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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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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 Water treatment

Ketchup Jellies Yarns Cardboard Coal

Marchmallows

Soups Marmalade Paper Detergent

Snacks Jam Fermentation Non-Wowen Printing paper Oil drilling

Pizza sauces Ice cream Vinegar Hygienic diapers Stain remover

Sauces Dairy cream Enzymes Baby diapers Packaging material Glue

Low fat foods Fruit fillings Sanitary napkins Foamed starch

Noodles

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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

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

• 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

Carbohydrates

sugar components– open chains

– ring structures

chair

H

C H O

O H

HH O

O HH

O HH

C H2 O H

O

H OO

H

H

H O

H

H O

O HHH

O H

o

Starch the chemical

Linking sugars

• link (1-4)– example maltose

• glucose -glucose

multiple links (ribbons and helices)

Amylose and Amylopectin

•link (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 ( 1-4) and amylopectin (1-4 and 1-6)• 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) 1-4

Number of glucose units~ 250-5,000

15-30% weight

Racemose modelAmylopectin

70-85% by weight

number of glucose units~ 10,000-100,000

branch chains ~20 glucose units

only one reducing end

Glucose units linked 1-4andsome 1-6 linkage

Diagram of the starch granule organisation

Glucose chains formhelices

Two types in native starch

A and B

mixture of A and Bknown 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

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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)

En

doth

erm

ic h

ea

t flo

w

65C

Growth ring

Wheat starchgranule, erosionduring germination

25(Gallent et al, 1997)

Size shape and morphology of the granules is characteristic of the botanical source

wheat lentil

rice

ryemaize

potato

shoti

avacado

green pea

10m

Starch Storage polysaccharidesexamples

cereal wheatriceoatbarley

seeds pea

tuber potatocassava / tapioca /manioc

stem sago

Different starches

Starch granule Amylose DegreepolymerisatonDP(amylose)um %

Cornregular 5--25 26 800waxy 5--25 ~1 -

Potato 15--100 22 3000Rice 3--8 17Sago 20--60 25Cassava 5--35 17 3000Wheat 2--35 25 800

From Pomeranz 1991Swinkels,1985

Moleculesper granule

10*10-12

0.01*10-12

10*10-12

4*10-12

5*10-12

Remember that with the starch can come other components within the granule

wheat maize potato

Amylose 26-31 24-32 23

Lipids 0.48-1.12 0.6-0.8 0.09Protein 0.20-0.33 0.27-0.39 0.05

Ash 0. 2 0.1 0.4Phosphorus 0.06 0.02 0.08*

Internal components

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, bluedepending on chain length)645nm d.p. 366 or higherbut 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

TextureCell wallsStarch

CookingCell/cell adhesionProperties of the starch

RAW

RAW

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Modified starch

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.