2.3.Functional properties of fat in foods

Question 1

Describe the structure of fats?

Answer 1

-lipids
- made from triglycerides (glycerol and three fatty acids)

Question 2

chemical structure of fats?

Answer 2

ON rc

Question 3

Examples of plant based fats and oils

Answer 3

-Oils (e.g. olive, sunflower, corn, sesame)
-Nuts (e.g. walnuts, peanuts) which can also be refined into oils
-Avocado
-Margarine made from plant based oils

Question 4

Examples of animal based fats and oils

Answer 4

Meat (e.g. bacon, steak,
Dairy foods (e.g. milk, cream, cheese, butter)
Lard & suet
Margarine made from animal based fats

Question 5

what is emulsification?

Answer 5

the process of dispersing two or more immiscible liquids together to form a semistable mixture.
eg.fat and water

Question 6

how does an emulsifier help create a stable emulsion

Answer 6

is attracted to both fat and water as it has a hydrophobic (water-hating) and hydrophilic (water-loving) part.

Question 7

what are the 3 parts of an emulsion?

Answer 7

Disperse phase
Continuous phase
Emulsifier

Question 8

Describe how emulsions work?

Answer 8

-An emulsion is a dispersed phase suspended in a continuous phase.
-In an oil-in-water emulsion, the continuous phase is the water and the dispersed phase is the oil
- in a water-in-oil emulsion the oil is the continuous phase.
-The emulsifier prevents joining of the dispersed phase and continuous phase droplets.

Question 9

Examples of emulsifiers?

Answer 9

-can be both natural and synthetic.
-Lecithin is a natural occuring phospholipid refined from soybean oil, used in the food industry for oil in water emulsions.
-Egg yolk contains two emulsifiers: lecithin, for promoting oil in water emulsions, and cholesterol, for promoting water in oil emulsions.

Question 10

What factors can affect emulsification?

Answer 10

temperature, agitation and the addition of salt.

Question 11

how can temperature affect emulsification?

Answer 11

-High temperatures make it harder for emulsifiers to hold the lipids and water together.
-The low temperatures of freezing changes the state of water and oil: the emulsifiers connections which hold water and lipids together are broken by crystallization. When the product defrosts the oil and water separate.

Question 12

How can agitation affect emulsification?

Answer 12

-when adding oil, to form an emulsification of oil and water, the mixture should be beaten while adding the oil slowly.
-overbeating can break the connections between the emulsifier and the oil and therefore destroy the emulsion.

Question 13

How can the addition of salt affect emulsification?

Answer 13

can cause water to separate and move towards the salt because there is a stronger chemical attraction between water and salt, than water and the emulsifier.

Question 14

give examples of food and their emulsions?

Answer 14

Milk- oil in water
margarine- water in oil
ice cream- oil and air in water with solid ice particles
mayonaise/ salad dressings- oil in water
Béarnaise and Hollandaise sauces- oil in water

Question 15

What is homogenisation and when is it used?

Answer 15

the process where the fat droplets from milk are emulsified and the cream does not separate.
-used in the production of milk (whole fat and semi skimmed milk) but is not required for skimmed milk because there is no fat present and so homogenisation is not required.

Question 16

how does homogenisation help emulsification

Answer 16

because fat globules are reduced in size to make smaller globules that are evenly distributed.

Question 17

What is hydrogenation and when is it used?

Answer 17

-used to harden unsaturated vegetable oils
-involves the addition of hydrogen to the carbon double bond of a fatty acid in the presence of heat (60ºC), pressure and a nickel catalyst.
-The double bonds of the unsaturated fat are converted to single bonds in the reaction. In this way unsaturated fats can be made into saturated fats – they are hardened.

Question 18

what is does a catalyst do

Answer 18

speeds up the rate of a reaction without being consumed during the process.

Question 19

why do saturated vegetable fats not need to undergo hydrogenation

Answer 19

-have a higher melting point than unsaturated fats and are solid at room temperature.
-This makes saturated fats suitable for the production of margarine, and for commercial production of cakes and pastry.

Question 20

Advantages of hydrogenation?

Answer 20

-A liquid oil is changed to a semi-solid or solid because the melting point of an unsaturated fat more becomes more like that of a saturated fat.
-The rate of oxidation decreases (stability increases with increasing saturation)
-Increases hardness and plasticity .

Question 21

disadvantages of hydrogenation

Answer 21

-Monounsaturated and polyunsaturated fats are healthier for the heart than saturated fats
-Trans fatty acids can form which are hard to metabolize, accumulate in fatty tissue, are difficult to excrete from the body,
-Increase levels of LDL (bad) cholesterol and are a low-quality energy source

Question 22

What is aeration?

