4.6.the food processing on texture

Question 1

what do colloidal systems do?

Answer 1

Colloidal systems give foods their structure, texture and mouthfeel.
- is defined as one substance being dispersed through another substance, but not combined to form a solution.

Question 2

what are the 2 phases of a colloidal system?

Answer 2

A disperse phase
A continuous phase

Question 3

what are the 4 types of colloidal systems?

Answer 3

sol, gel, emulsion, foam

Question 4

what is a hydrocolloid?

Answer 4

-can form sols, gels and emulsions. They are used in the food industry because of their ability to change the rheology of food
-are used for thickening gelling, emulsification. Stabilisation and controlling the growth of sugar and ice crystal

Question 5

sol colloidal system- name the disperse phase, continuous phase and examples

Answer 5

DP- solid
CP-liquid
EG- Gelatinised sauces, chocolate (powdered) milk
(can be made of starches, gums and cellulose)

Question 6

gel colloidal system- name the disperse phase, continuous phase and examples

Answer 6

DP- liquid
CP-solid
EG- jelly, jam
(are very thick and viscous, can be made by gums, starches, pectin, gelatine)

Question 7

emulsion colloidal system- name the disperse phase, continuous phase and examples

Answer 7

DP-liquid
CP-liquid
EG-Mayonnaise, milk

Question 8

solid emulsion colloidal system- name the disperse phase, continuous phase and examples

Answer 8

DP-liquid
CP-solid
eg. butter, margarine

Question 9

foam colloidal system- name the disperse phase, continuous phase and examples

Answer 9

DP-gas
Cp- liquid
EG. Whipped cream, whisked egg white

Question 10

what is syneresis?

Answer 10

when a gel shrinks and losses liquid. Syneresis can occur in both starch and protein based thickened foods.

Question 11

what is gelatinisation?

Answer 11

the process in which starch binds water and forms a sol or gel

Question 12

Give some examples of when starch has been used to thicken mixtures by gelatinisation?

Answer 12

-Bechamel sauce (wheat starch) SOL
-Lemon meringue pie filling (cornstarch) GEL
-Stir fries and gravy (cornstarch) SOL

Question 13

what is retrogradation?

Answer 13

the opposite to gelatinisation
-water is expelled, as the starch contracts and losses water. -

Question 14

examples of retrogradation?

Answer 14

-can take place in frozen food that contains starch
-Staling of bread is also a process of retrogradation
-

Question 15

affect of amylose on retrogradation?

Answer 15

-Retrogradation occurs more readily with amylose than with amylopectin.
-Amylose tends to form a gel that is hard and rigid and is prone to retrogradation. This is because amylose has smaller unbranched molecules.
- Therefore low amylose content starches can decrease the level of retrogradation

Question 16

what are natural starches and what are there amylose amylopectin content?

Answer 16

potatoes-amylose-23%, amylopectin- 77%
wheat -20%. 80%
rice - 15-35%, 65 - 85%
corn- 17% 83%
tapioca- 13% 87%

Question 17

example and Amylose and amylopectin content of modified starches

Answer 17

Pregelled waxy maize starch
amylose- <1
amylopectin- >95%

Question 18

examples of modified starches?

Answer 18

-Pregelatinized starch
-Corn syrup and high fructose corn syrup
-Phosphate cross linked starch
-Acid modified starch
-Stabilised starch

Question 19

Phosphate cross linked starch- function, type of modification, and examples in food

Answer 19

F-High gelatinisation temperature, stable to heat, acid, is a stable and not affected by retrogradation.
-Phosphate cross-linking allows starch to absorb more water and prevents syneresis
T-chemical
EG-Canned food, salad dressings, gravies.

Question 20

Corn syrup and high fructose corn syrup- function, type of modification, and examples in food

Answer 20

F-Used as a sweetener which is easy to blend. Also used for thickening and as a bulking agent.
T-chemical
EG-Ice cream, drinks, confectionery

Question 21

Acid modified starch -function, type of modification, and examples in food

Answer 21

F–to produce gels for cheese spreads, jelly beans and a fat replacer in low fat products.
-has smooth texture and is resistant to syneresis
T-chemical
EG-Jelly sweets, cheese spreads and as a fat replacer

Question 22

Pregelatinized starch- function, type of modification, and examples in food

Answer 22

F-Enables products to be thickened without heat
T-physical
EG-Instant desserts and sauces

Question 23

Stabilised starch- function, type of modification, and examples in food

Answer 23

F-has high water holding capabilities and so this prevents retrogration. This is useful for frozen foods in order to give freeze thaw stability.
T-physical
EG-frozen food

Question 24

what is pectin and what is it used for?

Answer 24

a polysaccharide found in the cell walls of fruit and vegetables
-used to make jam by heating fruit containing pectin with sugar.

Question 25

what happens if a fruit doesn’t contain enough pectin to form a gel?

