LIPIDS

1. LIPIDS(FATS)
Fats-Composition and chemistry,classification,
functions,requirements
Nutritional disorders-fats deficiency
Energy metabolism-digestion,absorption and utilization
INTRODUCTION
lipids are a group of naturally occuring substances charaterised by their
insolubality in water and solubility in some organic solvent.
They occur widely in the plant and animal kingdom in the form of oils and
fats respectively.The basic structure of lipids is comprised of
carbon,hydrogen,oxygen.
The lipid fat content of food is the major determinant of the energy
density of dites.

2. Classification
Lipids are classified as:
1.Simple lipids
These are esters of fattyacids and glycerol.Oils are liquid at 200C
while fats are solid at 200C
2.Component lipids
These lipids contain some other organic compounds,in addition to
fatty acids and glycerol they are further characterised as
i)phospholipids(Phosphasides)

3. These contain phospheric acid and a nitrogenous base in addition to
glycerol and fattyacids.lecithin,cephali,plasmalogns come under this
catagory.
ii)Sphingolipids
These contain the base sphingosine or dihydro sphingosine in
addition to glycerol and fattyacids.
iii)Glycolipids
Complex lipids containing carbohydrates in
combination with fatty acids and
sphinogosine.
iv)Sulpho lipids
These contain sulphuric acid in combination with hexose in a
cerebroside.

4. 3.Waxes
These are ester of fatty acids long-chain aliphatic alcohols.
4.Derivedlipids
These includes fatty acids,alohol,sterols
Lipids present in Diets
The lipids present in foods and also in the animals and
human body include:
Triglycerids,
Phospholipids and other compound lipids,and
cholestrol (present only in animals food)

5. Hydrogenation
 This is a process involving chemically
induced hydrogen saturation of the carbon
bonds,by which the structure of unsaturated
oils is changed.
 This alters the way the body metabolizes
these facts and often changes the physical
form.
 Margine and vanaspathi are hydrogenated
facts

6. Functions of Facts
• Fat has several important functions.
• It is a concentrated source of energy yielding more than twice the
energy supplied by carbohydrate per unit weight.
• Fats essential for the absorption of vitamins A,D,Eand K and
carotenoids.
Vegetable fats are good sources of vitamin E and red palm oil is a
good source of carotene while some animal facts such as butter and
fish liver oils are good sources of vitamin

7. • A.Certain vegetable fats are rich sources of the essential fatty acid-
lilolein-acid.
• Fats reduce the bulk of the diet as they provide twice as much
calories as carbohydrates per unit weight.
• Further starchy foods absord lot of water during cooking and
increase the bulk of diet
• Fats improve palatability and give a satiety value ie;a feeling of
fullness in the stomach
• Fats are deposited in adipose tissue acts as an insulting material
against cold and physical injury.

8. Properties of fats
Solubility Fats are soluble in organic solvents such as ethyer ether,
petroleum ether acetone acid Benzine .The quantity of fat present in
food materials is usually determined in by extraction with ethyl ether or
petroleum ether.
Saponification value : THe value is defined as the number of milligrams
of potassium hydroxide required to Saponify 1GM of fat or oil.
Iodine Value :It is the measure of the extent of unaturated fattyb acids
present in fats and oils.It is defined as number of branch of iodine
absorbed in 100Grams of fat.
Reicheit-Mreissl Value :The is defined as the number of milliliters of
0.1N alkali required to neutralize the steam volatile water soluble fatty
acids present in 5Gram sample of fat.that is determine the amount of
butyric acid and caproic acid ewhich are readily soluble in water and a
part of caprylic acid whicc is slightly soluble in water.

9. Thiocyanogen Value :The Thiocyanogen number is the amount of
Thiocyanogen absorbed by 100 g of fat or oil.
Rancidity in fats :
The development of all flavours in fats is known as rancidity.There are
three main types of rancidity,
1.Hydrolytic Rancidity
Hydrolysis of fats by lipase need notb always produce off-flaours.In
the case of butterfat and coconut oil butyric and other low molicular
weight Fatty acids are set free on hydrolysis by lipase.The orders of
these acids contribute largely to the smell of rancidbutter.The
saturated fatty acids such as palmitic and stearic acidsn have little
odour.

10. 2.Oxidative Rancidity
This is the common type of rancidity observed in all fats and oils.The
oxidation takes place at the unsaturated linkage.Certain metals,such
as Copper,Hasten the on set of oxidative rancidity,the addition
ofoxygen to the unsaturated linkage results in the formation of a
peroxide which, on decomposition,yelds aldehydes and ketones
having pronounced off odour.

11. 3.Ketonic rancidity
This type is most frequently as a result of action fungi such as
aspergilles niger and blue green mould,penicillium glaucum on
coconut or oil seeds.The tallow odour developed may be due to
aldehydes and ketones formed by the action of the engymes present
in the fungi on oil.

12. Effects of the essential fatty acid deficiency in
human beings
 Phrynoderma:Thus is one pf the common diorders of malnutrition
observed in adults and children.
 The condition is characterised by the presence of horny popular
eruptions on the posterior and lateral aspects of the limbs,on the
back and buttoks.
 Phrynoderma is cured rapidly by the administration of linseed or
safflower seed oil which are rich in essential fatty acids along with
B-complex vitamines but not by vitamine-A.

13. Deficiency in infants
 Hansen and co-workers have reported that infants fed on a
EFA deficient diet developed perennial irritation and changes
in the skin within a few weeks.
 The skin changes appears as dryness thickening and
desquamation with oozing in the intertriginous folds.
 Supplimemtation of the diet with linaleic acid restored the skin
th normal condition with in 2 weeks.

