Rheology of food materials www.anton-paar.com Food products: life cycle 2 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 Rheology road Rheology road and measuring system 3 Overview - 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 4 Typical shear rates 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 Process Dip coating Chewing, swallowing Pouring from a bottle 5 1 to 100 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 Viscosity values 6 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 Typically used measuring systems Cone - plate and plate - plate systems Use sandblasted or profiled measuring systems for oily and fatty substances ! Gel-like samples G‘ > G‘‘ and temperature tests Profiled geometries for mozarrella type of cheeses, sandblasted for cream cheese Viscoelastic, high viscous, caution to particles and structures sizes Paste like, sticky and almost not flowing Viscoelastic, medium viscosity (free flowing and significantly above 100 mPas (1000mPas) (larger particles or super structures ) Viscoelastic, medium viscosity (free flowing and significantly above 100 mPas (1000mPas) Flowing liquid but larger super-structures (CP50-2) PP25 CP25-1, CP25-2, CP2 PP50 CP50-1 Low viscosity CP75-0,5 7 CPxx: Cone & Plate Cone truncation Cone with truncation: cone truncation = measuring gap Crash!! Name - Cone Truncation [µm] CP25-1 CP25-2 CP25-3 CP35-3 CP50-0.5 CP50-1 CP50-2 CP50-3 CP60-0.5 CP60-1 CP60-2 CP75-1 CP75-2 50 105 170 240 50 100 210 345 60 120 250 150 315 + Shear rate and shear strain constant + Easy to clean - Measurement of friction if particles are below the tip of the cone 8 Standards: ISO 3219, DIN53019, DIN53018 Double Cone BI-C60-1° Applications: Food, Cosmetics, Pharma 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-hood heating & cooling by convection and radiation N2 Peltier basis-control by conduction 9 modular Bi-cone for inset-Peltier PTD – Peltier Temperature Device Excellent 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 optional evaporation blocker Peltier-Hood Heating / Cooling by Convection and Radiation Peltier Basis Temp.-Control by Conduction 10 Sealing the Gap: PP & CP Applications: Food, cosmetics, coatings evaporation of solvent / water ? skin formation ? 2 - guard ring oil (10 mPas Si-Oil) 11 Sealing the Gap: PP & CP Applications: Food, cosmetics, coatings evaporation of solvent / water ? skin formation ? 1a - solvent trap solvent sample 12 Typically used measuring systems Concentric cylinders systems Above 1000mPas (100mPas) CC27 Above 10mPas and below 1000mPas CC39 Above 10mPas and below 100mPas with super-structures DG27 (same dimensions like CC27), gap size = 1mm Below 10mPas und homogenous, small structure DG26.7, gap size = 0.4mm 13 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 Standards: ISO 3219, DIN53019, DIN53018 Flow Behavior: ideally viscous behavior water 10 1000 mPa mPas 10 lg 1 lg t constant viscosity 1 0.1 0.1 0.01 1 10 s-1 100 lg Double-gap measuring systems are special systems designed for low - viscosity liquids. 14 DG 42 (double gap MS) T = +20°C Natural Food Products Measure natural product without destroying the initial structure by cutting into the sample structure A special measuring system for: E.g. natural yoghurt ST22-4V-40 measuring system aluminum cup or stainless steel cup Advantages: allows measurement of brittle, natural materials excellent penetration characteristics dimensions similar to standard CC27 alternative: combination with flexible cup holder - > 15 Special Geometries CC with Surface Treatment or Vanes, Stirrers, Propellers Coarse disperse materials Building materials Slurries Food (Yoghurt) Better grip No slip More Stirrers on request: - User defined - Brookfield Spindels - Krebs Stormer Spindels 16 - ... Special Geometries (Relative Values) Helix 