2.

LIPIDS

2.1. Definition
Lipids encompass a large group of structurally diverse compounds. They share a
common biochemical origin and can be isolated in the same way. They are insoluble
in water but dissolve well in organic solvents: ether, chloroform, benzene,
tetrahydrofuran, propanone (acetone), etc.

2.2. Classification of Lipids

Lipids are esters of alcohols and carboxylic acids. The ester bond can be hydrolyzed,
yielding different products. According to the products obtained from hydrolysis, lipids
are divided into simple lipids and complex lipids.
Simple lipids yield alcohols and monocarboxylic (non) fatty acids upon hydrolysis.
Complex lipids yield other components in addition to alcohols and fatty acids upon
hydrolysis.

2.3. Glycerides (Fats and Oils)

2.3.1. Occurrence in Nature and Production
Fats and oils are found in both plant and animal organisms.
Fats are in a solid aggregate state. They are named according to their origin: butter
and lard are derived from milk, while (sheep, beef, etc.) are obtained from the fatty
tissues of cattle and sheep. Lard is obtained from the fatty tissue of pigs. Notable fats
of plant origin include coconut and palm oil.
Oils are in a liquid aggregate state and are named according to their origin: olive oil,
sunflower oil, fish oil, rapeseed oil, soybean oil, etc.
Fats are most commonly obtained by melting.
Oils are obtained by pressing (squeezing) or by extraction using suitable organic
solvents.

2.3.2. Chemical composition:

Fats and oils are esters of glycerol and fatty acids, whose general formula can be written as
follows:

CH2OH HOOC-R1 CH2-OOC-R1

CHOH + HOOC-R2 CH-OOC-R2 + 3H2O

CH2OH HOOC-R3 CH2-OOC – R3
These esters are called glycerides or acylglycerols. They can be simple or mixed. In simple
glycerides, the hydroxyl groups in glycerol are esterified with the same acid.

Glycerides are named according to the acid in their composition. If the composition of the
glyceride includes octadecanoic acid (stearic acid, C17H35COOH), it is called tristearin. In
mixed glycerides, the hydroxyl groups in glycerol are esterified with different acids.

In the molecule of glycerol, one hydroxyl (-OH) group can be esterified, and these are
monoglycerides. If two hydroxyl groups are esterified, they are called diglycerides. When all
three hydroxyl groups are esterified, they are called triglycerides.

Only acids with an even number of carbon atoms are included in the composition of
fats and oils. The most common saturated acids are:

 C15H31-COOH— hexadecanoic acid (palmitic acid)

 C17H35-COOH— octadecanoic acid (stearic acid)

From the unsaturated acids, the most significant ones are:

CH3-(CH2)6 (CH2)6-COOH

C=C

H H

cis-heksadec-8-en kiselina (palmitoeleinska)

CH3-(CH2)7 (CH2)7-COOH

C=C
H H

Cis-oktadec-9-en kiselina (oleinska)

Essential fatty acids, commonly referred to as "essential acids," are of particular

importance in human nutrition. These are acids that the human body cannot
synthesize and therefore must be obtained through diet. Human nutrition must be as
varied as possible. Essential fatty acids have multiple double bonds and possess a
cis configuration. Included in these fatty acids are:

 C17H31COOH = cis-oktadeka-6,9-dien acid (linol)

 C17H29COOH = cis-oktadeka-3,6,9-trien acid (linoleic)

In smaller quantities, some fats and oils also contain lower fatty acids, such as
butanoic acid (C3H7COOH). Natural fats and oils are mixtures of various
triglycerides. Along with triglycerides, there are also some components that are not
esters, but have very similar physical properties. These are most often sterols.

2.3.3. Physical Properties

The aggregate state of triglycerides depends on the acids that make up their
composition. If saturated acids are involved in the composition of triglycerides, then
they are solid fats, found in a solid aggregate state. However, if they contain more
unsaturated acids,then those are oils.

