Lecture 7Announcements Lab #1 due Today, 1/31 HW#5 due MONDAY, 2/5 HW#6 due Wednesday, 2/7 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Moisture Relationships Chpt 3, Pages 92-107 Water Activity: Used when referring to foods EMC used when referring to grains and seeds Chemical potential of a “system”…solution and the air above the surface of the solution Determines how states will change or interact. 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Moisture Relationships Chpt 3, Pages 92-107 Water Activity: ratio of vapor pressure above solution to vapor pressure of pure water Strongly influences microbial activity Molds don’t generally grow at less than 0.7 Yeats don’t grow at less than 0.8 Bacteria don’t grow at less than 0.9 Oxidation is at a minimum at 0.4 Browning reaches a maximum at 0.8 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Moisture Relationships Chpt 3, Pages 92-107 Water potential: describes the transfer of water into and out of cells and movement of water through cells. Characterizes the water status of cells in fruits and vegetables Osmotic pressure: measured with an osmometer 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Moisture Relationships Chpt 3, Pages 92-107 Osmotic Pressure depends on turgor potential and total water pressure Directly related to the solutions water activity When turgor potential = 0, plant tissue is flacid, not stretched or extended. When cells are placed in water that has a water potential different from the water potential in the cell, water will move across the cell membrane. 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Deformation and Viscoelasticity Chapter 4, pg. 111 - 169 Deformation due to applied forces varies widely among different biomaterials. Depends on many factors Rate of applied force Previous loading Moisture content Biomaterial composition 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Deformation and Viscoelasticity Chapter 4, pg. 111 - 169 Force deformation studies Texture of raw and processed, cooked and uncooked New variety selection Study damage during harvesting and handling Failure studies, cracking/splitting 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Deformation and Viscoelasticity Chapter 4, pg. 111 - 169 Deformation of solids and liquids/semi-solids Chapter 4: solids Chapter 6 & 7: liquids/semi-solids Chapter 4: Solids Damage to fruits, vegetables, grains, seeds during harvesting and handling 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Deformation and Viscoelasticity Chapter 4, pg. 111 - 169 Compression 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Deformation and Viscoelasticity Chapter 4, pg. 111 - 169 Definitions Normal stress: force per unit area applied perpendicular to the plane Normal strain: change in length per unit of length in the direction of the applied normal stress 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Deformation and Viscoelasticity Chapter 4, pg. 111 - 169 Example: 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Deformation and Viscoelasticity Chapter 4, pg. 111 - 169 Stress strain relationship Strain not recovered = plastic strain Recovered strain = elastic strain Ratio of plastic strain to total strain = degree of plasticity Ratio of elastic strain to total strain = degree of elasticity 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Deformation and Viscoelasticity Chapter 4, pg. 111 - 169 Stress strain relationship Strain not recovered = plastic strain Recovered strain = elastic strain Ratio of plastic strain to total strain = degree of plasticity Ratio of elastic strain to total strain = degree of elasticity 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Deformation and Viscoelasticity Chapter 4, pg. 111 - 169 Modulus of elasticity Linear region of stress strain curve E = σ/ε For biomaterials: apparent E = σ/ε at any given point (secant method) Tangent method: slope of stress/strain curve at any point 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

BAE2022/BAE4400 Physical Properties of Biological Materials HW#6 Assignment Problem 1: Explain in YOUR OWN WORDS how an osmometer works and give an example of how one might be used in food engineering. (you will need to do some outside research…web, library…) Limit your answer to one page in MSWord 12pt. Font, double spaced, 1” margins 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

BAE2022/BAE4400 Physical Properties of Biological Materials HW#6 Assignment Problem 2: A piece of carrot is cut in a cylindrical shape. The dimensions of the carrot cylinder are 25.8 mm in diameter and 20.3 mm in height. It is compressed to a height of 18.2 mm with a force of 579.3 N. Calculate the stress εz , and strain σz on the potato cylinder. 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials