Download Characteristics of Fats Saponification Number It is defined as the

Characteristics of Fats
Saponification Number
It is defined as the number of milligrams of potassium hydroxide
required to saponify one gram of fat. It is an indication of the
molecular weight of fat and is inversely proportional to it. Human
fat has a saponification number of 194 – 196, butter 210 – 230 and
coconut oil 253 – 262.
Iodine Number
The Iodine number of a fat is defined as the number of grams of
iodine taken up by 100 gm of fat. It is an index of unsaturation
and is directly proportional to the content of unsaturated fatty
acids. Higher the iodine number, the higher is the degree of
unsaturation. Different of fats and their iodine numbers are given
in Table 3.1.
Table 3.1
Fat / Oil
Iodine number
Human fat
65-69
Butter
26-28
Coconut oil
6-10
Sunflower oil
124- 136
Groundnut oil
84- 100
Palm oil
44-58
100 mg blood contains
Triglycerides
Phospholipids
Cholesterol
Nonesterified fatty acids
Total
80 - 240 mg
150 – 250 mg
130 – 260 mg
8 – 30 mg
385 – 675 mg
PHOSPHOLIPIDS
(PHOSPHOGLYCERIDES AND SPINGOMYELINS) Any lipid
containing Phosphor is called phospholipid. Phospholipids are
good emulsifying agents. They are found in cell membranes and
in subcellular structures where lipids and water soluble materials
interact. The most common phospholipid is the glycerol
phospholipids. They contain glycerol phosphate, two fatty acids
and a nitrogen compound that may be choline, ethanol amine, or
serine. Lecithins and cephalins are examples of phospholipids.
L
Y
C
E
R
O
L
Fatty acid
Fatty acid
P-N
O
║
CH2 –O-C-R
O
║
CH-O-C-R1
O
║
CH2-O-P-N compound
OH
Phospholipid
or Phosphoglycerides
Phosphatidyl Cholines (Lecithins)
This is the most common form of phospholipids and has cholin as
the nitrogen compound
O
║
CH 2O- C – OR1
O
║
CHO- C- OR 2
O
║
CH2 – P-O- CH 2CH 2N+ (CH3)3
OH
Choline Phosphoglyceride
Free choline is a compound with an alcohol group. Its linkage to
the phosphate portion of a lecithin like that of the glycerol to the
phosphate is that of a phosphate ester.
HO- CH2 – CH2- N+ – (CH3) 2
Choline
Lecithins are required for the normal transport and utilization of
other lipids especially in the liver. Anything which interferes with
the synthesis of choline also will block the synthesis of lecithins
and thus interrupt the normal transportation of lipids to and
from liver. This usually results in the accumulation of lipid
material in the liver giving rise to a condition called fatty liver
Cephalin
O
║
CH 2O – C- OR1
O
║
CHO – C- OR2
O
║
CH 2O –P- O- CH2-CH2 – NH2
OH
Cephalin
(Ethanolamine Phosphoglyceride)
Cephalin differs from lecithins with respect to base attached to
phosphoric acid. If the base is ethanol amine, then it is called
phosphatidyl ethanolamine or ethanolamine cephalin. If the base
is amino acid serine, then it is called phosphatidyl serine or serine
cephalin.
Cephalin on hydrolysis yields glycerol, fatty acids, phosphoric
acid, ethanol amine or serine. They are found in nerve tissues
cephalins are important in the clotting of blood and as sources of
phosphoric acid for the formatios of new tissues.
Plasmalogens
These compounds structurally resemble lecithin and cephalins,
with the result that the normal ester is replaced by the ether
linkage on the C1 atom. On treatment with acid they give rise to a
long chain fatty aldehyde. These compounds constitute as much
as 10 % of the phospholipids of the brain and the muscles
CH2 – O- CH =CH – R
O
║
CH- O- C – R 2
O
║
CH2 –O-P – O – Base
OH
Sphingomyelins
They are found in large quantities in brain and nerve tissue. No
glycerol is present. On hydrolysis yield a fatty acid, phosphoric
acid, choline and a complex aminoalcohol, sphingosine (in place of
glycerol).
Sphingosine
p
Choline
Fatty acid
Sphingomyelin
Cerebrosides (Glycolipids)
Glycolipids are carbohydrate – glyceride derivatives containing
sugar, sphingosine and a fatty acid. These compounds do not
contain phosphoric acid. If the sugar component is galactose, the
lipid is termed as galactolipid. The term cerebroside is used
because it is found in large quantities in brain tissues particularly
in white matter.
Sphingosine
Fatty acid
Cerebroside
Galactose
Steroids
Steroids are non–saponifiales lipids, biological compounds with
diverse physiological activities .All steroids are compounds having
a cyclopentanoper – hydrophenanthrene ring system. The
structures of a number of different types of steroids having
greatly varying biological activities.
Cholesterol is a light yellow crystalline solid. It is soluble in
chloroform and other fat solvents. The - OH group in the 3rd
position can be get esterified with fatty acids to form cholesterol
esters. This is how cholesterol level in the body is regulated.
Cholesterol in the most abundant lipid in the human body. It is
synthesized mainly in the liver, adrenal cortex, intestines, testes
and skin. Acetyl CoA is the precursor of all the C atoms in
cholesterol. The level of cholesterol in body fluids is of primary
importance due to its role in the development of atherosclerosis.