Answer 22

-involves adding air to a mixture and results in a change in the texture of a food product.
-The plasticity of saturated fat (e.g. butter) is more effective at aerating mixtures than using an unsaturated fat (e.g. olive oil, sunflower oil).

Question 23

methods of aeration?

Answer 23

-creaming method
-rubbing in
-layering fat in pastry
-whipping cream
-foams

Question 24

describe the creaming method of aeration

Answer 24

-when making cakes, creaming butter and sugar together until it becomes a creamy texture and light colour, will aerate the mixture.
-This is because sugar crystals are pressed into fats and small changes of air are added.

Question 25

describe the rubbing in method of aeration

Answer 25

-rubbing butter into flour introduces air into mixtures. It is a technique used to make shortcrust pastry, scones and crumbles.

Question 26

describe the layering fat in pastry method of aeration

Answer 26

flaky and puff pastry are laminated by creating layers of fat between a dough make of a high gluten content flour.

Question 27

describe the whipping cream method of aeration

Answer 27

-adds air to create a foam of a air trapped in a liquid.
-The foam is surrounded by a film of fat and protein.
-The fat is partly solidified and the protein partly denatured by the whipping process.
-These changes lead to a fairly stable foam: air in an oil and water emulsion.

Question 28

Describe how foams are formed?

Answer 28

-formed when air is whipped or beaten into a liquid.
eg. whipped cream
-The fat content of cream needs to be 22 to 35% before it can be whipped to form an aerated foam.

Question 29

what factors affect the foaming of cream?

Answer 29

-At a temperature of 1 to 7℃ cream whips more easily.
-Overbeating causes the fat globules to clump together on the surface of the air bubbles and the cream to look “cuddled” in appearance.
-Gelatin or an alginate can be used to make a cream foam.
-Sugar reduces the volume of the foam but added towards the end of whipping, prevents over-beating and a cuddled appearance.

Question 30

What does plasticity mean?

Answer 30

-melts over a range of temperatures eg.fat

Question 31

why does plasticity occur in fats?

Answer 31

-because fats contain a mixture of triglycerides and Each type of triglyceride has its own melting point.
-Some products are formulated with fats with lower melting points so they can spread from the fridge, such as spreadable butter type products.

Question 32

what does shortening properties give to fats?

Answer 32

gives shortcrust pastry, shortbread and other types of biscuits their characteristic crumbly texture.

Question 33

Describe the process of shortening?

Answer 33

-involves rubbing-in the fat to flour.
-This coats the protein gluten with fat and restricts the liquid being absorbed by the flour and developing the gluten.
-This results in a “shortness” in the texture e.g. butter used to make shortcrust pastry.
-The formation of gluten would cause the dough to become elastic.
-The type of fat used can impact the colour and flavour of the product.

Question 34

What is the melting point of fats and oils proportional to?

Answer 34

directly proportional to degree of saturation.

Question 35

what is the effect of heating fats and oils

Answer 35

causes the triglycerides to break down into their component parts and decompose

Question 36

what is smoke point?

Answer 36

-involves the chemical degradation of glycerol molecule caused by overheating the fat or oil.
-Smoke point leads to the glycerol breaking down into acrolein which is irritating to the eyes and nose.

Question 37

what is the smoke point of oil determined by?

Answer 37

-Saturated fatty acids are more resistant to high heat.
-Polyunsaturated fats are more sensitive to heat and light.
-The smoke point of oil decrease the more times it is heated to high temperature,.
-Contamination of oil with batter and bread crumb can cause the smoke point of an oil to decrease more rapidly.

Question 38

Affect of fat on flavour in foods?

Answer 38

-can add to the flavour of a product e.g. butter in cakes, sesame oil on stir fries

Question 39

How can fat function as a heat transfer?

Answer 39

-Some fats and oils can withstand high temperatures without smoking (high smoke point) and igniting during frying and roasting.

Question 40

how can fat increase shelf life of foods

Answer 40

can be extended by he softening, emulsifying and enriching properties of fats and oils.

Question 41

structure of saturated and unsaturated fats?

Answer 41

-Saturated fatty acids have hydrocarbon chains connected by single bonds only.
-Unsaturated fatty acids have one or more double bonds. Each double bond may be in a cis or trans configuration.
-In the cis configuration, both hydrogens are on the same side of the hydrocarbon chain