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Rheology of food materials

Rheology of food materials

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Rheology of food materials

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  1. Rheology of food materials

  2. Food products: life cycle

  3. Rheology roadRheology road and measuring system

  4. 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

  5. Typical shear rates

  6. Viscosity values

  7. Typically used measuring systems Cone - plate and plate - plate systems Usesandblastedorprofiledmeasuringsystemsforoilyandfattysubstances ! Gel-likesamples G‘ > G‘‘ andtemperaturetests Profiled geometries for mozarrella type of cheeses, sandblasted for cream cheese PP25 Viscoelastic, high viscous, caution to particles and structures sizes Paste like, sticky and almost not flowing CP25-1, CP25-2, CP25-2 Viscoelastic, medium viscosity (free flowing and significantly above 100 mPas (1000mPas) (larger particlesor super structures ) PP50 Viscoelastic, medium viscosity (free flowing and significantly above 100 mPas (1000mPas) Flowing liquid but larger super-structures (CP50-2) CP50-1 Low viscosity CP75-0,5

  8. CPxx: Cone & PlateCone truncation Cone with truncation: cone truncation = measuring gap Crash!! + 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

  9. 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 modular Bi-cone for inset-Peltier Peltier basis-control by conduction

  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 optional evaporation blocker Peltier-Hood Heating / Cooling byConvection and Radiation Peltier Basis Temp.-ControlbyConduction

  11. Sealing the Gap: PP & CP Applications: Food, cosmetics, coatings • evaporation of solvent / water ? • skin formation ? 2 - guard ring oil(10 mPas Si-Oil)

  12. Sealing the Gap: PP & CPApplications: Food, cosmetics, coatings • evaporation of solvent / water ? • skin formation ? 1a - solvent trap solvent sample

  13. 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 • 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

  14. Flow Behavior: ideallyviscousbehavior water 10 1000 mPa mPas 10 lg h 1 lg t constant viscosity 1 DG 42 (double gap MS) T = +20°C 0.1 0.01 0.1 1 10 s-1 100 lg Double-gapmeasuringsystemsarespecialsystemsdesigned forlow - viscosityliquids.

  15. Natural Food ProductsMeasure 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 - >

  16. Special GeometriesCC withSurface Treatment orVanes, 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 - ...

  17. Special Geometries (Relative Values) Helix 1 Helix 2 Blade Anchor Ball Measuring System All these stirrers are relative measuring systems Stirrer for Building Materials Starch Stirrer

  18. Rheometry with special GeometriesBall Measuring System (BMS) for dispersions containing coarse-grained particles (showing a diameter up to 10mm) Example: Marmalade containing fruit pieces

  19. Rheometrywithspecial GeometriesBall Measuring System (BMS) Flow and Viscosity Curves of two Marmalade Preparations

  20. Rheometrywithspecial GeometriesBall Measuring System (BMS) Flow and Viscosity Curves of a Sauce Bolognese 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 BehaviorRheo - Microscopy dispersions water / oil emulsion Size and shapeof the dropletsare dependingon shear rateand “shear history”. lg

  23. rest high shear rates high viscosity low viscosity Shear-Thinning flow Behavior Suspension 1: Orientation of particles (needle shaped) Suspension 2: Agglomerated particles Break-up of agglomerates Emulsion: Deformation and break-up of droplets

  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. Flow BehaviorShear-thickeningBehavior dispersions Suspensions shear - thickening of suspensions at - high solid concentrations- high shear loads 1 f ... volume fraction of solid particles

  26. Flow BehaviorYield Point High stress…sample starts moving t2 The applied force is higher than the structural force Low stress…no movement t1 Flow Curves on a linearscale  Yield Point as a limitingvalueoftheshear stress 2 Break ofthestructure - at - rest. Super - structureby a chemical- physicalnetworkvia interactiveforces. 1 ty  1 without a yield point 2 having a yield point y Examples: Pastes, concentrated dispersions, suspensions, ketchups, mayonnaises, chocolate melts, butter, gels

  27. Pa 2500 2000 1500 Ketchup t 1000 t shear stress 500 0 0 200 400 600 s-1 1000 shear rate Flow behavior: yield point Flow curveshowing a yield point(on a linear scale) Yield point can hardly be read-off

  28. Flow BehaviorYield Point, comparisonlin / log diagrams (2) food 104 Flowcurveshowing a Yield Point(on a logarithmicscale) Pa 1000 lg t Ketchup 100 yield point y = 48 Pa 10 1 10 100 s-1 1000 lg

  29. Flow behavior: yield point Flow curves on a logarithmic scale ty ty Yield point analysis in the low-shear range, e.g. read offon the - axis Yield point analysis in the low-shear range, e.g. read offat = 0.01 s-1

  30. Flow behavior: yield point Mathematical curve fittingfor flow curves on a linear scale(approximation, "regression") examples: models according to Bingham:flow curve of a material with a yield stressand a constant viscosity (foodor cosmetics) B- “yield pointacc. toBingham“ B - “Bingham viscosity“ Windhab:chocolate and other cocoa products 0- yield point 1- linear yield point  - “high-shearviscosity“ • other often used models: • - Cassonblood, food • Herschel / Bulkley • materials with a yield • stress and shear thinning or shear thickening behavior

  31. Flow BehaviorYield Point food Analysis using Approximation Functionsfor Flow Curveshere:accordingtoCasson (OICC 1973),andWindhab(IOCCC 2001 / ICA) Chocolate Melts(T = +40°C) Bitter White Whole Milk  shearrate Analysis CassonWindhab0(Pa) 0 (Pa)Bitter15 18 White1925Whole Milk2123 Summary: Yield Points are not material constants, sincetheyaredepending on themeasuringmethodand on theanalysismethod.

