Chapter 15: Fats and Oils

The Triglycerides We Eat

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Courtesy PhotoDisc Inc./Getty Images

Figure 15.1: The effect of polyunsaturation.

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Courtesy Ken Karp

Fats (solid triglycerides) and an oil (a liquid triglyceride).

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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.

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Figure 15.7: Geometric isomers.

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Figure 15.8: cis-2-Butene (left) and trans-2-butene (right).

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Courtesy Michael Pique, The Scripps Research Institute, CA

Figure 15.9: Molecular packing in glyceryl tristearate and glyceryl trioleate.

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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.

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Figure 15.3: Fatty acid content of fats and oils (typical percentages).

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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.

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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.

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Courtesy Andy Washnik

Figure 15.4: Cholesterol.

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Figure 15.5: The core molecular structure of a steroid.

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Plant products, including vegetables and vegetable oils, are all free of cholesterol.

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Courtesy Ken Karp

The body stores energy as the triglycerides of fat or adipose tissue.

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Courtesy Jerry Ohlinger’s

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Does catalytic hydrogenation tend to convert fats to oils or oils to fats?

QUESTION

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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

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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

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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

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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

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Why does the hydrogenation of a polyunsaturated triglyceride raise its melting point?

QUESTION

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Considering the Perspective as the terminal section of this chapter, what omega designation would you give to this current section?

QUESTION

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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