Transcript Lecture on Lipids

Overview of dietary fats and
lipid, in relation to rancidity
and per oxidation
What are Lipids?

A family of compounds that includes
–
Triglycerides (fats & oils)
 Fats:
lipids that are solid at room
temperature
 Oils: lipids that are liquid at room
temperature
–
•
–
•
Phospholipids
Cell
membrane,
amphipathic
Sterols (cholesterol).
Steroid alcohol
lipid
bilayers,
I. A Primer on Fats
A.
The Functions of
Fat in the Body


Energy source esp.
for muscles
Serves as an energy
reserve


1# body fat contains
3500 kcal
30-50%- of stored fat
Major component of cell membranes
 Nourishes skin & hair
 Insulates the body from temperature
extremes
 Cushion the vital organs to protect
them from shock

B. The Functions of Fat in Food
Provide calories (9 per
gram)
 Provide satiety
 Carry fat-soluble
vitamins & essential
fatty acids
 Contribute aroma &
flavor

Lipid Terminology

Triglycerides: the major class of
dietary lipids, including fats & oils
– Made up of 3 units known as fatty
acids and 1 unit called glycerol
(backbone)
– Comprise about 95% of lipids in
food and the human body

Phospholipids:
–
–

2nd of three main classes of lipids
similar to a triglyceride, but contains
phosphorous
Sterols
–
–
3rd of three main classes of lipids;
Cholesterol


one of the sterols
manufactured in the body for a variety of purposes

Fatty acids:
–
–
–
–
–
–
–
basic units of fat composed of
chains of carbon atoms
an acid group at one end and
hydrogen atoms attached all along
their length
If not attached with other molecule--free fatty acid
When metabolized yield ATP
Heart and muscle---prefer fatty acid
for fuel
Without double bond---saturated
With double bond---unsaturated
II. A Closer View of Fats
A.
Chain Length (number of carbons linked
together)

B.
Shorter = more soluble in water
Saturated vs. Unsaturated (number of
hydrogens the chain is holding)



Maximum = saturated
Unsaturated = one or more is missing
Point of unsaturation = site where hydrogen is
missing

Saturated fatty acid: a
fatty acid carrying the
maximum possible
number of hydrogen
atoms
– Animal foods such as
meat, poultry and fullfat dairy products
– Tropical oils such as
palm and coconut

Unsaturated fatty acid: a
fatty acid with one or more
points of unsaturation.
– Found in foods from
both plants & animal
sources
 Monounsaturated
fatty
acids (one double bond)
 Polyunsaturated fatty
acids (two or more)

Monounsaturated fatty
acid: also called a MUFA;
a fatty acid containing
one point of unsaturation
– Found mostly in
vegetable oils such as
olive, canola & peanut

Polyunsaturated fatty
acids: also called a
PUFA; a fatty acid in
which two or more point
of unsaturation occur
– Found in nuts,
vegetable oils such
as safflower,
sunflower and
soybean, and in fatty
fish
B. Essential Fatty Acids

The body can synthesize all of the fatty
acids it needs from carbohydrates, fat or
protein except for two:
1. Linoleic acid
2. Linolenic acid
– PUFAs
– Found in plant & fish oils
Deficiency causes scaly dermatitis
visual and neurologic abnormality
Omega - 6 versus Omega - 3
Omega – 6
 Linoleic
Omega – 3
 Linolenic
 Cold water fish
 Help dissolve blood clots
 Lower blood pressure
 Dilate the arteries
III. Characteristics of
Fats in Foods
A.
Liquid vs Solid
 More saturated a fat is, the
more solid it is at room
temperature
 More unsaturated a fat is, the
more liquid it is at room
temperature
III. Characteristics of Fats in Foods
A.
Hydrogenation
 The process of adding hydrogen to
unsaturated fat to make it more solid
and more resistant to chemical changes
such as spoiling
 Increasing a fat’s saturation can cause a
fat to lose its unsaturated health
benefits
C. Trans-Fatty Acids


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The adjacent two hydrogen atoms lie
on opposite sides of the chain.
“Partially hydrogenated vegetable oil”
Link between trans fatty acids and heart
disease
↑ serum LDL, ↑ risk of CHD
High in baked ones, fried food esp deep fried
V. Phospholipids




A lipid consisting of a water-soluble head
and a fat-soluble tail
Contain phosphorous
Component of cell membranes
Serve as emulsifiers (allow fats and water
to mix and travel in and out of cells into
watery fluid on both sides)

Lecithin is a
common
phospholipid
– Often used as an
emulsifier in
foods such as
margarine,
chocolate &
salad dressings
V. Cholesterol – a Sterol


Found only in animal products
Also made & used in the body:
– Structure of cell membranes
– Used to make bile for digestion
 Bile: a mixture of compounds, made by
the liver, stored in the gallbladder, &
secreted into the small intestine
 Emulsifies lipids to prepare them for
enzymatic digestion & helps transport
them into the intestinal wall cells
Used to make the sex hormones
estrogen & testosterone
 Made into vitamin D with the help of
sunlight
 Deposited in the artery walls leading
to plaque buildup & heart disease

VI. How the Body Handles Fat
A.
B.
C.
Digestion
Emulsification
Absorption
B. Lowering Blood Cholesterol
Levels



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
Eat no more than 30% of calories from fat
Eat no more than 8-10% of calories from
saturated fat
Eat no more than 10% of calories from
PUFAs
MUFAs should make up 10-15% of total
calories
Limit daily cholesterol intake to no more
than 300 milligrams
What is rancidity and why is it a problem?