1 Helix 2 Blade Anchor Ball Measuring System All these stirrers are relative measuring systems Stirrer for Building Materials 17 Starch Stirrer Rheometry with special Geometries Ball Measuring System (BMS) for dispersions containing coarse-grained particles (showing a diameter up to 10mm) Example: Marmalade containing fruit pieces 18 Rheometry with special Geometries Ball Measuring System (BMS) Flow and Viscosity Curves ofCurves two Marmalade Flow- and Viscosity of Jams at 23 °C Measured with the Ball Measuring System Preparations 1,000 1,000 Pa Pa·s 100 100 blueberry KMS-3 /Q1; d=0 mm Shear Stress Viscosity lemon 10 10 KMS-3 /Q1; d=0 mm Shear Stress Viscosity 1 0.1 1 10 Shear Rate . Anton Paar GmbH 19 1/s 1 100 Rheometry with special Geometries Ball Measuring System (BMS) Flow and Viscosity Curves of a Sauce Bolognese 3 4 10 10 Pa·s Pa 3 meat sauce 10 KMS - 1M 2 10 t shear stress 2 t 10 viscosity meat sauce (new sample) KMS - 1M 1 t shear stress 10 1 10 0 0 10 10 -4 10 -3 10 -2 10 Shear rate -1 0 10 10 1 10 . Copyright (C) 1999 Physica Meßtechnik GmbH 20 2 1/s 10 viscosity Spaghetti Sauce containing meat pieces (testing reproducibility) 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 21 Flow Behavior Rheo - Microscopy water / oil emulsion lg 22 dispersions Size and shape of the droplets are depending on shear rate and “shear history”. Shear-Thinning flow Behavior rest high shear rates Suspension 1: Orientation of particles (needle shaped) Suspension 2: Agglomerated particles Break-up of agglomerates Emulsion: Deformation and break-up of droplets high viscosity 23 low viscosity Shear-Thickening flow Behavior At low shear load: The rod inclines slowly. Low viscosity 24 At high shear load: Solidification of the liquid due to shear thickening. High viscosity Flow Behavior Shear-thickening Behavior dispersions Suspensions shear - thickening of suspensions at - high solid concentrations - high shear loads 1 f ... volume fraction of solid particles 25 Flow Behavior Yield Point High stress …sample starts moving Low stress …no movement t2 t1 The applied force is higher than the structural force Flow Curves on a linear scale Yield Point as a limiting value of the shear stress Break of the structure - at - rest. Super - structure by a chemical - physical network via interactive forces. t 2 1 ty 1 without a yield point 2 having a yield point ty Examples: Pastes, concentrated dispersions, suspensions, ketchups, mayonnaises, chocolate melts, butter, gels 26 Flow behavior: yield point Flow curve showing a yield point (on a linear scale) Pa 2500 2000 1500 t Ketchup t shear stress 1000 500 Yield point can hardly be read-off 0 0 200 400 shear rate 27 600 s-1 1000 Flow Behavior Yield Point, comparison lin / log diagrams (2) food 104 Flowcurve showing a Yield Point (on a logarithmic scale) Pa 1000 lg t Ketchup 100 yield point ty = 48 Pa 10 1 10 lg 28 100 s-1 1000 Flow behavior: yield point Flow curves on a logarithmic scale ty 29 ty Yield point analysis in the low-shear range, Yield point analysis in the low-shear range, e.g. read off on the t- axis e.g. read off at = 0.01 s-1 Flow behavior: yield point Mathematical curve fitting for flow curves on a linear scale (approximation, "regression") examples: models according to Bingham: flow curve of a material with a yield stress other often used models: and a constant viscosity - Casson (food or cosmetics) blood, food tB - “yield point acc. to Bingham“ B - “Bingham viscosity“ 30 -Herschel / Bulkley materials with a yield stress and shear thinning or shear thickening behavior Windhab:chocolate and other cocoa products t0 - yield point t1 - linear yield point - “high-shear viscosity“ Flow Behavior Yield Point food Analysis using Approximation Functions for Flow Curves here: according to Casson (OICC 1973), and Windhab (IOCCC 