why is starch is the most important food thickener? - step itn
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Starch as a HydrocolloidWhy is starch is the mostimportant food thickener?
John Mitchell
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The starch granule
Gelatinisation and gelation: What is thedifference?
Modified starches
What is the difference between starch andhydrocolloid solutions at the same viscosity
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Size shape and morphology of the granulesis characteristic of the botanical source
wheat lentil
rice
ryemaize
potato
shoti
avacado
greenpea
10mm
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Amylose / amylopectin contentsAmylose / amylopectin contents
Starch Source % amylose % amylopectin
Maize 26 76
Wheat 25 75
Potato 24 76
Tapioca 17 83
Rice 17 83
Waxy maize <1 >99
High amylose 50 / 75 50 / 25
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Amylose and Amylopectin
Starch normally contains twopolysaccharides amylose andamylopectin
Amylose
Almost entirely linear (α 1-4 linked)
Molecular size ~ 5. 105 g mol-1
Amylopectin
Highly branched (α 1-4 and α 1-4 linkages)
Molecular size ~ 108 g mol-1
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Racemose model
Amylopectin
70-99% by weight
Mol weight ----108 g mol-1
branch chains~20 glucose units
only one reducing end
Glucose units linked 1-4andsome 1-6 linkage
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Diagram of the starch polymer organisation
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Packing of the molecules to form a starch granule
lamellae
growth ring
Jenkins and Donald, 1995
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Gelatinisation vs Gelation
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Gelatinisation
Description of structural transformation which occurswhen starch granules are heated in excess water Swelling of starch granules
Increase in viscosity
Loss of birefringence (maltese cross pattern seen underpolarising microscope)
Accompanied by heat adsorption as seen by endotherm indifferential scanning calorimetry
Occurs in temperature range ~55-75 OC as measured byloss of birefringence (high amylose starches higher)
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Gelation
Formation of crosslinked network on coolingas a result of formation amylose doublehelices
Individual polysacchardies
Amylose forms “strong gels rapidly at minimumconcentrations ~2%.
Amylopectin forms weak gels slowly much higherconcentrations required (~20%)
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ElectronMicrograph
ShowingStructure ofan Amylose
Gel
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Modified Starches
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Modified starch e numbersModified starch e numbers
E 1404 oxidised starch
E 1410 monostarch phosphate
E 1412 distarch phosphate
E 1413 phosphated distarch phosphate
E 1414 acetylated distarch phpsphate
E 1420 acetylated starch
E 1422 acetylated distarch adipate
E 1440 hydroxypropyl starch
E 1442 hydroxypropyl distarch phosphate
E 1451 acetylated oxidised starch
E 1450 Starch sodium octenyl succinate
Acid thinned starches like unmodified starches are deemed to be ingredients NOT additives
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Properties of native starchesProperties of native starches
Starch
Source
Granule
Size m.
Gel TempoC
SolutionClarity
Gel
Texture
Stability toretrogradn.
Resistanceto shear
Freeze /thawstability
Maize 10 - 20 62 - 74 Opaque Short Poor Fair Poor
Wheat A 25 –35
B 2 -5
52 – 64 Opaque Short Poor Fair Poor
Rice 3 - 8 61 – 78 Opaque Short Poor Fair Poor
Potato 15 - 100 56 – 69 Clear VeryCohesive
Fair Poor Poor
Tapioca 20 - 60 60 - 72 Clear Soft Fair Poor Poor
Sago 15 - 25 52 – 64 Clear Soft Fair Poor Poor
WaxyMaize
6 - 30 63 - 72 Clear Cohesive Good Poor Fair
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Chemical ModificationChemical ModificationModification Reagent Product
Acid Thinning Hydrochloric acid Acid thinned starch
Oxidation Sodium hypochlorite Oxidised starch
Cross linking Phosphorusoxychloride
Distarch phosphate
Sod. Tri metaphosphate
Distarch phosphate
Adipic anhydride Distarch adipate
Epichlorohydrin Distarch glycerol
Esterification Acetic anhydride Starch acetate
Etherification Propylene oxide PO starch ester
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Effect of Cross linking on BrabenderEffect of Cross linking on BrabenderViscosityViscosity
Viscosity
0 95 95
Temperature oC
Control
0.03% POCl3
0.05% POCl3
0.075% POCl3
0.15% POCl3
50
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What is the difference between starchand hydrocolloid “solutions” at thesame viscosity ?
