- HW due Friday 2/13 - Lab report due Wednesday 2/18 - ASABE student branch meeting 2/10Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14HW#6 AssignmentHW#5 Assignment2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 71- HW due Friday 2/13- Lab report due Wednesday 2/18- ASABE student branch meeting 2/10Lecture 7 – Water Potential2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 72•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.Lecture 7 – Water Potential2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 73•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–Yeasts 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 0.80wwpawp=Lecture 7 – Water Potential2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 74•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 osmometerLecture 7 – Water Potential2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 75•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.Lecture 7 – Water Potential2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 76•Deformation due to applied forces varies widely among different biomaterials.•Depends on many factors–Rate of applied force–Previous loading–Moisture content–Biomaterial compositionLecture 7 – Deformation and Viscoelasticity2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 77•Force deformation studies –Texture of raw and processed, cooked and uncooked–New variety selection–Study damage during harvesting and handling–Failure studies, cracking/splittingLecture 7 – Deformation and Viscoelasticity2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 78•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 handlingLecture 7 – Deformation and Viscoelasticity2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 79•CompressionLecture 7 – Deformation and Viscoelasticity2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 710•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 stressLecture 7 – Deformation and Viscoelasticity2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 711•Example:Lecture 7 – Deformation and Viscoelasticity2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 712•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 elasticityLecture 7 – Deformation and Viscoelasticity2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 713•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 elasticityLecture 7 – Deformation and Viscoelasticity2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 714•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 pointLecture 7 – Deformation and Viscoelasticity2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 715HW#6 AssignmentProblem 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” marginsLecture 7 – Deformation and Viscoelasticity2/01/2008 BAE2023 Physical Properties of Biological Materials Lecture 716HW#5 AssignmentProblem 2: A piece of carrot is cut in a cylindrical shape. The dimensions of the carrot cylinder are 30.1 mm in diameter and 19.3 mm in height. It is compressed to a height of 17.9 mm with a force of 438.2 N. Calculate the stress εz , and strain σz on the potato cylinder.Lecture 7 – Deformation and
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