1. Lecture 11 Announcements
HW#7 due Today, 2/12
Lab #2 due Wednesday 2/14
HW#8 due Wednesday 2/14
HW#9 due Friday 2/16
No Homework #10!!!!! ( you are still responsible for the material in Lecture 11 on the test, however)
Upcoming test #1: Feb. 21
12/8/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

2. Food Rheology and Texture Chapter 7
Rheology: “a science devoted to the study of deformation and flow” (considers the time effect during the loading of a body) –Mohsenin
Express in terms of 3 parameters: force, deformation and time
Ex: time-dependent stress and strain behavior, creep, stress relaxation, and viscosity
Mech. Properties that are NOT rheo. properties: drag coefficient, terminal velocity, rebound and coefficient of restitution in impact, flow of the material in bulk (motion of material under applied forces)
12/8/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

3. Food Rheology and Texture Chapter 7
Food rheology data used for:
Sizing processing equipment such as pumps and tubes
Determining energy requirements
Effects of processing on flow processes
Filling operations
Rate of chemical reaction
Data is usually observed and empirical
12/8/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

4. Food Rheology and Texture Chapter 7
The volume fraction is the concentration variable affecting flow behavior
Highest volume fraction w/o particle deformation is called the packing fraction
Intrinsic viscosity: η
Determined by particle shape, flexibility and size
Using glass capillary viscometer
η/ρ = Cvt, where Cv is a viscometer constant
12/8/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

5. Food Rheology and Texture Chapter 7
Often used as an indicator of the effective volume occupied by molecules or dispersed particles. Can be used to find molecular weight
Increases due to heating…molecules, particles unfold and change shape
Decreases during enzymatic hydrolysis…breaks long, linear or random coil molecules into pieces.
12/8/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

6. Food Rheology and Texture Chapter 7
More about viscometers and rheometers (handouts)
12/8/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

7. Food Rheology and Texture Chapter 7
12/8/2018
BAE2022/BAE4400 Physical Properties of Biological Materials