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Food Analysis Lecture 14 (3/9/2010) Rheological Principles for Food Analysis Qingrong Huang Department of Food Science http://foodsci.rutgers.edu/huang/Food_Analysis/FA2010.htm
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Reading Materials Reading Chapter 30 Questions: Page 515, Study Questions: 4-6
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Shear Rate Shear flow between parallel plates Shear rate =d( L/h)/dt or
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Fluid Viscosity Newtonian Fluids: where is the stress, is the shear rate, and is the Newtonian the viscosity. Apparent viscosity ( ) is defined as If is a constant, then it is a Newtonian fluid; otherwise it is non-Newtonian fluid.
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Newtonian Fluids
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Shear Thinning vs. Shear Thickening Most of the fluid foods are not Newtonian fluids;
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Rheological Fluid Models Herschel-Bulkley Model =0] Newtonian Model: [n=1; k=µ;σ 0 =0] Power law Model: [=0] Power law Model: [σ 0 =0] Bingham Plastic Model [n=1;K=µ pl ] Bingham Plastic Model [n=1;K=µ pl ]
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Rheometry Concentric Cyclinders M: torque
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Cone and Plate
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Stress shear rate
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Steady Shear Rotational Viscometry Experimental Procedures: Test fixture selection - e.g. cone plate or C.C. Speed (shear rate) selection Data collection - values of torque & speed Shear calculations - shear stress and shear rate Model parameter determination - applicable rheological model
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Rheological Properties of Solids Large strain testing - compression and tension (i.e., extension) test can be used to determine large strain and fracture food properties. - Texture Profile Analysis (TPA) Effective of relative huminity
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Scope of the Mid-Term Class notes; Food Analysis book Quiz, labs, and end-of-chapter questions 80 min in-class exam, close book, no discussion
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1. Solutions & Concentration ppm ppt wt% Mol/L N Dilution Solution preparation Buffer, pH meter Lab
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2. Data Analysis Mean Standard deviation Accuracy and precision Confidence Interval Q-test Curve fitting
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3. pH Total acidity pH, degree of ionization, pKa Buffer and buffer capacity pH meter Lab
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4. Spectroscopy Basic Principles of UV, Fluorescence, IR E=h Interference Energy level Beer’s law Absorption and emission Instrumentation : - monochromator, interferometer, PMT, thermocouple detector, light source, photo diode detector Data interpretation Applications Labs
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Rheological Properties of Foods Basic concepts of stress, strain, deformation Relationship between stress and strain Different rheological models: Newtonian, power law Lab
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