www.anton-paar.com rheology of food materials. 2 food products: life cycle food productsrheological...
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www.anton-paar.com
Rheology
of food materials
2
Food products: life cycle
Food products Rheological characterization
Formulation-- Composition, additives and stabilizers
Viscosity and flow behavior of formulation
Production Flow behavior, viscosity, elasticity
Storage Sedimentation stability, thermal stability
Application (usage) Flow behavior under shear conditions, Thixotropy
3
Rheology roadRheology road and measuring system
4
- Measuring systems for rotational and oscillatory rheometers- Flow and viscosity curves in a wide shear rate range
Examples: Water; Polymer solutions (polysaccharide); Emulsions; Binder solutions- Special measuring systems: measuring with the ball measuring system
Examples: Marmalade, Bolognese sauce with meat chunks- Yield point in flow curves (via rotational tests)
Examples: Creams; Ketchups- Yield point as the limiting value of the linear-elastic deformation range (via rotational tests)
Example: Ketchup- Structure at rest as G’ value (via oscillatory tests: amplitude and frequency sweeps)
Examples: 1) Butter; 2) Starch gels; 3) Pudding; 4) Milk drinks; 5) Emulsions- Structure regeneration of coatings, leveling, sagging behavior and layer thickness- Step tests (oscillatory and rotational tests)
Example: Ketchup- Temperature-dependent behavior during heating, softening, melting, cooling, solidification, crystallization (using rotational and oscillatory tests)
Examples: Chocolate; Ice creams; Spreading cheese and melting cheese- Gel formation (using time-dependent and temperature-dependent rotational and oscillatory tests)
Examples: Corn starch; Gelatin
Overview
5
Typical shear rates
Process Shear rate range [s-1] Examples of application
Sedimentation (fine particles in a suspension)
10-6 to 10-4 Salad dressing, fruit juice
Leveling - due to surface tension
10-2 to 10-1 Coatings, printing inks, lacquers, chocolate
Dip coating 1 to 100
Chewing, swallowingPouring from a bottle
10 to 100 Cheese, yogurt, chocolate
Transport in tubes, pipe flow, pumping, filling into containers
1 to 104 Blood, crude oils, paints, juices
Mixing, stirring 10 to 104 Emulsion, plastisol, polymer blends
Brushing, painting, spraying, blade coating
100 to 104 Brush coating, tooth paste, butter
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Materials Shear viscosity
Gases / air 0.01 to 0.02 / 0.018 mPas
Water at 20°C(at 0 / 40 / 60 / 80 / 100°C)
1.0 mPas(1.8 / 0.65 / 0.47 / 0.35 / 0.28 mPas)
Milk, coffee creams 2 to 10 mPas
Olive oil approx. 100 mPas
Glycerin 1480 mPas
Polymer melts (T=+100 to +200°C and at shear rates of 10 to 1000 1/s)
10 to 10 000 Pas
Polymer melts (zero-shear viscosity) 1 kPas to 1MPas
Bitumen (T = +80 / +60 / +40 / +20 / +0°C)
200 Pas / 1 kPas / 20 kPas / 0.5 MPas / 1 MPas
Viscosity values
7
Typically used measuring systems Cone - plate and plate - plate systems
Use sandblasted or profiled measuring systems for oily and fatty substances !
Viscoelastic, high viscous, caution to particles and structures sizesPaste like, sticky and almost not flowing
Viscoelastic, medium viscosity (free flowing and significantly above 100 mPas (1000mPas)(larger particles or super structures )
Low viscosity
CP75-0,5
CP50-1
PP50
CP25-1, CP25-2, CP25-2
PP25
Gel-like samples G‘ > G‘‘ and temperature testsProfiled geometries for mozarrella type of cheeses, sandblasted for cream cheese
Viscoelastic, medium viscosity (free flowing and significantly above 100 mPas (1000mPas)Flowing liquid but larger super-structures (CP50-2)
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Cone with truncation:
CPxx: Cone & PlateCone truncation
+ Shear rate and shear strain constant+ Easy to clean- Measurement of friction if particles are below the tip of the cone
Standards: ISO 3219, DIN53019, DIN53018
Crash!!
