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Chapter 15: Fats and Oils
The Triglycerides We Eat
© 2003 John Wiley and Sons Publishers
Courtesy PhotoDisc Inc./Getty Images
Figure 15.1: The effect of polyunsaturation.
© 2003 John Wiley and Sons Publishers
Courtesy Ken Karp
Fats (solid triglycerides) and an oil (a liquid triglyceride).
© 2003 John Wiley and Sons Publishers
Courtesy Ken Karp
18.1 Lipids18.2 Fatty Acids
Chapter 18 Lipids
Lipids
Lipids are:• Biomolecules that contain fatty acids or a
steroid nucleus.• Soluble in organic solvents, but not in
water.• Named for the Greek word lipos, which
means “fat.”• Extracted from cells using organic solvents.
Classes of Lipids
Fatty acids are:• Long-chain carboxylic acids that have an even
number (usually 12-18) of carbon atoms. • Insoluble in water.• Saturated or unsaturated.
Fatty Acids
Fatty Acid Formulas
• The formulas for fatty acids are written as condensed and line-bond formulas. For example caprylic acid with 8 carbon atoms can be written as:
CH3—(CH2)6—COOH
CH3—CH2—CH2—CH2—CH2—CH2—CH2—COOH O
||CH3—CH2—CH2—CH2—CH2—CH2—CH2—C—OH
OH
O
Saturated Fatty Acids
Saturated fatty acids have single C–C bonds.
Review
Saturated fatty acids have:• Molecules that fit closely
together in a regular pattern.• Strong attractions between
fatty acid chains.• High melting points that
makes them solids at room temperature.
Saturated Fatty Acids
Unsaturated Fatty Acids
• Unsaturated fatty acids typically contain cis double bonds.
Unsaturated Fatty Acids
Unsaturated fatty acids have cis C=C bonds.
Figure 15.6: Planarity and the carbon—carbon double bond. The two carbons and atoms W, X, Y, and Z, all lie in the same plane.
© 2003 John Wiley and Sons Publishers
Figure 15.7: Geometric isomers.
© 2003 John Wiley and Sons Publishers
Figure 15.8: cis-2-Butene (left) and trans-2-butene (right).
© 2003 John Wiley and Sons Publishers
Courtesy Michael Pique, The Scripps Research Institute, CA
Figure 15.9: Molecular packing in glyceryl tristearate and glyceryl trioleate.
© 2003 John Wiley and Sons Publishers
Unsaturated fatty acids:• Have nonlinear
chains that do not allow molecules to pack closely.
• Have low melting points.
• Are liquids at room temperature.
Unsaturated Fatty Acids
Assign the melting points –17°C, 13°C, and 69°C to the following 18 C fatty acids. Explain.
Stearic acid saturated
Oleic acid one double bond
Linoleic acid two double bonds
Learning Check
stearic acid mp 69°Coleic acid mp 13°C
linoleic acid mp -17°C
Stearic acid is saturated and would have a higher melting point than the unsaturated fatty acids. Because linoleic acid has two double bonds, it would have a lower mp than oleic acid, which has one double bond.
Solution
Olive Oil
• Olive oil contains a high percentage of oleic acid.
• Oleic acid is a monounsaturated fatty acid with one cis double bond.
Figure 15.2: The general structure of a triglyceride. R, R’ and R” represent the long, fatty acid side chains.
© 2003 John Wiley and Sons Publishers
Figure 15.3: Fatty acid content of fats and oils (typical percentages).
© 2003 John Wiley and Sons Publishers
Omega-6 and Omega-3 Fatty Acids
The first double bond:• In vegetable oils is at carbon 6 (omega-6).• In fish oils is at carbon 3 (omega-3).
Learning Check
Write a fatty acid with 10 carbon atoms that is:
A. Saturated
B. Monounsaturated omega-3
C. Monounsaturated omega-6
Solution
Write a fatty acid with 10 carbon atoms that is:A. Saturated CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—CH2—COOH
B. Monounsaturated omega-3CH3—CH2—CH=CH—CH2—CH2—CH2—CH2—CH2—COOH
C. Monounsaturated omega-6CH3—CH2—CH2—CH2—CH2—CH=CH—CH2—CH2—COOH
Partial hydrogenation of vegetable oils produces a mixture of triglycerides that soften and melt near body temperature.
