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CHE2810 - Food Chemistry > Lipids > Flashcards

Flashcards in Lipids Deck (49)
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1

What is a lipid?

It is a substance that is soluble in non-polar solvents.

2

What are some naturally occurring lipids?

Waxes, Fats, Sterols and some Vitamins (A, B, E and K)

3

What are the two general categories of lipids in food?

Oils, being liquid lipids
Fats, being solid Lipids

4

What qualities of food do lipids effect?

Texture, Flavour, Stability, Nutrition and Available Energy.

5

What is the major component of lipids?

Lipids are typically consist of fatty acids, which are long carbon chains consisting between 14 - 24 carbon count (14 - 24, always even). Fatty acids have a carboxylic group on the end of the chain.

6

What is the difference between a saturated and unsaturated fat?

A saturated fat consists of no double/triple bonds as it has bonded with hydrogen as much as feasibly possible.
An unsaturated fat consists of at least one double, and is therefor possible to undergo hydrogenation.

7

In terms of fatty acid structure forming, what effect does a double carbon bond cause?

A naturally occurring formation of a carbon bond causes an interruption of bond rotation, as there is a preference to form the bond on the 'same side.' This would be known as a -cis structure.

8

What is a -trans structure?

If in a carbon chain a double bond forms whilst maintaining the bond rotation a -trans structure is formed. This formation is typically unfavourable and generally unnatural.

9

In consumption, what is the difference between a cis-fat and a trans-fat?

The human body is capable of metabolising cis-fats, however ill-suited to metabolise trans-fats. The consumption of trans-fats can cause a build in systems such as the eyes.

10

How does a cis-bond react to temperature and density?

A cis-bond causes a lower melting point, such as in margarine. In some products a cis-bond will be hydrogenised in order to raise the melting point of a product.
A cis-bond will also decrease density.

11

How do we name a fatty acid?

The prefix- is the IUPAC name for the carbon count
The -body- is defined by amount of double bonds (0 = an , 1 = en, 2 = dien)
the -Suffix is 'oic' acid as fatty acids contain a carboxylic functional group.

12

There are two ways to number count carbons in a chain, what are they?

You have the delta method, which counts from the carboxylic group.
There is a omega method which counts from the methyl group on the other end.

13

What is cyto-toxicity

it is a substance that is toxic to cells.

14

How are fatty acids typically found in animals?

As free fatty acids are typically cytotoxic, the are esterified with glycerol to decrease toxicity and create a unit for energy storage.

15

What is triacylglycerol?

It is a glycerol unit that has esterified with with three free fatty acids (same or different) to create a stable energy unit.

16

How does the climate effect the production of Fatty Acids?

A colder climate will allow for more unsaturated fats to be produced, as there is no need for the higher melting point you would get from saturated fats.
A warmer climate will produce more saturated fats to prevent the liquification of fatty acids in the body.

17

What is the smoke point?

The smoke point is the temperature that fats start to decompose. This gives of volatile products that have been broken down.

18

What is a volatile?

It is a product that readily evaporates under normal conditions.

19

What is a flash point and a fire point?

The flash point is where enough volatiles from the decomposition are produced from heat that it causes an unsustainable combustion.
The fire point is where the volatiles produced can create a sustained combustion

20

What does a sharp melting point for solid fats suggest?

That there is little to no variety in the Solid fat content. This causes all the solid fats to melt at the same temperature and therefor create a sharp decline on a solid:liquid comparison.

21

What is the 'plastic range?'

The plastic range is the temperature range that a mixture of solid fats will melt across, the intermediate mixture of liquids and fats will act 'plastic like'

22

What does SFC represent?

It is the solid fat content which characterises the percentage of solid fats to liquid fats. This defines the melting point.

23

Why is the SFC vs Temperature profile important?

It provides important information for selecting the appropriate material for a product. It can predict whether a product will have good spreadability, meltability, taste and etc.

24

What are the stages of Fat crystallisation?

Supercooling, nucleation, crystal growth and post-crystallisation events.