Name Cone Truncation- [µm]CP25-1 50CP25-2 105CP25-3 170CP35-3 240CP50-0.5 50CP50-1 100CP50-2 210CP50-3 345CP60-0.5 60CP60-1 120CP60-2 250CP75-1 150CP75-2 315
cone truncation=
measuring gap
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Double Cone BI-C60-1°Applications: Food, Cosmetics, Pharma
modularBi-conefor inset-Peltier
precise determination of melting and crystallization temperature homogenous heating and cooling low temperature measurements without condensation (inert, dry) no evaporation of water or solvents
Peltier basis-control by conduction
Peltier-hood heating & coolingby convectionand radiation
N2
10
PTD – Peltier Temperature DeviceExcellent temperature control from the bottom to the top
unique combination of radiation, convection (frost protection) & conductive heating & cooling
homogenous heating and cooling low temperature measurement without having
- condensation (inert, dry)- frost formation
Peltier-Hood Heating / Coolingby Convectionand Radiation
Peltier Basis Temp.-Control by Conduction
optional evaporation blocker
11
Sealing the Gap: PP & CP Applications: Food, cosmetics, coatings
2 - guard ring
oil (10 mPas Si-Oil)
evaporation of solvent / water ? skin formation ?
12
Sealing the Gap: PP & CPApplications: Food, cosmetics, coatings
evaporation of solvent / water ? skin formation ?
1a - solvent trap
sample
solvent
13
Typically used measuring systems Concentric cylinders systems
Standards: ISO 3219, DIN53019, DIN53018
Easy to prevent sample from drying-out (oil film on top of sample) No trimming Good solution for all kind of liquids in rotational mode CC: not recommended for oscillation; DG: also recommended for oscillation CC: Helical groove if phase separation or vertical profiling to prevent slippage
Above 10mPas and below 100mPas with super-structures DG27 (same dimensions like CC27), gap size = 1mm
Above 1000mPas (100mPas) CC27
Above 10mPas and below 1000mPas CC39
Below 10mPas und homogenous, small structure DG26.7, gap size = 0.4mm
14
0.1
1
10
mPas
0.01
0.1
1
10
1000
mPa
1 10 100s-1
DG 42(double gap MS)
T = +20°C
Double-gap measuring systems are special systems designed for low - viscosity liquids.
constant viscosity
water
lg h lg t
lg
Flow Behavior: ideally viscous behavior
15
A special measuring system for:E.g. natural yoghurt
Natural Food ProductsMeasure natural product without destroying the initial structure by cutting into the sample structure
Advantages: allows measurement of brittle, natural materials excellent penetration characteristics dimensions similar to standard CC27 alternative: combination with flexible cup holder - >
ST22-4V-40 measuring system aluminum cup or stainless steel cup
16
Coarse disperse materials
Building materials Slurries Food (Yoghurt)
Special GeometriesCC with Surface Treatment or Vanes, Stirrers, Propellers
Better grip No slip
More Stirrers on request:
- User defined
- Brookfield Spindels
- Krebs Stormer Spindels
- ...
17
All these stirrers are relative measuring systems
Special Geometries (Relative Values)
Helix 1 Helix 2
Stirrer forBuilding Materials
StarchStirrer
Blade Anchor
Ball Measuring System
18
Rheometry with special Geometries Ball Measuring System (BMS)
for dispersions containing coarse-grained particles(showing a diameter up to 10mm)
Example: Marmaladecontaining fruit pieces
19
Rheometry with special Geometries
Ball Measuring System (BMS)
1
10
100
1,000
Pa
1
10
100
1,000
Pa·s
0.1 1 10 1001/s
Shear Rate .
Flow- and Viscosity Curves of Jams at 23 °CMeasured with the Ball Measuring System
Anton Paar GmbH
blueberry
KMS-3 /Q1; d=0 mm
Shear Stress
Viscosity
lemon
KMS-3 /Q1; d=0 mm
Shear Stress
Viscosity
Flow and Viscosity Curves of two Marmalade Preparations
20
Rheometry with special Geometries Ball Measuring System (BMS)
Flow and Viscosity Curves of a
Sauce Bolognese
10 0
10 1
10 2
10 3
Pa
10 0
10 1
10 2
10 3
10 4
Pa·s
10 -4
10 -3
10 -2
10 -1
10 0
10 1
10 2
1/s
Shear rate .
