Lipids
Chapter 16
What are Lipids?
• Lipids = are a family of chemical compounds that
are a main component in every living cell. They
include the following 3 categories:
– Triglycerides – largest class of lipids. They include nearly
all of the fats and oils people typically eat. (of the lipids
95% are fats and oils)
– Phospholipids - these lipids have a structure that
enables them to dissolve in both fat and water. – use as an
emulsifiers (found in eggs and peanuts)
– Sterols – compound, bile acids and certain hormones
perform vital functions. Both plant and animal food contain
sterols, but food contains cholesterol (a sterol)
Triglycerides
• Main function is to fuel the body and keep it
warm.
• Adipose Tissue = pockets of fat-storing cells
– Also adipose tissue under each kidney forms a
cushion to help protect it from impact.
– Natural body oils help keep supple and hair
glossy and healthy.
– Fat also carries certain vitamins in the body.
Structure of Triglycerides
• Triglycerides are composed of carbon,
hydrogen, and oxygen.
Fatty Acids
• Organic compounds that contain a carboxyl group
at one end are classified as organic acids or fatty
acids.
• These fatty acids are organic compounds that have a carbon
chain with attached hydrogen atoms and carboxyl group at one
end.
• Carboxyl group = carbon bonded to oxygen by a double
covalent bond, and to a hydroxyl group with a single bond. –
COOH
– Not all fatty acids are the same, the length of the carbon chain
makes the different.
– To form triglycerides (tri meaning 3), three fatty acids react with the
alcohol glycerol
– The human body can make all but two fatty acids, linoleic and
linolenic.
» These are needed for normal growth and development are
obtained from foods as vegetables, grains, nuts, seeds, and
soybeans.
Saturated vs. Unsaturated Fat
• Saturated fat – most of the fatty acids are
saturated, in other words, the fatty acids contain all
their hydrogen atoms their molecular structure can
hold, making 4 single bonds.
• Single bond – covalent bond in which each atom donates only
one electron to form the bond (sharing one pair of electrons
between them)
• Unsaturated fat – most of the fatty acids are also
unsaturated, meaning they’re missing hydrogen
• When hydrogen atoms are missing, a single bond cannot form, to
make up the difference a double bond forms
• Double bond – covalent bond in which each atom donates two
electrons to form the bond
Unsaturated fat continued
• Unsaturated fats are classified by the
number of hydrogen atoms that “drop out”
and produce double bonds
– Monounsaturated fat – lacks two hydrogen's,
which creates one double bond between carbons
ex oleic acid or avocados, canola and peanut oil
– Polyunsaturated fat – has two or more double
bonds between carbons ex linoleic acid or nuts,
sesame seed and sunflower oils
Properties of Triglycerides
Energy Value
– The structure of triglycerides makes them bundles of
energy
– Energy is released by oxidation
– Triglycerides supply over twice the energy of glucose – 9
kcalories per gram compared to 4
Solubility
– Slightly soluble in water
Phase Differences
– Fats which usually come from animals are saturated –
their single bonds allow them a full set of hydrogen's,
which makes them solid at room temperature
– Most plant oils are unsaturated, the molecule forms a
double bond making the oils less compact, so they are
liquid at room temperature
Properties of Triglycerides
Continued
Melting Range
– Molecular structure has related effect on how fats change
• Most substances have a melting point and a freezing point
• Fatty acids with more carbon have higher melting point ex olive
oil
Solidification Point = the temperature at which
melted fat regains its original firmness
• Ex you put carrots you cooked in butter the night before in your
refrigerator, the next day they are coated with firm butter flecks
Functions of Fats in Food
Tenderizing
• One of the most important uses of fats in foods is tenderizing baked
goods (fat coast the flour, creating a flaky, delicate, lighter texture)
Aeration
• Add air or gas to batters and dough's – this decreases viscosity, making
the batter flow more easily
Emulsions
• Lipids play two roles in creating emulsion, they might be part or they
might influence one to form.
• Ex. adding mayonnaise creates an emulsion between oil and vinegar
• Triglycerides can be broken down into monoglycerides, these have one
fatty acid attached and are stable enough to emulsify other fats with
liquids
Flavor
• Fats carry flavor, they dissolve aromatic molecules in food and distribute
their essence through out the recipe
– Ex. bacon is a salty fat, olive oil is mildly flavored
Oxidation
• The oxidation of fats occur as the surface of foods react with
oxygen.
