carnauba wax (Copernicia cerifera)
• Beeswax (Apis mellifera)

Characterization of fats.
• Acid number. It is the number of milligrams of potassium hydroxide required to
neutralize the free fatty acids in 1 g of the oil or fat.
• Saponification number. It is number of milligrams of potassium hydroxide required
tо completely saponify l00 g of the oil or fat.
• Iodine number. It is the number of grams of iodine that combine with 100 g of oil or
fat. It is а measure of the degree of unsaturation of а fat or oil; а high iodine number
indicates а high degree of unsaturation of the fatty acids of the fat.
• Ester value. It is number of milligrams of potassium hydroxide required tо combine
with fatty acids which are present in glyceride form in 1 gm sample of fat or oil.
• Unsapopnificable matter: It is substances such as sterols, stigmasterol which remain
after saponification of oil
• Peroxide value: amount of peroxide formed in lipid oxidation.
Value indicates rancidity of oil.

Lipids (fixed oils and fats )

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Lipids (fixed oils and fats )