Fats and oils
Fats and oils comprise one of the three major classes
of foods, the others being carbohydrates and proteins.
Chemically they may be defined as esters of the three
carbon trihydroxy alcohol, glycerol and various
monocarboxylic acids known as fatty acids.
All fats and oils are a mixture of saturated fatty acids
and unsaturated fatty acids.
Solid fats contain more saturated fats and than oils.
Oils contain more monounsaturated (MUFA) and
polyunsaturated (PUFA) fats.
Saturated fats, trans fats, and cholesterol tend to
raise “bad” (LDL) cholesterol levels in the blood,
which in turn increases the risk for heart disease.
To lower risk for heart disease, cut back on foods
containing saturated fats, trans fats, and cholesterol.
Difference between fat & oil
1. Remains solid at room
2. Relatively more
4. More stable
1. Remains liquid at
3. Low melting point
4. Less stable
Corn oil contains 86% polyunsaturated fatty acids
Therefore is a liquid at room temperature.
Olive oil contains monounsaturated fatty
Therefore is a liquid at room temperature,
likely to solidify when refrigerated.
Saturated fatty acids (animal fats) are
solids, or nearly solids at room
Fats are esters of fatty acids and glycerol. Most fats
occur in the form of triglycerides, in which three
fatty acids are attached to the glycerol. Fatty
acids contain the carboxyl group (COOH) and an
aliphatic carbon chain of variable length
Ester-The chemical linkage that holds an alcohol group
(OH) and an acid group (such as COOH) together. An
ester bond is the connection between a fatty acid and
glycerol in glycerides.
Glycerol-A three-carbon chain, with each carbon containing
an alcohol group. One, two, or three fatty acids may be
attached to glycerol to give a mono-, di-, or triglyceride.
Triglyceride-Three fatty acids attached to a glycerol
molecule. If the three fatty acids are the same, it is a
simple triglyceride; if they are different from each other, it
is a mixed triglyceride. Mixed triglycerides are the most
common chemical components in fats and oils.
Fatty acids- A group of chemical compounds
characterized by a chain made up of carbon and
hydrogen atoms and having a carboxylic acid (COOH)
group on one end of the molecule. They differ from each
other in the number of carbon atoms and the number and
location of double bonds in the chain. When they exist
unattached to other compounds, they are called free fatty
The oil and fat products used for edible purposes can
be divided into two distinct classes:
Liquid oils, such as olive oil, peanut oil, soybean oil,
or sunflower oil; and
Plastic fats, such as lard, butter and margarine.
Properties of fats and oils
When liquid fat is cooled, the molecular movement slows
down as energy is removed and the molecules are attracted
to each other by Van Der Waals forces.
Symmetrical molecules and molecules with fatty acids that
are similar in chain length align most easily to form crystals.
Fats containing asymmetrical molecules and molecules
containing links due to double bonds align less easily,
because they cannot pack together closely in space.
Molecules that align easily need less energy to be
removed before they will crystallize, and so they have
high melting points.
They also tend to form large crystals.
Fats can exist in different crystalline forms, and this
phenomenon is known as polymorphism.
A fat may crystallize in one of four different crystal forms:
The smallest and least stable crystals are called
alpha crystals. These are formed if fats are chilled
Beta prime crystals:
The alpha crystals of most fats are unstable, and
change readily to beta prime crystals. These are small
needle like crystals, approximately 1 µm long.
Fats that can form stable β crystals change
to the intermediate crystal form, about 3-5 µm in
Coarse beta crystal:
Finally convert to coarse beta crystal,
which can range from 25 to 100µm in length.
Beta crystals have the highest melting point.
Formation of small crystals is favored by rapid
cooling with agitation. Growth of large crystals
occurs if cooling is slow.
Melting point: The melting point of a solid is the temperature
at which it changes state from solid to liquid. For example
in animal fat Back Fat: 30-40 degrees, Leaf Fat: 43-48
degrees, Mixed fat: 36-45 degree.
