starch plants. starch granule in plant cell

Starch plants

Starch granule in plant cell

Cassava starch

Canna starch

Mung bean starch

Barley & Wheat starches;

•large A granules: 20-25 m (disk shape)

•small B granules: < 10 m (spherical/irregular shape)

Starch granule structure

Semi-crystalline structure

-Amorphous phase (gel phase)

-Crystalline phase (15-45%)

The granule structure is due to amylopectin, and based on a super helical structure in which the

double helices wind around each other

Growth Ring

Granule structureGranule structure

Granule structure

Cluster

A-, B-, and C- chain of amylopectin

A-chain: those that are linked to the rest of the molecule only through their reducing ends

B-chain: those that are linked to the rest of the molecule through their reducing ends but, in

addition, are branched at a C-6 position in one or more of their glucose residues

C-chain: is the one that bears the reducing end group

Amylopectin Helix

Hybrid amylose/amylopectin helix

V-amylose helix

Free lipid

Free amylose

15 nm

6 nm

4 nm

1. Composition of raw materials (all values as percentage)

Source Starch Moisture Protein(N6.25)

Lipids Fiber Starch (as drysubstance)

Potato 17 78 2 0.1 1 77Maize 60 16 9 4 2 71Wheat 64 14 13 2 3 74

Tapioca 26 66 1 0.3 1 77Waxymaize

57 20 11 5 2 71

Composition of raw materials

Starch VS Flour

Composition of Starch

Major components: starch

Amylose (15-30 %)

Amylopectin (70-85%)

Minor components:

Lipids (0.1-1.0%)

Protein (0.1-0.4 %)

Phosphorus (0.005-0.08 %, 50-800 ppm)

Composition of Starch

Starch composition

Starch Moisture65%RH,

20 C

Lipids(% d.s.)

Protein(% d.s.)N6.25

Phosphorus(% d.s.)

taste&odorsubstances

Potato 19 0.1 0.1 0.08 LowMaize 13 0.8 0.35 0.02 HighWheat 13 0.9 0.40 0.06 High

Tapioca 13 0.1 0.10 0.01 very lowWaxymaize

13 0.2 0.25 0.01 Medium

RH = relative humidity of the atmosphered.s. = Dry substanceN = Nitrogen content

Amylose

Starch Molecules

Amylopectin

180/162

Reducing end

Reducing end

Amylose

-linear polymer containing 500-5,000 glucose units

-extent of branching varies from 5-20 per molecule

-forms inclusion complex with iodine and various organic compounds (butanol, fatty acids, phenol, surfactants, hydrocarbon,..)

-Molecular size: potato, tapioca > maize, wheat

-content: maize, wheat> potato, tapioca

Chain length (glucose unit)

Number of helix turns

color

12 2 None

12-15 2 Brown

20-30 3-5 Red

35-40 6-7 Purple

>45 9 Blue

Amylopectin

-highly branched structure

-branch chain length: DP 10-60 units. (aver. DP 22-28)

-the glucose units with an alpha-1,6 linkage are the branching points and make up about 5% of the total glucose units

-branches of amylopectin are arranged in a cluster

-cluster; alternating regions of ordered tightly packed parallel glucan chains and less ordered regions composed mainly of branch points

-OH groups tend to attract each other (H-bond) and thus preventing the dissolution of starch granules in cold water

-MW of amylopectin is about 1000 times of MW of amylose

Amylose and amylopectin contents and degree of polymerization (DP)

Starch Amylose Amylopectin Average DP amylose

Average DP amylopectin

Potato 21 79 3,000 2,000,000 Maize 28 72 800 2,000,000 Wheat 25 72 800 2,000,000

Tapioca 17 83 3,000 2,000,000 Waxy maize 0 100 - 2,000,000

Minor Components

-tuber (potato) and root (tapioca) starches contain a small percentage of lipids (≈ 0.1%)

-common cereal starches (maize, wheat, rice, sorghum) contain 0.8-1.0% lipid)