Answer 25

-sugar with addition pectin is added to it, or commercial pectin.
-Lemon juice is added to lower the pH and help the process of gelation.

Question 26

what is gelatine and how is it produced?

Answer 26

-a protein and the only food hydrocolloid extracted from an animal source.
-is produced by the partial hydrolysis of the protein collagen, which is extracted from animal skin and bones.

Question 27

describe how gelatine is used for thickening and give examples?

Answer 27

gelatine swells in cold water and is soluble in hot water and forms a gel which sets at 20°C and melts at 30°C
-used to set many types of desserts such as panna cotta, cheesecakes and table jellies

Question 28

what ar the 2 types that gelatine is available in?

Answer 28

-from pork skin treated with acid
-from beef bones and calfskin treated with alkali.

Question 29

what is an emulsifier and give examples?

Answer 29

-a substance that helps to make emulsions of water in an oil or oil in water remain stable
-helps to ensure the emulsion does not separate into the two phases
-eg.lecithin, glyceryl monostearate (MS), whey protein and gums.

Question 30

Name some other functions of an emulsifier?

Answer 30

-can help to prevent staling in bread by combining with amylose and prevent loss of water by preventing retrogradation
-can prevent the fat in chocolate forming crystals that separate out of the product

Question 31

what do stabilisers do?

Answer 31

-help to maintain the consistency or uniformity of a food product and the conditions the product undergoes during processing, storage and use

Question 32

3 functions of stabilisers?

Answer 32

-thickeners or gelling agents to maintain consistency
-emulsification stabilisation - stabilisers prevent the separation of ingredients that are bound together by emulsifiers.
-prevent the formation of large crystals in product such as ice cream

Question 33

what is the function of gums?

Answer 33

-have the ability to absorb large quantities of water and can be used to for thickening, gelling, emulsifying or stabilising.
-They are often complex carbohydrates

Question 34

examples of gums?

Answer 34

Gum arabic
Guar gum
Xanthan gum
Gellan gum
Alginates
Carageenans

Question 35

Alginate gum- sources and uses

Answer 35

-Extracted from brown seaweed
-used for Thickening sauces and syrups as they have the ability to retain moisture, thus preventing absorption of moisture into pastry.
-Used as a thickener for ice cream and yogurt to give a creamy texture.
-In Molecular Gastronomy sodium alginate is mixed with calcium chloride to form a gel. This is flavoured to create a variety of food caviars to create unexpected flavours

Question 36

Xanthan gum -source and uses

Answer 36

• comes from The fermentation of Xanthomonas campestris.
  -is thixotropic which means it is thicker on standing, and thinner when shaken or agitated
  -used in canned foods as it can be pumped due to its thixotropic nature.
  -is also used in gravies, salad dressings and milkshakes.
  -It has good freeze-thaw stability and so can be used in starch thickened sauces.
  -does not form a solid gel on its own, but it will gel in combination with other gums.

Question 37

what is cellulose?

Answer 37

-is indigestible and cannot mix with water,
- can be modified to make it more soluble or dispersible in water and is used as a food stabiliser
examples-Carboxymethyl cellulose, Methylcellulose

Question 38

Carboxymethyl cellulose- uses

Answer 38

• helps Cakes and bread to retain water and prevent staling
  -used in Ice-cream, milk drinks in order to give a smooth texture and prevent large ice crystals forming
  -used in Fillings of pizza to prevent the sauce filling dripping during cooking.
  -Can prevent syneresis in products such as pie fillings

Question 39

Methylcellulose uses

Answer 39

-used in Fillings of pizza to prevent the sauce filling dripping during cooking.
- when mixed with water and heated it becomes thicker and then becomes thinner once again when it is cooled.

Question 40

what is a foam?

Answer 40

-a colloidal system of gas trapped in a solid or liquid.
-they enhance the texture of food by giving a pleasurable texture e.g. ice cream, mousses, marshmallows.

Question 41

how can foams be created?

Answer 41

-mechanical action can create foams that alter texture due to aeration. Proteins in egg white is used to create meringues.
-by carbon dioxide acting as raising agents e.g. sponge cakes, honeycomb .

Question 42

how can preservation techniques impact texture?

Answer 42

-Heat processing such as canning will soften the texture of food
-Freezing can also affect texture due to damage to cells, Fast freezing will help form smaller ice crystals, which cause less textural damage than large ice crystals which are formed when food is frozen slowly.
-Heating and freezing can also lead to retrogradation of starch.
- phosphate cross bonded starch is used to prevent the retrogradation of starch in canned and frozen foods.

Question 43

give an example of a traditional thickener?

Answer 43

maize and wheat

Question 44

why is starch modified?

Answer 44

-to increase their stability against excessive heat, acid, time, cooling, or freezing
-to change their texture (improve mouthfeel)
-to decrease or increase their viscosity
-to lengthen or shorten gelatinization time