Starch
Sandra Hill
• LEARNING OUTCOMES
– Usage of starch
– Understand the structure and nomenclature used for starch
polysaccharides
– Appreciate some of the structural features of starch granules
– Recognition that starch is only one component of storage organs
– Modified starches
Nov 2004
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Starch
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Major food for animals
Usage in the paper industry
Bioethanol production
Filler component for many pharmaceuticals
Building material
Some times eaten by people
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Food
Beverage
Animal Feed
Plastic
Pharmacy
Building
Mayonnaise
Soft drinks
Pellets
Biodegradable plastic
Tablets
Mineral fibre tiles
Baby food
Beer
By products
Dusting powder
Gypsum board
Bread
Alcohol
Concrete
Buns
Coffee
Gypsum plaster
Confectionery
Agriculture
Textile
Paper
Various
Meat sausages
Jelly gums
Seed coating
Warp
Corrugated board
Foundries
Meat rolls and loaves
High-boiled sweets
Fertiliser
Fabrics
Ketchup
Jellies
Yarns
Water treatment
Cardboard
Coal
Paper
Detergent
Printing paper
Oil drilling
Marchmallows
Soups
Marmalade
Snacks
Jam
Fermentation
Non-Wowen
Pizza sauces
Ice cream
Vinegar
Hygienic diapers
Sauces
Dairy cream
Enzymes
Baby diapers
Low fat foods
Fruit fillings
Sanitary napkins
Stain remover
Packaging material
Glue
Foamed starch
Noodles
3
Given the right crops and new technology,
bioethanol could make a real contribution to
world fuel needs, writes Giuliano Grassi.
Bioethanol plant in Nebraska, USA,
processes corn to produce 925 litres
per day (Minnesota Corn Producers).
http://www.jxj.com/magsandj/rew/2000_
03/bioethanol.html
4
Starch based products
High proportion of human requirement for energy
supplied by starch
– potatoes
• crisps
• chips
– maize
• extruded products
– rice
• variety and preference
– wheat
• (bread and cake and the bubble)
– cassava
• a staple for much of the world
Starch
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Starch the chemical
Starch the macromolecule
Starch the supermacromolecule
Starch the granule
Starch the stuff that comes in a sack
In Europe a starch factory consumes between
1,000 and 2,000 tonnes of cereals each day.
http://www.aac-eu.org/html/everydayuses.html
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Carbohydrates
C H O
H
sugar components
O H
H O
– open chains
– ring structures
H
H
O H
H
O H
C H2 O H
O
o
chair
Starch the chemical
H OH
H
O
HO
HO
H
H
H
OH
HO
Linking sugars
• link a (1-4)
– example maltose
• glucose -glucose
multiple links (ribbons and helices)
Amylose and Amylopectin
•link a (1-6)
–example amylopectin
•glucose -glucose
Amylose helix
Pitch 0.8nm
6 residues per turn
Double helix,
association of 2 left
handed helices
Starch
• carbohydrate reserve
– seeds
– roots
– tubers
– stem
Native starch always is:
• glucose polymers
– amylose ( a1-4) and amylopectin (a1-4 and a1-6)
• packed into granules
– different size and shape depending of the botanical
source
– semi crystalline structures
How starch is laid down in the plant
Smith, Denyer & Martin, 1993
Starch
• complex assembly of two macromolecules
• amylose
Glucose units linked (mostly) 1-4a
Number of glucose units
~ 250-5,000
15-30% weight
Amylopectin
Racemose model
Glucose units linked 1-4a
and
some a 1-6 linkage
70-85% by weight
number of glucose units
~ 10,000-100,000
branch chains
~20 glucose units
only one reducing end
Diagram of the starch granule organisation
Glucose chains form
helices
Two types
in native starch
A and B
mixture of A and B
known as C
differ in the amount of
water in the helix
Can tell the structure of the helices by X-ray
X-ray wavelength 10-10 m
Packing of the molecules to form a starch granule
Polarised Light-optical microscope
Measurement of the amount of
crystallites
• DSC (Differential scanning calorimetry)
Endothermic heat flow
– Temperature at which the crystallites melt
– Amount of energy required to melt them
65C
• NMR (nuclear magnetic resonance)
• FTIR (Fourier transform infra red)
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Growth ring
Wheat starch
granule, erosion
during germination
(Gallent et al, 1997)
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Size shape and morphology of the granules is characteristic
10m
of the botanical source
wheat
potato
lentil
rice
rye
maize
shoti
avacado
green
pea
Starch
cereal
Storage polysaccharides
examples
wheat
rice
oat
barley
seeds
pea
tuber
potato
cassava / tapioca /manioc
stem
sago
Different starches
granule Amylose Molecules Degree
per granule polymerisaton
um
%
DP(amylose)
Starch
Corn
regular
waxy
Potato
Rice
Sago
Cassava
Wheat
5--25
5--25
15--100
3--8
20--60
5--35
2--35
26
~1
22
17
25
17
25
10*10-12
800
0.01*10-12
10*10-12
3000
4*10-12
5*10-12
3000
800
From Pomeranz 1991
Swinkels,1985
Remember that with the starch can come other
components within the granule
wheat
Internal components
maize
potato
Amylose
26-31
24-32
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Lipids
Protein
0.48-1.12
0.20-0.33
0.6-0.8
0.27-0.39
0.09
0.05
0. 2
0.06
0.1
0.02
Ash
Phosphorus
0.4
0.08*
Note : the amount of amylose depends on the method used to measure
Amylose :
a)the straight chain portion
(but there are often some 1-6 linkages)
b)the portion that incorporates iodine
(chains of less than 10 glucose units -no colour
colour goes from red, red-purple, purple, blue
depending on chain length)
645nm d.p. 366 or higher
but long chains of the amylopectin, often B1 chains, can
do this)
c)hot water soluble fraction
(amylose not water soluble at
above 2mg/ml, it
precipitates)
Remember that with the starch can come
other components from outside the granule
External components
Maize:
starch in protein matrix
Texture
Cell walls
Starch
RAW
RAW
Cooking
Cell/cell adhesion
Properties of the starch
Modified starch
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Starch and Water
• starch is biosynthesised
in an aqueous environment
• drying starch can cause shrinkage and cracks
• most water goes to the amorphous phase or to the
surface of the crystallites
• material up to 1000 daltons can enter the starch
granule-might be pores
• dry starches in water can absorb up to 50% of its
weight -will expand 30-100%, this is reversible.