Pure glycerides are odorless and tasteless. Natural fats and oils contain impurities
that give them color, smell, and taste. Glycerides are lighter than water and do not
mix with it. They dissolve in non-polar solvents.
By shaking oil and water, an emulsion is created. This is a mixture of two liquids that
do not mix or dissolve in each other. During this process, one liquid is dispersed in
the other in the form of tiny droplets. Some substances can stabilize emulsions and
are called emulsifiers.

2.3.4. Chemical Properties

Glycerides can be broken down into their components: glycerol and fatty acids. This
breakdown occurs through the action of water in a chemical reaction known as
hydrolysis. In living organisms, hydrolysis is facilitated by enzymes called hydrolases.
The hydrolysis reaction is particularly easily carried out in the presence of metal
hydroxides, resulting in the formation of glycerol and the alkaline salts of higher fatty
acids, which are commonly referred to as soaps. Because soap is produced in this
reaction, it is known as saponification, and it can be represented by the following
equation:

CH2-OOC-C17H35 CH2OH
CH-OOC-C17H35 + 3NaOH CHOH+3C17H35COONa

CH2-OOC-C17H35 CH2OH

Saponification reactions are used in chemistry and food technology to distinguish

certain fats and oils and to detect counterfeits. In practice, the so-called
saponification number. The saponification number depends on the size of the fatty
acid molecules in a fat. If the saponification number is lower, then the content of high
molecular fatty acids is higher and vice versa.
Various atoms or atomic groups can be attached to unsaturated (double) bonds in
fatty acid molecules.
 The saponification number represents the number of mg of NaOH needed to
saponify 1g of fat.

This was used to determine the amount of unsaturated fatty acids. The easiest way
to do this is with iodine, and that's how you get the so-called Iodine number. If the
iodine number is higher, there are more unsaturated acids and vice versa.
The iodine number indicates the number of mg of iodine that affects 100g of fat
and oil
A double bond is much more reactive than a single bond, which is why fats and oils
acquire an unpleasant smell and taste. For this reason, hydrogen (H2) is often
attached to double bonds with the use of a catalyst. The process is called
hydrogenation. In doing so, simple bonds, i.e. saturated fatty acids, are obtained.

Hydrogenation also changes the aggregate state. Fats are obtained from oils.

Fresh fats and oils do not have an unpleasant odor and react neutrally. By standing,
during which bacteria, light and oxidizing agents act, glycerides break down and free
fatty acids are formed. This gives the fats an unpleasant odor and a bitter taste that
originates from free acids. This phenomenon is called fat and oil rancidity. The
degree of rancidity of fats and oils is expressed by the acid number.
The acid number represents the number of mg of KOH required to neutralize
free fatty acids in 1g of fat and oil.

2.3.5. Importance of fats and oils

Fats and oils are regular food ingredients. They have the highest energy value. 1g of
fat gives 38kJ of heat. If more fats are introduced into the body than the body needs,
then they are deposited in certain tissues. The organism uses them as necessary,
they serve as reserve food. Such fats appear as fatty deposits or fat. This is how the
body becomes fat. Fat deposits are a good thermal insulator, which is important for
the body. Some organs are also mechanically protected by fat, for example the
kidneys. Fats are necessary for the life of every cell. Fats are used to lubricate joints,
etc.

In industry, fats are used to obtain glycerol, soaps, paints and many other products.

2.4. Cerides (waxes)

Waxes are esters of higher monohydroxyl alcohols and fatty acids. They can be of
plant or animal origin.
Plant waxes are found on the surface of the leaves and fruits of some plants. They
serve to protect against excessive evaporation of water from plants. The most
famous is carnauba wax, which is secreted by the leaves of the Brazilian palm
Corypha cerifera. Wax is a mixture of esters of monohydroxyl alcohols and
monocarboxylic acids that have from 24 to 34 carbon atoms in the molecules. It is
used for the production of pastes for polishing cars and floors and as a protection for
the surface of paper.
Animal waxes are substances secreted by some animals. Cetacecum wax is
obtained from the head of some types of whales. It is an ester of hexadecanol (cetyl
alcohol) (C16H33OH) and hexadecane (palmitic) acid (C15H3COOH).
Lanolin is a product of the secretion of the sebaceous glands of sheep, so there is a
lot of it in wool. Its composition is a mixture of esters of high-molecular acids and
alcohol.
Beeswax is a mixture of different substances. The main ingredient is myricyl
palmitate (C15H31COOC31H63), an ester of myricyl alcohol (C31H63OH) and
palmitic acid.

