Food Chemistry Chapter 17 in Green / Damjii

F.2: FATS AND OILS

• Read F2 – Fats and Oils - pp. 476-477• Do Q 7-11• on p 491

Homework

F.2: Fats and Oils• F.2.1: Describe the difference in structure

between saturated and unsaturated (mono- and poly-unsaturated) fatty acids

Remember… 3 molecules of fatty acids react with 1 molecules of glycerol to form a lipid

F.2: Fats and Oils• F.2.2: Predict the degree of crystallization

(solidification) and melting point of fats and oils from their structure, and explain the relevance of this property in the home and in industry.

F.2: Fats and Oils• Melting point and hardness (degree of

crystallization) depend on– Length of hydrocarbon chain

• Longer chain = greater molar mass = more vdW forces = higher mp

– Degree of unsaturation• More double bonds = crooked chains = less contact =

fewer vdW forces = lower mp

– Cis or trans conformation• more cis = more crooked chains = less contact = fewer

vdW forces = lower mp• more trans = less crooked chains = more contact = more

vdW forces (compared to cis) = higher mp

Triglycerides• SATURATED (no double or triple bonds)– Tend to be SOLIDS at room temperature– Tend to come from animal products– “Fat”– Examples:• Coconut oil• Butter • lard

Triglycerides• Unsaturated (has one double or triple bond)

– Tend to be LIQUIDS at room temperature– Tend to come from plant material– “Oil”– Examples

• Olive oil• Canola oil• Peanut oil

• Polyunsaturated (has multiple double or triple bonds)– Example

• Sunflower oil• Corn oil• Fish oil

F.2: Fats and Oils• F.2.3: Deduce the stability of fats and oils

from their structure.• Unsaturated– More reactive, less stable– C=C double bond reacts with oxygen (auto-

oxidation)• Especially in sunlight (photo-oxidation)• Margarine gets discolored

– Hydrogenation– Degradation by microbes

F.2: Fats and Oils

• F.2.4: Describe the process of hydrogenation of unsaturated fats.

Hydrogenation• Addition of hydrogen– Hydrogen @ high pressure– Temp ~ 200 C– Nickel catalyst

F.2: Fats and OilsF.2.5: Discuss the advantage and disadvantages

of hydrogenating fats and oils. • A hydrogenated product is

– more saturated… or fully saturated…– semi-solid or solid…

• Advantages of a hydrogenated product is– Form is more convenient for some cooking

techniques– More stable (rate of oxidation is decreased)– Texture can be controlled ( hardness / plasticity)

can be controlled

F.2: Fats and OilsDisadvantages: …. health related• Mono- and poly-unsaturated are healthier for

the heart than saturated fat.• Partial hydrogenation can form trans-fats– trans-fats don’t occur naturally – difficult to

metabolize– accumulate in fatty tissues of body– Increase levels of LDL chloesterol (associated with

atherosclerosis… strokes… heart problems)

What is this?

Olestra – a fat substitute that isnot digested by the body

Copyright © 1997 by Daniel J. Berger.

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