starch extraction tech

1. Starch and Extrusion Technology
(Ftpe 4153)
By:- Chernet T.

2. Chapter 3: Properties,
Functions of Starch and Impact
of Processing
• Properties and Physical Methods of
Analysis
• State and Phase Transitions
– Gelatinization and Pasting
– Changes During Cooking
– Effects of Time and Temperature
– Changes that Occur During
Cooling, Storage and Distribution

3. Introduction
• Starch
– being an essential energy source in the human
diet
– an excellent raw material
• texture modification of foodstuffs
– New applications
– uses of starch rely
• the colloidal properties of
–amylose and amylopectin

4. Cont…
• Most starches
– 70 – 75% amylopectin
– mutants
• no amylose (waxy) or
• much higher amylose
• In native starches,
– amylose and amylopectin molecules,
– small amounts of water
corn, barley and rice

5. Granule Structure

6. Cont…

7. Cont…
• physical and functional properties
– botanical origins
• polymer composition,
• molecular structure,
• interchain organization, and
• minor constituents
• Furthermore
– chemical,
– enzymic and
– physical modification
preservation or
destruction
the native granule

8. Starch Properties and Physical
Methods of Analysis
• starch materials
– stability,
– transformations and
– physical properties
• to probe the structural - physical techniques
– light and electron microscopy,
– wide and small -angle x-ray scattering and
diffraction
– solid-state C-NMR,
– various viscometric techniques and
– differential scanning calorimetry (DSC)
nature of the amorphous
and crystalline domains

9. Cont…
Physical Properties of Starch in Water
• Important aspects of starch functionality
– Granule swelling,
– gelatinization,
– pasting and
– retrogradation
(starch granules + heat) in excess water
– progressively higher temperatures
– polarization cross starts to disappear and
– the granules begin to swell irreversibly
– associated with the disruption of granular structure,
= ‘gelatinization’

10. Aleqa Gebrehana???

11. Mulla Nasrudin???
• Mulla/Hodja/Hoca Nasrudin
–Lived in the 1300s
–amusing tales told in regions all over the
world, particularly countries in or near the
Middle East
–He is sometimes wise, sometimes foolish, and
sometimes both
–He tends to be illogical yet logical, rational yet
irrational, bizarre yet normal, and simple yet
profoundly wise.

12. Walnuts and Watermelons
As Nasrudin rested under a tall walnut tree one day, he looked a
few yards to his side and noticed a big watermelon growing on a
thin vine near the ground.
Nasrudin looked up and said, “Great God, please permit me to
ask you this: why is it that walnuts grow on big strong trees, while
watermelons grow on think weak vines. Shouldn’t it be the other
way around?”
But at that very moment, a walnut fell from high on up in the tree
and hit Nasrudin square on the head.
“Ah!“ remarked Nasrudin. “I suppose Nature’s ways might not be
as backward as I thought. After all, if a big watermelon fell out of
the tree and onto my head, it might have killed me!“

13. Starch Functionalities

14. Cont…
• Gelatinization =
– the collapse (disruption) of molecular orders
• breaking of H-bonds within the granule
– with all concomitant and irreversible changes in
properties such as
• water uptake,
• granular swelling,
• crystallite melting,
• birefringence loss, (Maltese cross)
• Starch solubilization and
• viscosity development

15. Cont…
• At temperatures above the gelatinization
temperature,
– considerable increase in swelling of the granules
– swelling
• starts at the onset temperature (To) of the DSC
endothermic transition and
• continues well above the concluding
temperature (Tc)
– Different starches exhibit
• different swelling behaviors,
–the final gel volumes obtained and
–in the temperature response

16. Cont…
• Swelling
– primarily a property of intact amylopectin
• waxy (all-amylopectin) varieties
–highest gel volumes than starches with
amylose content
• Swelling is also accompanied
– leaching of starch molecules from the granules
• largely amylose,
• amylopectin may also solubilize
–nature of the starch and
–severity of heat-shear conditions

17. Cont…

18. • Changes in rheological behavior of a heated starch
– granule swelling and
– solubilization (leaching)
• Pasting behavior of starches
– monitored by viscosity measurements
– under constant stirring and
– following a programmed heating and cooling cycle
• Brabender Visco Amylograph was - traditionally
• Rapid Visco Analyzer (RVA) - recent
Cont…

19. Cont…

20. Cont…
• The pasting temperature
– usually higher than the gelatinization temperature
– measured by the loss in birefringence
• Tuber and root starches
–sharper rise in viscosity during cooking and
–higher peak viscosity than normal cereal
starches
»The peak viscosity is a measure of the
thickening power of a starch
–pastes from tuber and waxy starches
»break down more readily than those from
cereal starches

