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Food Analysis Lecture 13 (3/2/2010)

Food Analysis Lecture 13 (3/2/2010). Infrared (3). Qingrong Huang Department of Food Science http://foodsci.rutgers.edu/huang/Food_Analysis/FA2010.htm. Reading Materials. Reading Chapter 24 & chapter 30 Questions: Page 515, Study Questions: 1-3. ATR-FTIR.

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Food Analysis Lecture 13 (3/2/2010)

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  1. Food Analysis Lecture 13 (3/2/2010) Infrared (3) Qingrong Huang Department of Food Science http://foodsci.rutgers.edu/huang/Food_Analysis/FA2010.htm

  2. Reading Materials Reading Chapter 24 & chapter 30 Questions: Page 515, Study Questions: 1-3

  3. ATR-FTIR ATR-FTIR: Attenuated Total Reflectance FTIR - A surface sensitive technique; - The evanescent wave penetrates only a small distance through the crystal (typically about a micro meter), depending on the refractive index of the IR-transparent crystal, the internal reflectance element (IRE).

  4. Near-IR Spectroscopy NIR (800-2500 nm) is more widely used for quantitative analysis of foods than are mid-IR.

  5. Near-IR Spectroscopy

  6. Near-IR Spectroscopy Reflectance (R) is defined as: R=I/I0 I: the intensity of radiation reflected from the sample at a given wavelength I0: the intensity of radiation reflected from the reference at the same wavelength Reflectance data are expressed most commonly as log (1/R), analogous to absorbance in transmission spectroscopy.

  7. NIR Applications

  8. Rheological Principles for Food Analysis Qingrong Huang Department of Food Science Reading Chapter 30 Questions: Page 515, Study Questions: 4-6

  9. Flow Properties of Foods

  10. Fundamentals of Rheology • Rheology: the study of the deformation and flow of all materils. • Viscosity: defined as the internal resistance to flow. • Stress (): the measurement of force, defined as the force (N) • divided by area (A, meters2), Pascals (Pa) • Two types of stress: • Normal stress: the force directly perpendicular to a surface • - tension or compression, eg. Chewing gum • Shear stress: the force parallel to the sample surface • - e.g. the spreading of butter over a slice of toast

  11. Normal vs. Shear Stress Normal stress Shear stress When a stress is applied to a food, the food deforms or flow. Strain (): is a dimensionless quality representing the relative deformation of a material.

  12. Shear Rate Shear flow between parallel plates Shear rate =d(L/h)/dt or

  13. 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.

  14. Newtonian Fluids

  15. Shear Thinning vs. Shear Thickening • Most of the fluid foods are not Newtonian fluids;

  16. Rheological Fluid Models • Herschel-Bulkley Model • Newtonian Model: [n=1; k=µ;σ0=0] • Power law Model: [σ0=0] • Bingham Plastic Model [n=1;K=µpl]

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