The differences between margarine and butter

Original Reference: C&E News, August 16, 2004,
p. 24
Premise/Problem and Goals: The goal is to show the chemical structures of butter and margarine and discuss the chemical differences between them.
Importance: Butter and margarine are different
chemical compounds with different implications for
human nutrition. It is useful and interesting to
understand this difference and make one’s food
decisions accordingly.
Relevance to Course: Butter is made up of fatty
acids, which are long chains of carbon atoms with a
carboxylic acid group at one end. Fatty acids can
be saturated (no double bonds between the
carbons) or unsaturated (some double bonds
between the carbons). The saturated fatty acids
include myristic acid (14 carbons, including the
carboxylic acid carbon), palmitic acid (16 carbons),
and stearic acid (18 carbons) carbons). Saturated
fatty acids are simple linear chains that pack
together easily and stay solid to higher
temperatures (e. g., the melting point of stearic acid
is 70 degrees C). Butter is made mostly of
saturated fatty acids.
Unsaturated fatty acids can be
monounsaturated (one double bond per chain), or
polyunsaturated (several double bonds per chain).
The chains usually have a cis conformation around
the double bond, causing bends in the molecules.
The bends and stiffer chains mean that unsaturated
fatty acids do not pack together well. Thus
unsaturated fatty acids melt at lower temperatures
and tend to be liquids at room temperature. Oils
such as olive oil or corn oil have mostly unsaturated
fatty acids.
Unsaturated fatty acids can be converted to
saturated acids by hydrogenation: heating under
pressure in the presence of hydrogen and a metal
catalyst. The hydrogenation can be complete (all
carbon double bonds changed to single bonds) or
partial (some double bonds remaining). Partial
hydrogenation can convert some cis double bonds
to trans double bonds, producing trans fatty acids.
If the double bonds oxidize in air, then the oil
becomes rancid, so saturated fatty acids keep
better than do unsaturated fatty acids.
Margarine is made from partially
hydrogenated oils. The greater the hydrogenation,
the harder the margarine. Other ingredients are
added for flavor: buttermilk, salt, preservatives,
vitamins. Margarine is lower in cost than butter.
Margarines can be made to have fewer calories per
serving, by reducing the ratio of fats to water.
Saturated fats are known to raise the level
of cholesterol (LDL - low density lipoprotein) in the
blood, which increases the danger of heart disease.
Margarine has no inherent cholesterol and is made
of only partially saturated fatty acids, so it may be
preferable to butter. On the other hand, trans fatty
acids are also known to increase LDL cholesterol,
and margarine has more trans fatty acids than
butter. The makers of margarine are now finding
ways to reduce the trans fatty acid content.
In general, saturated fatty acids and trans
fatty acids are to be avoided in the diet.
Stearic acid is a saturated fatty
acid with a melting point of
53.9 °C.
Oleic acid is a monounsaturated
fatty acid with a melting point
of 16.2 °C.
Linoleic acid is a
polyunsaturated fatty acid with
a melting point of –5 °C.