14. Sources
Rich sources of EFA
safflower,sunflower,nigerseed,cottonseed,linseed,corn,walnut,sesame
and soybean oils are rich in sources of EFA.These oils must form
atleast 50% of the fat in the diet.
Good source:Egg yolk fat,poultryfat and pig body fat are fair sources
of EFA
Poor sources:coconut oil,palmkerneloil,vanaspathy and animal fats
butter and ghee,beef and mutton fat are poor sources of EFA

15. Fat requirements
The approximate fat reqiurements of individuals for different age groups are
given in table.Atleast 50% of the fat oils rich in EFA.
Table:Fat Requirements
Group %
Adults pregnant and lactating mothers 10 to 20 % of total calories from fat
children and adolescents(0 to 18 years) 15 to 20 % of total calories from fat
Infants (Birth to 1 year) 25 to 30 % of total calories from fat

16. 1.Triglycerides and fatty acids :
• Triglycerides comprise about 95% of the food lipids and body lipids.
• They are the storage form of fat.
• When we eat a high calorie diet,the calories in excess of our energy
needs Triglycerides and srored in the body.
• All Triglycerides have a similar structure.It is composed of three fatty
acids attached to a glycerol molecule.
• Glycerol is a short-chain carbohyrate molecule that is soluble in water.

17. • When Triglycerides are metabolized the glycerol is converted to
glucose.
• Fatty acids may differ in their length and their degree of saturation.
• They are commonly composed of a series of 16-18 carbon
molecules attached to hydrogen molecule.
• The number of hydrogen molecules determines the saturation of the
fat.
• When each carbon has its maximum number of hydrogens attached
the fat is set to be saturated.ie., filled to capacity with hydrogen.

18. Saturated fats
Unsaturated fats
Essential fattyacids
Saturated fatty acids: A fatty acid with no carbon-carbon double
bonds.
Monounsaturated fatty acid:A fatty acid containing one double bond.
Polyunsaturated fatty acid:A fatty acid containing two or more double
bond.
Essential fattyacids: THese are fatty acids must be present in the diet
to maintan health,and include lineleic acid and alpha-lineleic acid.

19. Phospholipids :
• Phospholipids are important in the structure of all membranes.
• Their structure is similar to that of triglycerides,but they contain only
two poly unsaturated fatty acids.
• The third molecule attached to the glycerol is a phosphatidylcholine
molecule.
• The most common phospholipid is lacithin.Certain phospholipids also
contain inositol and designated as phosphatldyiinositol.
• Phosphatidylethanolamine is another phosopholipid thatb has
several functions, such as being a precursor to choline and
acetylcholine.
• Lecithin is found in highest concentration in soybeans and
eggyolk.Recently,egg lecithin has been used in the treatment of
accuired immunp deficiency syndrome(AIDS).

20. 3.Sterols/cholesterol
• cholestrol,is the precursor of the bile acids and the sex harmones.it is
manufactured in all tissues of the body except the brain, Cholestrol is
present in all cells and its concentration is particularly high in the liver,
brain and nervous tissue, and the blood.
• Cholestrol, like lecithin is also present in foods,eggyolk,meats,and
other animal fats, milkproducts .It is not present in vegetable foods.

21. • A transport mechhanism of cholestrol called the low density
lipoprotein is the likely cause of risk for the cardiovascullar
disease called atherosclerosis.
• In this condition ,Cholestrol in the form, of LDL cholestrol
accumulates in the living of the arteries these two is the bolld
test currently favoured to elevate risk of cardiovascular disease.

23. Factors affecting requirements
Food intake in is influenced by several factors,two of the most
important being socio-economic status and cultural
preferences.Psychological conditions and risk of certain chronic
diseases such as heart dusease and diabetes also affect fat
requirements.
Digestion and absorption of fat
Several theories have been proposed for the mechanism of absorption
of fats after digestion.The important theories are:
Lipolytic hypothesis of varzar,
Partilition theory of frazer,and micelie theory of borgstrom.

24. Lipolytic hypothesis of varzar
According to this theory,the hydrolysis of fat to fatty acids is complete
and the fatty acid and glycerol are absorbed.The fatty acids combined
with bilesalts to form loosewater miscible complexes which are
absorbed into the intestinal mocosa
The triglycerides are passed on into the lactals of the intestinal
bile.They then enter the lymphasics and reach the systemic the
circulation via thoracduct.

25. Present views on the digestion and
absorption of fat
• Present views on the digestion and absorption of fat are briefly
described below.
• The digestion of the triglyceride proceeds the removal of fatty acid at
the 1 position yeilding fatty acid and a diglyceride, The fatty acid in
the 3 position is then removed by action of lipase leaving 2-
monoglyceride.
• The removal of fatty acid from the 2-monoglyceride is the slow
process.2-monoglyceride will be converted at a slow rate in to 3-
monoglyceride by an enzyme called isomerace.

26. • The monoglyceride and free fatty acids are converted into micelle in
the presence of bile salts and are absorbed into the intestinal wall.
• The free glycerol also is absorbed.3-monoglyceride is hydrolized in the
intestinal wall by the intestinal lipase to fatty acid and glycerol
The in testinal wall has enzyme systemd for fat synthesis.
• The resynthesized fatty acids converted into chylomicrons.
• The chylomicrons enter the lymphatics through lacteals and are
delivered in to the circulation via thoracic duct.
• The fatty acid composition of chylomicrons of the lymph is different
from that of the fat and in the diest as resynthesised in the intestines
using fatty acids derived from food fatand fatty acids present in bile