© 2003 John Wiley and Sons Publishers
Courtesy Marti Pie/The Image Bank
Steroids are: • Lipids containing the
steroid nucleus, which is a fused structure of four rings.
• Found in cholesterol, bile salts, hormones, and vitamin D.
Steroids
Steroid nucleus
Estrogen: Female sex hormone
Fertilized egg can grow
breast make milk
Cortisol : maintain
blood pressure, immune function
anti-inflammatory
burst of energyregulator of the salt and water balance
Cholesterol is:• The most abundant steroid in the body.• Composed of the steroid nucleus with methyl
CH3– groups, an alkyl chain, and a hydroxyl group –OH attached.
Cholesterol
CH3
HO
CH3
CH3 CH3
CH3
Cholesterol in Foods
Cholesterol: • Is considered
elevated if plasma cholesterol exceeds 200-220 mg/dL.
• Is synthesized in the liver and obtained from foods.
Types of Lipoproteins
Lipoproteins:• Differ in density, composition, and function.• Include low-density lipoprotein (LDLs) and
high-density lipoprotein (HDLs).
Transport of Lipoproteins in the Body
Chilomicrons
Bile Salts
Bile salts:• Are synthesized from cholesterol and stored in the
gall bladder.• Emulsify fats and oils to give a greater surface area
for lipid digesting enzymes.
CH3
HO
CH3
CH3OH
C
O
N
H
CH2COO- Na+
OH
glycine, an amino acid
cholic acid, a bile acid
sodium glycocholate, a bile salt
Steroid Hormones
Steroid hormones:• Are produced from
cholesterol. • Include sex hormones
such as androgens (testosterone) in males and estrogens (estradiol) in females.
Anabolic Steroids
Anabolic steroids: • Are derivatives of testosterone.• Are used illegally to increase muscle mass.• Have side effects including fluid retention, hair
growth, sleep disturbance, and liver damage.
Cholesterol: a sterol that contributes to cardiovascular disease.
© 2003 John Wiley and Sons Publishers
Courtesy Andy Washnik
Figure 15.4: Cholesterol.
© 2003 John Wiley and Sons Publishers
Figure 15.5: The core molecular structure of a steroid.
© 2003 John Wiley and Sons Publishers
Plant products, including vegetables and vegetable oils, are all free of cholesterol.
© 2003 John Wiley and Sons Publishers
Courtesy Ken Karp
The body stores energy as the triglycerides of fat or adipose tissue.
© 2003 John Wiley and Sons Publishers
Courtesy Jerry Ohlinger’s
© 2003 John Wiley and Sons Publishers
Does catalytic hydrogenation tend to convert fats to oils or oils to fats?
QUESTION
© 2003 John Wiley and Sons Publishers
Of the fats and oils of Table 15.2, which contains the most highly saturated side chains? Which contains the most highly unsaturated side chains?
QUESTION
© 2003 John Wiley and Sons Publishers
Which of the following triglycerides would you expect to be least useful in the manufacture of a chocolate candy bar: (a) glyceryl trilinoleate; (b) glyceryl tripalmitate; (c) glyceryl trioleate? Explain. (You may find it useful to refer to Table 15.1)
QUESTION
© 2003 John Wiley and Sons Publishers
Give two reasons why switching from a diet rich in red meat and animal products to one with plenty of fruits, vegetables, and other plant products might help lower serum cholesterol.
QUESTION
© 2003 John Wiley and Sons Publishers
You are a manufacturer of varnishes that have drying oils as major ingredients. One of your laboratory chemists suggests that you add an antioxidant to the varnishes to improve their shelf life. How would you respond to this suggestion? Explain.
QUESTION
© 2003 John Wiley and Sons Publishers
Why does the hydrogenation of a polyunsaturated triglyceride raise its melting point?
QUESTION
© 2003 John Wiley and Sons Publishers
Considering the Perspective as the terminal section of this chapter, what omega designation would you give to this current section?
QUESTION
© 2003 John Wiley and Sons Publishers
Suppose you’re 15 pounds overweight. That is, you are carrying around, at all times, an excess of 15 pounds of adipose tissue. Translate this into the equivalent number of excess stored Calories you are carrying with you at all times.
QUESTION