The melting point is an index of the force of attraction
The greater the attractive forces between molecules, the
more easily they will associate to form a solid.
A lot of energy in the form of heat must be put in to
convert a solid to a liquid; thus, the melting point will be
A fat or oil, which is a mixture of several triglycerides, and
therefore, do not have a sharp melting point, but melt over
a range of temperature, depends on the composition of the
The melting points of individual fatty acids depend on such
factors as chain length , number of double bonds and
The smoke point is the temperature at which a fat
or oil gives off a thin bluish smoke.
Fats and oils with low molecular weight fatty acids
have low smoke point.
Normally, oils that are selected for deep fat frying
are those, which have a high smoke point.
If oils with low smoke points are used for deep fat
frying, then the foodstuff is fried at a lower
temperature and thus will take a longer time to
acquire the stage of doneness.
In this case, the exposure of the foodstuff to the oil
Fats may either be liquid, plastic, or solid at room
A plastic fat is moldable because it contains both
liquid oil and solid crystals of triglycerides.
Its consistency depends on the ratio of solid to
liquid triglycerides; the more liquid triglycerides,
the softer the fat will be, and the more solid
triglycerides, the harder it will be.
A plastic fat is two-way system, containing solid
fat crystals surrounded by liquid oil.
The liquid phase acts as a lubricant, enabling the
solid crystals to slide past one another, and thus
conferring moldability to the fat.
A fat that contains only solid triglycerides is hard
and brittle and cannot be molded.
Refractive index: It indicates the purity and
identity of fat.
The specific gravity of oils and fats is about
0.9, which indicates that they are lighter
Though insoluble in water, they can form an
emulsion with water when beaten up with it
to form tiny globules in the presence of
suitable emulsifying agent.
The presence of minute amounts of milk
protein helps to stabilize these emulsions.
Lecithin, a phospholipid from egg yolk helps
to stabilize mayonnaise.
Emulsification of fats is a necessary step in
a number of products such as cakes, ice
cream and other frozen desserts.
Creaming of Fats
Creaming is a process that achieves temporary
Stabilizers may be added to an emulsion to decrease
the tendency of the emulsion to separate, which
creates a viscosity similar to soft yogurt; this is
referred to as a semi-permanent emulsion.
Permanent emulsions are very viscous and stable, to
the point that they do not separate.
Solid fats like butter and margarine can be
creamed or made soft and fluffy by the
incorporation of air.
Fat and sugar are usually creamed together in the
preparation of cakes.
Chemical Properties of Oils &
Iodine value – express the degree of
unsaturation of the FAs in the fat (the amount of
iodine absorbed by a fat/100 g basis). The higher
iodine value indicates the greater the degree of
Ester cleavage- The ester bonds in fat can
undergo a variety of splitting reactions. Some of
these are important in food applications, while
others have other industrial significance
Hydrolysis- (breaks down into simpler forms )
A chemical reaction in which a molecule splits into two parts.
A molecule of water also splits into H and OH, which are
added to the places where the original bond was broken.
A fatty acid is removed from a glyceride by hydrolysis of
the ester bond.
Saponification Number –
saponification : A chemical reaction caused by addition of
alkali in which the fatty acids attached to a glycerol are
cleaved off to produce soap (fatty acid salts) and a
Is may defined as the number of mg of potassium
hydroxide needed to sponify 1 g of fat or oil.
Glycerolysis- A chemical reaction in which glycerol is
combined with one or more fatty acids to form a
Alcoholysis- A chemical reaction in which fatty acids
react with alcohol to form an ester.
