Lipids

Question 1

When is a lipid saponifiable?

Answer 1

If it has an ester group.

Question 2

Which two components are waxes made of?

Answer 2

FAs and alcohols

Question 3

Which two components are sterol esters made of?

Answer 3

FA and sterols

Question 4

Which three components are phospholipids made of?

Answer 4

Glycerol, FA, and phosphoric acid

Question 5

Which three components are glycolipids made of?

Answer 5

Glycerol, FA, and saccharides

Question 6

What is a 1,4-pentadiene segment?

Answer 6

It is a segment in a FA where five (penta-) carbon atoms are sequentially bonded, by two double (di-) bonds are divided by two single bonds.

Question 7

Why are trans fats less preferred?

Answer 7

They can lead to high cholesterol levels in the blood, which may lead to cardiovascular diseases.

Question 8

What is a furane FA?

Answer 8

A FA with a furane ring.

Question 9

What is an oxy FA?

Answer 9

FA with a double bonded oxygen atom in the C-chain

Question 10

Explain short notations of FA (Delta, Omega, c, t)

Answer 10

• Number of carbon atoms in the chain
• Number of double bonds in the chain
• Delta + number indicates the location of the first double bond counting from the carboxyl side
• Omega + number indicates the location of the first double bond counting from the non-carboxylic side (sometimes noted as n)

Question 11

What is the most prevalent FA in cow/beef fat?

Answer 11

C18:1

Question 12

What is the most prevalent FA in coconut oil?

Answer 12

C12:0

Question 13

What is the difference in FA composition between fish oil and coconut oil?

Answer 13

Fish oil has more long-chain-(poly-)unsaturated FA whereas coconut oil has more shorter-chain-saturated FA.

Question 14

How can you distinguish a carotenoid? And what are its properties?

Answer 14

It is a highly unsaturated FA with a large conjugated system. This creates a yellow to red colour and it has anti-oxidant activity.

Question 15

What does a tocopherol look like?

Answer 15

It is synthesized from 5-carbon precursor molecules; it has an extra methyl group attached every fifth C atom. It also has a double ring structure as an R-group.

Question 16

How can you recognize sterols?

Answer 16

R-group with four adjacent rings, one of which has five c-atoms, the rest has six c-atoms.

Question 17

Rank TAGs with three uniform FA from lowest to highest melting point:
- 12:O
- 12:1
- 14:O
- 10:O

Answer 17

Lowest
1) 12:1
2) 10:O
3) 12:O
4) 14:O
Highest

Question 18

What is the difference between photo-oxidation type I and type II?

Answer 18

First, light reacts with a Sensitizer, hereby activating it.

In type I, this then directly reacts with the substrate, forming an alkyl radical. This will subsequently follow normal autoxidation reaction.

In type II, the activated sensitizer activates oxygen, causing the formation of singlet O2. This reacts with the double bond of the substrate, hereby shifting it. Consequently, the hydroperoxides formed are different from those of autoxidation. The number of different hydroperoxides formed is twice the number of double bonds.

Question 19

What is beta-scission?

Answer 19

After the formation of primary reaction products (hydroperoxides) the alkoxyl group is split off. This usually occurs at the single bond between the alkoxyl group and the double bond.

Question 20

What is the difference between primary and secondary reaction products with regard to flavour and taste?

Answer 20

Primary reaction products are odourless and tasteless, whereas secondary reaction products are volatile carbonyl compounds which contribute significantly to the smell and taste of a product.

Question 21

Why is the fat-oxidation rate higher at low temperatures (equal but low pO2)?

Answer 21

At low temperatures, the solubility of oxygen is higher.

Question 22

Is the fat-oxidation rate higher at high or at low temperature (equal but high pO2)?

Answer 22

At high temperatures. Fat oxidation increases with temperature as reactions proceed faster at higher temperatures.

Question 23

At which aw does fat-oxidation occur fastest?

Answer 23

At very low aw < 0.2 fat-oxidation occurs extremely fast due to:
- Metal ions are no longer surrounded by a water jacket and are directly available to catalyse fat-oxidation.
- Less hydrogen bonds between water and hydroperoxides exist.
- Oxygen migrates better into the fat

At aw 0.2 - 0.4 minimal fat oxidation.

At aw > 0.4: oxidation increases again because the catalysts are more mobile in water.

Question 24

Which reactions take place during deep-frying? What are the compounds that are formed? Also indicate which compounds are formed because of the food present.

Answer 24

1) Oxidation –> Volatile acids, esters, aldehydes, alcohols
2) Isomerization –> Epoxides.
3) Dimerization –> Branched FA, dimers.
4) Polymerization –> Mono- and dbicyclic compounds formed of trans double bonds, Hydrogen, CO2.

Addition of food:
5) Hydrolysis –> Free FA, mono/diglycerides, glycerol.

Question 25

What are the effects of the reactions taking place in deep-frying?

Answer 25

Increase of:
- Viscosity
- Refractive index
- Acid value
- Foaming
- Brown colouring

Decrease of:
- Iodine value
- Aroma and flavour.