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Solutions can be thickened withswollen particles or polymers insolution
Swollen starch granules
Plant cells
Gel particles
Guar gum
Pectin
Hydroxypropylcellulose
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The next slide shows the appearance of apredominantly paticulate suspension (wheat starch)and a polymer solution (hydroxpropylmethylcellulose(HPMC)) which have been stained with a red fooddye and gently hand mixed with water. Prior tomixing the viscosity of the stainedsuspension/solution was 380mPa.s at ambienttemperature and a 50s-1.
In contrast to wheat, waxy maize starch whichcontains no amylose will disrupt on gelatinisationbehaving more like a polymer solution than asuspension of particles. The modified waxy maizestarch maintains the particulate structure .
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Five Minutes After Mixing
WheatStarch
ModifiedWaxyMaizeStarch
NativeWaxyMaizeStarch
HPMC
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Consequence of Good Mixing ofSolutions Thickened by Swollen
Starches
Good taste perception
Short non-stringy texture
Longer gastric emptying time
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1.5
1.6
1.7
1.8
1.9
2
2.1
-0.25 0.25 0.75 1.25 1.75
log (Kokini shear stress (Pa))
log
(mean
flavo
ur
)
w axy maize
(crosslinked)w heat
w axy maize
nativeHPMC (Anne-
Laure)HPMC (Dave
Cook)
Perceived Flavour Plotted Against KokiniShear Stress
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Mouthfeel of Hydrocolloid Solutions (Szcznesniak
and Farkas (1962), Mitchell (1979))
Least Slimy
Most Slimy
Slimy material thick, coats the mouth and is difficult to swallow
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Effects in the stomach
MRI pictures of stomach content following the ingestion of400g of water and 100g of(a)a crosslinked waxy maize starch and (b)HPMC at anequivalent viscosity of 500mPa.s at 50s-1.
(a) (b)
• some remains unmixed
• fully mixed• longer gastric emptying time
Acknowledgements: L. Marciani
SPINE
LIVER
STOMACH CONTENTS
SPLEEN
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Consequences of changingmicrostructure of starch
Origin of Starch
Waxy maize (100% amylopectin)
Waxy maize physically treated to preventgranule break up
Wheat
Salivary amylase
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Heatshear
Nativewaxy maize
starch
Modified/crosslinkedwaxy maize
Wheat
Polysaccharidereleased fromswollen granule
Granuledisruption
Swelling
Botanicalorigin
Salivaryamylase
Processing
Effect of processing, origin andamylase on microstructure of paste
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Cooked starch CharacteristicsCooked starch CharacteristicsUndercookedUndercooked OptimalOptimal
cookingcookingOvercookedOvercooked
Appearance Cloudy Clear Clear
Texture Thin, starchytaste
Heavy bodied,short textured
Cohesive, longtexture
Stability Poor Good Manyfragments, fewintact granules
Viscosity Low Good Viscosity drop
Microscope Small granules,under swollen,birefingentcross
Well swollen,somefragments
Manyfragments,fewintact granules
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Consequences of changingmicrostructure of starch
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Starch systems – impact oforigin
Wheat – Modified waxy maize give higher mixingefficiency / sodium release / taste perception thannon-modified waxy maize
100 μm
Wheat
100 μm
Waxy maize
100 μm
Modified waxy maize
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Starch systems – impact ofsalivary amylase
α-amylase is an enzyme present in saliva,can cleave α 1-4 bonds between glucoseresidues in starch molecules
At the concentrations present in saliva it canhalve the viscosity of a starch paste in a fewseconds
Large variation in in-mouth amylase activitybetween subjects
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Starch systems – impact ofsalivary amylase
0 50 100 150 200Modified waxymaize starch
0 50 100 150 200Waxy maizestarch
100 μm
0 50 100
100 μm
2-a 50 100
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Thickener typeSaltiness Thickness
HPMC 0.11ns 0.09ns
Waxy maize starch -0.20* -0.28***
Modified waxy maize starch -0.43*** -0.19*
Wheat starch -0.25*** -0.14ns
Correlations between perceivedsaltiness and thickness andpanellists saliva amylase activity
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Conclusions from amylasestudy
Amylase activity in the mouth releasespolymeric material from swollen starchgranules reducing mixing efficiency andsalt perception
Data suggests that consumers whohave a high in-mouth amylase activityperceive flavour/taste in starchthickened foods less well
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Microstructure
Mixing
Rheology
Sensory/inbody
performance
The Weakest Link?