The reaction of fat with alcohol is usually catalyzed with
an acid such as HCI or a sulfonic acid resin. For
example, reaction of fat with methanol yields the
methyl esters of the fatty acids, which are used to
analyze the composition of the fat by gas-phase
Changing the positions of the fatty acids on
A free fatty acid can displace another fatty acid from an
ester, leaving a glyceride with somewhat changed
properties because its fatty acid structure has
changed. This reaction is used to change fat
Oxidation- ( exposure to Oxygen)
Chemical reaction in which the double bond
on a lipid molecule reacts with oxygen to
produce a variety of chemical products. The
consequences of this reaction are loss of
nutritional value and formation of the off-
flavors associated with rancidity.
Reduction- Changing an acid group on a
fatty acid to an alcohol group. This is done
with metal reducing agents to create fatty
The quota for polyunsaturated fatty acids. In
particular, the ratio of omega-6 to omega-3 acids
should be between 5 and 10 to 1 (or less). Since
the presence of α-linolenic acid leads to oxidative
instability and reduced shelf life.
Fats and oils have a high caloric value, 2.25 times
more energy than carbohydrates or proteins.
Each gram of fat contains 9 kcal of energy.
Fats and oils carry the fat soluble vitamins.
Textural qualities (body
and mouth feel)
Medium for transferring
Aeration and leavening
(fullness after eating)
shock in frozen desserts
Solubilising flavours and
Refining (Neutralization or
In general, fat and oil undergo four processing
Fats and oils are extracted from either plants or
animals. Extraction methods vary. For example, the
adipose tissue of the pig is heated, melts the fat and it
is further processed. Butter is made by reversing the oil
in water emulsion of cream into a water in oil emulsion.
Plant extraction procedures involve a variety of
different extraction methods.
The melted fat is then separated by skimming or
The melted fat then rises, water and remaining tissue
Meat scraps are heated in steam or water to cause the
fat to melt
The fat can be obtained from any of the following
a. Dry rendering
b. Wet rendering
c. Low-temperature wet rendering
Pressing: Used for removing oil from oilseeds or
fruit rich oils.. The oil bearing tissues are rolled ,
crushed or ground into flakes, and then heated by
steam at 70 deg. C.
PRESSING OR EXPELLING
Various types of mechanical presses and expellers are used to squeeze oil from
Seeds are usually first cooked slightly to partially break down the cell structure
and to melt the fat for easier release of oil.
The heat from cooking or grinding should not be excessive or it may darken the
color of the oil
With some seeds (e.g. corn) only the germ portion of the seed is pressed to obtain
oil, whereas with seed residues by being pumped through multiple filter cloths or
by centrifugal clarification.
It is common in large scale operations to remove the oil from cracked
seeds at low temperatures with a nontoxic fat solvent such as hexane.
The solvent is percolated through the seeds, and after the oil is
extracted, the solvent is distilled from the oil and recovered for reuse.
Combined processes employ pressing to remove most of the oil
followed by solvent extraction to recover final traces.
The oil-free residual seed meal is then ground for animal feed.
Refining of Crude Oil
Crude oils as received from the extraction plant
contain several non-triglyceride components which
must be removed.
Refining consists of several processes which
accomplish this aim.
A refining process is carried out extraction of crude
edible oils by means of screw presses and/or solvent
In refining, physical and chemical processes are
combined to remove undesirable natural as well as
environmental-related components from the crude oil.
These components comprise for example
phosphatides, free fatty acids, pigments (such as
chlorophyll), odors and flavors (including aliphatic
aldehyde and ketone), waxes as well as heavy
metals, pesticides etc.
Depending on the requirements, the following basic
processes are implemented:
Degumming for removal of phosphatides,
Neutralization for removal of free fatty acids,
Bleaching for removal of color,
Deodorization to distill odors and flavors as well as free
fatty acids and
Winterization for separation of waxes.
The first step in the refining process of many oils is
degumming. Oils are mixed with water to hydrate
phosphatides, which are removed by centrifuging.
Phosphoric or citric acid or silica gel are added to
enhance the process.