The process which causes a substance to become rancid,
that is, having a rank, unpleasant smell or taste. OR
the hydrolysis and/or autoxidation of fats into shortchain aldehydes and ketones which are objectionable in
taste and odor.

A. Foods that are high in lipids and might become
rancid include potato chips, peanut butter, crackers,
and others.

B. Light, oxygen, trace elements such as iron and
zinc, salt, water, bacteria, and molds are factors that
speed up the oxidation process.
What causes the off-flavors and odors in foods
caused by oxidative rancidity?


There are two types of rancidity.
A. Hydrolytic Rancidity is caused by a
breakdown of the fat into glycerol and fatty
acid.
–
–
1. Fatty acids are organic compounds containing
carbon, hydrogen, and oxygen that combine with
glycerol to make a lipid.
2. Glycerol is the storage form of fat in animals.

B. Oxidative Rancidity results from oxidation
of unsaturated and polyunsaturated fatty
acids producing undesirable flavors and
odors.
–
–
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1. Oxidation is when a chemical reaction occurs
forming oxides by reacting with oxygen in the air.
2. Saturated fatty acids are fatty acid molecules
containing no double bonds between carbon
atoms—the molecule is “saturated” with hydrogen
atoms. Saturated fatty acids are the “bad
cholesterol.”
3. Unsaturated (polyunsaturated) fatty acids are fatty
acid molecules containing double bonds between
carbon atoms—plant oils are unsaturated. These are
considered the “good fats.” Unsaturated fats are
more susceptible to oxidative rancidity than
saturated fatty acids.
What practices are used for controlling oxidative
rancidity?

A. Adding antioxidants—Antioxidants are
substances that are added to some foods to
slow down oxidative deterioration.
–
–


1. BHA—butylated hydroxyanisole
2. BHT—butylated hydroxytoluane
B. Package food protected from light because
light accelerates oxidation.
C. Vacuum packaging to keep oxygen out
because oxygen accelerates oxidation.
However, this process is too costly for most
potato chip manufacturers.
D. Adding nitrogen to the bag to replace the
oxygen.
E. Speed up distribution to shorten the time from
processing to consumption.
F. Shelf dating products allows for consumers to
know when to use food products. Factors that
affect the storage life of a perishable food include:
1. length of storage
2. temperature
3. relative humidity
4. light
G. Vitamin E and Vitamin C also slow oxidative
rancidity.
VIII. Fat in the Diet
A.
Food Guide Pyramid
 3 groups traditionally account
for nine-tenths of the fat in the
U.S. diet
 Fats, oils & sweets group
 Meat, poultry, fish, dry
beans, eggs & nut group
 Milk, yogurt & cheese group
 Most of the fat in our diets
comes from animal
products
B. Fat Substitutes

Carbohydrate-based
–
–

Help retain moisture to maintain the juiciness or
creaminess that is lost with fat reduction
Carrageenan, fruit purees, gelatin, gums,
starches & products made from fiber
Protein-based
–
–
Proteins are cooked & blended to form tiny
round particles that trap water to maintain the
mouth feel of fat
Whey protein concentrate (Dairy-Lo), or milk &
egg white protein (Simplesse)

Fat-based
– Are either only partially digestible or
completely undigestible to prevent
absorption of fat
– Caprenin (substitute for cocoa butter in
candy), Salatrim (found in low fat baking
chips), and olestra (often found in fat free
potato chips)
C. At the Grocery Store

Read labels to
determine both
the amounts &
types of fat
contained in
foods
D. In the Kitchen

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Use canola & olive oil for
baking & cooking
Prepare lean cuts of meat
Bake, boil & steam instead of
frying
Use low-fat or fat-free dairy
products & dressings
Season with herbs & spices
rather than with fats
Incorporate plant-based
protein sources such as soy
& legumes
E. At the Table

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Eat more fresh fruits &
vegetables
Use jam instead of butter
Limit use of high-fat
condiments including mayo,
butter & sour cream or use
low-fat varieties
Use mostly
monounsaturated vegetable
oils such as olive or canola
Eat fewer high-fat desserts
F. Recipe Modification
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Egg whites
Fat-free evaporated
milk
Fat-free sour cream
Fruit purees
Fat-free cream
cheese
Oils
IX. Diet & Heart Disease
A.
Risk Factors

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High cholesterol
High blood pressure
Smoking
Diabetes
Lack of exercise
Stress
Obesity
Unhealthy diet
Age
Gender
Genetics
B.
Ways to Reduce Risk
 Limit intake of cholesterol
& saturated fat
 Quit smoking
 Maintain a healthy weight
 Eat high fiber foods
 Increase physical activity
 Increase fruit & vegetable
consumption
 Limit alcohol
consumption