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Nutrition > Polysaccharides > Flashcards

Polysaccharides Flashcards

1
Q

What is a polysaccharide?

A

A polymer of monosaccharides (10 or more)

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2
Q

What is a homopolysaccharide? Give three examples

A

Polysaccharide composed of a single type of monomer

  • starch = D-glucose
  • glycogen = D-glucose
  • cellulose = D-glucose
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3
Q

What is a heteropolysaccharide? Give two examples

A

Polysaccharides composed of two or more different monomers

  • alginate
  • gellan gum
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4
Q

What is the predominant food reserve in plants?

A

Starch

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5
Q

What are the two main sources of starch?

A

Cereal grain = corn, wheat, rice

Tubers/roots = potatoes and tapioca

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6
Q

What are the functional uses of starch in food?

A

Thickening sauces
Binding
Dusting surfaces
Gelling agent

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7
Q

What is the structure of amylopectin?

A

D-glucose chains joined by alpha 1,4 and 1,6 glycosidic bonds
These chains form hydrogen bonds producing helices
These helices clump to form crystals
Crystallites line up to give crystalline and amorphous regions

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8
Q

What must starch undergo in order to gelatinise it?

A

Heating in excess water

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9
Q

Describe the process of gelatinisation of starch.

A
  1. Water uptake
  2. Granule swelling
  3. Loss of bifringence
  4. Crystallite melting
  5. Unwinding of double helices
  6. Amylose leaching
  7. Starch solubilisation
  8. Increased viscosity
  9. Gelling of amylose on cooling
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10
Q

Describe the process by which starch is used in sauces.

A
  1. Flour is added to hot fat and cooked off to produce a roux
  2. Liquid is added gradually
  3. Heated gently until thickened
  4. Left to cool
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11
Q

Why is flour added to hot fat and cooked off?

A

In order to coat the starch granules so that they stay separated

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12
Q

Why is liquid added to the roux gradually?

A

So that the swelling of starch granules is gradual

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13
Q

Why is the roux heated gently until thickened?

A

Boiling would disintegrate the starch granules

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14
Q

Why is the roux left to cool?

A

To allow amylose to assemble into a network

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15
Q

Why does overcooked roux have less thickening power?

A

Because the sugars have been broken down

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16
Q

What is the function of starch in pasta?

A
  • Granules are trapped in a solid = less water access
  • Proteins compete with starch for water
  • Limited expansion of the granule
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17
Q

What is the function of starch in boiled mash potato?

A
  • Granules swell but only some burst

- Bulging cells separate to give a floury texture

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18
Q

What happens if boiled mash potato is blended?

A

All cells will burst producing a slimy paste

19
Q

What is the function of starch in chips and roast potatoes?

A
  • At high temperatures water evaporates and fat enters

- Dextrinisation forms colour, texture, flavour and crust

20
Q

What is naturally occurring starch?

A

Starch which has not been chemically processed

21
Q

How is naturally occurring starch labelled?

A

Maize starch

22
Q

Give four examples of naturally occurring starch.

A

Waxy maize
Rice
Tapioca
Hylon

23
Q

What are the properties of waxy maize?

A

Low amylose and high amylopectin content
Granular integrity is maintained
Freeze thaw stability

24
Q

What are the properties of rice?

A

Small, uniform granule size

25
Q

What are the properties of tapioca?

A

Clear solutions

26
Q

What are the properties of hylon?

A

High amylose content and therefore resistant to digestion

27
Q

How is pregelatinized starch produced?

A

Preheating with water to gelatinise and then rapid drying to make a powder

28
Q

What are the properties of pregelatinized starch?

A

Weak gels

Less viscous paste

29
Q

What does natural variation cause among starch?

A

Less consistency

30
Q

Name three ways in which starch may be modified.

A

Acid modification (depolymerised/thin boiling)
Stabilised starch phosphate and esters
Cross-linked starch

31
Q

How is starch acid modified and how does that affect it?

A
  • Acid treatment at 22-25 degrees for 6-24 hours

- Hydrolysis breaks down some glycosidic bonds which therefore increases solubility

32
Q

What is acid modified starch used in?

A

Gummy sweets

33
Q

How is phosphate stabilised starch different to naturally occurring starch?

A

Increased viscosity

34
Q

How is ester stabilised starch different to naturally occurring starch?

A

Freeze thaw resistant

35
Q

How is cross-linked starch different from naturally occurring starch?

A

Increased strength

pH resistant

36
Q

What is cross-linked starch used in?

A

Canned fruit pie fillings

37
Q

Why might modified starches have E numbers?

A

Because they are considered additives

38
Q

What is cellulose?

A

A polysaccharide found in cell walls

39
Q

What is the major component of dietary fibre?

A

Cellulose

40
Q

What is the structure of cellulose?

A

D-glucose monomers joined by beta 1,4 connections

41
Q

What are cellulose microfibrils?

A

Individuals D-glucose chains connected by hydrogen bonds

42
Q

How does the structure of cellulose provide strength in all directions?

A

Adjacent microfibril layers are laid down in different directions

43
Q

Name six other polysaccharides found in foods.

A 
Alginate = thickner and gelling agent 
Arabinoxylan
Beta-glucan = reduces cholesterol
Glucomannan = treating constipation 
Pectin = jam and fruit 
Xyloglucan = fruit and veg cell walls

Nutrition (27 decks)

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