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Observation of droplet breakup in two fluid systems
Easy break up of the viscous fluidelement will result in good mixing
Rheooptics
CaBER rheometer
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Counter rotating shear cell
FV
G
3
1
21: Transparent parallel rotatingplates.2: Observed object in suspendingfluid3: Image acquisition unit: opticalmicroscope +camera+ monitor +DVD recorder
- 2 transparent plates rotating in opposite directions
- Gap (h) is 1mm, radius (r) at which the droplet sits 5-10mm
- droplet is submitted to a known shear rate calculated as follows:
with ωu and ωl the relative velocities of upper and lower plate respectively
- Suspending fluid: high viscosity silicon oil (transparent, inert towards aqueous systems,induces high stresses)
h
rlu *
Observed system is static in laboratory reference
Silicon oil
Fluid droplet
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HPMC and cross linked waxy maize starch atequivalent shear viscosities
100µm
100µm
100µm
HPMC
CLWM
0
1
2
3
4
5
6
7
0 50 100 150 200 250 300
Strain
L/D
o
HPMC
CLWM
HPMC overshoot, no breakup
Starch deformation and breakup
HPMC and CLWM at shear stress 640Pa. D0 =80μm
Under the same conditions, HPMC and CLWM behave differently;
- HPMC reaches a steady-state deformation
- CLWM deforms and breaks up.
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CaBER Extensional Rheometer
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Experimental Conditions
The sample is placed between two parallel plate (6mmdiameter) separated by a 3mm gap.
The fluid is then exposed to a rapid extensional stepstrain by moving the upper plate upwards (final gap11.3mm, linear strike, 50ms), thereby forming a fluidfilament.
A laser micrometer measures the midpoint diameter ofthe gradually thinning fluid filament, after the upperplate has reached its final position, until its break-up.
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Processed xanthan
Wheat
Waxy maize
M odif ied waxy
maizeGelat ine
0.00
0.01
0.02
0.03
0.04
0.05
0.2 0.3 0.4 0.5 0.6
Viscosity 50s -1 (Pa.s)
Bre
ak-u
pti
me
(s.)
Filament break-up times for goodmixers
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1.5
1.6
1.7
1.8
1.9
2
2.1
-0.25 0.25 0.75 1.25 1.75
log (Kokini shear stress (Pa))
log
(mean
flavo
ur
)
w axy maize
(crosslinked)w heat
w axy maize
nativeHPMC (Anne-
Laure)HPMC (Dave
Cook)
Perceived Flavour Plotted Against KokiniShear Stress
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Conclusion
As a thickener for foods starch has afundamental advantage over most otherpolysaccharide hydrocolloids due to its moreefficient mixing with bodily fluids
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References
Murphy, P and Mitchell, J, (2009) Starch in Handbook ofHydrocolloids edited and Phillips G.O and Williams P.A,Woodhead Publishers
Ferry, A-L et al. Viscosity and flavour perception. Why is starchdifferent from hydrocolloids? Food Hydrocolloids (2006) 20:855
Ferry, A-L et al. In-mouth amylase activity can reduce perceptionof saltiness in starch thickened foods. J of Agricultural andFood Chemistry (2006) 54:8869
Desse, M, Wolf, B, Mitchell, J. and Budtova, T Experimental studyof the break up of starch suspension droplet in step-up shearflow . J Rheology (2009) 53: 943
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Thanks
Ann-Laure Ferry (Nestlé, DEFRA Food Link) Melinda Desse (European Polysaccharide Network of
Excellence) Bettina Wolf Tatiana Budtova Sandra Hill Tim Foster Luca Marciani Andy Taylor Dave Cook Dave Howling Margaret Hill