2001 / ICA) 300 Pa 250 Chocolate Melts Zartbitter (T2 = 200 t +40°C) Schubspannung Bitter 150 Weiße 1; A4...A4 100 1,200 50 Pa Schubspannung White Cream 1 Vollmilch; A4...A4 t Shear Stress Schubspannung 0 0 Analysis Bitter White Whole Milk 31 Whole CreamMilk 2 800 10 20 shear rate. Scherrate Casson t0 (Pa) 15 19 21 30 40 t Anton Paar GmbH Windhab t0 (Pa) 18 25 23 1/s 50 t Shear Stress 600 Cream 1 Herschel-Bulkley 400 tau0 = 705.01 Pa; b = 11.503; p = Summary: 200 t Shear Stress Cream 2 Herschel-Bulkley Yield0Points are not material constants, tau0 = 31.224 Pa; b = 4.7648; p = 1/s 100 on the measuring since 0they are50depending t Shear Stress method and on the analysis method. Viscoelastic Behavior Yield Point (using a / t - Diagram) Yield point as the limiting value of the shear stress: The sample starts to flow not before the external forces are exceeding the network-of-forces of the internal structure. Testing with controlled shear stress lg lg Below the yield point there is elastic deformation. lg t yield point ty using the best fit straight line (“ tangent“) in the linear-elastic deformation range 32 lg t yield point ty using the „tangent crossover“ method Viscoelastic Behavior Yield Point (using a / t - Diagram) food Comparison of two Ketchups 106 % without binder yield point 13.5 Pa 104 lg deformation with binder yield point 114 Pa 102 100 10-2 0.1 1 shear stress 33 10 lg t 100 Pa 1000 Introduction Viscoelastic Behavior viscous G'' >> G' G'' > G' liquid - like structure with tand = G'' / G' 34 tand >> 1 tand > 1 viscoelastic G'' = G' „at the gel point“ tand = 1 G' > G'' elastic G' >> G'' gel - like structure tand < 1 tand << 1 0 Application Shear 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 Holland Gouda (young) 0.1 MPa Swiss Emmentaler 0.5 MPa Italian Parmigiano 1 MPa 3 semi-hard 4 hard 5 extra hard 35 1 2 5 4 Viscoelastic Behavior Amplitude Sweeps Gel Strength, Dependence on the Binder - Concentration food 10,000 Pa 15 w-% Starch Gel (in water) 1000 10 w-% Summary: Gel strength is dependent on the binder concentration lg G' 7.5 w-% 100 5% w-% 10 First check in the LVE range: tand < 1 for all samples ( = gel structure) ? Yes ! 1 lg tand 0.1 0.1 36 1 10 strain lg % 100 ω = 10 rad/s T = +23°C loss factor tand = G‘‘ / G‘ Viscoelastic Behavior Amplitude Sweeps food Temperature Dependence of Butter 10 MPa T = +10°C 1 Summary: cold butter shows brittle break, hence poor spreadability lg G' 0.1 lg G'' T = +23°C 0.01 ω = 10 rad/s 0.01 0.1 1 strain lg 37 % 10 Amplitude Sweep /CSD /CSS Margarine as semi-solid material with flow point 5 10 Pa G' 10 10 Pa 4 Margarine CSD 10 G'' 10 10 10 0,001 0,01 0,1 Deformation 1 5 10 10 10 % 100 0 G' Speichermodul G'' Verlustmodul Schubspannung -1 10 Pa 4 10 2 Margarine css CP 50-2; d=0,05 mm G'' 10 3 10 2 10 0,001 0,01 0,1 Deformation 1 10 am03014 CSD CP 50-2; d=0,05 mm 3 am03014 10 Pa 38 1 3 2 G' 3 10 % 100 1 0 CSS G' Speichermodul G'' Verlustmodul Schubspannung Application Sedimentation, Long-term Storage Stability dispersions Stability of Dispersions Example: Salad Dressings in the beginning after 15min Behavior in the low-shear range or at rest, respectively 39 Frequency Sweep Stability of suspensions 1 2 Time dependent structural strength 1 t = 1 / omega G‘ G‘‘ - 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 2 2 1 w=1/Time 40 G’ decreasing Amplitude Sweep Sedimentation-Stability Milk: Geometry DG26.7* Mechanical storage stability 41 Pure milk Chocolate Milk Plus Chocolate Milk Budget Ca enriched Mill Amplitude Sweep Structural strength G´ as function of stress TAULVE = Yield stress = External force to overcome the structure at rest -1 10 Pure Milk (no G‘ ) Pa CHOC budget CA Milk CHOC plus -2 10 G' -3 10 -4 10 0,0001 42 tLVE 0,001 Shear stress *) Strain-Test, plottet as function of strain tLVE tLVE 0,01 t Pa 