-Fatty acid substances in cereal starches are predominantly free fatty acids (palmitic, linoleic, oleic in maize starch)/phospholipids (in wheat starch)

-have a tendency to become rancid on storage

1. Lipids

Tend to reduce the swelling and solubilization of cereal granules

-lipids form complex with amylose

> 125C are required to disrupt the organized native amylose-lipid complex structure in cereal starch granules

2. Proteins-Tuber and root starches contain ≈ 0.1% proteins

-Cereal starches (maize, wheat) contain ≈ 0.2-0.4% proteins

-have a tendency to foam

3. Phosphorus

-in cereal starches; mainly present as phospholipids

-tapioca starch contain a low amount of phosphorus compounds.

-Potato starch contains as appreciate amount of chemically bound phosphate groups (at C-6 of amylopectin, 1 phosphate group per 200-400 glucose units).

B-type pattern is typical to tuber and root starches (Hoover, 2001) and is characterized by a small peak at 5.6, only one peak at 17 and a doublet at 22 and 24. Mung bean and cassava starch, displayed A–type pattern (a doublet at 17 and 18 and a single peak at 23). Even cassava is a root starch, but has been shown A-type (or CA -type in some reports)

- Amylopectin double helical chains can either form the more open hydrated Ty

pe B hexagonal crystallites or the dens er Type A crystallites, with staggered m

onoclinic packing , dependent on the pl ant source of the granules. Type A is fo und in most cereals with Type B being f

ound in some tubers and high amylose cereal starches.

Starch Properties

Swelling and Gelatinization

• Native starches are insoluble in water (below gelatinization temp.)

due to H-bond

In cold water “limited reversible swelling”

Swelling and Gelatinization

“irreversible loss of the crystallites in the granules, all molecules in granule are accessible to water and will swell irreversibly”

Gelatinization

Conditions:

-Heat and excess water

-dissolve in solvents; alkali. DMSO, CaCl2 at 25 C

Semi-crystalline native granule

Swollen amorphous granule

Heat

Heat + Shear

Gelatinization

Pasting

Cooling

Short term storage

Amylose retrogradation (gelation)

Crystallization of amylose-lipid complex

long term storage Amylopectin retrogradation

Starch Conversion

Heating starch in water; sequence of events

1. Swelling begins in the least organized, amorphous, intercrystallite regions

2. As this phase swell, it exerts a tension on the neighboring crystallites and tend to distort them

3. Further heating leads to uncoiling/dissociation of double helical regions and break-up of crystallite structure. Liberated amylopectin chains become hydrate, excerting increased stress on the remaining crystallites.

4. Smaller, linear amylose molecules diffuse out of the swollen granule

5. Further heating and hydration weaken the granule and a sol results

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Heating of starch

Molecular solubilization of starch

• starches cooked at 95 C for one hour may still contain highly swollen, hydrated starch aggregates. True solubilization of all starch substance occur normally at 100-160 C

• Tuber, root and waxy starches can be cooked to a completely dissolved state at about 100 C

• Maize starch required about 125 C

• amylomaize starch about 150 C

Viscosity rise at the pasting peak is due to;

1. Loss of water from the continuous phase to the inside of starch granules

2. Migration of amylose or other solubles from the granules into the continuous phase

3. Increasing size of the starch granules as they occupy more and more volume in the liquid phase

Behavior of amylose in solution (retrogradation)

Factors affecting the retrogradation of

starch

Factors affecting the retrogradation of

starch• amylose/amylopectin ratio

• amylose/amylopectin size and structure

• starch concentration

• temperature

• other components (lipids)

Maize starch pastes and solutions retrograde ralatively quickly

-high amylose (28%)

-small molecular size of amylose

-high lipid (0.8%)

amylose-lipid complex reduces hydration capacity

Potato starch has low tendency to retrograde

-low amylose (21%)

-high MW of amylose

-low lipid (0.1%)

Stabilization

Preventing retrogradation (esterification/etherification)