Lecture 5 Announcements

Lecture 5 Announcements
HW #3 due today HW#4 due Monday, 1/29 Lab #1 due Wednesday, 1/31 HW#5 due Friday, 2/2 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

BAE2022/BAE4400 Physical Properties of Biological Materials
Structure Chpt 3, Pages 49-79 Organization of the Plant Body Cells are the structural units of the plant body Cells are grouped together to form tissues 3 kinds of tissues: protective, conductive and ground 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Structure Chpt 3, Pages 49-79 Protective Tissues Composed of guard cells that: protective organ from mechanical injury, insects, fungi, microorganisms control transpiration and aeration in the tissue system Include: Epidermis and periderm tissues: primary and secondary outer protective covering of plant body 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Structure Chpt 3, Pages 49-79 Protective Tissues Epidermis contains minute valves called stomata that are responsible for the exchange of gases 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Structure Chpt 3, Pages 49-79 Conducting Tissues (vascular tissues) Contain phloem and xylem Phloem conducts food Xylem conducts water 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Structure Chpt 3, Pages 49-79 Ground Tissues (supporting tissues) Parenchyma: chief type of cells in plant materials, may contain plastids or store water and reserve foods such as starch Collenchyma and Sclerenchyma: provide strength and support for the plant body 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Structure Chpt 3, Pages 49-79 Cell wall Composed mainly of cellulose microfibrils that are largely responsible for the form and structural properties of the cell wall. Microfibrils are the same diameter and structure in all cell walls. The arrangement of microfibrils is not equal in all cell walls. 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Structure Chpt 3, Pages 49-79 Cell wall Semicellulose: alkali-soluble, nonfibrous compound (not well defined) found mostly in wood but also in alfalfa hay, sugar cane, cornstalks, oat hulls Pectic Substances: straight chain polymers of great interest in fruits and vegetables. Insoluble in young plant materials. Soluble in mature plant materials. Capable of forming gels with sugar and acid. “mealiness” in over-ripe fruits Act as cementing agent between cells along with lignin. 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Structure Chpt 3, Pages 49-79 Cell Contents Refer to earlier lecture on plant cell structure and parts 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Structure Chpt 3, Pages 49-79 Cell Contents Turgor pressure: hydrostatic pressure exerted by “cell sap” (droplets of solution from the vacuoles) Responsible for keeping cell walls in a state of elastic stress 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Moisture Relationships Chpt 3, Pages 49-79
Amount of moisture affects: Density: particle density decreases with increasing moisture content Force-deformation characteristics Thermal conductivity Heat capacity Electrical resistance: lower resistance with higher moisture content 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Amount of moisture affects: Fruits and veggies: % mc Grains, seeds, dry food products: < 14% Meats: % MC influences market value 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Three concepts: Equilibrium mc Water activity Water potential 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Equilibrium mc Moisture transfers from product to air during drying. EMC describes the final moisture reached during drying of lower moisture food products, grains, seeds Affects rate of drying Explains mold growth in grain 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Water Activity Describes rate of deterioration Water Potential Describes the effect of moisture loss or gain on volume change and force deformation behaviour of fruits and veggies 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Determining Moisture Content (VERY IMPORTANT) Wet Basis % of total weight with water Dry Basis Ratio of water weight to dry matter weight One can be calculated using the other 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Equations: Wet basis Dry basis 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Equations: Conversion Wet to dry Dry to wet 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Wet basis example 700 kg of wheat contains 84 kg of water. What is the MCw ? 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Dry basis example 950 kg of oats contains 105 kg of water. What is the MCd ? 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Conversion example Convert the wheat and oat examples above 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

“How much water did we lose” example 750 kg of canola is dried from 17% MCw to 12% MCw How much water is removed during the drying process? 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Another example A bin holds 2000 kg of wet grain containing 500 kg of water. This grain is to be dried to a final MC of 14% (wb). What are the initial and final moisture contents of the grain (wb and db)? How much water is removed during drying? 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Another example An elevator has 14,000 kg of wheat at 12% MCw and 25,000 kg of wheat at 17% MCw. The manager has a rule that all stored wheat must be below 15% MCw. If the wheat is mixed together, will it meet the storage criteria? 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Another example A bag containing 1.5 kg of popcorn has been stored in the cabinet for a long time. When heated appropriately, only a few kernels popped. Testing showed that the MCw was 9%. Popcorn pops best at 13%. How much water should be added to bring it to this moisture? 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

HW#5 Assignment Problem 1: A grain storage facility in Oklahoma must store canola at 10% mcw or less to prevent molding and rancidity due to the summer temperatures. The facility has kg at 8% % mcw storage. A producer would like to sell kg of his canola at 15% % mcw to the facility. Should the manager of the facility buy this canola to mix with the seed already in storage? Problem 2: A drying system must remove excess moisture content from barley so that the barley will not mold. The barley is placed in the bin at 22% % mcw . Safe storage takes place at 13.5% % mcw should the drying system be sized for to remove the necessary moisture? Problem 3: Convert each of the moisture contents listed above to Dry Basis. 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

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