Copyright (C) 1999 Physica Meßtechnik GmbH
meat sauce
KMS - 1M
shear stress
viscosity
meat sauce (new sample)
KMS - 1M
shear stress
viscosity
Spaghetti Sauce containing meat pieces(testing reproducibility)
21
Further measuring systems/ temperature control systems
Starch (pressure) measuring cell
Tribology cell
Penetration measurements
Interfacial rheology (IRS)
Sentmanat extensional rheology(SER)
Flexible Toolholder
Rheo-Microscopy
22
Flow Behavior
Rheo - Microscopy
Size and shapeof the dropletsare dependingon shear rate
and “shear history”.
water / oil emulsiondispersions
lg
23
Shear-Thinning flow Behavior
Suspension 1:Orientation of particles(needle shaped)
Suspension 2:Agglomerated particlesBreak-up of agglomerates
Emulsion:Deformation and break-up of droplets
high viscosity low viscosity
rest high shear rates
24
Shear-Thickening flow Behavior
At low shear load:The rod inclines slowly.
Low viscosity
At high shear load:Solidification of the liquid due to shear
thickening.High viscosity
25
Suspensions shear - thickening of suspensions at - high solid concentrations- high shear loads
Flow BehaviorShear-thickening Behavior
1
f ... volume fraction of solid particles
dispersions
26
Flow Curves on a linear scale
Yield Point as a limiting value of the shear stress
1 without a yield point2 having a yield point y
2
1
ty
Flow Behavior
Yield Point
Break of the structure - at - rest.Super - structure by a chemical - physical
network via interactive forces.
The applied force is higher than the structural force
Low stress…no movement
High stress…sample starts moving
t1
t2
Examples: Pastes, concentrated dispersions, suspensions, ketchups, mayonnaises, chocolate melts, butter, gels
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0
500
1000
1500
2000
2500
Pa
t
0 200 400 600 1000s-1
shear rate
Ketchup
t shear stress
Yield point can hardly be read-off
Flow curveshowing a yield point(on a linear scale)
Flow behavior: yield point
28
10
100
1000
104
Pa
1 10 100 1000s-1
Ketchup
Flowcurveshowing a Yield Point(on a logarithmic scale)
yield point y = 48 Pa
food
Flow BehaviorYield Point, comparison lin / log diagrams (2)
lg t
lg
29
Flow curves on a logarithmic scale
ty
Flow behavior: yield point
Yield point analysis in the low-shear range,
e.g. read off at = 0.01 s-1
ty
Yield point analysis in the low-shear range,
e.g. read off on the - axis
30
Mathematical curve fitting for flow curves on a linear scale (approximation, "regression")
other often used models: - Cassonblood, food - Herschel / Bulkleymaterials with a yieldstress and shear thinning or shear thickening behavior
Flow behavior: yield point
Bingham: flow curve of a material with a yield stress and a constant viscosity(food or cosmetics)
B - “yield point acc. to Bingham“B - “Bingham viscosity“
Windhab:chocolate and other cocoa products
0 - yield point
1 - linear yield point
- “high-shear viscosity“
examples: models
according to
31
0
200
400
600
800
1,200
Pa
0 50 1001/s
Cream 1
Shear Stress
Cream 2
Shear Stress
Cream 1 Herschel-Bulkley
tau0 = 705.01 Pa; b = 11.503; p = 0.84742
Shear Stress
Cream 2 Herschel-Bulkley
tau0 = 31.224 Pa; b = 4.7648; p = 0.94538
Shear Stress
Analysis using Approximation Functions for Flow Curveshere: according to Casson (OICC 1973), and Windhab (IOCCC 2001 / ICA)
0
50
100
150
200
250
300Pa
0 10 20 30 40 501/s
Scherrate .
Anton Paar GmbH
Zartbitter 2
Schubspannung
Weiße 1; A4...A4
Schubspannung
Vollmilch; A4...A4
Schubspannung
ChocolateMelts(T = +40°C)
Bitter
White
Whole Milk
Analysis Casson Windhab 0 (Pa) 0 (Pa)
Bitter 15 18 White 19 25Whole Milk 21 23
shear rate
food
Summary:
Yield Points are not material constants,since they are depending on the measuring method and on the analysis method.
Flow BehaviorYield Point
32
Viscoelastic Behavior
Yield Point (using a / - Diagram)
Testing with controlled shear stress
Yield point as the limiting value of the shear stress:
The sample starts to flownot before the externalforces are exceeding thenetwork-of-forces of the internal structure.
