Lecture 2 - Chemistry of Food (Lipids)

Polar molecules are:

Hydrophilic and have a dipole

Why are Lipids hydrophobic?

Even though they contain a polar carboxylic acid group, they have a long carbon chain

A hydrophilic molecule:

Has a dipole, electronegativity difference, and possibly has charges

Why do polar/hydrophilic molecules dissolve in water?

Water is polar, and “like dissolves like”

What is a functional group?

A group on a molecule that is responsible for giving a molecule certain properties

4 Categories of Lipids:

1. Triglycerides

2. Phospholipids

3. Steroids

4. Waxes

Do lipids dissolve in water?

No, because they are hydrophobic

What are the building blocks of lipids?

Fatty acids; they are monomers that form lipids (responsible for lipid properties)

Most fatty acids are insoluble in water except…

Short chain fatty acids

Saturated Fatty Acid Structure

Contain no double bonds; most hydrogens as possible

Unsaturated Fatty Acid Structure

Contain at least 1 double bond; can be cis or trans

Which fatty acid is solid at room temp?

Saturated Fatty Acids

Which fatty acid is liquid at room temp?

Unsaturated fatty acids

Melting Points of Fatty Acids

• Unsaturated Lower (Liquids at Room Temp)

• Saturated Higher (Solids at Room Temp)

Solidification Points of Fatty Acids

• Unsaturated higher (Liquids at Room Temp)

• Saturated lower (Solids at Room Temp)

Cis-unsaturated Fatty Acids

Hydrogens on SAME side of double bond; found in nature

Trans-unsaturated Fatty Acids

Hydrogens on OPPOSITE side of double bond; Synthetic, unhealthy effects on cholesterol metabolism

Esterification

Glycerol (Alcohol) + 3 Fatty Acid → Triglyceride + 3H2O

-OH + 3 -COOH → Triglyceride + 3H2O

How are esters named?

-ate ending (-COOR)

Hydrogenation

Unsaturated Fatty Acid + H₂ → Saturated Fatty Acid

Butter to margarine

Interesterification Types

Chemical or Enzymatic

Both replace one ester group with another

Chemical Interesterification

Unspecific, using a chemical catalyst

Enzymatic Interesterification

Use of enzymes to produce specific esters

Trigylceride Structure

Glycerol backbone with 3 long-chain fatty acids

Glycerol Structure

3 carbons, each attached to an -OH group

Delta End of Fatty Acid

Carboxylic Acid end

Delta Naming System

Count number of carbons (including carboxyl), count double bonds, delta symbol, and positions of double bonds

EXAMPLE: 18:3Δ9,12,15

18 carbons, 3 double bonds at positions 9, 12, 15

Omega End of Fatty Acid

Opposite side to carboxylic acid

Omega Naming System

Number of carbons, number of double bonds, only 1 position listed

EXAMPLE: 20:5ω-3 (20:5Δ5,8,11,14,17)

Why are saturated fats and trans-unsaturated fats worse for health?

They stack better, so they have a better chance clogging arteries by building up and interfering with cholesterol metabolism (hardening arteries)

Mono vs. Di vs. Triglycerides

1 vs. 2 vs. 3 fatty acids attached to the glycerol backbone

Fats vs. Oils

• Fats are solid; Oils are liquids

• Fats are saturated; Oils are unsaturated

• Fats in animals/tropical plants; Oils are in plants ONLY

• Fats have high melting point; Oils have low melting point

• Fats have high solidification point; Oils have low solidification

• Fats have cholesterol; Oils have phytosterol

Phospholipid Structure

Polar head with non-polar tails, glycerol and phosphate backbone

Important Features of Phospholipids

Amphipathic (both nonpolar/polar properties); found in cell membrane

Steroids/Sterols Structure

4 rings, either 6 or 5 carbons, making them all hydrophobic

Types of Sterols

Cholesterol in animals, phytosterols in plants

Importance of Sterols/Steroids

• Sex hormones

  • Signaling molecules acting in another area of body (androgens)

• Cholesterol

  • Determines rigidity/flexibility important to cell membrane structure, but harmful in high amounts (harden artery)

• Bile Salts

• Vitamin D Synthesis

Waxes

Esters made from long chain fatty acids + alcohol (Esterification)

-COOH + -OH → Wax

Dietary Sources of Lipids

• Milkfats

• Lauric Acids

• Vegetable Butters

• Oleic and Linoleic Acids

• Linolenic Acid

• Animal fats

• Marine oils

Milkfats

Short chain fatty acids from cows, sheep, goats

Lauric Acids

Found in oils of tropical plants; saturated fats because tropical

Vegetable Butters

From tropical plant seeds (cocoa butter); saturated due to tropical origin

Oleic and Linoleic Acids

Corn oil, olive oil, cottonseed oil, etc.

Linolenic Acid

Omega-3 acids, soybean oil, flax/linseed oils; from plants

Animal Fats

Saturated fats consumed from meats and poultry products

Marine Oils

Long-chain PUFA (polyunsaturated), omega-3, EPA and DHA

MUST KNOW about tropical plants

Produce saturated fats more often; other plants often produce UFA

Ways Fatty Acids Deteriorate

1. Auto-oxidation (Oxygen)

2. Hydrolysis (Add water)

Rancidity

Producing wrong flavor or smell due to deterioration

Auto-oxidation

Oxygen taking electron from double bond, DNA, or cell membrane
(Often double bond, but mutation or instability CAN occur)

Hydrolysis

Release of carboxyl group after addition of water (acting as enzyme)

Optimal Storage for Lipids

• Cool, dry, and dark place to decrease rate of reaction

• Antioxidants

  • Give oxygen an electron so it doesn’t take from double bond

    • Vitamins C and E