LEARNING OUTCOMES

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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

• 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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(No Transcript)
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http//www.jxj.com/magsandj/rew/2000_ 03/bioethano
l.html
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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

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Starch

• Starch the chemical
• Starch the macromolecule
• Starch the supermacromolecule
• Starch the granule
• Starch the stuff that comes in a sack

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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

• sugar components
• open chains
• ring structures

o
chair
Starch the chemical
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Linking sugars

• link a (1-4)
• example maltose
• glucose -glucose

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multiple links (ribbons and helices)
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Amylose and Amylopectin
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• link a (1-6)
• example amylopectin
• glucose -glucose

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Double helix, association of 2 left handed
helices
Amylose helix
Pitch 0.8nm 6 residues per turn
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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

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How starch is laid down in the plant
Smith, Denyer Martin, 1993
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Starch

• complex assembly of two macromolecules
• amylose

Glucose units linked (mostly) 1-4?
Number of glucose units 250-5,000 15-30
weight
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Amylopectin 70-85 by weight number of
glucose units 10,000-100,000 branch chains
20 glucose units only one reducing end
Racemose model
Glucose units linked 1-4? and some ? 1-6
linkage
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Diagram of the starch granule organisation
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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
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Can tell the structure of the helices by X-ray
X-ray wavelength 10-10 m
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Packing of the molecules to form a starch granule
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Polarised Light-optical microscope
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Measurement of the amount of crystallites

• DSC (Differential scanning calorimetry)
• Temperature at which the crystallites melt
• Amount of energy required to melt them
• NMR (nuclear magnetic resonance)
• FTIR (Fourier transform infra red)

Endothermic heat flow
65C
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Growth ring
Wheat starch granule, erosion during germination
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(Gallent et al, 1997)
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Size shape and morphology of the granules is
characteristic of the botanical source
10mm
shoti
wheat
lentil
potato
avacado
rice
green pea
rye
maize
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Starch Storage polysaccharides examples cere
al wheat rice oat barley seeds pea
tuber potato cassava / tapioca
/manioc stem sago
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Different starches
Molecules per granule 1010-12 0.0110-12 1010
-12 410-12 510-12
From Pomeranz 1991 Swinkels,1985
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Remember that with the starch can come other
components within the granule
Internal components
wheat maize potato Amylose 26-31 24-32
23 Lipids 0.48-1.12 0.6-0.8
0.09 Protein 0.20-0.33 0.27-0.39
0.05 Ash 0. 2 0.1 0.4 Phosphorus
0.06 0.02 0.08
Note the amount of amylose depends on the
method used to measure
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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)
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Remember that with the starch can come other
components from outside the granule
External components
Maize starch in protein matrix
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Texture Cell walls Starch
RAW
RAW
Cooking Cell/cell adhesion Properties of the
starch
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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.