Fats study material

Fats

Lipids are very important food materials that serve in
storing the energy.  A Carbohydrate   molecule gives 38ATPs where as a lipid
molecule gives 129ATPs. Lipids are completely insoluble in water.

A lipid is defined as the water insoluble biomolecule which
has high solubility in nonpolar solvents. 
The simplest lipids are fats, which are trimesters madeup of glycerol
and fatty acids.

Classification
of lipids

Bloor
classified the lipids into three major categories,  they are 1. Simple lipids  2. Compound Lipids 3. Derived Lipids

Simple Lipids

Lipids
that are madeup of Fatty acids and glycerol. 
They are further classified as Fats/Oils and waxes.

Fats/Oils:
Simple lipids that are madeup of fatty acids and glycerol are called
triglycerides or fats/oils.  A
triglyceride is the most potential form of lipid that constitutes 98% of our
dietery lipid.  When one molecule of
glycerol combines with three molecules of a fatty acid, the resulting structure
is called triglyceride. The three fatty acids may be different or same.

Waxes:  when a fatty acid is in combination with any
other alcohol otherthan glycerol then those compound lipids are called waxes.

            In
their most common form, wax esters consist of fatty acids esterified to
long-chain alcohols with similar chain-lengths. The latter tend to be saturated
or have one double bond only. Such compounds are found in animal, plant and
microbial tissues and they have a variety of functions, such as acting as
energy stores, waterproofing and lubrication.

In some tissues, such as skin, avian preen glands or plant
leaf surfaces, the wax components are much more complicated in their structures
and compositions.

Compound Lipids

Lipids
that are usually made up of a fatty acid, an alcohol and a non lipid group are
called compound lipid.  Based on the non
lipid group or prosthetic group, these lipids are classified into

a.
Phospholipids   b. Glycolipids   c. lipoproteins  d. sulpholipids.

1. Phospholipids: These are the lipid compounds that contain a phosphoric acid
   group in their structure. The following are some of the examples of
   phospholipids

i.                   
Lecithins:  These are
abundantly found in membranes and equally found in plant and animal
kingdom.  In the plant kingdom they are
found in soyabeans, yeast etc.  in the
animal kingdom they are present in nervous tissue.  These are responsible for transmission of
nerve impulse.

ii.                 
Cephalins:  these are
equally found in plant and animal kingdoms. 
These are responsible for blood clotting and formation of cell membranes

iii.               
Phosphotidyl serine: 
these are fomed when phosphatidic acid combined with serine.  These are responsible for transport of ions
across the membranes

iv.               
Phosphatidyl inositol: 
these are formed when phosphtidic acid combines with a hexahydric
alcohol called insositol.  It is found
abundantly in brain and nervous tissue. 

Phospholipase enzyme: 
phospholipase enzyme is an enzyme that hydrolyzes phospholipids into
fatty acids and lipophilic substances. 

2. Glycolipids:  in this kind of
   lipids the non lipid group is carbohydrates.  In this kind of lipids the instead
   of  glycerol  sphingosine is present.  The basic composition of glycolipid is
   sugar, fattyacid and sphingosine.  These
   are further classified as cerebrosides and gangliosides.

i.                   
Cerebrosides: cerebrosides are present in the white mater
of the brain.  They are responsible for
normal function of nervous system

ii.                 
Gangliosides: these are present in the grey matter of the
brain.  They are responsible for the
transport of lipids across the membranes and normal function of nervous system.

3. Lipoproteins:
    Inthese lipids
   the nonlipid group is a protein.  Plasma
   lipoproteins found in blood help in transport of other lipids through
   blood.  Lipo proteins are classified
   as a. LDL (low density lipoproteins), they carry cholesterol synthesized
   in liver and carry them to adipose for storage.   HDL (High density
   Lipoproteins) they transport cholesterol from peripheral tissues to the
   liver.

4. Sulpholipids:  in these lipids
   the non lipid group is a sulphur containing group.  They are found in few bacterial
   species. 

Derived lipids

Lipids that are
obtained on the hydrolysis of a simple or compound lipid are called derived
lipids. 

The major derived
lipids are monoglycerides, diglycerides, glycerol and fatty acids.  Cholesterol and prostaglandins are also good
examples of derived lipids. Steroids are other examples.  These
compounds include the bile salts, cholesterol and
related compounds, and certain hormones (such
as cortisone and the sex hormones).

Cholesterol:
It is a derived lipid that is obtained from acetic acid. It has a molecular
formula of C₂₇H₄₅OH. 
It contains CPP ring. (cyclopentane
perhydro phenanthrene)  It
is a steroid, built from four linked hydrocarbon rings.

It is insoluble in water and soluble in all organic solvents. Excess cholesterol is believed to be a
primary factor in the development of atherosclerosis and heart disease,

Fatty acids: Fatty
acids are long chain or short chain organic acids that contain a primary
carboxylic acid group and terminal methyl group. 

Based on the presence
or absence of double bonds the fatty acids could be saturated or
mono-unsaturated and poly unsaturated fatty acids. 

The saturated fatty
acids are called anoic
fatty acids and the unsaturated fatty acids are called enoic
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.

The terms saturated,
mono-unsaturated, and poly-unsaturated refer 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.  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”. Therefore these oils are
called unsaturated fats. Because of the kinks in the hydrocarbon tails,
unsaturated fats can’t pack as closely together, making them liquid at room
temperature.

Many
people have heard that the unsaturated fats are “healthier” than the saturated
ones. Hydrogenated vegetable as “good” unsaturated oil.

Sources of food

Saturated fat
is found mostly in foods from animals and some plants.Saturated fats are
usually solid at room temperature.  Foods
from animals — These include beef, beef fat, veal, lamb, pork, lard, poultry
fat, butter, cream, milk, cheeses and other dairy products made from whole
milk. These foods also contain dietary cholesterol. Foods from plants — These
include coconut oil, palm oil and palm kernel oil (often called tropical oils),
and cocoa butter.

Polyunsaturated and monounsaturated fats  — Polyunsaturated and monounsaturated fats
are the two unsaturated fats. They're found primarily in oils from plants. Polyunsaturated
fats — These include safflower, sesame and sunflower seeds, corn and soybeans,
many nuts and seeds, and their oils. These fats are usually liquid at room
temperature and in the refrigerator. Monounsaturated fats — These include
canola, olive and peanut oils, and avocados. These fats remain liquid at room
temperature but may start to solidify in the refrigerator.

Table 1: Common Fatty Acids

Fatty Acids
Acid Name	Structure	Melting Point	Graphic
SATURATED
Lauric	CH3(CH2)10COOH	+44
Palmitic	CH3(CH2)14COOH	+63
Stearic	CH3(CH2)16COOH	+70
UNSATURATED
Oleic	CH3(CH2)7CH=CH(CH2)7COOH	+16
Linoleic	CH3(CH2)4(CH=CHCH2)2(CH2)6COOH	-5
Linolenic	CH3CH2(CH=CHCH2)3(CH2)6COOH	-11
Arachidonic	CH3(CH2)4(CH=CHCH2)4(CH2)2COOH	-50

Properties of lipids

Saponification;  a process by which triglycerides are reacted
with sodium or potassium hydroxide to produce glycerol and fatty acid salt
called soap.  This process is very much
useful industrially. 

Oxidation of lipids
flavor is considered as the most essential characteristic of food
products.  The oxidation of lipids is due
to the presence of unsaturated fatty acids present in them, the unsaturated
fatty acids undergo oxidation, resulting in the formation peroxides and free
radicles.  These substances spoil the
taste of food.  Sometimes these
substances be also poisonous.