Degumming removes valuable emulsifiers such as
Cottonseed oils are not degummed, but
degumming is necessary for such oils as soybean
The aim of degumming operation;
The emulsifying action of phospholipids increases oil
losses during alkali refining.
Gums lead brown discoloration of oil after heating during
Salts may be formed with cooper, magnesium,calcium
and iron, accelerating oxidative degredation of oil.
Different degumming processes are carried out to
remove phosphatides. For efficient and economic
application of this procedure appropriate
machines and equipments are used.
1. Water degumming
2. Acid degumming
3. Enzymatic degumming
A large part of the phosphatides (gums) can be
hydrated quickly and easily. If the pressed or extracted
oil contains a considerable quantity of gums the oil is
subjected to the water degumming process
immediately following extraction.
In this process, water is added to the oil. After a certain
reaction period the hydrated phosphatides can be
separated either by decantation (settling) or
continuously by means of centrifuges.
In this process step a large part of hydratable and
even a small proportion of the non-hydratable
phophatides are removed. The extracted gums can be
processed into lecithin for food, feed or for technical
Water Degumming Process
• Heat oil to 60 -70 °C
• Water addition and mixing
• Hydration mixing 30 minutes
• Centrifugal separation of hydrated gums
• Vacuum drying of degummed oil
• Gums -dried for edible lecithin or recombined in
Phosphorous in degummed oil -50 to 200 ppm max
Moisture in dried and degummed oil -< 0.1%.
Dry acid degumming: Dry acid degumming is particularly
suitable for processing oils with low gum contents such as
palm oil, coconut oil, palm kernel oil or animal fats. Intensive
mixing is implemented following addition of acid to the pre-
heated crude oil.
The benefits of the dry acid degumming process are:
long service life (the components are acid proof),
low investment costs,
environmental-friendly as no wastewater or soap stock
Wet acid degumming
Initially oils with higher gum contents (e.g. corn oil)
are similarly processed as in dry acid degumming.
However, to achieve gum hydration water is added
following acid apportioning. The gums are
removed by a separator prior to bleaching.
This process is beneficial as
centrifuges enable easy separation of gums in oil
types with higher non-hydratable gums contents
(e.g. rape oil and soybean oil),
Acid Degumming Process Steps
• Heat oil to 60 -70 °C
• Acid addition and mixing
• Hydration mixing 30 minutes
• Centrifugal separation of hydrated gums
• Vacuum drying of degummed oil
• Gums -recombined in meal
Crude oil heater acid
mixer To drying / storage
Phosphorous in degummed oil -20 to 50 ppm max.
Moisture in dried and degummed oil -< 0.1%
Enzymatic degumming was first introduced by the
German Lurgi Company as the “Enzy Max process” .
The EnzyMax process can be divided into four different
(i) the adjustment of the optimal conditions for the
enzyme reaction, i.e. optimal pH with a citrate buffer
and the optimal temperature;
(ii) the addition of the enzyme solution;
(iii) the enzyme reaction;
(iv) the separation of lysophosphatide from the oil at
Objective:Removal of free fatty acids
Neutralisation of vegetable oils is essential to
ensure removal of gums, waxes, phosphatides and
free fatty acid (F. F.A.) from the oil; to impart
uniform colour by removal of colouring pigments
and to get rid of unpleasant smell from the oil by
removal of odiferous matter.
Two different Neutralising principles:
1.Chemical Neutralisation:Removal by a chemical reaction
with alkali(caustic soda)
2. Physical Neutralisation :Removal by distillation at higher
temperature and low vacuum
Trace metals, colour bodies such as chlorophyll,
soaps and oxidation products are removed using
bleaching clays which adsorb the impurities. Bleached
oils are nearly colourless and have a peroxide value of
near zero. Depending on the desired finished product,
oils are then subjected to one or more processes of
the following processes..