In addition cholesterol plays an important role as a component of
biomembranes and has a modulating effect on the fluid state of
the membrane. Poly unsaturated acids (essential fatty acids) tend
to lower the plasma cholesterol level. Cholesterol in body fluids
can be estimated by colour reactions, e.g. Lebermann Burchard
reaction. A solution of chloroform gives a blue or green colour,
when acetic anhydride and concentrated sulphuric acid are
added. This reaction is the basis of a colorimetric estimation of
blood cholesterol.
Functions of Cholesterol
1. Cholesterol is an important tissue component. It has a
modulating effect on the fluid state of the membrane.
2. Because of its conductivity, cholesterol plays an important role
in insulating nerves and brain structure.
3. For the transport of fatty acids in the body through the for –
mation of esters of fatty acids.
4.Cholesterol neutralizes the hemolytic action of a number of
agents, such as snake venoms, bacterial toxins, etc.
5. Cholesterol gives rise to provitamin D.
6. It is a precursor of cholic acid in the body.
7. It gives rise to sex hormone.
LIPOPROTEINS
Lipoproteins transport neutral lipids in the blood. These are
lipids attached to proteins . These are formed by the combination
of proteins with lipids which include the phospholipids lecithin
and cephalin, fatty acids, cholesterol, glycerides and fat soluble
vitamins. The lipoprotein molecule has lower density than the
ordinary protein molecule, due to its combination with lipids.
Lipoproteins are widely distributed in body
1. Cell membranes
2. Certain internal structures of cell, such as nucleus,
mitochondria and microsome.
3. Thromboplastin which converts prothrombin to thrombin.
4. Egg yolk contains two lipoproteins called α - lipovitellin and lipovitellin.
5. The film that stabilizes the fat droplets in milk contains
lipoproteins.
6. Rhodopsin or visual purple is a combination of a protein opsin
and retinal aldehyde of vitamin A (fat soluble vitamin).
7. Blood lipoproteins are present in plasma. The lipid fraction
consists mainly of cholesterol, phospholipids, neutral fat, traces of
fat soluble vitamins and steroid hormone.
Lipids such as cholesterol and triglycerides are not soluble in
water and are thus need to be complexed to water soluble carrier
proteins for transporting them in the blood between different
organs.
Plasma lipoproteins consist of a neutral lipid core of triglyceride
and cholesterol ester that is surrounded and stabilized by free
cholesterol protein and phospholipids. The relative proportion of
nonpolar lipid, protein and polar lipid, protein and polar lipid
determine the density, size and charge of the resulting
lipoproteins.
The total plasma lipid is 700-1000 mg per dl. Roughly 1/ 3 is
cholesterol and rest 1/3 is phospholipids. These are complexed
with proteins to form lipoproteins.
1. Chylomicrons are the lipoprotein particles lowest in density
and largest in size and contain the most lipid and smallest
percentage of protein. They transport mainly TG and smaller
amounts of PL, cholesterol ester and fat soluble vitamins from
intestines to liver and adipose tissues. The lipids carried by
chloromicrons principally in dietary lipids. The lipids carried by
chloromicrons principally in dietary lipids. They are formed in
the intestinal mucosa VLDLs are synthesized in the liver and
released into blood. They transport triacylglycerides synthesized
in the liver and cholesterol esters from liver to peripheral tissues.
Fatty liver occurs in conditions in which there is an imbalance
between hepatic triacyl glyceride synthesis and the secretion of
VLDC. Diseases such as diabetes mellitus and chronic ethanol
ingestion can cause fatty liver. As VLDL passes through the
circulation their structure is altered to LDL .
VLDL are composed mainly of TAG , asset are more enriched in
cholesterol esters than are chylomicrons . LDL provides
cholesterol for cellular needs . LDL promotes coronary heart
disease by first penetrating the coronary artery wall and then
depositing cholesterol to form atherosclerosis plaque .
Estimation of Plasma Lipids
The serum lipids tests commonly done are total cholesterol , HDL
cholesterol and triglycerides .
Total cholesterol is estimated colorimetrically
1. Serum is used for Lieberman – Buchard reaction . Cholesterol
in presence of ion H2SO4 , acetic acid and acetic anhydride is
oxidized to cholestrapolyenes to give blue green colour .
2. More modern is the enzymatic oxidase method . Cholesterol is
oxidized . The H2O2 Produced in this reaction is split peroxidase
to produce nascent oxygen which is used to oxidase a colourless
chromogen to a coloured product .
The plasma cholesterol is distributed in different proteins
fractions . In normal persons , cholesterol level varies from 150 to
220 mg / dl with 70 % being esterified cholesterol and 30 % free .
In this average normal adult male , the plasma cholesterol should
preferably below 200 mg / dl . The females have a lower because
of the high estrogen level which also affords protection against
atherosclerosis .
Normally almost 60 % of total cholesterol in LDL 22% HDL ,
13% VLDL and 5% chylomicrons .
HDL and LDL
HDL cholesterol is estimated after precipitating LDL and VLDL
. The LDL cholesterol can be calculated from total cholesterol ,
HDL cholesterol and serum triglycerides LDL cholesterol = Total
cholesterol – [HDL Chol +TAG /5] 1/5 of the triglyceride value is
believed to represent VLDL in fasting plasma . The sample
serum should be taken after 14-16 hours of fasting . Elevated
LDL levels have been associated with increased of developing
coronary artery disease , whereas elevated HDL levels appear to
reduce the risk . Women have higher HDL levels than men ( 55
Vs 45 mg / dl ) and this may account for women's lower rate of
heart disease . Aerobic exercise increases HDL levels ( more
runners average 65mg/ dl) .