25

What is the supercooling stage?

Even though the temperature is favourable to form solid fats, time is necessary for the reorganisation of the TAG's. With time the initial crystals can begin to form.

26

What is the nucleation stage?

To have crystal growth a stable nuclei (initial crystal) has to be formed in the liquid. Nucleation getting the nuclei to its critical size so that it becomes stable and allows for crystallisation.

27

What is the difference between homogeneous and heterogeneous nucleation?

Homogeneous nucleation has to interference from outside sources, whereas heterogeneous nucleation does. This interference may include dust, bubbles and other foreign particles.

28

What is the effects of freezing fast versus freezing slowly?

Freezing slow will create a solid well structured crystalline formation, whereas freezing fast does not allow for optimum crystallisation and causes a more random (amorphous) structure.

29

What factors affect the rate of crystal growth?

Viscosity, Thermal conductivity, crystal morphology and degree of agitation.

30

What is the relationship between the 'growth rate vs temperature' and 'nucleation vs temperature'?

If growth rate is higher then nucleation rate, there will be fewer crystals but they will be larger. If the nucleation rate is higher then growth rate, there will be more crystals of a smaller size.

31

What Post-crystallisation physical changes are there?

There is packing, size, composition and interaction

32

What is Ostwald ripening?

This is where large crystals grow at the expense of smaller crystals. This normally occurs closer the melting point of a fat, where there is a small fluctuation between liquid and solid.

33

What is an emulsion?

An emulsion is a mixture of liquids that under normal circumstances are immiscible (unmixable)

34

What is the difference between the dispersed phase and the continuous(bulk) phase?

The dispersed phase is the liquid that is dispersed throughout the continuous phase

35

What is a emulsifier?

It is a substance that consists of both a hydrophillic (polar) and lipophillic(non-polar) part allowing to stabilise a emulsion.

36

Why does water negatively effect TAG's in food products?

It is the hydrolysis of TAG with water, the introduction of water breaks the ester linkage between the fatty acids and glycerol.

37

Why are free fatty acids bad to have in food?

Because they produce off flavours, reduce stability, cause foaming and reduce the smoke point.

38

What is 'lipase' main function

Lipase is the protein responsible for breaking down TAG into glycerol and free fatty acids in organisms.

39

What is ROS?

They are Reactive Oxygen Species, such as hydroxylradical (HO), Hydrogen peroxide (HOOH) and super oxide O2-

40

How does oxidative processes degrade TAG?

The free radicals from ROS will react the fatty chains to create smaller volatile molecules which cause off flavours and aromas.

41

What are the three steps of the fatty acid oxidation?

1) Initiation
2) Propagation
3) Terminiation.

42

What is the Initiation step in fatty acid oxidation?

The free radical is transferred from the ROS to the short fatty acid chain (unsaturated position), removing a hydrogen.

43

What is the Propagation step in fatty acid oxidation?

An Oxygen molecule will react with the carbon free radical on the fatty acid. This causes a Lipid-O2 bond.
The 2nd oxygen takes the radical which creates a peroxyl radical. Peroxyl radicals are high energy and can propagate a domino effect by abstracting other TAG hydrogens.

44

What is the Termination step in fatty acid oxidation?

This is where two of the radicals bond together to stabilise, preventing further oxidation.

45

What is an anti-oxidant?

It is a substance that improves the oxidative stability of food.

46

What are some methods that anti-oxidants can prevent oxidation?

It may control the free radical formation.
It could interfere with the actions of peroxidants
It may destroy oxidation intermediates.

47

What is a Free Radical Scavenger?

They are antioxidants that will react faster with free radicals, then the free radicals will with the unsaturated fats.

48

What are Phospholipids?

They are a modification of TAGs, where a phosphate group replaces one of the ends of fatty acid groups.
They are a major compound of cell membranes and can act as a surfactant.

49

What are Sterols?

A sterol is a subgroup of natural steroids.
Cholestrol is a common one in animals
Stigmasterol and Sitosterol are common in plants