Below the yield pointthere is elastic deformation.
yield point y using the best fit straight line (“ tangent“) in the linear-elastic deformation range
yield point y using the „tangent crossover“ method
lg
lg lg
lg
33
10-2
100
102
104
106
%
lg g
0.1 1 10 100 1000Pa
shear stress lg t
without binderyield point 13.5 Pa
with binderyield point 114 Pa
Comparison of two Ketchups
deformation
food
Viscoelastic Behavior
Yield Point (using a / - Diagram)
34
IntroductionViscoelastic Behavior
liquid - likestructure
„at the gel point“
gel - like structure
G'' >> G' G'' > G' G'' = G' G' > G'' G' >> G''
tand>> 1
tand> 1
tand= 1 tand< 1
tand<< 1
0
with
tand= G'' / G'
viscous
viscoelastic elastic
35
ApplicationShear Modulus
Material Stiffness and Shear Moduli
Example: different types of cheese
cheese type
example shear modulus(around)
1 cream Philadelphia 1 kPa
2 soft French Camembert
10 kPa
3 semi-hard Holland Gouda (young)
0.1 MPa
4 hard Swiss Emmentaler
0.5 MPa
5 extra hard Italian Parmigiano
1 MPa
5
1
2
4
36
100
1000
10,000
Pa
1
0.1 1 10 100%
Gel Strength, Dependence on the Binder - Concentration
15 w-%
10 w-%
7.5 w-%
5% w-%
0.1
10
Viscoelastic Behavior Amplitude Sweeps
ω = 10 rad/sT = +23°Closs factortan = G‘‘ / G‘
Starch Gel (in water)
Summary: Gel strengthis dependent on the binderconcentration
First check in the LVE range:tan < 1 for all samples ( = gel structure) ? Yes !
food
lg tand
lg G'
strain lg g
37
0.01
0.1
1
10
MPa
0.01 0.1 1 10%
ω = 10 rad/s
Temperature Dependence of Butter
Viscoelastic BehaviorAmplitude Sweeps
Summary:cold butter shows
brittle break,hence
poor spreadability
T = +10°C
T = +23°C
food
lg G'
lg G''
strain lg g
38
102
103
104
105
Pa
G'
G''
100
101
102
103
Pa
0,001 0,01 0,1 1 10 100%
Deformation
am03014
Margarine css
CP 50-2; d=0,05 mm
G' Speichermodul
G'' Verlustmodul
Schubspannung
102
103
104
105
Pa
G'
G''
10-1
100
101
103
Pa
0,001 0,01 0,1 1 10 100%
Deformation
am03014
Margarine CSD
CP 50-2; d=0,05 mm
G' Speichermodul
G'' Verlustmodul
Schubspannung
Amplitude Sweep /CSD /CSSMargarine as semi-solid material with flow point
CSD
CSS
39
ApplicationSedimentation, Long-term Storage Stability
in the beginning
Stability of DispersionsExample: Salad Dressings
after 15min
Behavior in the low-shear range or at rest, respectively
dispersions
40
Frequency SweepStability of suspensions
t = 1 / omega
Time dependent structural strength G’ decreasing
- Long term behavior = Fluid -like- Strength of the structure G’ decreases- Good flow
characteristics - Low stability
G’ constant, light decreasing - Long time structural strength G‘ - Bad flow characteristics - High stability
11 2
=1/w Time
G‘‘
2
G‘
1
2
41
Milk: Geometry DG26.7*
Pure milk Chocolate Milk Plus Chocolate Milk Budget Ca enriched Mill
Mechanical storage stability
Amplitude SweepSedimentation-Stability
42
Amplitude Sweep Structural strength G´ as function of stress
TAULVE = Yield stress = External force to overcome the structure at rest
Shear stress t
*) Strain-Test, plottet as function of strain
10-4
10-3
10-2
10-1
Pa
G'
0,0001 0,001 0,01 0,1Pa
Pure Milk (no G‘ )
tLVE tLVE tLVE
CA MilkCHOC budget CHOC plus
43
Measurement of structural strength at rest or mechanical stability of milk
Frequency SweepSedimentation Stability
10-4
10-3
10-2
10-1
100
Pa
G'
0,1 1 10 1001/s
w
Pure milk
DG 26.7
G'
Choc milk, plus
DG 26.7
G'
Choc milk, Std.