• When fatty food oxidize, they lose electron which is a main
reason that high-fat foods spoil
• Oxidation involves the loss of a hydrogen atom from a singlebonded carbon, this is why unsaturated fats are more prone to
oxidation because they have more double bonds
• Heat speeds the rate of oxidation, cooling slows but doesn't stop
the process
• Water prevents slow oxidation as well by preventing contact
between substances and elemental oxygen
• Rancid = the term that describes the unpleasant flavors that
develop as fats oxidize
» Rancidity produces a distinctive flavor, but different for each
type of food
Commercial Uses of Fats
• Commercially important fats fall into two main groups: animal fats and
plant oils
• Animal Fats
• Butter is a natural emulsion, 80% fat and 18% water, remaining 2%
is the protein that binds the other two ingredients
• Lard or rendered hog fat is popular in baking
• Beef fat is usually combined with vegetable fats for uses in food
• Plant Fats
• Plant lipids are derived from certain oil-rich seeds, in liquid form
they are often called vegetable oil ex corn, olive, canola and oil
blends
• Hydrogenated Oils
• Ex. vegetable shortening
• Hydrogenation = a chemical process in which hydrogen is added
to unsaturated fat molecules, breaking some double bonds and
replacing them with single bonds
– Partial hydrogenation changes liquid oil to spreadable, semisolid fat
– Hydrogenation adds stability by eliminating some of the double bonds
in fatty acids
– Hydrogenated oil resists rancidity better than liquid oil because it
doesn't develop a stale flavor and odor as quickly
Cooking with Fat
Effects on Fats
– Repeated exposure to intense heat causes a decomposition similar to
oxidation
– Also foods release some of their own fat, water and other substances
into the frying oil, which deteriorates the fat, a process called cracking
– Cracking can discolor oil and produce off flavors and odors
– Smoke point = the temperature at which a fat produces smoke
» Reaching a smoked point is part of a cycle of fat breakdown:
smoking makes the fat less stable
» Vegetable oils generally have a higher smoke point than animal
fats, making them more useful for frying
Frying Safety
– Safe frying starts with the correct equipment (a deep-fat fryer or a
frying pan with heavy-duty metal sides)
– Food needs to be dry – WHY
– Using the correct amount of oil, if oil spills out of the pan you need to
shut off heat IMEDIATELY
– How do you put out a grease fire?
Triglycerides in the Diet
• Fats in food are broken down into fatty acids
and glycerol, then absorbed by villi in the
small intestine
• Some of these fatty acids are stored in the liver,
remaining fats end up as adipose tissue (tissue
designed to store fat)
• A typical American diet gets 45% of its calories from
fat, well over the 30% recommended (Recommended
daily value limit is 65g for fat and 20g saturated fat)
Low-Fat Options
• According to a recent survey, as many as 56% of
American adults are trying to limit their fat intake
• You have to be careful, because often low-fat and fatfree foods are often high in calories
Triglycerides in the Diet
Continued
• Fat Replacers
• Fat replacers are loosely grouped as either fat, protein, or carbohydrate
based
– Fat-based replacers are manufacture from, very short and long carbon-chain
acids, which supply fewer kcalories
– Protein-based replacers use milk or protein particles to stabilize and
texturize dairy products and some baked goods, sauces, and soups
– Carbohydrate fat replacers include cellulose, gums, and modified food starch
• Trans Fat (also known as trans fatty acids)
• Is a manmade type of fat formed when a liquid vegetable oil is made into
solid fat, like margarine
• Trans fat is made when hydrogen is added to vegetable oil in a process
called hydrogenation
• Hydrogenation is popular because it increases the stability and shelf life
of foods
• Partial hydrogenation – is when some of the double bonds and the
hydrogen atoms end up on different sides of the chain
• Trans fat behaves in the human body much like a saturated fat
» It raises the LDL or bad cholesterol
» Found in foods like vegetable shortening, some margarines, cookies,
snack foods, fried foods, baked goods, and other processed foods
made with partially hydrogenated veg. oils
Cholesterol
• Cholesterol = is not a triglyceride, but a sterol, a
fatty alcohol made from glucose or saturated fatty
acids
• Formula is C27H45OH
• Cholesterol is vitamin in producing vitamin D and some
hormones
• The liver makes all the cholesterol you need
• Cholesterol in the blood is though to contribute to the
manufacture of plaque = a mound of lipid material mixed with
calcium and smooth muscle cells
– Atherosclerosis (hardening of the arteries) = buildup of plaque
along the inner walls of the arteries
LDL and HDL Cholesterol
• Lipoproteins = large, complex molecules of
lipids and protein that carry lipids in the blood
• LDL – low-density lipoproteins, they carry about 75%
of cholesterol in the blood
» Bad cholesterol (want a low number)
• HDL –high-density lipoproteins – they return
cholesterol to the liver for breakdown and disposal
» Good cholesterol ( want a high number)
Omega 3 Fatty Acids
• Scientists believe that omega-3 fatty acids,
found in some fish, promote heart heath in
two ways:
• First they make it more difficult for plaque to form or
clump
• They also make plaque less sticky and less likely to
collect in the arteries
• Sardines, salmon, tuna, herring, and other ocean fish
are highest in omega-3 fatty acids or cod liver oil
capsules and marine oils
Questions
1.
2.
3.
4.
Describe the tree categories of lipids.
What functions do triglycerides serve in the body?
Describe the structure of triglycerides.
Why does the body need to obtain linoleic and
linolenic acids from plant sources?
5. How are unsaturated fats classified? Give
examples.
6. How do fats compare to carbohydrates as an
energy source?
Questions Continued
7. How does carbon bonding affect the phase of a
fat?
8. Why do fats have a melting range rather than a
melting point?
9. From a chemical standpoint, why might stale
potato chips become rancid?
10. How does hydrogenation affect oils?
11. If you fried chicken in a restaurant, what signs
might tell you the frying oil needed changing?
12. Compare low-and high-density lipoproteins.
13. How do marine oils differ from animal fats?