0,1 Frequency Sweep Sedimentation Stability Measurement of structural strength at rest or mechanical stability of milk 10 0 Pure milk Pa 10 DG 26.7 G' -1 Choc milk, plus DG 26.7 G' G' 10 -2 Choc milk, Std. DG 26.7 G' 10 -3 CA-Milk DG 26.7 G' 10 -4 0,1 1 10 w 43 1/s 100 Amplitude Sweep Representation as function of stress to determine the flow points Spread cheese Temperature behavior Flow point = Spreadability as crossover point at G‘ = G“ 5 10 Spread cheese 5°C G' G'' Spread cheese 20°C G' G'' Spread cheese 36°C G' G'' Pa G' 4 10 G'' 5°C 20°C 36°C 3 10 2 10 3 4 10 10 t Pa 44 Penetration measurements Soft cheese Presetting 0.3N contact pressure Temperature 60°C Temperature of cheese before test ca. 25°C Penetration Test 60 10 Start Depth °C mm 40 d 6 30 4 20 End 2 10 0 0 0 2 4 6 8 Zeit t Time Anton Paar GmbH 45 10 12 min 14 T Penetration measurement Margarine Presetting: Penetration velocity down/up = 2000µm/s Alternatively: Normal force controlled testing down 2 2.000 µm/s N 1.000 1 FN 500 0 0,5 stop -500 0 -1.000 -0,5 -1.500 up -2.000 -1 0 46 5 10 Zeit t Time 15 20 s 25 v Flow Behavior Temperature - dependent Behavior softening and melting, or solidification and crystallization preset: constant shear conditions (shear rate or shear stress) T 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) min result: viscosity / temperature curve showing a viscosity minimum T 47 Flow Behavior Temperature - dependent Behavior food 10 Cooling process: Crystallization Temperature of Cocoa Butter Pas 8 Chocolate Melt 6 4 2 crystallization 0 20 25 30 temperature T 48 35 °C 40 Starch gelling Electrical heated cell Watercooling Fast heating and cooling rate Stirrer acts against sedimentation of particles 49 Viscoelastic Behavior Temperature - dependent Behavior 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) result: steep decrease or increase, resp., in a narrow temperature range Tk ... crystallization temperature 50 Viscoelastic Behavior Temperature - dependent Behavior food Comparison of two Ice Creams 8 10 1 Old Freezer 2 New Freezer 1 Pa 6 Advantages of icecream 2: 1) better separable at –20°C 2) less cold - feel when melting 3) creamier feel at molten state 10 lg G' 5 10 lg G'' 2 4 10 3 melting 10 2 10 -20 -15 -10 -5 temperature T 51 0 5 °C 10 preset: = 0.02 % ω = 10 rad/s T = T(t) Crystallization of a Vegetable Fat Rheo-Microscopy =1 % w=10 1/s 2 75 °C 70 10 Pa 65 1 60 10 55 G' 50 G'' 0 45 10 40 35 -1 10 30 0 20 40 Time t 60 Vegetable Fat 10% G' Storage Modulus Anton Paar GmbH 52 80 min G'' Loss Modulus T Temperature 100 T Viscoelastic Behavior Time - dependent Structure Recovery Different Behavior of two Ketchup Samples fast structure recovery for coatings: high wet-layer thickness, good film stability 53 slow structure recovery for coatings: small wet-layer thickness, good levelling Viscoelastic Behavior Time - dependent Structure Recovery Step test with 3 intervals, as oscillation / rotation / oscillation (measuring „thixotropic behavior“) 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 rest 2 structure decomposition 3 structure regeneration 2nd test interval: liquid, at high shear rates 1st & 3rd test interval: G‘ > G‘‘ („gel-like structure“ at rest) 54 Viscoelastic behavior: time - dependent structure recovery Step test: oscillation / rotation / oscillation 1000 Pas Pa G' Ketchup 1.0 100 G' 0.8 G'' G'' 0.6 0.4 1 = 3 = 0.3 % 10 0 50 100 time 150 200 s 250 ω = 10 rad/s =100 s-1 T = +23°C t www.anton-paar.com Interfacial Rheology System (IRS) MCR Rheometer + Interfacial Rheology System (IRS) H1 = 22,5 mm H2 = 45 mm R = 40 mm R2 = 34,14 mm 2 = 10° P. Erni et. al. J.Rev.Sci.Instr., 74(11), 4916-4924 (2003) 56 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 0 10 Pa·m -2 G i' 10 -3 10 Gi'' Gi´= 3*10-5 Pa*m -4 10 -5 10 -6 10 57 0 200 400 Time t 600 min 800