  32. Viscoelastic BehaviorYield Point (using a / - Diagram) Yieldpointasthelimitingvalueoftheshear stress: The sample startstoflownot beforetheexternalforcesareexceedingthenetwork-of-forcesoftheinternalstructure. Belowtheyieldpoint thereiselasticdeformation. Testingwithcontrolledshear stress lg  lg  lg  lg  yieldpointyusingthe best fit straightline (“tangent“) in the linear-elasticdeformationrange yieldpointyusingthe „tangentcrossover“method

  33. 106 % without binderyield point 13.5 Pa 104 lgg with binder yield point 114 Pa 102 100 10-2 Pa 0.1 1 10 100 1000 shear stress lgt Viscoelastic BehaviorYield Point (using a / - Diagram) food Comparisonoftwo Ketchups deformation

  34. IntroductionViscoelastic Behavior   viscous viscoelastic elastic with tand= G'' / G'

  35. ApplicationShearModulus Material StiffnessandShear Moduli Example: different typesofcheese 1 2 5 4

  36. Viscoelastic BehaviorAmplitude Sweeps food Gel Strength, Dependence on the Binder - Concentration 10,000 15 w-% Pa Starch Gel (in water) 10 w-% 1000 Summary: Gel strengthis dependent on the binder concentration lgG' 7.5 w-% 5% w-% 100 10 ω = 10 rad/sT = +23°C loss factor tan = G‘‘ / G‘ First check in the LVE range: tan < 1 for all samples ( = gel structure) ? Yes ! lg tand 1 0.1 0.1 10 % 100 1 strain lg g

  37. Viscoelastic BehaviorAmplitude Sweeps food TemperatureDependenceof Butter 10 MPa T = +10°C 1 Summary: cold butter shows brittle break,hence poor spreadability lgG' 0.1 lg G'' T = +23°C 0.01 ω = 10 rad/s 0.01 0.1 1 % 10 strain lg g

  38. Amplitude Sweep /CSD /CSSMargarine as semi-solid material withflowpoint CSD CSS

  39. ApplicationSedimentation, Long-term Storage Stability dispersions Stability of DispersionsExample: Salad Dressings in the beginning after 15min Behavior in the low-shear range or at rest, respectively

  40. FrequencySweepStabilityofsuspensions Time dependentstructuralstrength • G’ decreasing • - Long termbehavior= Fluid -like- StrengthofthestructureG’ decreases • Goodflowcharacteristics- Low stability • G’ constant, lightdecreasing- Long time structuralstrengthG‘ - Bad flowcharacteristics- High stability 2 1 1 t = 1 / omega G‘ G‘‘ 2 2 1 w = 1 / Time

  41. Amplitude SweepSedimentation-Stability Milk: Geometry DG26.7* • Pure milk • Chocolate Milk Plus • Chocolate Milk Budget • Caenriched Mill Mechanicalstoragestability

  42. Amplitude SweepStructuralstrength G´ asfunctionof stress -1 10 Pure Milk (noG‘ ) Pa CA Milk CHOC plus CHOC budget -2 10 G' -3 10 tLVE tLVE tLVE -4 10 Pa 0,0001 0,001 0,01 0,1 TAULVE = Yield stress = Externalforcetoovercomethestructureatrest Shear stress t *) Strain-Test, plottet asfunctionofstrain

  43. FrequencySweepSedimentation Stability Pure milk DG 26.7 G' Choc milk, plus DG 26.7 G' 0 10 Choc milk, Std. Pa DG 26.7 G' -1 10 CA-Milk DG 26.7 G' -2 10 G' -3 10 -4 10 1/s 0,1 1 10 100 w Measurement ofstructuralstrengthatrestormechanicalstabilityof milk

  44. 5 10 Pa G' 4 10 G'' 5°C 20°C 36°C 3 10 2 3 4 10 10 10 t Pa Amplitude SweepRepresentationasfunctionof stress todeterminetheflowpoints • Spreadcheese • Temperaturebehavior • Flow point= SpreadabilityascrossoverpointatG‘ = G“ Spreadcheese5°C G' G'' Spreadcheese20°C G' G'' Spreadcheese36°C G' G''

  45. Penetration measurementsSoft cheese • Presetting 0.3N contactpressure • Temperature60°C • Temperatureofcheesebeforetest ca. 25°C Start Depth End Time

  46. Penetration measurementMargarine • Presetting: Penetration velocity down/up= 2000µm/s • Alternatively: Normal forcecontrolledtesting down stop up Time

  47. Flow BehaviorTemperature - dependentBehavior softeningandmelting, orsolidificationandcrystallization  preset: constantshearconditions (shear rate orshear stress)result: viscosity / temperaturecurvewithsteadilydecreasingorincreasingviscosityvalues, respectively T gelformationandcuring preset: constantshearconditions (shear rate orshear stress)result: viscosity / temperaturecurveshowing a viscosityminimum  min T

  48. Flow BehaviorTemperature - dependentBehavior food 10 Coolingprocess: CrystallizationTemperature ofCocoa Butter Pas 8  ChocolateMelt 6 h 4  crystallization 2 0 20 25 30 35 °C 40 temperature T

  49. Starch gelling • Electrical heated cell • Watercooling • Fast heating and cooling rate • Stirrer acts against sedimentation of particles

  50. Viscoelastic BehaviorTemperature - dependentBehavior meltingorcrystallizationprocess preset: constantshearconditions (amplitudeandfrequency) (with an amplitude in the LVE-range, andmostlywithω = 10 rad/s) result: steep decrease or increase, resp.,in a narrow temperature range Tk ... crystallization temperature