Triglycerides Are Esters of
Glycerol and Fatty Acids
Glycerol
"backbone" is a
water-soluble
alcohol
Fatty Acids are chains of carbon atoms
with a methyl (-CH3) group at one end and
a carboxylic acid (-COOH) group at the
other
condensation
reaction
Glycerol + 3 Fatty Acids
Triglyceride + 3 water molecules
Structures linked by ester bonds (R-COOR') and water is released
What is the difference between fats and oils?
•In the world of nutrition, they are the same.
•They belong to a class known as triglycerides. They are
composed of fatty acids and glycerol.
•Sometimes, referring to the state at room temperature, the
word "fat" is used for a solid triglyceride and "oil" is used
for a liquid triglyceride.
•Below, we will discuss saturated and unsaturated fats.
•Unsaturated fats tend to be lower melting point than their
saturated counterparts. For example, the fatty acid oleic
acid (unsaturated, found in olive oil) melts at about 5.5°C,
while its counterpart, the fatty acid stearic acid (saturated,
found in tallow), melts at about 73°C.
•Unsaturated fats (i.e. triglycerides made from unsaturated
fatty acids) tend to be liquids at room temperature, while
saturated fats (i.e. triglycerides made from saturated fatty
acids) tend to be solid.
•Unsaturated fats can be partially converted to saturated
fats by a process called hydrogenation.
FATS AND OILS
Fats and oils are triglycerides with
varying degrees of saturated and
unsaturated fatty acids
– Fats – generally solid at room
temperatures and high in saturated fatty
acids
– Oils –generally liquid at room
temperatures and low in saturated fatty
acids
What is hydrogenation?
• Many years ago, we discovered how to convert liquid fats into solid
fats by means of this process called hydrogenation.
• Here, the liquid fat is put into a strong vessel, heated, and put under
high pressure with hydrogen in the presence of a catalyst. The
catalyst, usually platinum, palladium or nickel, is necessary
because the process would be so slow otherwise that it would, for
all practical purposes, never happen.
• Under these catalytic conditions, however, the liquid fat becomes a
solid fat. In this process, unsaturated fats are partially converted
into saturated fats.
• Hydrogenation was employed by the food industry in an effort to
convert liquid fats (unsaturated ones) to solids (saturated fats).
• There were two main topics that could be addressed by this
approach: separation of oils (for example, in peanut butter), and
shelf life problems.
• As a matter of fact, converting the liquid fats to solid fats did indeed
solve both problems. Separation could be halted, and the off-tastes
and odors produced over time by oxidation of the unsaturated fats
(which is called rancidity) could be avoided, because the saturated
fats do not oxidize (turn rancid).
Cardiovascular risk
• But the price the consumer pays for the benefit of the
food industry is a cardiovascular risk, in the form of
trans fats, which is why the government required the
amount of trans fats to be listed on labels starting in
January 2006.
• More recent studies have suggested that, even with
the same caloric intake (including fat calories) in two
groups, the group with the higher trans fats intake
gained more weight.
• In addition, this weight tended to gather around the
middle, giving the “apple” shape, which has been
implicated in giving rise to an increased
cardiovascular risk.
• The bad news about trans fats has been gathering for
years, but commercial interests would rather bury the
information (as well as their victims) than give up any
profits.
Symbols
• C represents a carbon atom
• H represents a hydrogen atom
•
or | (i.e. horizontal line or vertical line)
represents a single bond (that is, saturation)
• = represents a double bond (that is,
unsaturation)
• R represents the rest of the molecule
• COOH represents the acid portion of the
molecule
• → means “goes to”
cis form
• Here we will discuss the hydrogenation
process in terms of the structures of the fatty
acids, which are the major components of
the fats involved.
• The structure
H
H
R
C
C
COOH
cis form
• cis formis the usual molecular geometry, or
shape, of the unsaturated fatty acids.
• This shape is called cis which means the two
H’s are on the same side of the molecule.
• This is the geometry preferred by nature and
the human body.
Primary reaction hydrogenation
The hydrogenation process can be represented as follows:
unsaturated
This is the desired result.
saturated
Secondary reaction, isomerization
Unfortunately, this is not the whole picture. The problem of trans fats
arises because the above reaction (Primary reaction, hydrogenation) is
necessarily accompanied by the second reaction (Secondary reaction,
isomerization), in which the molecular geometry, or shape, is rearranged to convert the cis geometry to the trans geometry, like this
R
H
H
C
C
H
COOH
R
C
C
H
cis form
trans form
COOH
Isomerization
 Notice that no hydrogen was taken up in this second reaction,
and the double bond (or unsaturation) remains, but with a
different geometry. Now the two H’s are on the opposite sides of
the molecule.
 Such a re-arrangement is called an isomerization, and the two
shapes are referred to as isomers, which can be defined loosely
as molecules which have the same composition, but with
different arrangements.
 Trans means “across” when describing molecular arrangements.
Cis means “on the same side”.
 Because total hydrogenation has not been found to be
commercially viable, all hydrogenated fats in foods are partially
hydrogenated fats, and trans fats are an inescapable result in
their presence.
 Unfortunately, then, we see that one type of by-product formed in
the hydrogenation process is the group called the trans fats.
 Trans fats are unsaturated fats, but their molecular geometry is
what makes them so harmful. These are a very bad form of fats
from a cardiovascular point of view.
Fatty Acids Vary in Chain
Length and Saturation
Add Double Bonds 
Lower Melting Point
saturated
stearic acid
m.p. 73 oC
“cis”
monounsaturated
oleic acid
m.p. 5.5 oC
Longer Chain 
Higher Melting
Point
Poly-Unsaturation Confers Liquidity
(And Reactivity Toward Oxygen)
“cis, cis, cis”
linolenic acid
m.p. –24 oC
“cis, cis”
linoleic acid
m.p. –13 oC
More Double Bonds 
Lower Oxidative and
Thermal Stability
Hydrogenation Improves Stability
BUT…
“sat”
stearic acid
m.p. 73 oC
“cis”
oleic acid
m.p. 5.5 oC
H2
“trans”
elaidic acid
m.p. 42 oC
Trans fats behave
more like
saturated fat
Summary
• Unsaturated fats tend to be liquid at room temperatures: the
double bond is, in the normal cis configuration, asymmetric and so
forces a kink or bend into the carbon chain. As a result the
unsaturated fatty acids are unable to pack so closely together, or
crystallise so readily as straight-chain saturated fatty acids. This is
why unsaturated oils are mostly liquid at room temperature, while
more saturated fats (such as tallow) are hard.
• However a trans double bond does not form a sharp angle, as does
a cis double bond. Instead the molecular chain forms a straight
line similar to a saturated fat, except with a small kink at the double
bond site. Consequently the trans isomer of a given fatty acid will
always have a higher melting point than the cis isomer, but one
lower than the corresponding saturated fatty acid.
• In a "monounsaturated" fatty acid, there is only one such doublebonded pair of carbon atoms. In a "polyunsaturated" fatty acid,
there are two or more such pairs.
• When an unsaturated oil is hydrogenated, hydrogen is absorbed
into the fatty acid molecules. The hydrogen atoms bind to the
carbon chain in the vacant double-bonded sites, where only one
hydrogen atom is attached to the carbon atoms. In so doing the
extra hydrogen removes the double bond, straightens the chain,
and makes the molecule more saturated.