Waxes have no nutritional value because they are indigestible in the human body.
They are used for the production of candles, polishes, balms and bases for
medicines and cosmetic ointments.

2.5. Steroids
Steroids are constant companions of fats and oils. These are alcohol esters of sterols
and fatty acids. The ester bond in steroids is more stable than in glycerides, which is
why it is not hydrolyzed or saponified.
Alcohol molecules that enter the composition of steroids have sterane or
cyclopentanoperhydro-phenanthrene as the basic part of the molecule. It is a
compound that is obtained when a molecule of phenanthrene is hydrated and one
molecule of cyclopentane is attached to it

The most important alcohol that is a derivative of sterane is cholesterol. It is found in

all cells. It is part of the cell membrane. It is found in abundance in gallstones, bile,
skin, brain and nervous tissue.
About 1g of cholesterol is taken into the human body per day. Part is used for the
synthesis of hormones and bile acids, vitamin D, etc. The excess is excreted through
urine and sweat.

Ergosterol is an alcohol that is included in the composition of steroids of plant origin.

Vitamin D2 is synthesized from ergosterol under the action of ultraviolet light.

Bile acids are similar in composition to alcohols from the sterol group. They have one
carboxyl group in the side chain. The most widespread is cholic acid.
Bile acids are found in bile, intestines and liver ducts. It appears in urine in larger
quantities in patients with hepatitis.

In the digestion of food, bile acids serve for the resorption (absorption) of fats and as
emulsifiers and activators of enzymes for fat digestion.

2.6. Phospholipids

Phospholipids are esters of glycerol, higher fatty acids and phosphoric acid, which is
most often esterified with another alcohol. Simpler phospholipids are cephalin and
lecithin

Kephalins contain ethanolamine or cholamine (HO-CH2-CH2-NH2) in their

composition.

Lecithins contain alcohol choline whose formula is: (HO-CH2-CH2-N(OH) (CH3)3.

Serinphospholipids contain the amino acid serine instead of amino alcohol.

Phospholipids enter the cell membrane structure. They are found in a very thin
monomolecular or dimolecular layer. The phospholipid layer is semipermeable. Only
lipid-soluble substances pass through this layer. This explains the presence of
alkaloids in cells,

There are other more complex phospholipids that enter the composition of nerve
cells, blood plasma, etc.

2.7. Glucolipids
Glucolipids are included in the composition of various tissues and there are several
types according to their composition. Better known are cerebrosides that are isolated
from the brain (lat. cerebrum - brain). They contain alcohol sphingosine, fatty acids
and hexoses (glucose or galactose).

They are named after the acids that make up their composition. So nervon contains
nervonic acid. The structure of nerves can be represented by the following formula:

O=C-(CH2)12-CH=CH-(CH2)7-CH3

N-H nervic acid

I
 CH-CH(OH)-CH=CH-(CH2)12-CH3
I

CH2 sfingozin

I
O

H-C-(CHOH)3-CH-CH2OH
O

Cerebrosides are part of the white brain matter, but they are also found in the spleen,
kidneys, adrenal gland, lungs, blood, etc. In living organisms, they have similar
physiological functions as phospholipids.
Sulfolipids were isolated from the brain. It differs from cerebroside in that, in addition
to fatty acid, sphingosine and galactose, its molecule contains one molecule of
sulfuric acid, which is ester-linked to the -OH group on the sixth carbon atom in
galactose (2.7). Sulfolipids are particularly important in blood clotting.