21. Cont…
• important paste properties in practical usage
– viscosity,
– texture,
• potato starch pastes cohesive, long-bodied, stringy
and rubbery
• Other root, tuber and waxy starches
– similar texture to that of potato starch, but are
generally less cohesive
– paste transparency,
• potato – translucent
• common cereal starches - opaque
– resistance to shear and
– tendency to retrograde

22. Cont…

23. Cont…
• On cooling sufficiently starch dispersions
– the restoration of molecular order in starch
– amylose and amylopectin molecules begin to
reassociate
– collectively described ‘retrogradation’
• exert a major influence on the texture of foods
rich in starch
–retrogradation - major factor in the staling
forming crystallites of the B-type

24. Cont…
– Retrogradation
• gradual increases in rigidity and
• a phase separation between
– solvent and
– polymer chains
– causing a decrease in water-holding capacity
» development of syneresis
• depends on
– source of starch,
– starch concentration,
– cooking and cooling temperature regimes,
– pH, and
– presence of solutes - Lipids and sugars
• Video

25. State and Phase Transitions
Glass Transitions of Amorphous Structural Domains
• Amorphous and partially crystalline polymers
– at low temperatures
• solid-like or glassy state
• large-scale molecular motions stop
– applying thermal energy
• large-scale segmental motions ‘entanglement
slippage’
• characteristic temperature = Tg
– Tg is exceeded
• changes in material properties and
• physical state (brittle- highly viscous rubber)

26. Cont…

27. Cont…
• state transitions are accompanied by
– changes in the mechanical properties (texture) and
– stability of the composite network
• many processed cereal foods
(e.g. breakfast cereals, wafers, biscuits)
–moisture content - Tg is close to storage
temperatures
»small deviations in moisture content or
»its temperature
changes in the rheological properties

28. Cont…

29. Cont…
Annealing and Structural Modifications in H/M
• Starch granules – partially cristalline
– modest molecular reorganization (annealing)
• held in excess of water at temperatures
• above the Tg and
• below the equilibrium Tm of the crystallites
–softening of the amorphous granular regions
causes crystallite growth and/or perfection
• manifested by an increase in gelatinization
temperature and
• narrowing of the temperature range over which
the heat-treated granules melt

30. Cont…
• Depending on the annealing
– temperature,
– time and
– starch type
• Annealing is also accompanied by
– progressive loss in the inter-cluster distance
– substantial loss in long-range radial order
(birefringence) and
– no apparent change or a slight increase in
crystallinity
– Swelling and solubility are both affected by
annealing
• usually decrease
might be an increase in the
gelatinization enthalpy of starch
granules

31. Cont…
Melting Transitions of Crystallites in Granular Starch
• Several endothermic events
– on heating aqueous suspensions of granular
starches
• M1 and M2 - low temperature (100 ° C)
–melting of ordered chain of amylopectin
–Total losses of granule birefringence and
–crystalline properties 79,92 are associated with
–passage through the M 2 endotherm.
• M3 and M4 - high-temperature (100 – 130 ° C)
–attributed to order → disorder processes of
amylose – lipid complexes

32. Cont…

33. Cont…
Gelation and Retrogradation of Starch
• Gelation can be characterized as
– the process by which dispersed starch molecules in
an aqueous medium begin to reassociate and
– form three-dimensional network structures
– structures constitute what are known as
• ‘crosslinks’ or ‘junction zones’ in a gel network

34. Cont…
– starch gels
• intermolecular double helix formation
– stabilized by hydrogen bonding
• influenced by
– thermal and processing history,
– molecular composition (amylose, amylopectin) and
– polymer fine structure
– Annealing processes also occur on storage of
starch gels,
• as long as the temperature is kept between Tg
and the Tm

35. Cont…
Amylose Gels
• Aqueous solutions of amylose are quite unstable,
• cooling to room temperature
– develop turbidity and
– form a precipitate or a gel
• depending on
– concentration and
– molecular size of the polymer chain
– Gidley and Bulpin
• Short chain amyloses (DP 110)
– precipitate at all concentrations up to 5
– gelation has always occurred with amyloses of DP
1100 in solutions above 1%

36. Cont…
Amylopectin Gels
• generally regarded as stable,
– under conditions
• usually low temperature and
• high polymer concentration
• Amylopectin gelation
– much slower process than amylose and
– occurs at
• higher concentrations (usually 10%)
• the kinetics
–more sensitive to storage temperature (1 – 25 °
C) than those of amylose
form gels

37. Cont…
Starch Pastes and Gels
• during heating of starch granules in water
• results changes in rheological behavior
• include
– swelling of the granules,
– crystallite melting,
– (partial) demixing of amylose and amylopectin,
– changes in the extent of molecular entanglements
– rearrangements in the granules and
– (partial) fragmentation of the swollen granules

38. Cont…
• Effect of added ingredients
– Sugar
• Thins
–competes for water
– Fat
• Thins
–coats granules and
–prevents water absorption
– Acid
• Thins
–hydrolyzes starch