Starch

Question 1

Plant Cell structure

Answer 1

Nucleus
Cell membrane
Cytoplasm and cytoskeleton
Mitochondria
Protein Synthesis
Paroxysm
Cell wall
Plastids
Vacuoles

Question 2

Cell wall

Answer 2

Glucose

Beta-glucan

Question 3

Plastids

Answer 3

Chlorophyll
Carotenoids
Starch granules

Question 4

Starch

Answer 4

Amylose and Amylopectin

Question 5

Starch in water

Answer 5

Gives low viscosity slurries
Easily Mixed

Thickening properties are released when heated

Question 6

Amylose

Answer 6

Usually 25% starch
Linear polymer
Molecular weight 20-50 kDa
Branches are small and very very far apart
Mostly alpha, 1-4 glyosidic bonds

Question 7

Amylopectin

Answer 7

75% of starch
Highly branched dendritic polymer
>1000kDa
95% of bonds are alpha, 1-4
5% are alpa, 1-6

Question 8

Starch granule

Answer 8

Amylose and amylopectin molecules arrange radially (different structures altering layers)
Branches of amylopectin occur as packed double helices
Leads to amorphous layers rich in amylose

Amylose interact with amylopectin

Question 9

Gelatinisation

Answer 9

Irreversible swelling
Loss birefringence
Loss of crystallinity
Amylopectin when undergoing gelatinisation goes from tightly coiled and organised to loose bundle

Question 10

Retrogradation

Answer 10

Cooling of hot starch 
First stage of recrystallisation
Progressively less soluble
Syneresis
May form small crystalline regions

Question 11

Uses of starch in food

Answer 11

Adhesion
Dusting
Gelling
Moisture
Stabilising
Texture
Thickening

Question 12

Bread making

Answer 12

Amylose - Moderate fragmentation of intragranular amylose leads to accelerated crystallisation and less amylose/amylopectin interaction
Amylopectin - Shortening of side chains reduces tendency to retrograde (fresh bread)

After aging - amylose moderate fragmentation of intragranular amylose weakens starch network

Question 13

Alpha-amylase

Answer 13

Endoenzyme
Randomly hydrolyses alpha1-4 bonds in amylose and amylopectin creating oligosaccharides
Degrade ungelatinized starch
Rapid decrease in viscosity of gelatinised starch but little monosaccharide production
Important for germinating cereals

Question 14

Beta-amylase

Answer 14

Natural in flour
Only really useful if alpha-amylase is present
Exo-enzyme hydrolysing alpha,1-4
Removes beta-maltose units from non-reducing end of polymer
Cannot degrade ungelatinized starch
Important when need to be converted to fermentable sugar