DG 26.7
G'
CA-Milk
DG 26.7
G'
44
Spread cheese Temperature behavior Flow point = Spreadability as crossover point at G‘ = G“
Spread cheese 5°CG'G''
Spread cheese 20°CG'G''
Spread cheese 36°CG'G''
103
104
105
Pa
G'
G''
102
103
104
Pa t
5°C20°C
36°C
Amplitude Sweep Representation as function of stress to determine the flow points
45
Penetration measurementsSoft cheese
Presetting 0.3N contact pressure Temperature 60°C Temperature of cheese before test ca. 25°C
0
2
4
6
10
mm
d
0
10
20
30
40
60
°C
T
0 2 4 6 8 10 12 14minZeit t
Penetration Test
Anton Paar GmbH
Start
End
Depth
Time
46
-1
-0,5
0
0,5
1
2
N
FN
-2.000
-1.500
-1.000
-500
0
500
1.000
2.000
µm/s
v
0 5 10 15 20 25sZeit t
Penetration measurement Margarine
Presetting: Penetration velocity down/up = 2000µm/s Alternatively: Normal force controlled testing
stop
up
down
Time
47
Flow Behavior
Temperature - dependent Behavior
softening and melting, or solidification and crystallization
preset: constant shear conditions (shear rate or shear stress)
result: viscosity / temperature curve with steadily decreasing or increasing viscosity values, respectively
gel formation and curing
preset: constant shear conditions (shear rate or shear stress)
result: viscosity / temperature curve showing a viscosity minimum
T
T
min
48
0
2
4
6
8
10
Pas
h
20 25 30 35 40°C
temperature T
Chocolate Melt
Flow Behavior
Temperature - dependent Behavior
Cooling process:Crystallization Temperature
of Cocoa Butter
food
crystallization
49
Starch gelling
Electrical heated cellWatercoolingFast heating and cooling
rateStirrer acts against
sedimentation of particles
50
melting or crystallization process
preset: constant shear conditions (amplitude and frequency)(with an amplitude in the LVE-range, and mostly with ω = 10 rad/s)
Tk ... crystallization temperature
result:steep decrease or increase, resp.,in a narrow temperature range
Viscoelastic Behavior
Temperature - dependent Behavior
51
preset:
g= 0.02 % ω = 10 rad/s T = T(t)
Viscoelastic BehaviorTemperature - dependent Behavior
food
melting
102
103
104
105
106
108
Pa
-20 -15 -10 -5 0 5 10°C
temperature T
Advantages of icecream 2:1) better separable at –20°C2) less cold - feel when melting3) creamier feel at molten state
lg G' lg G''
1
2
Comparison of two Ice Creams
1 Old Freezer2 New Freezer
52
10-1
100
101
102
Pa
G'
G''
30
35
40
45
50
55
60
65
70
75
°C
T
0 20 40 60 80 100minTime t
Anton Paar GmbH
Vegetable Fat 10%
G' Storage Modulus
G'' Loss Modulus
T Temperature
=1 % =10 1/s
Crystallization of a Vegetable FatRheo-Microscopy
53
Different Behavior of two Ketchup Samples
fast structure recovery
slowstructure recovery
Viscoelastic BehaviorTime - dependent Structure Recovery
for coatings: high wet-layer thickness, good film stability
for coatings:small wet-layer thickness, good levelling
54
Viscoelastic BehaviorTime - dependent Structure Recovery
preset:1 low - shear conditions
(strain in the LVE-range, oscillation)2 high - shear conditions (rotation)3 low - shear conditions
(strain in the LVE-range, oscillation)
measuring result:1 state of rest2 structure decomposition3 structure regeneration
Step test with 3 intervals, as oscillation / rotation / oscillation (measuring „thixotropic behavior“)
2nd test interval:liquid, at high shear rates
1st & 3rd test interval:G‘ > G‘‘ („gel-like structure“ at rest)
www.anton-paar.com
10
100
1000
Pa
G'
G''
0.4
0.6
0.8
1.0
Pas
h
0 50 100 150 200 250s
time t
Ketchup
G'
G''
h
g1 = g3 = 0.3 %
ω = 10 rad/s
=100 s-1 T = +23°C
Step test: oscillation / rotation / oscillation
Viscoelastic behavior: time - dependent structure recovery
56
Interfacial Rheology System (IRS)
MCR Rheometer + Interfacial Rheology System (IRS)
H1 = 22,5 mm
H2 = 45 mm
R = 40 mmR2 = 34,14 mm
2 = 10°
~~~~~~~~ ~~~~~~~~
~~~~~~~~~~~~~~~~~~~~
Air
Liquid 2
Liquid 2
Liquid 1 R2
R
z = H2
z = H1
z = 0
MotorTransducers
P. Erni et. al. J.Rev.Sci.Instr., 74(11), 4916-4924 (2003)
57
IRS: Film Formation of a Coffee Sample at different Concentrations
0.1% strain, frequency 1Hz 0.05g, 0.15g, and 0.3g coffee powder / 114ml double distilled water
10-6
10-5
10-4
10-3
10-2
100
Pa·m
Gi'
Gi''
0 200 400 600 800minTime t
Gi´= 3*10-5 Pa*m