Week 3 Triglycerides

Question 1

Revision of structure

Answer 1

Mono - 1 Fatty acid
Di - 2 FA
Tri - 3 FA

Glycerol + FA –> Mono/di/triglyceride

If R1, R2, R3 = same, then simple
If more than two R groups are different (different FA’s) = mixed

• Crystallization of Triglycerides can show there are many different TG’s present
• TG’s are simple but huge capacity for variation

Question 2

TG’s Melting point

Answer 2

• Varies considerably & influences its use
• TG’s with high MP’s = solid at room temp = fats (margarine)
• TG’s with low MP’s = liquid at room temp = oils
• Properties of the TG’s is what contributes properties of lipid rich foods
• TG MP depends on fatty acids and crystal structure (polymorphism)

Question 3

Source of TG’s and their nature

Answer 3

1. Milk: Short-chain FAs and trans FAs - branched and odd-numbered FAs
2. Vegetable oil & fat:
   i) Seed oil - Low saturated FAs
   ii) Vegetable fats - High saturated, no fully saturated TG’s
3. Animal fat (lard): Fully saturated TG’s, some saturated FAs
4. Marine oils: Low saturated FAs, but high long-chain PUFAs

Question 4

Factors affecting FA/ TG melting point

Answer 4

1. Melting point
   Melting fatty acids from solid to liquid occurs when intermolecular bonds are broken by heat energy
2. Longer chain length (more carbons) = higher melting point. More energy required to break down
3. Unsaturated = lower melting point because of C=C double bonds
   i) Trans bond = slight kink = lower intermolecular bonds, less energy required to melt
   ii) Cis bond= = big kink = even lower bonds so even less energy required to melt
4. Crystallisation of fats. TG’s polymorphic so have more than 1 crystal form..

Question 5

The crystallisation of fats - polymorphic states

Answer 5

3 polymorphic states:

α
Formed by rapid cooling, low melting range and least stable. Fragile platelets

β’
Formed my medium cooling, medium melting range and mid stability. Small needle-like crystals

β
Formed by slow cooling, high melting range and most stable. Large coarse crystals

Question 6

Polymorphism affects on lipids

Answer 6

α - limited food application

β’ - small needle-like crystals. Form soft plastic fats used in margarine

β - large crystals giving grainy texture. Used in cocoa butter/ lard

Question 7

Tempering —> Chocolate

Answer 7

Controlled crystallisation method to prepare food with desired polymorphic state of a lipid. Last stage of process

Cocoa butter gives chocolate smooth/glossy/ melt in mouth textures

Cocoa butter has 6 polymorphic states but only type V has desired properties. Type V = a β-3 mp 33.8C/ 34C

Type V results: Glossy, firm, best snap, melts near body temperature (37 °C)

Question 8

Art of chocolate

Answer 8

1. Liquid cooled to crystallisation state
2. Reheated to 32C and held, melts out unwanted crystals
3. Stir at 32C, allow the formation of small Beta 3 crystals and then solidify