Deordization is a steam distillation process
carried out in a vacuum, removing volatile
compounds from the oil. This may be a batch or
continuous process. The end product is a bland
oil with a low level of free fatty acids and a zero
peroxide value. This step also removes any
residual pesticides or metabolites that might be
present. Some manufacturers favour the use of
cottonseed oil because it can be deodorized at
lower temperatures, which results in more
tocopherols (natural antioxidants) being retained.
Deordization produces some of the purest food
Oils such as salad oils, or oils that are to be stored
in cool places undergo a process called
winterization so that they will not become cloudy
when chilled. The refined, deodorized oils are
chilled with gentle agitation, which causes higher
melting fractions to precipitate. The fraction which
settles out is called stearin. Soybean oil does not
require winterization, but canola, corn, cottonseed,
sunflower, safflower and peanut oils do.
Treatment of fats and oils with hydrogen gas in the
presence of a catalyst results in the addition of
hydrogen to carbon-carbon double bond.
Hydrogenation produces oil with mouth feel, stability,
melting point and lubricating qualities necessary to
meet the needs of many manufacturers. It is important
to note that hydrogenation is a selective process that
can be controlled to produce various levels of
Sun flower oil
Trans fats are made through the chemical
process called hydrogenation of vegetable
oils. Hydrogenation solidifies liquid oils and
increases the shelf life and the flavour
stability of oils and foods that contain them.
Margarine from Oil
Mild off flavour developed by a refined oil when
exposed to oxygen. Reversion occurs rather easily,
and the off- flavour, while undesirable, is not as
objectionable as rancidity caused by oxidation.
Effect of heat on fats
There is increase in free fatty acids
Smoke point is lowered
Iodine number decreases
Melting point falls
Fat turns darker in colour
Fat gets polymerised
Refractive index increases
This occurs when fats are subjected to intense heat. Free fatty
acids are released, colour darkens and gum is formed at the
edge of the vessel.
Use of fats and oils
AS A MEDIUM OF COOKING
Fat is used in shallow and deep fat frying.
Cooking oil is a better heat transfer medium
than air or water in that it heats up very
quickly because of its greater specific heat,
and its operating temperature of about
200°C is considerably higher than that of
Pan frying is used to cook dosas, cutlets
In basting, foods to be grilled like meat, poultry or
vegetables are applied with fat to prevent the
Deep fat frying method is used in preparing pooris,
bajia etc. In deep fat frying, water is lost from the
exterior surface of the food as it is converted to
The steam carries off energy from the surface of
the food and prevents charring or burning.
Water then migrates from the central portion of the
food outward to the edges to replace that loss by
evaporation. Finally the interior of the food is
FOR IMPROVES THE TEXTURE OF FOODS:
FAT AS A SHORTENING AGENT
In many preparations, such as cakes, biscuits etc,
fats are added to improve the texture.
The fat covers the surface of the flour particles
and prevents the sticking of particles together.
Many factors such as the nature of the fat, the
amount added, the temperature, presence of other
ingredients, manipulation and the extent of mixing,
affect the shortening power.
FAT AS A LEAVENING AGENT:
In making cake, leavening occurs by incorporating air
into the fat during the leavening process. When the
butter is heated in the oven, the small air bubbles
expand and fill with steam.
The greater percentage of leavening in cake comes
from the steam that collects in the tiny air bubbles
rather than from the air itself.
Gluten in the flour forms the walls around each little
bubble and during baking they act to a fairly rigid
When the cake is removed from the oven and is
FAT FOR SMOOTHNESS
Fats have textural effects in ice creams and frozen
desserts. They limit the size of water crystals and help in
maintaining smooth texture.
AS A SEASONING
Fats and oils are used to season most food preparations in
sweet preparations, fats, such butter, ghee, vanaspati are
used, as they have mild flavor, which blends with the sweet
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B. Srilakshmi, (2007), Food Science, New Age
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A.Karleskind (1996)Oils & Fats Manual . Published by
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Caisimir C.Akoh and David B.Min (2002) Food Lipid.
Printed by The united State of America.